atomic spectrometry update. advances in atomic emission ...lib3.dss.go.th/fulltext/journal/j.anal....

Atomic spectrometry update. Advances in atomic emission,

absorption and fluorescence spectrometry and related techniques

E. Hywel Evans,a Jason A. Day,bAndrew Fisher,a W. John Price,c Clare M.M. Smithd

and Julian F. Tysone

aSchool of Earth Ocean and Environmental Sciences, University of Plymouth,

Drake Circus, Plymouth, UK PL4 8AAbDepartment of Earth Sciences, University of Cambridge, Cambridge, UK CB2 3EQcEllenmoor, East Budleigh, Budleigh Salterton, Devon, UK EX9 7DQdDepartment of Chemistry, University College Cork, Cork, IrelandeDepartment of Chemistry, University of Massachusetts, 701 Lederle Graduate Research

Tower, 710 North Pleasant Street, Amherst, MA 01003-9306, USA

Received 21st April 2004

First published as an Advance Article on the web 28th May 2004

1 Sample introduction1.1 Flow injection1.2 Preconcentration1.2.1 On-line methods1.2.1.1 Flame atomic absorption spectrometry1.2.1.2 Electrothermal atomic absorption spectrometry1.2.1.3 Inductively coupled plasma optical emission

spectrometry1.2.2 Off-line methods1.3 Nebulization1.4 Chemical vapour generation1.4.1 Fundamental studies in hydride generation1.4.2 Other volatile compounds1.4.3 Vapor generation of the individual elements1.4.3.1 Arsenic1.4.3.2 Bismuth1.4.3.3 Cadmium1.4.3.4 Germanium1.4.3.5 Lead1.4.3.6 Antimony1.4.3.7 Selenium1.4.3.8 Tin1.4.3.9 Tellurium1.4.3.10 Mercury1.5 Solid sampling1.5.1 Electrothermal vaporisation1.5.2 In-torch vaporisation1.5.3 Slurry sampling1.5.4 Glow discharge1.6 ET-AAS2 Instrumentation2.1 Spectrometers2.2 Sources and atom cells2.2.1 Sources for AES2.2.2 Atom cells for AAS2.3 Detectors for AES3 Fundamentals3.1 Plasmas3.1.1 Microwave induced plasmas3.1.2 Inductively coupled plasmas3.1.3 Glow discharges3.1.4 Flames3.1.5 Other sources3.2 Furnaces4 Laser-based analytical atomic spectrometry4.1 Lasers as energy sources

4.1.1 Laser induced breakdown spectroscopy (LIBS)4.1.1.1 Fundamental studies4.1.1.2 Instrumentation3.1.1.3 Applications4.2 Lasers as sources of intense monochromatic radiation4.2.1 Laser excited atomic fluorescence4.2.2 Laser atomic absorption4.2.3 Laser enhanced ionisation4.2.4 Cavity Ringdown Spectroscopy (CRDS)5 Chemometrics6 Coupled techniques for speciation6.1 Gas chromatography6.1.1 GC-AES6.1.2 GC-AFS6.1.3 GC-AAS6.2 Liquid chromatography6.2.1 LC-AAS6.2.2 LC-AES6.2.3 LC-AFS6.3 Electrophoresis7 References

This review covers a relatively mature area of atomicspectrometry, so there are consequently fewer newdevelopments than in newer research fields. The review periodhas seen consolidation of research in AES using lasers asexcitation sources, particulalry making use of their principaladvatage for remote analysis. Considerable activity relating topreconcentration, matrix separation and sample introductionwas evident during the review period, though very few newdevelopments were reported. Vapour generation of non-tradiational elements continues to attract some interest. Veryfew new developments in solid sampling, fundamental studiesor new instrumentation have been reported in the open peer-reviewed literature. Speciation continues to grow in popularitywith speciation of As compounds being the popular choice overthe review period.

1 Sample introduction

1.1 Flow injection

There appears to be no diminution in the level of activityrelated to the development of new analytical procedures inD

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which sample pretreatment is coupled directly to the atomicspectrometer by some form of continuous or intermittent flowtechnique. While the majority of these procedures are pre-concentrations, in the broad sense of producing an increasedsignal by increasing the mass flux to the spectrometer, there area number for which the primary goal is the dissolution of theanalyte, the separation of analyte species from the matrix, oreven the separation of analyte species from each other. Withregard to the latter situation, if the procedure could beclassified as high performance gas or liquid chromatography,the relevant publication is discussed later in sections 6.1 or 6.2,respectively. Preconcentration procedures in which the analyteis ultimately transformed into a gaseous derivative are dis-cussed later in section 1.4. Other preconcentrations, in whichthe analyte is introduced to the spectrometer in the liquidphase, are discussed in section 1.2.1.Wang and Hansen1 review what they termed ‘‘the third

generation of flow injection analysis’’, namely ‘‘sequentialinjection lab-on-valve’’ and emphasize applications in auto-mation, the micro-miniaturization of on-line sample pre-treatment, and bead injection (BI) for on-line separation andpreconcentration of ultra-trace levels of metals by exploitingthe renewable micro-column approach.Yebra, et al. devised2 a continuous ultrasound-assisted extrac-

tion system for the FAAS determination of total chromium inmussels. The procedure was much faster than a single off-lineultrasonic-assisted extraction with a sampling frequency of11 per hour. The accuracy was verified for TORT-1 CRM.They also applied the procedure to the determination of Fe inmeat.3 Burguera, et al. developed4 a flow-injection microwave-assisted mineralization and a precipitation/dissolution systemfor the determination of molybdenum in blood serum andwhole blood by ETAAS. After irradiation, molybdenum wasprecipitated by merging with potassium ferrocyanide, collect-ing on the walls of a knotted reactor, and finally being dissolvedin 1 mL of 3.0 mol L21 NaOH. The interfering effects of iron,copper and zinc were minimized by 5% (w/v) sodium potassiumtartrate (for iron) and 2% (w/v) of thiourea (for copper andzinc) in a 5% (v/v) ammonia and 2% (v/v) ammonium chloridesolution upstream of the precipitation reaction. The enrich-ment factor was 4 for a 0.5 ml sample at a flow rate of1.0 mL min21. Two human whole blood CRMs were accur-ately analysed. Fili et al.5 digested orange juice on-line in afocused microwave-assisted oven for the determination of Ca,Cu, Fe, K, Mg, Mn, Na, P, and Zn ICP-OES. The reactor coilwas a PTFE tube (4.0 m long and 1.6 mm id) and 500 mL ofsample and 1000 mL of reagent (80% v/v HNO3) were mixed ata confluence point and carried to the reactor coil by an aircarrier. The throughput was 12 h21. Jacob and Berndt6

constructed a high-temperature/high-pressure flow digestionsystem, from an electrically heated Pt–Ir capillary tube, forbiological and environmental samples with determination byFAAS. The whole procedure took 3–8 min, of which digestionof various materials (wheat flour, spinach, orchard leaves,tomato leaves, bovine liver, pig kidney, sewage sludge, and coalfly ash), as 2% suspensions in 2.5 M HNO3, was about 1 min.As the system was glass-free, samples with high silicate contentscould be digested by the addition of hydrofluoric acid. TheLOD were between 0.25 mg g21 (Cd) and 4.5 mg g21 (Pb).Japanese workers, Asano et al., removed the iron inter-

ference7 in the determination of Zn in steel samples by AASby precipitating the iron(III) as hydroxide, which was thenquantitatively extracted into an organic phase containingdi-(2-ethylhexyl)phosphate. Burguera et al.8 determined totaland dissolved silica in waters by ETAAS in a sequentialprocedure in which total silicon was determined (in the range300–1000 mg L21) first, followed by the precipitation of dis-solved silicon (in the range 280–850 mg L21) with ammoniumchloride, with dissolution in ammonium molybdate and nitricacid; a sub-sample was then collected in the sampling arm

assembly. In both cases, 10 mL of the sub-sample were injectedinto the atomizer along with 20 ng of Eu as chemical modifier.In most natural waters, 85–95% of the silicon was dissolved.For bigger silica particles, coated with hydrous iron oxide(geothite), Chantiwas et al.9 employed gravitational field-flowfractionation in combination with ETAAS.Tao et al.,10 constructed an on-line dilution system for FAAS

from an injection valve and two computer-programmed, stepper-motor-driven syringe pumps. Carryover was less than 0.4% evenfor solutions containing 10% glycerol. At a sampling frequencyof 60 h21, precisions were better than 2% RSD (n ~ 40) fordilution factors of 10–2000. The systemwas verified by analysinga copper alloy CRM, whose concentration was 57.4%Several indirect procedures have been developed: Zhang

et al.11 determined ciprofloxacin by FAAS by forming acationic complex with Fe(III) that was retained on a cation-exchange mini-column while the excessive Fe(III) was removedas the anion (FeF6)

32 and the adsorbed ciprofloxacin–Fe(III)was eluted with HNO3; Ferreira et al.12 determined tannin inpigeon pea samples by FAAS with a precipitation reaction withhemoglobin, followed by solubilization in 1% (w/v) sodiumdodecylsulfate solution and measurement of the Fe; Cassellaet al.13 devised a slurry sampling procedure for the determina-tion of zineb (down to 1.0 mg mL21) in commercial pesticideformulations in which an on-line alkaline hydrolysis of thepesticide was performed releasing Zn(II) ions, which were deter-mined by FAAS; and Chinese workers, Xie et al., determined14

nitrofurantoin by precipitation with ammoniacal AgNO3

solution and determination of the excess Ag.

1.2 Preconcentration

Researchers around the world are developing preconcentrationprocedures at an increasing rate. The motivation for this effortappears to be largely the need to extend the capability ofprocedures in which the quantitative measurements are madeby FAAS, but as the procedures also separate analytes frommatrix components, this may also be considered a motive forthe method development. Solid-phase extraction (SPE) onceagain dominates as the method of choice, but there seems to beno emerging consensus as to what the best material might befor any given element. Most procedures are designed for theisolation of a single element from a given matrix, though thereis perhaps a growing interest in devising procedures that willyield information about different species of the element ofinterest. In this latter case it might be argued that the primemotive for the method development is speciation, and thatpreconcentation was a by-product of the process. However, asthe structure of the Update does not include a section devotedto non-chromatographic speciation these procedures areincluded here. It should also be borne in mind that proceduresfor ICP-MS are considered outside the scope of this Update,and a complete picture of preconcentration (including analyte–matrix separation and non-chromatographic speciation) is onlyobtained when the material in the August Update is included.In this section, procedures that involved direct coupling of thepreconcentration with the spectrometer are considered first(section 1.2.1), then the various so-called ‘‘off-line’’ proceduresare described (section 1.2.2).Camel has reviewed15 SPE for trace element determination.

The review considers both theory and practice, with guidelinesprovided for the development of procedures. Particular atten-tion is devoted to the determination of Cd, Cr, Fe, Pb, Hg, Se,and Sn for which just over 250 literature references are cited,most in the last 5 years. A survey of all preconcentrationprocedures was made by Pereira and Arruda16 with the goal ofidentifying trends from the 1996–2001 literature. They con-clude that ‘‘synthetic resins are extensively employed for metalextraction by SPE. Nevertheless, in recent years, the utilisationof natural resins (microbial cells, mainly) has increased due to

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their low cost and acquisition facilities.’’ They also providesome quantitative information about the literature including,for example, that the off-line to on-line ratio was 45 : 55 (avalue very different from that reflected in the papers retrievedfrom the literature for this review period, which shows aconsiderable bias towards off-line methods). They identify SPEas the leading procedure (60%), followed by liquid–liquidextraction (14%) and coprecipitation (11%). They cited justover 200 references. Luque-Garcia and de Castro17 examinedtrends in the nature and uses of microwave-based analyticalequipment for solid sample pre-treatment and reviewed dyna-mic approaches based on the coupling of microwave-baseddevices to other steps of the analytical procedure, such as pre-concentration, chromatographic separation or detection, whichallow total or partial automation of the whole analyticalprocess. The accumulation of mercury by naturally growingfeather moss Hylocomium splendens at approximately 500 sitesin Norway was examined by Steinnes et al.18 as part of anationwide survey of atmospheric deposition of heavy metalsin 2000. Compared with the situation for the period 1985–1995,the 2000 data are approximately 30% lower. The researcherswrite that ‘‘a satisfactory explanation of this difference remainsto be found’’.

1.2.1 On-line methods. In this section preconcentration pro-cedures are classified according to the nature of the detectorand within those categories by alphabetical order of the chemi-cal symbol of the analyte element.

1.2.1.1 Flame atomic absorption spectrometry. Liu et al.19

determined Ag in ores after retention on amidino-thioureaimmobilized on glass beads. The LOD for a preconcentrationtime of 60 s at a flow rate of 5.0 mL min21 were 0.50 ng mL21

(peak-height) mode and 1.3 ng mL21 (peak-area), respectively.They also devised procedures for the determination of Au andPd20,21 in ores, anode slime and a nickel alloy. In the first ofthese, the analytes were immobilized on a silica gel micro-column modified with 2-mercaptopyrimidine and then elutedwith 0.5 or 1.0% thiourea solution. The LOD were 3.1 ng mL21

for Au and 6.1 ng mL21 for Pd. In the second procedure,21

the column was modified with 2-mercaptothiazole, whichallowed retention from acidities up to 6 MHCl at a flow rate of4.0 mL min21. The LOD for a preconcentration time of 60 sfor Au and Pd were 10 ng mL21 and 26 ng mL21, respectively.However, it appeared that for longer loading times (up to30 min), slightly lower concentrations could be determined,suggesting that the relationship between LOD and samplevolume needs further investigation. Chinese workers, Ye andXue,22 determined Au in waters by retention on N1923Levextrel resin with elution by a sulfuric urea solution downto an LOD of 1 ng mL21. Levextrel resins were introduced onan industrial scale by Bayer AG in 1977. They are prepared byincorporating the extractant into the vinyl monomers using abead polymerization process, but they appear not to have beenused to any extent for analytical chemistry purposes.Plamboeck et al.23 determined Ba after co-precipitation with

lead chromate to give a crystalline precipitate that adhered tothe inner walls of a knotted nylon reactor. The enrichmentfactor was 24, the sampling frequency 50 h21, and the LOD0.8 mg L21. Wu et al.24 determined Bi in high-purity lead andcadmium by retention on a microcolumn packed with silica gelmodified with 2-mercaptobenzothiazole at pH 3.0 and a flow-rate of 5.6 mL min21, followed by elution with 3.0 mol L21

HClO4, 0.5 mol L21 NaClO4 and 0.2 mol L21 NaNO3 at aflow-rate of 2.2 mL min21. The LOD was 10 ng mL21.Ye et al.25 measured Cd in rice after on-line, filterless pre-

cipitation by ammonia solution, collection in a knotted reactor,and dissolution in 1 mol L21 HNO3. At a loading flow rate of3.8 mL min21 for 35 s, the enhancement factor was 44 and theLOD was 2 ng g21. Chinese workers, Wang et al.,26 developed

a fast sequential SPE procedure for the determination of Cd,Cu, Co, Mn, Ni and Pb, in environmental samples. Theanalytes were retained as either the DDC or APDC com-plexes on PT–C18. The LOD were 0.35, 2.9, 3.6, 1.9, 4.0 and5.8 mg L21, respectively. Chinese workers, Gao et al.,27

measured Cd and Pb in atomospheric particulates with aprocedure that involved both ultrasonic leaching and on-lineFI preconcentration.Lemos and co-workers have evaluated two SPE proce-

dures28,29 for the determination of Co in waters in which theanalyte was retained on a modified XAD resin. In the first ofthese the reagent was tert-butylphenoxyacetyl and in thesecond it was a nitroso-R salt. The LOD, based on 180 sloading time, were 0.13 mg L21 and 0.39 mg L21. It is not clearwhat advantages the second procedure has over the first. Inneither case was the LOD as good as that claimed by Shabaniet al.30 of 0.02 ng mL21 for retention on a microcolumn of2-nitroso-1-naphthol immobilized on surfactant coated alumina.Workers at Hebei University31–33 have determined Cr(III) and

Cr(VI) in water by retention on a cation-exchange resin and onan anion-exchange resin, with elution directly by 15% HNO3

and 8% NH4NO3, respectively. The corresponding LOD were1.0 mg L21 and 0.54 mg L21, respectively. In the secondprocedure32 both species were eluted with 3 mol L21 HNO3 andderivative signal processing was applied. Wuilloud et al.34

retained Cr (oxidation state not specified), from parenteralsolutions, as the complex with 4-(2-thiazolylazo)resorcinol(TAR) on Amberlite XAD-16 at pH 5.0. The Cr–TAR complexwas removed from the microcolumn with ethanol. An enrich-ment factor of 50 was obtained for 50 mL, for which the LODwas 20 ng L21. Anthemidis et al.35 determined Cr(VI), Cu andPb in natural waters and biological materials. The metal–APDC complexes were sorbed on polyurethane foam andsubsequenly eluted with IBMK. For a 60 s preconcentrationtime, the enhancement factors were 28, 170 and 131 and, theLOD were 2.0, 0.2, 1.8 and mg L21, respectively.Saracoglu et al.36 determined Cu in natural water samples,

after retention on solid Ambersorb 563 resin followed byelution with a stream of 0.25 mol L21 HNO3 at 5.0 mL min21.The LOD was 1.0 mg L21. Gladis et al.37 retained the 5,7-dichloroquinoline-8-ol complex onto C18 bonded silica gel forthe determination of Cu in sea-water followed by elution withacidified methanol (pH w2). For a one minute preconcentra-tion the enrichment factor was 100, which can be furtherimproved by increasing the preconcentration time (thoughthis does not necessarily lead to lower LOD). The LOD was0.05 mg L21; the method was validated by the analysis of sea-water CRM CASS 4. Chinese workers, Kang et al.38 deter-mined Cu, Fe and Zn in tapwater by ion-exchange SPEwith derivative signal processing. The LOD were 0.28, 5.8 and0.68 mg L21, respectively.Ampan et al.39 compared three procedures for the deter-

mination of Fe in beer: an SPE-FI-FAAS procedure, a spectro-photometric FI system with a column placed at the detectionpoint, and an FI-spectrophotometric system with beadinjection (BI). Cation exchange resin Dowex 50W X8 andiminodiacetate chelating resin, Chelex-100, were employed forthe FI-spectrophotometric and FI-FAAS systems, respectively.The spectrophotometric FI system with a Chelex-100 columnlocated in the cell holder of the spectrophotometer was based onthe formation of iron(II)–1,10-phenanthroline complex sorbedonto the resin for which no eluent could be found, hence the BIalternative approach. The results obtained by FI-FAAS andFI-BI agreed with those of the AOAC spectrophotometricmethod.Antheraidis et al.40 retained Ga as the gallium chloride

complex sorbed onto polyether-type polyurethane foam,followed by elution with IBMK. For 90 s loading, the enhance-ment factor was 40, and the LOD 6 mg L21. The method wasvalidated by the analysis of a silicon–aluminium alloy SRM

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and applied to the analysis of aluminium alloys, natural watersand urine.Bakircioglu et al.41 evaluated the peformance of two mani-

fold designs for the determination of trace Pb in water and winein which SPE by Pb-Spec was the basis of the preconcentration.The eluent, 0.1 mol L21 ammonium oxalate, was injected viaa six-port rotary valve. The LOD for the water samples,estimated from the noise on the signal obtained for 250 ml of asolution containing 10 mg L21, loaded at 19.1 mL min21, was1 mg L21. For 50 mL of wine digest loaded at 4 mL min21, thevalue was 3 mg L21. The roles of loading flow rate and samplevolume were investigated in detail: the variation in retentionefficiency with loading flow rate showed that the amount oflead retained (during a fixed loading time) increased with flowrate until the upper performance limit of the peristaltic pumpwas reached. The variation of detection limit with samplevolume followed the expected hyperbolic relationship andshowed that only small improvements in LOD were obtainedfor volumes greater than 50 mL. The concentrations of lead inthree Port wine samples ranged from not detected to 190 mg L21.Lemos et al.42 also devised an SPE procedure for thedetermination of Pb in wine that could measure both ‘‘freeavailable’’ Pb(II) and total Pb. Determination of free Pb(II) wasbased on sorption from pH 7 solution onto polyurethane foam,modified by addition of 2-(2-benzothiazolylazo)-p-cresol(BTAC) followed by elution with 0.1 mol L21 HCl. Totallead was measured after digestion with nitric acid and hydro-gen peroxide. The total Pb varied from 8 to 42 mg L21 withconcentrations of free Pb(II) less than the LOD of 1 mg L21.Ensafi et al.43 devised an SPE procedure for the determinationof Pb in waste water in which the analyte was retained on activecarbon loaded with pyrogallol red followed by elution with5.0 ml of 0.50M nitric acid solution. The enrichment factor wasabout 100 and the LOD was 1 ng mL21. Ye et al.44 developedan on-line filterless precipitation–dissolution procedure for thesame analysis. The analyte was precipitated on mixing withammonia solution, collected on the inner walls of the knottedreactor, and dissolved in 1 mol L21 HNO3. For a 40-s loadingat 3.5 mL min21, the enhancement factor was 37 and theLOD was 7.5 mg L21. The method was validated by theanalysis of river water CRM GBW 08607 (certified value1.00 ¡ 0.02 mg g21).Iglesias et al.45 retained Pd on polyamine Metalfix-Chelamine

resin, which is highly selective for Pt(IV), Au(III) and Pd(II). Asample volumes of 4.7 mL resulted in an enrichment factor of20 and an LOD of 0.009 mg L21. The method was evaluated bydetermining the Pd content of synthetic geological samples aswell as in a pellet-type automobile catalyst RM. Chineseworkers, Zhou et al.46 also determined Pd in a catalyst materialwith an SPE porcedure in which the analyte was retained on tri-isooctylamine Levextrel resin from 0.5 mol L21 HCl pumpedat 7.8 mL min21, followed by elution with 0.5 mol L21 HCl 10.1 mol L21 thiourea solution. For a 90-s loading the enrich-ment factor was 50 and the LOD was 0.34 mg L21. Wu et al.47

determined Pt in two metals by SPE on a novel polymelaminedendrimer immobilized on silica gel. For loading at 5.0mLmin21

for 60 s, the LOD was 0.065 mg mL21.Preetha et al.48 devised an SPE procedure for the determina-

tion of Zn in fractionated soil samples in which the complexwith 1-(2-thiazolylazo)-2-naphthol (TAN) was adsorbed ontoC18-bonded silica gel and eluted with acidified methanol. For a1-min preconcentration, the enrichment factor was 120 and theLOD was 0.15 mg L21. A similar LOD was obtained by Lemoset al.,49 who measured Zn in natural water samples fromSalvador by retention of the complex with 2-{2’-(6-methylben-zothiazolylazo)}-4-bromophenol (Me-BTA-Br) on polyur-ethane foam loaded with reagent followed by elution with0.10 mol L21 hydrochloric acid solution at flow rate of5.5 mL min21. At a sampling rate of 48 h21 the enrichmentfactor was only 23, but the LOD was 0.37 mg L21.

1.2.1.2 Electrothermal atomic absorption spectrometry. Thetrapping of chemical vapours on the interior wall of anelectrothermal atomizer might be considered preconcentrationin the sense that the procedure increases the atom numberdensity in the atomizer for a given analyte concentration in theoriginal sample solution. These in-atomizer trapping techni-ques are considered later in the appropriate part of section 1.4.Japanese workers, Sakuragawa et al.50 devised a liquid–

liquid extraction procedure for the determination of As in steelsbased on the reaction of As(III) with iodide ion in concentratedhydrochloric acid medium to produce AsI3, which was extractedinto benzene and back-extracted intowater. Cobalt, 800 mg L21,was the matrix modifier. The LODwas 2 mg g21 of steel sample.Sung and Huang51 devised an SPE procedure for the simul-taneous determination of Bi, Cd, and Pb in urine. A miniatureMuromac A-1 resin column was inserted at the top of theautosampler arm and the retained analytes eluted with 50 mL of20% (v/v) sub-boiled HNO3 directly into the graphite furnace.For a 213 mL sample loop, the sample throughput was 10 h21

and LOD were 130, 2 and 4.5 ng L21 for Bi, Cd, and Pb,respectively. The accuracy of the method was confirmed by theanalysis of SRM Seronorm (Trace Elements Urine) at twoconcentrations. Su et al.52 determined Cd, Mn and Pb in somewater samples after retention on activated carbon from anNH4Cl–NH3 solution. After rinsing with 0.02% (v/v) HNO3,the analytes were eluted with 30 mL of 2 mol L21 HNO3, givingenrichment factors of 32, 26 and 21 and LOD of 0.4, 4.7 and7.5 ng L21 for Cd, Mn and Pb, respectively, for 60 s sampleloading at 3.0 mL min21. Interferences caused by alkali andalkaline earth metals were eliminated.Li et al.53 developed a procedure for the determination of

trace Hg in environmental and food samples based on the on-line formation of copper pyrrolidine dithiocarbamate, whichwas sorbed onto the inner walls of a knotted reactor, followedby selective retention of the Hg(II) by the displacement reactionbetween Hg(II) and the presorbed copper complex. The retainedanalyte was subsequently eluted by 50 mL of ethanol. Inter-ferences from metal ions with lower stability of their APDCcomplexes relative to that of the copper complex wereminimized without the need for masking reagents. No addi-tional chemical modifiers for the stabilization of mercury wererequired owing to the stability of the Hg complex at the dryingstage, and no pyrolysis stage was necessary due to the effectiveremoval of the matrix. For 2.5 mL of sample, the enhancementfactor was 91, compared with the direct injection of 50 mL ofaqueous solution, and the LOD was 6.2 ng L21. The sameresearch group later modified the procedure for the determina-tion of methylmercury in fish:54 Cu–DDTC was retained on thesorbent from a cigarette filter to give an extractant that wasselective for methylmercury in the presence of Hg(II), ethylmer-cury, and phenylmercury at pH 6.8. The retained methylmer-cury was eluted with 50 mL of ethanol; for 3.4 mL of samplesolution the enhancement factor was 75, and the LOD was6.8 ng L21 as Hg (corresponding to 3.4 ng g21 in an originalsolid sample of which 0.1 g was taken and for which the finaldigest volume was 50 mL). The method was validated by thedetermination of methylmercury in CRM DORM-2 (dogfishmuscle).Nakajima et al.55 devised a two-stage procedure for the

determination of Pb in sea-water. After coprecipitation with10 mg of iron, as iron(III) hydroxide, the precipitate wasdissolved in 25 mL of 1 mol L21 nitric acid and 4 mL of thesolution was pumped through the lead-selective resin, Pb.Spec,and eluted with a 1.06 1024 mol L21 EDTA solution. A 30-mLportion of the eluate, corresponding to the highest analyteconcentration zone, was injected into the graphite furnace. Theoverall enhancement factor was about 200 for a 250 g sample,and the recovery was 93.7 ¡ 5.0% for sea-water spiked with20 ng kg21. The method was applicable to the determination ofPb at slightly higher concentrations. Nan et al.56 determined Pb


in biological materials by formation of the analyte-entrappedsurfactant micelles by merging with APDC and Triton X-114solutions sequentially, followed by adsorption onto silica gel,and elution with 50 mL of acetonitrile. For a 2.2 mL sample, theconcentration factor was 22.5 and the LOD was 44.6 ng L21.Researchers at the University of Malaga in Spain have

evaluated57,58 two SPE procedures for the determination of Ptin catalyst, vegetation, soil, and natural water samples. In thefirst procedure, the analyte was retained on an anion-exchangeresin (Dowex 1 6 8–200), placed in the autosampler arm,modified with [1,5-bis(2-pyridyl)-3-sulfophenylmethylene thio-carbonohydrazide. For a 60-s loading time, at a flow rate of2.4 mL min21, and an eluent of 40 mL, the enrichment factorwas 14 and the LOD was 1 ng mL21. In the second procedurethe extractant was silica gel functionalised with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide Although the enrich-ment factror was 41.7, the LOD was only slightly improved at0.8 ng mL21.Wojcik et al.59 incorporated SPE on Al2O3 into an ion

chromatography procedure for the speciation of inorganicselenium. As the LOD achieved with UV detection were notlow enough, ETAAS was also used.

1.2.1.3 Inductively coupled plasma optical emission spectro-

metry. Karthikeyan and Hirata60 devised a procedure for thesimultaneous determination of As(III) and As(V) in waters.Arsenic(III) was retained, after complexation with APDC atpH 3, on Muromac A-1, and the As(V) was retained on ananion-exchange resin. The species were eluted sequentially with0.6 M sodium hydroxide. Enrichment factors were 136 (617for the SPE and68 for ultrasonic nebulization,USN) for As(V)and 160 (620 for the SPE 68 for USN) for As(III) for 4 minloading. The LOD were 0.7 mg L21 for As(V) and 0.8 mg L21 forAs(III). Very few papers describe SPE procedures in which As(III)is retained.Cerutti et al.61 measured Cd in drinking water by retention of

the Cd–8-hydroxyquinoline complex at pH 10.0 on activatedcarbon, followed by elution with 20% (v/v) nitric acid. Theenrichment factor was 80 for a 50 mL sample and the LOD was18 ng L21. Worrasettapong et al.62 determined a number ofanalytes (Cd, Co, Cu, Fe, Mn, Ni, Pb, U, V and Zn) in mineral,rain and sea-water samples, after retention on the iminodia-cetate chelating resin Muromac A-l, followed by elution with250 mL of 2.0 M nitric acid. Sensitivity enhancement factorsbetween 26 and 44 were achieved with the help of ultrasonicnebulisation, and LOD were improved by up to two ordersof magnitude relative to those for conventional pneumaticnebulisation. A similar procedure was developed by Vassilevaand Furuta63 for a slightly different suite of elements (Cd, Co,Cu, In, Ni, Ti, Tl and Y). The eluent was a mixture of nitric andhydrochloric acids. Low recoveries of Hg, Pb and Pd wereobtained.Liang et al.64 determined both Cr(III) and Cr(VI) in natural

waters with a procedure in which the Cr(III) was retained on‘‘nanometer’’ titanium dioxide at pH 6, then eluted with2.0 mol L21 HCl. Total Cr was determined after the reductionof Cr(VI) to Cr(III) by ascorbic acid. The capacity of nanometerTiO2 for Cr(III) was 7.6 mg g21 and, for an enrichment factorof 50, the LOD was 0.32 mg L21. Chinese worker Fan65

determined the two Cr species by a procedure in which theywere retained on activated alumina. The LOD were 0.8 mg L21

for Cr(III) and 0.6 mg L21 for Cr(VI) at a sampling frequency of60 h21.Ortega et al.66 devised a procedure for the determination of

Dy in urine in which the Dy(III)-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex was formed on-line at pH 9.2 inthe presence of nonionic micelles of PONPE-7.5 and, followingheating to 30 uC in order to promote phase separation, thesurfactant-rich phase was retained in a microcolumn packed

with cotton. The analyte was then eluted with 4 mol L21 nitricacid. For a 50 mL sample the LOD was 0.03 mg L21.Zara et al.67 developed a multielemental determination in

which Hg was preconcentrated by retention on Chelite-Sfollowed by reductive elution with a mixture of SnCl2–HCl.The throughput was 30 h21 and the working range was 50–2500 ng L21. Zougagh et al.68 determined Mn in biologicalsamples after retention on silica gel functionalized with 1,5-bis-(di-2-pyridyl)methylene thiocarbohydrazide followed by elu-tion with nitric acid. For a 60 s preconcentration time theenrichment factor was 26, the throughput was 40 h21 and theLOD was 1.5 ng mL21.Japanese researchers, Seki et al.,69 determined Mo in steel.

The analyte was retained from 0.05 M sulfuric acid solutionon TEVA resin and then eluted with 7 M nitric acid andintroduced to the spectrometer via an ultrasonic nebulizer. Fora 50 mL sample, the LOD in 50 mg of steel was 8 mg g21. Yuneset al.70 determined Ni in natural water samples after sorptionon a conical minicolumn packed with activated carbon at pH5.0 followed by elution with 20% nitric acid. For 50 mL ofsample, the enrichment factorwas 80 and theLODwas 82 ngL21.Cerutti et al.71 also used activated carbon, this time to retain Pbfrom bee honey as the 8-hydroxyquinoline complex at pH 10followed by elution with 20% (v/v) nitric acid. With the help ofultrasonic nebulization, which accounted for a factor of 10, theoverall enhancement factor compared with that for conven-tional nebulization was 500 for a 25 mL sample, and the LODwas 0.04 mg L21. They also determined72 Sc in river water byretention of the Sc–2-(5-bromo-2-pyridylazo)-5-diethylamino-phenol complex, at pH 9.5, on the interior walls of a knottedreactor, followed by dissolution in 30% (v/v) nitric. This timethe ultrasonic nebulizer contributed a factor of 25 to theoverall enhancement of 1120. For 300 s loading the LOD was0.45 ng L21.Abbas-Ghaleb et al.73 preconcentrated various Se-compounds

on a porous graphitic carbon column, prior to HPLC separa-tion on a methanoic acid mobile phase, when the analyteswere injected in nitric acid or trifluoroacetic acid. This allowed2.5 mL to be injected, leading to LOD of (2–6 mg L21).

1.2.2 Off-line methods. Again, research efforts in this areacontinue unabated and, as was noted for previous years, themotivation appears to be the desire to improve the methodperformance by lowering the detection limits and removingpotential interferences. Possibly for the first time publicationsdealing with ‘‘multi-element’’ (two or more) preconcentrationsoutnumber those dealing with just one analyte. This is certainlytrue for the SPE procedures. There are also signs of a growinginterest in the use of off-line preconcentration, especially bysolid-phase extraction, in speciation measurements, sometimesin combination with another separation technique such asHPLC. As always, classification of the published material isdifficult. The organization of this section follows that of lastyear’s ASU: procedures are classified firstly according to thechemical process involved and secondly by the alphabeticalname of the analyte. Procedures in which volatile derivativeswere trapped on the interior of ET atomizers are discussed laterin section 1.4.

1.2.2.1 Solid phase extraction. This is by far the largestsubsection of the off-line preconcentration section and afurther classification of the procedures might be possibleaccording to the nature of the solid phase (chelating agentbound to solid support, both natural and synthetic, non-polarsorbent, ion-exchange resin, co-precipitate—crystalline orfoam, inorganic solid, electrode surface, naphthalene). How-ever, it was felt that this was of less use than a classification byanalyte, on the basis that most readers will be primarilyinterested in methods for the determination of analytes ofinterest, and be only secondarily concerned about how this was


achieved. Procedures in which a single analyte was the targetare described first, followed by those in which multiple analyteswere determined. This latter section is arranged in increasingorder of number of analytes.Chen et al.74 speciated Al in tea infusions by retention of

labile monomeric species on a weakly acidic cation-exchangeresin followed by elution with 1.0 mol L21 HC1. The variousspecies and total Al were determined by fluorination-assistedETV-ICP-OES. Yu et al.75 determined Au in natural water byETAAS following enrichment on thiol cotton fiber. For a 5 Lsample, the LOD was 0.02 ng L21. The procedure also includeda liquid–liquid extraction step. Bagheri et al.76 determined Auin some pharmaceutical samples by FAAS after sorption onoctadecyl silica membrane disks modified with pentathia-15-crown-5. Japanese researchers, Shinohara et al.,77 measured Bin steel by ICP-OES after retention on an anion-exchange resin,Bio-Rad AG1, preconditioned with fluoride. The iron in thesample solution passed through the column, while the B wasadsorbed as BF4

2 and recovered with 6.5 mol L21 nitric acid.The LOD was 1.3 mg g21. Yebra et al.78 sampled sea-waterthrough a minicolumn packed with Amberlite XAD-4 impre-gnated with the complexing agent 4-(2-pyridylazo)resorcinol toretain Cd for subsequent elution back in the laboratory anddetermination by FAAS. For a preconcentration time of 57 min(200 mL), the enrichment factor was 1053 and the LOD was6 ng L21. Cerny and Bhattacharyya79 measured Cd in wholeblood and urine by ETAAS after retention on an anion-exchange resin, and elution into 100 mL of 1 M nitric acid. TheLOD were 0.008 ng mL21 for blood and 0.003 ng mL21 forurine.For the speciation of Cr in natural waters, Japanese workers

Narukawa et al.80 studied the retention of Cr(III) and Cr(VI) onvarious powdered calcium compounds and found that Cr(III)could be collected on CaO, CaCO3, CaSO4 and CaHPO4. In amethod based on adding CaHPO4, 100 mg was added to100 mL of sample and, after stirring and suction filtration, thesolid was dissolved in 2 mol L21 HCl and the Cr determined byICP-OES. Total Cr was determined after reduction of Cr(VI).The LOD was 0.3 mg L21 for a 500 mL sample. Eid et al.81

measured Cr(VI) in tannery effluents by two methods; Cr(III) waseither precipitated as Cr(OH)3 or retained on a cation exchangeresin (Amberlite IR 120H) while Cr(VI) was measured in thesolution remaining by ICP-OES. Mondal and Das devised82 aFAAS procedure for the speciation of Cr in waste waters byseparation on a column containing 6-mercaptopurine anchoredby an azo group to a styrene–divinylbenzene polymeric resin.They found that the maximum exchange capacity for Cr(III) atpH 6.5 was 0.44 mmol g21 and that for Cr(VI) at pH 1.0 it was1.06 mmol g21.Filik83 and co-workers84 have devised two Cr speciation

methods. The first was based on the sorption of Cr(III) ionsonto a column of Amberlite XAD-2 resin functionalized with5-palmitoyl-8-hydroxyquinoline followed by elution with HCland measurement by FAAS. Total Cr was determined afterreduction with hydroxylamine. The second method was basedon the retention of Cr(VI) on a new resin prepared by reactionwith bromosuccinic acid and cross-linking with melamine, forwhich the active sequestering group was –NH–(succinic acid),followed by elution with 0.1MNaOH. TheLODwas 5.3 mg L21.Both methods were applied in the analysis of electroplatingwastewater. Yaman85 achieved a LOD of 0.9 mg L21 for Cr(VI)by collecting the DDC complex on activated carbon. Latvaet al.86 retained the Cr(VI) on ‘‘iron-loaded’’ activated charcoaland measured the remaining Cr(III) by ETAAS. Followingelution with 2.0 M HCl, the Cr(VI) was also measured byETAAS. Dirilgen and Dogan87 investigated the Cr speciationin common duckweed with the ‘‘differently activated alumina’’procedure and found that Cr(III) accumulated in smaller quan-tities, producing relatively larger growth responses, whereasCr(VI) was accumulated in larger quantities but yielded

relatively smaller growth responses. Different interactions,depending on the oxidation state, between Cr, Cu, Zn wereclassified as synergistic, antagonistic, or additive.Japanese workers, Kobayashi et al.,88 devised an SPE

procedure for Cu in which the analyte was retained on theinner walls of a Teflon tube, coated with Zephiramine, as thecomplex with oxine-5-sulfonate. The LOD was 0.01 ng mL21

and the sensitivity was 14.2-times greater than that obtained byinjecting 20 mL directly into the furnace. Say et al.89 precon-centrated Cu on ‘‘ion-selective imprinted polymer microbeads’’.The Cu(II)-imprinted poly(ethylene glycol dimethacrylate–methacryloylamidohistidine/Cu(II)) (poly(EGDMA–MAH/Cu(II)))microbeads, with an average size of 150–200 mm, were preparedby dispersion polymerization. After equilibrating for about anhour, the adsorption of Cu(II) ions was 48 mg g21. The materialwas selective for Cu over zinc, nickel and cobalt, in that order.The Cu was released by EDTA; the researchers claimed that‘‘LOD was increased at least 1000-fold’’. Bati and Cesur90

determined Cu in edible oils by FAAS after SPE on leadpiperazinedithiocarbamate and back-extraction with potas-sium cyanide.Divrikli et al.91 devised a method for Ga based on retention

of the 4-(2-thiazolylazo)resorcinol (TAR) complex on theAmberlite XAD-4 resin and elution by 1 M nitric acid inacetone. The method was validated by the analysis of an SRMsediment material (GBW 07309).Mondal and Das92 retained both Hg(II) and methylHg on a

resin functionalized with a 1,2-bis(2-aminophenylthio)ethanemoiety. The LOD of the resulting CVAAS measurement was0.09 ng mL21. Krata et al.93 removed the interferences fromcopper and iron in the determination of Hg by retaining allthree metals on Dowex 50W 6 4, followed by selective elutionof the copper and iron with 0.5 mol L21 KF solution. The Hgwas eluted with 0.1% thiourea in 8% HCl and determined byCVAAS with borohydride as the generating reagent. The LODwas 27 ng L21 and the method was validated by the analysis ofa sewage sludge CRM (BCR-144R).Okumura et al.94 determined Mn in brackish lake waters by

ETAAS by collectingMn as the complex with 4-(2-pyridylazo)-resorcinol (PAR) at pH 10 on a Sep-Pak C18 cartridge andelution with 0.5 M hydrochloric acid. The complex was stableon the column for up to a month. Yu et al.95 measured Mo insea-water by ICP-OES following retention on a new SPEmaterial diethylenetriaminetetraacetic acid–functionalizedpolysiloxane (DETAP). For a preconcentration factor of100, the LOD was 0.17 mg L21. The method was validatedby the analysis of CRM, NASS-2 (open ocean sea-water) andCASS-2 (coastal sea-water). Oshita et al.96 synthesized achitosan (a polysaccharide found in the exoskeleton of shellfishsuch as shrimp or crabs) resin possessing leucine moiety cross-linked with ethylene glycol diglycidyl ether for SPE precon-centration of Mo from sea and river waters followed byelution with 1 M nitric acid prior to the determination by ICP-OES or ETAAS. The LOD, for 100-fold enrichment, were0.007 ng mL21 and 0.009 ng mL21, respectively. Csaszmaet al.97 evaluated various sample preparation and measurementtechniques for the determination of Mn and Mo in humanbrains. The concentration of Mo was too low for directdetermination ETAAS and this analyte was preconcentrated byretention on iminodiacetic acid ethylcellulose (IDAEC) chelat-ing resin. Methods based on ETAAS, ICP-MS, ICP-AES andNAA were compared for the determination of Mn and resultsof the different techniques were in good agreement. The meanconcentration (dry weight) of Mn in human brain sampleswas between 1.1–2.9 ppm, while for Mo it was between 90and 330 ppb. Significantly higher values were found inAlzheimer’s diseased patients (Mo 330 ¡ 42 ppb, Mn 2.90 ¡0.07 ppm) than in control patients (Mo 219 ¡ 16 ppb, Mn2.40 ¡ 0.08 ppm).Mothes et al.98 extracted organophosphorus insecticides


from natural waters by stir-bar-sorptive extraction, a proce-dure that took 50 min for accumulation and 6 min for thermaldesorption. The LOD for measurement by GC with AE detec-tion of P were between 0.8 ng L21 (ethion) and 15.4 ng L21

(fenamiphos), making the procedure suitable for real watersamples. The recovery of a highly water-soluble analyte,fenamiphos, was only 15%.Yebra et al.99 developed a field preconcentration system in

which Pb from sea-water was retained on Amberlite XAD-4impregnated with 1-(2-pyridylazo)-2-naphthol followed byelution with HCl and detection by FAAS. A factorial designoptimization led to the conclusion that sample flow-rate andeluent volume were statistically significant factors. For a samplevolume of 1000 mL, the LOD was 5 ng L21. Losev et al.100

extracted Pd from 6 M HCl with silica gel modified withmercapto groups followed by elution with hot (50 uC) 8%thiourea in 1 M HCl for determination by AAS with a LOD of0.05 mg mL21. The procedure was applied to the analysis ofcopper–nickel ore SRM and copper concentrate.Marin et al.101 preconcentrated Se on thiol cotton after

digestion of lichens and plants in HNO3–H2O2–HF for deter-mination by ETAAS down to an LOD of 0.02 mg g21 in thesolid sample. They found that it was necessary to add a mineralmatrix before decomposition to obtain high and constantrecoveries. Dias et al.102 determined Se in foods by ETAASafter preconcentration as the diethyldithiophosphate complexon a minicolumn containing 30 mg of SiO2–C18 and elutionwith ethanol. Rh proved to be the best modifier and for 6 minloading the enrichment factor was 65, allowing determinationdown to 0.05 mg kg21 in fish, meat and flour. Li and Deng103

devised a procedure for the ETAAS determination of Se(IV) andSe(VI) via selective adsorption onto nanometer-sized titanium.For a 100mL samplemethod the concentration factor was 50 forvolume, and the LOD were 4.7 ng L21 for Se(IV) and 6.3 ng L21

for Se(VI). Sahin et al.104 preconcentrated Se(IV) from aqueoussamples on silica gel modified with 3-mercaptopropyl-trimethoxysilane followed by elution with acidic periodateand determination by HGAAS. The method was applied tospiked sea-water samples containing as low as 800 ng L21

Se(IV). As the procedure was highly selective for Se(IV) over Se(VI)any change on storage of the sample did not affect the inter-pretation of the results.Abbasse et al.105 evaluated several complexing agents

(dithizone, luminol and 8-hydroxyquinoline) with retention onC18 and elution with 2 mol L21 nitric acid for the determinationof V in sea-water by ICP-OES. The performance was comparedwith that of procedures in which the analyte was retained onchelating resins, such as chelamine, chelex-100 and immobilised8-hydroxyquinoline.Procedures for the determination of two analytes were

developed by several research groups. Liang et al.106 retainedAl and Cr(III) as the complexes with 8-hydroxyquinoline onTiO2 nanoparticles. The enrichment factor was 50 and theLOD were 1.96 and 0.32 mg L21, respectively, and the methodwas applied to the analysis of biological samples and lakewater. Tangen et al.107 devised a procedure based on SPE(cation exchange, anion exchange and chelation) for thefractionation of Al and Fe in soil water. Both strong cationexchange and chelation were found to work well, whereas lowrecoveries for Al were found with anion exchange. For Fe, thesum of the anionic and cationic fractions that passed throughthe cartridges was nearly 100%. The ICP-OES results for thelabile Al fraction (Al bound to the strong cation-exchangecartridge) showed an acceptable correlation with the resultsobtained by the equilibrium calculations, except for thesamples with the highest dissolved organic carbon. Bakirciogluet al.108 extracted Bi and Cr with rice plus husk, rice husk or itsash (rice husk heated at 300 uC for one hour and 600 uC for tenhours in a muffle furnace). The ash was found to be the mostsuitable adsorbent, with retention above pH 3 and elution with

2.0 M hydrochloric acid; the FAAS LOD were 13 mg L21 for Biand 1.5 mg L21 for Cr. Sweileh109 determined Cd and Pb afterretention on human hair shavings at pH 7, followed by elutionwith 0.1 mol L21 EDTA. After 40-fold pre-concentration of Cdand Pb from treated wastewater samples, the analytes weremeasured by FAAS. Budziak et al.110 devised a procedure forthe determination of Cd and Cu in which the analytes wereretained on niobium(V) oxide, chemically adsorbed on silica gelsurface followed by elution with 2.0 mol L21 nitric acid anddetermination by FAAS. For a 10.2 mL sample (2 min precon-centration), the enrichment factors were 20.3 and 17.5 for Cdand Cu, respectively; the corresponding LOD were 0.5 mg L21

and 1.0 mg L21. The method was tolerant to other ions usuallypresent in water samples. Demirel et al.111 determined Cd andPb in waste waters after preconcentration on Purolite C- 100 Ecationic resin packed into the housing of a membrane filtermounted to the tip of a plastic syringe. If the sample solutionwas drawn into the syringe over 30 s and discharged over thesame time, the analytes were quantitatively retained at pHgreater than or equal to 2. They were eluted with 2.5 M HCl aseluent via the same procedure. The elements were concentratedby drawing and discharging several portions of sample succes-sively but eluting only once. The FAAS LOD were 10 mg L21

for Cd and 15 mg L21 for Pb. Saglam and Koklu112 determinedCo and Ni by AAS in brine and sea-water after preconcentra-tion on silica modified with 3-aminopropyltriethoxysilane. Forthe same analysis, Shemirani et al.113 were able to load theanalytes on a minicolumn of alumina modified with sodiumdodecylsulfate and Schiff’s base at a flow rate of 15 ml min21.The LOD were 0.007 ng ml2l for Co(II) and 0.014 ng ml21

for Ni(II). The same group114 determined Cu and Pb usingoctadecyl-bonded silica membrane disks modified with anew hexadentate Schiff’s base {1,8-bis(salicylaldiaminato)-3,6-dioxaoctane}. The capacities of the modified disks were 550and 650 mg for Cu and Pb, respectively, and the correspondingLOD were 0.2 and 0.7 ng mL21. The method was applied to theanalysis of various matrices: water, wastewater, black tea,black and hot pepper. Matoso et al.115 used silica gel chemicallymodified with zirconium phosphate for the preconcentration ofCu and Pb from industrial and river waters prior to deter-mination by FAAS. Interferences from cobalt, iron, manga-nese, nickel, and zinc were overcome with an appropriateaddition of a KI or NaF solution. The analytes were elutedwith 1.0 mol L21 HNO3 at a flow rate of 2.0 mL min21. Theenrichment factor was 30 for both metals and the LOD were1.1 and 6.1 mg L21 for Cu and Pb, respectively. Akman andTokman116 measured Ni and Pb in Apple Leaves (NIST SRM1515) and sea-water by ETAAS after SPE with Chromosorb-107. The sample solution treated with or without APDC wasdrawn into the syringe filled with Chromosorb-107 anddischarged back manually; Ni was quantitatively retained atpH values greater than or equal to 6 irrespective of whether ornot it was complexed with APDC, while the quantitativesorption of lead was achieved at pH values greater than orequal to 8 only if it was treated with APDC. The metals wereeluted with 4.5 MHNO3. Godlewska-Zylkiewicz117 determinedPd and Pt in acidifed (pH 1.6–1.8) water samples by ETAASafter preconcentration on bakers’ yeast, Saccharomycescerevisiae, or green algae, Chlorella vulgaris, either free orimmobilized on silica gel. The method based on the immo-bilized algae in the column mode was preferred. The metalswere eluted with 0.3 mol L21 thiourea in 1 mol L21 hydro-chloric acid.Moving up to three analytes, there are still several research

groups involved. Qing et al.118 investigated the adsorptionbehaviour of noble metal ions (Ag Au, Pd) on nanometer-sizedtitanium dioxide for determination by ICP-OES after elutionwith a mixture of 5% thiourea solution and 3 mol L21 HNO3.The LOD for an enrichment factor of 50 were 0.006, 0.016 and0.012 mg mL21, for Ag, Au and Pd, respectively. The method


was applied to geological samples. Matsubara et al.119 deter-mined Au, Pd and Pt in industrial waste solutions by ETAASfollowing preconcentration on an anion-exchange resin. Therice husk material discussed earlier for Bi and Cr108 was alsoshown by Doner and Akman120 to retain three analytes (Cd,Cu and Pb) from polluted wastewaters. Bermejo-Barreraet al.121 determined the same three elements in river water byFAAS after preconcentration on Amberlite XAD-2 loadedwith 1-(2-pyridylazo)-2-naphthol. The optimum pH for simul-taneous retention was 8.5, and the cations were eluted simul-taneously. The preconcentration factor was 50. Tokmanet al.122 extended their syringe method to the preconcentrationof three analytes, Cd, Cr, and Cu, on silica gel modified with3-aminopropyltriethoxysilane. The analytes were quantita-tively retained at pH 5 and eluted with 2.0 M of HCl. TheETAAS LOD were 6.6, 6.0 and 7.5 mg L21 for Cd, Cu, and Cr,respectively. Mondal et al.123 determined Cd, Cu and Znby AAS in biological samples after preconcentration on6-mercaptopurinylazo resin. Divrikli et al.124 determined(FAAS) Cr, Fe and Pb in urine after enrichment on a cellulosenitrate membrane filter. For the analysis of tap, ground andlake waters, Bakircioglu et al.125 retained Co, Fe and Ni ondiethylenetriamine polymer prior to FAAS determination.The metals were retained on the adsorbent at pH 2.1 andeluted with 2M hydrochloric acid or nitric acid. The LOD were1.5 g L21, 2.1 g L21 and 1.9 g L21 for Co, Fe and Ni, res-pectively. For somewhat similar samples, Karatepe et al.126

preconcentrated Cu, Fe and Pb as the O,O-diethylphosphoro-dithioic acid complexes on Chromosorb-105 resin prior todetermination by FAAS. Much the same group of researchers,Soylak et al.,127 determined the same analytes in the samesamples by the same technique following adsorption on chro-motrope 2R-coated Amberlite XAD-1180. Roldan et al.128

determined Cu, Ni, and Zn in fuel ethanol by FAAS afterenrichment on a column packed with 2-aminothiazole-modified silica gel followed by elution with 2.0 mol L21 HCl.Also from Brazil, but writing in Portuguese, Santos et al.129

describe the determination of Cu, Mn and Zn in saline matricesby FAAS after separation and preconcentration on AmberliteXAD-7 impregnated with Alizarin Red S. They obtainedenrichments factors of up to 50.Even for four analytes, there is still a lot of activity. Carrilho

et al.130 determined Al, Co, Cu and Fe by ICP-OES afterpreconcentration on silica-immobilized brown alga (Pilayellalittoralis). The analytes were retained at pH 5.5 and eluted atpHv2 with dilute HCl, giving enrichment factors of between 7and 16. Chinese researchers, Fan et al.,131 preconcentrated Au,Pd, Pt and Rh on diphenylthiourea immobilized on aluminiumoxide prior to determination by ICP-OES obtaining LOD of0.008, 0.015, 0.022, and 0.022 mg g21, respectively, for theanalysis of geological samples. Chang et al.132 synthesized apoly(acryl-p-aminobenzenesulfonamideamidine-p-aminoben-zenesulfonylamide) chelating fibre for preconcentrating Au, Bi,Hg and Pd with elution by 0.25 M HCl and 2% thioureasolution at 50 uC. They found that 1000-fold excesses ofaluminium, barium, calcium, copper, iron(III), magnesium,manganese, potassium, sodium and zinc did not interfere.Reddy and Reddy133 synthesized and characterized chelatingpolymers derived by the condensation of poly(3-hydroxy-4-acetylphenyl methacrylate) with different diamines and theefficiency of the material for the retention of Cd, Cr, Hg and Pbstudied. Cesur134 determined Cd, Cu, Mn and Pb by FAASafter SPE of the phenylpiperazine dithiocarbamate complexeson activated carbon; they obtained enrichment factors up to400. Hanna et al.135 preconcentrated Co, Fe, Ni and Zn insurface water samples on porous silica modified withN-propylsalicylaldimine prior to determination by AAS. Ascitrate and EDTA interfered severely, organic matter in thesamples was oxidized. Goswami and Singh136 prepared andcharacterized 8-dihydroxyanthraquinone anchored to silica gel

for the SPE of Co, Cu, Fe and Ni prior to determination byFAAS. The lowest concentration for quantitative recovery wasabout 4.0 ng mL21. Soylak et al.137 retained Co, Cu, Fe and Nias the calmagite chelates on Chromosorb-102, obtaining FAASLOD of between 6.0–110 mg L21. Chinese researchers, Changet al.,138 prepared (sol–gel method) and characterized highsurface area nanometer-sized alumina and investigated theretention of Cr, Cu, Mn and Ni, all of which could be elutedwith 1.0 mol L21 HCl for determination by ICP-OES. Hanget al.139 determined trace rare earth elements (REEs) Ho, Nd,Sm and Tm in geological samples by ICP-OES afterpreconcentration on nanometer-size titanium dioxide. Theanalytes were recovered quantitatively with 2.0 mol L21 HClfor an enrichment factor of 50, and the LOD were 0.08, 0.1,0.18, and 0.06 ng mL21, respectively.Finally, in this sub-section, a survey of research in which

more than four analytes have been preconcentrated. Japaneseresearchers, Ninomiya et al.,140 synthesized a dithiocarbamate–chitosan resin which could absorb Ag, Bi, Cu, Hg, Mo, Te andW, but from which elution was difficult unless it was firstsaturated with copper ions that were washed off with 1 M nitricacid. Singh, Venkataramani and co-workers have reported, in a‘‘series’’ of investigations, on 8-hydroxyquinoline anchored tosilica gel,141 8-hydroxyquinoline anchored to cellulose142 and2,3-dihydroxypyridine anchored to cellulose.143 The threesystems have been used to retain Cd, Co, Cu Fe, Pb and Znprior to determination by FAAS. The oxine material alsoretained Ni. Enrichment factors of up to 300 were obtainedwith LOD between 0.7 and 5 mg L21. A similar series of reportsby Solyak and co-workers describes 1-(2-pyridylazo)-2-naphtol(PAN) impregnated Ambersorb 563,144 membrane filtration ofpyrrolydine dithiocarbamate chelates145 and retention ofxylenol orange metal complexes on Amberlite XAD-16.146

Each system was evaluated for the determination of Cd, Co,Cu, Ni and Pb by FAAS, with Cr added to the mix for the firstsystem. The filter was dissolved in nitric acid, and the xylenolorange complexes were eluted with 1 M HNO3 in acetone. TheLOD were between 0.2 and 1.4 mg L21 for the PAN system.Farajzadeh and Vardast report147 that rice bran is an excellentsorbent for heavy metals (Cd, Cu, Fe, Ni, Pb and Zn) fromaqueous media. After treating with saturated sodium chloridesolution, its efficiency for Ni and Zn improved. For all metalsthe exchange speed was very high. Grotti et al.148 investigatedthe retention of Cd, Cu, Fe, Mn and Pb from sea-water byan iminodiacetic resin (200 mg) with a loading flow rate of2 mL min21, elution volume of 3 mL and sample volume of50–450 mL. Only Cu was not completely retained. The ETAASLODwere 1.0, 6.8, 53, 3.3, and 4.7 ng L21, respectively, and forICP-OES the values were 12, 17, 21, 3.4, and 1229, ng L21. Theproblem caused by complexation by natural organic matterwas addressed by Abbasse et al.,149 who showed that totalmetal could be determined by ICP-OES following retention ofthe 8-hydroxyquinoline complexes on C18. Lee et al.150 deter-mined Mo, Pd, Rh, Ru, Te and Zr by ICP-OES in spentpressurized water reactor fuels following separation by ion-exchange and SPE with di(2-ethylhexyl)phosphoric acid.Zhang et al.151 evaluated a dibromodibenzo-18-crown-6 cross-linked chitosan material for the SPE of a number of metalsand found that retention was greater than 95% at pH 7.5, theenrichment factor was 50, and the ETAAS LOD were greatlyimproved.Japanese researchers predominate in methods based on

coprecipitation. Kashiwagi152 describes (in Japanese) proce-dures for the selective coprecipitation of As and Se species. Theselective reductive coprecipitation of Se(IV) in the presence ofSe(VI) was achieved: (a) on a tellurium collector from 1 M HClafter boiling for 15 for min with L-ascorbic acid and tin(II)

chloride; and (b) on a palladium collector from 0.2MHCl afterboiling for 30 min with hydrazinium sulfate. Inorganic As wasselectively coprecipitated in the presence of organoarsenic


compounds by lanthanum hydroxide at pH 12. In addition theyfound that dimethylarsinic acid, monomethylarsonic acid andp-aminophenylarsonic acid could be quantitatively distilled aschloroarsine compounds from 0.2 M SnCl2, 2.75 MH2SO4 and4 M HCl. The procedures were applied to the analysis byETAAS of waste waters containing ppb concentrations of Asand Se. Nakamoto et al.,153 also writing in Japanese, report onthe determination of As and Te in crude oils by coprecipitationwith ferric hydroxide after combustion of the samples anddissolution of the ash in 0.01 M hydrochloric acid. Theprecipitate was dissolved in concentrated hydrochloric acid andthe analytes determined by ETAAS; the LOD were 1 ng g21 forboth elements.Elci et al.154 determined Cd, Co, Cu, Fe, Ni and Pb in

wastewater, stream sediment and zinc CRM by FAAS follow-ing collection of the analytes on a cellulose nitrate membranefilter after coprecipitation with hexamethylenedithiocarbamicacid hexamethyleneammonium salt. The LOD ranged from6 mg L21, for Cd, to 60 mg L21, for Pb. Minami et al.155

determined Co and Ni in river water by ETAAS aftercoprecipitation with scandium hydroxide. The concentra-tion factor was 400 and the LOD, for a 200 mL sample,were 5.0 pg cm23 for Co and 10.0 pg cm23 for Ni.Wang et al.156

devised a Cr speciation procedure based on selective co-precipitation of the different oxidation states with leadpyrollidine dithiocarbamate: Cr(III) at pH 4 and Cr(VI) at pH9. The final determination was by slurry sampling ETAAS withPTFE as chemical modifier and the LOD was 0.02 ng mL21.Water and tea infusion samples were analysed. Minamisawaet al.157 developed an ETAAS procedure for the determinationof In in water after coprecipitation with chitosan followed bydissolution in acetic acid. The chemical modifier was lantha-num and the LOD was 0.04 mg L21. Saitoh et al.158 describe, inJapanese, a procedure for the rapid preconcentration of tracemetals as the chelates with 8-hydroxyquinoline or ammoniumpyrrolidine dithiocarbamate, following coprecipitation withthermoresponsive polymers, including poly(N-isopropylacryl-amide) and poly(vinyl methyl ether), which are water-soluble atroom temperature, but become sparingly soluble above theircritical solution temperatures to form gum-like precipitates.After dissolving the polymer phase in a small amount oforganic solvent, the solution was directly analyzed by ETAASor ICP-MS. An earlier report of the procedure is available inEnglish.159 Enrichment factors of up to 100 were obtained.Ghazy and Mostafa160 determined Ag in natural waters by

FAAS after coprecipitation with mercuric sulfide, flotation ofthe precipitate with oleic acid (as surfactant) and redissolutionwith (1 : 1) concentrated nitric and sulfuric acids. Pavlovskaet al.161 coprecipitated Ag, Cd, Cr, Mn, Tl and Zn fromaragonite (calcium carbonate) with hydrated iron(III) oxide, andiron(III) hexamethylenedithiocarbamate, and determined theanalytes by ETAAS (Ag, Cd, Cr and Tl) and FAAS (Mn andZn) after flotation separation. The LOD were 0.02 mg g21

for Ag, Cd and Cr, 0.117 mg g21 for Tl, 2 mg g21 for Mn and0.8 mg g21 for Zn. The same group162 investigated two pro-cedures for the ETAAS determination of Cu in fresh waters,based on coprecipitation with either cobalt(III) hepthyldithio-carbamate, or cobalt(III) hexamethylendithiocarbamate andfroth flotation separation. The enhancement factor was 40 andthe LOD between 0.03 and 0.1 mg L21.Najafi and Manouchehri163 developed a microelectrolysis

system for in-atomizer electrodeposition of Au prior to mea-surement by ETAAS. To prevent the highly corrosive effect ofthe aqua regia digestion media, the graphite tube surface waspre-coated by electrodeposition of Pd prior to sample introduc-tion. The method was validated by the analysis of severalCRM; the LOD was 0.1 ppb. The identical procedure is des-cribed by Komarek and Houserova.164 Manova et al.165

preconcentrated Hg(II) and total Hg in waters, for determina-tion by FAAS, on a porous working electrode made of glassy

carbon particles coated with gold in a flow-through electro-chemical cell. The LOD was 0.01 mg L21. Krenzelok et al.166

evaluated an in-atomizer electrodeposition technique for thedetermination of Pb by ETAAS. The original Teflon auto-sampler injection tube was replaced by a composite Pt/Tefloncapillary that served as the anode in the electrodepositioncircuit. The LOD was 20 pg. Amin et al.167 determined Sb inwaters by ETAAS (tungsten tube atomizer) after preconcen-tration on a tantalum wire. High concentrations of matrixelements could be tolerated and the LOD was 50 pg mL21.Wang et al.168 determined Sn in canned food by ETAASafter electrodeposition on a tungsten probe down to an LOD of0.08 mg L21 for a 200 s deposition.Roman-Silva et al.169 devised liquid–liquid extraction (LLE)

procedures for the determination of Ag, Al, Ba, Be, Bi, Cd, Co,Cr, Cu, Fe, Mn, Mo, Pb, Sr, Tl and V by either FAAS withhydraulic high pressure nebulization (HHPN) or a techniquereferrred to as ‘‘flame furnace’’ AAS, also with HHPN. Themethods, which included back extraction, were applied for theanalysis of river and sea-water, river and marine sediments, softtissue of mussels, tunicate siphons, aquatic plants, and samplesof clinical interest such as placentas, umbilical cords, andcardiovascular tissues from surgical procedures. Chamsazet al.170 determined As by ETAAS by ‘‘headspace liquidphase microextraction’’ following batch HG. The arsenicspecies were converted to arsine in 3 mol L21 HCl solution bysodium tetrahydroborate (NaBH4) in a closed headspace vialinto which a 4 mL microdrop, containing AgDDC dissolved ina mixture of pyridine and benzyl alcohol (1 1 3), was extrudedfrom the tip of a microsyringe. After 7 min extraction at 35 uC,the drop was transferred to the graphite furnace. For 2 ml ofsample solution, the enrichment factor was 150 and the LODwas 45 pg mL21. As the overall efficiency of HG, transport andtrapping was 30%, it is not clear what advantages the techniqueoffers over HG with in-atomizer trapping of the evolvedhydride. Japanese wokers, Anzai and Akama171 developed aprocedure for the determination of Au and Pd in a platingsolution. An aqueous two-phase system was obtained byadding 1 ml of sample solution to 3.0 ml of 1.0 mol L21 TBABaqueous solution and 1.0 ml of a buffer solution (pH 4) anddiluting with water to 6.0 mL. Then, 1.8 g of Na2SO4 wasadded and the mixture was shaken for about 1 min. Aftercomplete phase separation, a 0.5 mL aliquot was taken fromthe upper phase and then diluted with 10 mL of water forFAAS determinations. Ndung’u et al.172 compared the perfor-mance of a LLE-ETAAS procedure with that of an SPE-ICP-MS procedure for the determination of Cd, Co, Cu, Mn, Ni, Pband Zn in estuarine waters (South Bay of the San FranciscoEstuary). Although there was good agreement between the twosets of analyses for Cd, Mn, Pb, and Zn concentrations, thoseof Co, Cu, and Ni determined by SPE were found to be 10–20%lower than those determined by LLE. The different yields werepositively correlated (R w 0.961, simple linear regression) withthe dissolved organic carbon (DOC) in the samples. Goodagreement between the two methods for Co and Cu was achi-eved after UV irradiation of the acidified samples. Stasinakiset al.173 speciated Cr in wastewater and sludge by extractionwith the liquid anion-exchanger Amberlite LA-2. Total Cr wasdetermined directly by ETAAS, Cr(VI) was extracted at pH 6.4and determined in the organic extract. Cr(III) was determined bydifference. The LOD were 0.39 and 0.45 mg L21 for total Crand Cr(VI), respectively. By combining with filtration through a0.45 mm membrane filter, the procedure was extended to thespeciation of Cr in suspended solids. Japanese workers, Fukuiand Fujino,174 determined Cu, Fe, Mn and Zn in hard tissues ofshellfish by extraction of the DDC complexes into hexyl acetatefollowed by measurement by ICP-OES.Wu et al.175 describe, inChinese, a microdrop solvent extraction technique combinedwith low temperature electrothermal vaporization ICP-OES.They achieved 500-fold concentration of La by extraction into


a single micro-drop of ‘‘PMBP–benzene’’ suspended on the tipof a 10 mL microsyringe. Rajeswari et al.176 investigated therole of Cyanex-272 (2,4,4-trimethylpentylphosphinic acid) asan extractant for U in the determination of REEs by ICP-OES. Agrawal and co-workers177 have devised a supportedliquid membrane procedure for the extraction, separation,preconcentration and recovery of Ta with the help of dibenzo-18-crown-6 (DB18C6) in dichloromethane. The Ta-DB18C6extract was directly inserted in the plasma for ICP-OES mea-surement enhancing the sensitivity 20 times. A similar proce-dure was developed for V178 down to an LOD of 0.05 ng mL21.This element was also determined by ICP-OES after extraction,separation and preconcentration in new reagent N-phenyl-(1,2-methanofullerene C-60) 61-formohydroxamic acid. Directnebulization of the organic phase gave a sensitivity enhance-ment of 50 times.Manzoori and Karim-Nezhad179 devised a selective cloud

point extraction and preconcentration procedure for the deter-mination of Ag by FAAS. Dithizone (diphenylthiocarbazone)was used as the complexing agent and Triton X-114 was thesurfactant. After separation, the surfactant-rich phase wasdiluted with tetrahydrofuran. The preconcentration factor was43 for 10 mL of sample, and the LOD was 0.56 ng mL21.Sombra et al.180 developed a micelle-mediated phase separationwithout the addition of a chelating agent for the preconcentra-tion of Al for determination by ICP-OES. The surfactant wasnon-ionic polyethyleneglycolmono-p-nonylphenyl ether andfor 50 mL of parenteral solution, the LOD was 0.25 mg L21.Borges et al.181 determined Cd, Pb and Pd in blood by ETAAS(with iridium or ruthenium as permanent modifiers) by com-plexation with O,O-diethyldithiophosphate (DDTP) in hydro-chloric acid medium, and extraction into the phase rich in thenonionic surfactant octylphenoxypolyethoxyethanol (TritonX-114) The enrichment factors were 71, 34 and 100 for Cd, Pband Pd, respectively, and the corresponding LOD were 0.02,0.08 and 0.014 mg L21. Two blood CRM (lyophilized bovineblood and reconstituted human blood) were analyzed.Shemirani et al.182 determined Cr(III) and Cr(VI) in waters byAAS down to a LOD of 0.17 mg L21. The cloud-pointextraction was selective for Cr(III), and Cr(VI) was determined bydifference after reduction with ethanol in concentrated H2SO4.Manzoori and co-workers measured Co183 in urine and Co andNi184 in waters by FAAS. In the first procedure, water wasremoved from the final diluted surfactant-rich phase, whichincreased the enhancement factor 4-fold. 1-(2-Pyridylazo)-2-naphthol (PAN) and octylphenoxypolyethoxyethanol (TritonX-114) were used as hydrophobic ligand and nonionicsurfactant, respectively. The enhancement factor was 115 for10 mL of sample, and the LOD was 0.38 mg L21. In the secondprocedure, 1-nitroso-2-naphthol and polyethylene glycol-p-nonylphenyl ether (PONPE 7.5) were the hydrophobic ligandand nonionic surfactant, respectively. The enhancement factorwas 28 ¡ 1 for both analytes. Kulichenko et al.185 investigatedthe extraction with monocarboxylic acids and their mixtureswith amines into the nonionic surfactant OP-10 for the deter-mination of Cu by FAAS. The combination of 0.005 M capricacid and 0.01 M octylamine gave a LOD of 0.01 mg mL21.Luconi et al.186 determined Pb by ICP-OES with preconcen-tration by cloud point extraction without chelating agents byextraction into the surfactant-rich phase of polyethyleneglycolmono-p-nonylphenyl ether. The enrichment factor was 300,and the LODwas 0.08 mg L21. Wuilloud et al.187 measured V inparenteral solutions by ICP-OES; the vanadium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex was extracted atpH 3.7 into micelles of the nonionic surfactant polyoxyethylenenonylphenol. The extracted surfactant-rich phase was diluted1 1 1 with ethanol. For 50 ml sample solution the enrichmentfactor was 250 and the LOD was 16 ng L21.Taher has devised a number of procedures in which the analyte

is retained as an ion-association complex on microcrystalline

naphthalene or benzophenone from a large volume of solutionand dissolved in a small volume of DMF prior to determinationby FAAS: Cd188 was retained by 2-nitroso-1-naphthol-4-sulfonicacid (nitroso-S) and tetradecyldimethylbenzylammonium chlor-ide, Pb189 was retained as the 1-(2-pyridylazo)-2-naphtholcomplex, Ni190 was with retained 2-nitroso-1-naphthol-4-sulfonic acid (Nitroso-S) and tetradecyldimethylbenzyl-ammonium chloride on benzophenone, and Tl191 with1,10-phenanthroline on benzophenone. Costa et al.192 pre-concentrated Cd, Cu, Ni, Pb and Zn from synthetic brines asthe dithizone chelates co-crystallized with microcrystallinenaphthalene, in the pH range 8.5–9.1. Following extractionwith nitric acid, the analytes were measured by ICP-OES. TheLOD were 30, 11, 11, 47 and 44 mg L21, respectively. Pancrasand Puri193 determined Cu, Fe, Ni and Zn in various water,beverage and human hair samples.by FAAS after co-precipita-tion of the ion-pairs of 2-(5-bromo-2-pyridylazo)-5-diethyl-aminophenol (5-Br-PADAP) and tetraphenylborate (TPB),with microcrystals of naphthalene, followed by dissolution inDMF. Bispo et al.194 determined Pb in sea-water by ICP-OESafter separation and pre-concentration with co-crystallizednaphthalene and alizarin red. The solid quantitativelysorbs Pb(II) at pH 8–9, and the metal was eluted using 5.0 mlof 2 mol L21 nitric acid. The pre-concentration factor was 40and the LOD was 53 mg L21.Altman and Panichev195 collected tobacco smoke from

ambient air by electrostatic precipitation on the interior of agraphite tube atomizer for the determination of Cd. Permanentmodification with iridium allowed pyrolysis at temperaturesup to 1000 uC. It was possible to detect Cd in ambient air for25min after the smoking of a cigarette (theLODwas 0.2 ngm23).It was concluded that the results confirmed ‘‘the danger ofpassive smoking due to the presence of Cd in smoking areas’’.Korkmaz et al.196 investigated the nature of re-volatilizationfrom atom trap surfaces in flames by AAS. Analytes Au, Bi,Cd, Mn and Pb were trapped on a water-cooled, U-shapedsilica trap or a slotted silica tube trap and revolatilized byorganic solvent aspiration. They concluded that, althoughheating was not necessarily associated with re-volatilization,direct contact between the flame and the active silica surfacewas required. They found that the C : O ratio in the flame was acritical parameter.

1.3 Nebulization

There are still one or two research groups with an interest ingaining as complete an understanding as possible of the variousprocesses that occur in the conversion of ions in bulk aqueoussolution into atomic vapor, with a view to increasing the effi-ciency of the process and eliminating the effects of othersolution components. Most of the devices that are currentlystudied are for plasma spectrometers. One relatively new topicis the combination of nebulization with HG, allowing the deter-mination of the hydride-forming elements at lower concentra-tions while using the spectrometer in a pseudo-conventionalnebulization mode.Mora et al.197 reviewed liquid-sample introduction for

plasma spectrometry with particular emphasis on the processesthat affect the aerosol between generation and reaching theplasma. Karanassios198 reflects on alternatives to pneumaticnebulization sample introduction for ICP and speculates on theadvantages of devices capable of introducing small amounts ofsolids. He suggests that such devices have the potential to causea ‘‘paradigm shift in classical elemental analysis by ICPspectrometry by taking analysts from the millisize (e.g., mg ormL) to the micro-size (e.g. mg or mL), sub-micro and even nano-sample-size regime’’. One consequence of this, he foresees, isthat portable elemental analysis micro-instruments that can betaken out of the laboratory and into the field are poised tocause another ‘‘paradigm shift in classical elemental analysis’’


by allowing analysts to bring (part of) the laboratory to thesample.Schaldach et al.199 have extended their modelling of cyclonic

spray chamber processes, by computational fluid dynamics, toinclude the effect of flow spoilers. They modelled both typicalsample introduction conditions and low-flow sample uptake.The performance of six different chambers (no spoiler, a singlespoiler in four different positions, and 3 spoilers) was modelled.They found that (a) the position of the spoiler was critical indetermining the flow field in the chamber and hence theefficiency and washout time, and (b) that the chamber geo-metry had maximum impact under low uptake conditions if thelimited dispersion primary aerosol could follow the gas flowlines. Results were confirmed by experiment and a chamberconstructed according to the model results gave, for ICP-OES,LOD 1.5–19 times better than those obtained with the chambersupplied with the instrument. They concluded that a chamberwith 3 spoilers created a low-volume ‘‘virtual cyclone’’ insidethe containing walls that combined rapid washout withacceptable efficiency.Benson et al.200 developed a numerical model for coales-

cence, transport, heating and desolvation in an argon ICPbased on Monte Carlo method and the Ashgriz–Poo model,whose use for small droplet coalescence was supported bymolecular dynamics simulations. The performance of a con-ventional nebulizer–spray chamber arrangement, a direct injec-tion high efficiency nebulizer (DIHEN), and a large boreDIHEN (LB-DIHEN), were modelled. They found that: (a)collisions between droplets in the plasma lead primarily tocoalescence, particularly for direct aerosol injection; (b)DIHEN droplets penetrate further into the plasma whencoalescence is considered; and (c) LB-DIHEN droplets coalesceless frequently than those from a DIHEN. Todoli andMermet201 also modelled behaviour in a spray chamber: thistime it was solvent evaporation that was of interest. Theirresults indicated that in the torch integrated sample introduc-tion system (TISIS, basically a 5 cm3 cavity at the base of thetorch) a significant fraction of the solvent contained in primaryaerosol evaporated, while the remaining droplets first impactedthe inner walls and then evaporated. They concluded that thelonger the cavity, the higher the sensitivity, whereas an increasein its diameter did not significantly modify performance. Theoptimized TISIS cavity, with a conical shaped end, proved tosignificantly shorten the wash-out times with respect to those ofa double pass spray chamber and a low volume cyclonicchamber when used in conjunction with a micronebulizeroperating at deliveries of 20–200 mL min21. When used fordiscrete sample introduction (0.3–32 ml), the signal peaks werenarrower and higher than those produced by a double passspray chamber. Matrix effects caused by sodium, acetic acidand ethanol were less severe for the TISIS than for the doublepass and cyclonic spray chambers, while transient effectscaused by nitric acid solutions almost disappeared. They havealso reviewed the development of the TISIS device.202

Hoang et al.203 have made further developments with theoscillating capillary nebulizer (OCN) by fabricating the devicefrom silica and PEEK capillaries to make it sturdier and toimprove sensitivity. They measured droplet size distributionsand Sauter mean diameters of aerosols by laser Fraunhoferdiffraction and found that an OCN fabricated with PEEK witheither a thicker capillary wall or a larger inner diameter liquidcapillary tube performed better than the original OCN design.This increased the signal by 3–4 times, corresponding to a 2.5–3.0 times improvement in transport efficiency. The effects ofspray chamber design, droplet size and turbulence on thetransport efficiency of low molecular weight organoseleniumcompounds (selenocystamine, selenomethionine and trimethyl-selenonium iodide) were also investigated. Contrary to litera-ture reports, they found that that moderate increases in meandroplet sizes resulted in improved analyte transport efficiencies

and higher signal intensities for the volatile compounds tested.However, aerosols with Sauter mean diameters, greater thanapproximately 9.5 mm, gave lower transport efficiencies withconsequent reduced signal intensities. They also found that,although greater turbulence in the gas flow inside a single-passspray chamber decreased net analyte transport efficiencies(which is what they expected), the overall loss of aerosol wasunexpectedly 3–5 times greater for small droplets (v3 mm) thanfor larger droplets (3–9 mm).Davies and Berndt204 have provided further information on

the performance of their thermospray flame furnace AASdevice. The liquid to be analyzed is transported by a low orhigh-pressure pump through a very hot, simple, inexpensiveceramic capillary tip acting as a flame-heated thermospray. Theaerosol is directed into a nickel tube in the acetylene–air flame,thereby increasing the residence time in the absorption volumeand leading to LOD improvements of between 3- and 110-foldfor 17 elements. Rychlovsky et al.205 describe the performanceof a device they call a ‘‘heated electrospray interface’’ thatconnected the HPLC separation of organotin and organoleadcompounds with AAS detection. However, it appears that theelectrospray phenomenon is not involved because the vitreousbody of the ‘‘electrospray’’ interface was externally heatedabove the boiling point of the solvent and quartz furnace AASwas used for detection. With this device a wide range of flowrates, from 50 to 1000 mL min21, was possible but, in com-parison with post-column conversion of the organotin com-pounds to gaseous hydrides, the LOD were approximately oneorder of magnitude higher. Nonetheless, the system was used todetermine the tributyltin content of BCR RM 477, MusselTissue, and the tetraethyllead content of gasoline samples.Carrion, Murillo and co-workers206 have developed a direct

HG nebulizer for the determination of Se by ICP-OES. Thissystem is simpler than conventional hydride generationsystems, and does not need to be changed to work in thenormal mode. It produced a rapid response with low memoryeffect and reduced the interference level of cobalt, copper andnickel to 500, 5 and 600 mg L21, respectively. The LOD was0.2 mg L21. The device was used in the determination ofselenium in several food and clinical SRMs. The device has alsobeen used for the determination of As and Sb.207 McLaughlinand Brindle208 evaluated their new sample introduction system,combining vapour generation and nebulization, which they callthe ‘‘multimode’’ sample introduction system. For a variety ofelements that can be transformed into volatile species byreduction of aqueous ions in the appropriate oxidationstate with tetrahydroborate(III), the LOD are 10- (for Te at238.578 nm) to 90-fold (for Sb at 217.582 nm) lower thanconventional nebulization. In addition, the device minimizesthe transfer of solution from the vapour generation process tothe excitation source but has similar mass transfer efficiencycompared with conventional nebulization when used in thismode. The device can be operated as either a vapour generatoror as a conventional spray chamber, separately or simulta-neously, while retaining the sensitivity and LOD of both modesof sample introduction.O’Brien et al.209 investigated the direct injection high effi-

ciency nebulizer (DIHEN) for introduction of the sampleaerosol into the central channel of axially and radially viewedplasmas and found that signal-to- background ratios (SBR),LOD, and precision for the DIHEN were comparable orsuperior to those for conventional sample introductionsystems. The Mg II 280.270/Mg I 285.213 nm ratios werelower with the DIHEN, indicating that the DIHEN is moresusceptible to matrix effects for both the axial and radialsystems. Replacement of Ar with Ar–O2 and Ar–N2 mixtures inthe outer gas flow of the plasma improved SBR and Mg II280.270/Mg I 285.213 nm ratios of the DIHEN, and reducedmatrix effects.The use of an ultrasonic nebulizer still seems to be of


sufficient novelty to warrant mention in the title of an article oreven to be the subject of an investigation. Desboeufs et al.210

compared the performance of pneumatic and ultrasonic sampleintroduction systems for ICP multichannel-based emissionspectrometry in an ultra-clean environment. They found thatthe ultrasonic nebulizer offered a large increase in signalintensities (10–133 greater) compared with those obtained witha cyclone chamber coupled to a pneumatic Meinhard nebulizer.The increases were associated with an average increase of signalto background ratio by a factor of 86 and an average decreasein LOD by a factor of 6. They conclude that as, typically, theseLOD were lower than those obtained in non-ultra-cleanconditions, clean conditions are essential for avoiding crosscontamination and obtaining low LOD. Several groups ofresearchers have enhanced the performance of a precon-centraion method with the help of an ultrasonic nebuli-zer.60,62,69,71,72 A hydraulic high pressure nebulizer has beenused in this fashion also.211 Hislop and Hornbeck212 evaluatedseveral strategies, including the use of ‘‘sampling accessories’’,for coping with the effects of high dissolved solids in ICP-OESdeterminations. Isoyama et al.213 modified a PTFE Babingtonnebulizer (with a hood) for the determination of traceimpurities in silica powders by ICP-OES. A review by Polec-Pawlak and Jarosz214 of the evolution in the coupling ofcapillary electrophoresis (CE) with ICP-MS, with emphasisplaced on the application to speciation analysis, is of interest,as they consider the nebulizer to be the key component.

1.4 Chemical vapour generation

There is no diminution in the numbers of publications dealingwith some aspect of chemical vapour generation for analyticalpurposes. If anything, the numbers appear to be increasing asthe numbers of ‘‘applications’’ papers grows. Deciding whethera paper in which results of the analyses of some hydride-forming element has been performed by HG-AS are reported isto be included in this Update is problematical. In the past, mostof the papers describing the determination of Hg by CVtechniques have been included as this gave a complete pictureof the activity related to the determination of this key elementin the past twelve months (apart from the comparatively smallnumber publications describing work with ICP-MS). This yearnot all publications have been cited; those omitted are of apurely application nature. The numbers of papers appearingthis year indicates that the special position of Hg is beingchallenged by As. As in previous years, the chemistry isdominated by reaction with borohydride, though there are stilla few reports of electrochemical HG and, of course, Sn(II) hasbeen used to generate CV Hg. Interest in the HG of non-metalloid elements is increasing as the performance of thesemethods makes incremental progress towards that which isneeded if the chemistry is to form the basis of a viable methodof analysis. As has been discussed earlier in section 1.3, devicescapable of simultaneous nebulization and HG have beendescribed. It is for the determination of As, Se and Hg thatAFS instrumentation has secured a niche.Takase et al.215 reviewed the historical development of

chemical vapour generation techniques by both batch and flowinjection sampling formats. All detection techniques wereconsidered including FANES. Niedzielski et al.216 reviewedthe conditions used for the HG-AAS determination of As, Sband Se.

1.4.1 Fundamental studies in hydride generation. D’Ulivoand Dedina217 investigated the formation of double peaks,observed in continuous flowHGwith quartz atomizers, and thefate of free analyte atoms in the determination of As and Se byAAS. They concluded that a mechanism based on incompleteatomization of hydrides could not account for the experimentalresults because double peaks were observed with a microflame

atomizer that was able to produce quantitative atomization ofa large amount of hydride, even when the supply rate of oxygenwas close to that of the extinction threshold of the flame. Theysuggested that heterogeneous gas–solid reactions betweenfinely dispersed particles, formed by free atom recombination,and the free atoms in the gaseous phase are at the origin ofdouble peak formation.Bolea et al.218 made a critical study of the influence of

experimental parameters relevant to the FI electrochemicalgeneration of hydrogen selenide in a flow-through concentriccell with a ‘‘packed cathode made of particulated lead’’. Theyfound that both sample flow rate and electrolysis current wereimportant. Sima and Rychlovsky219 also studied the electro-chemical generation of hydrogen selenide with determinationby ET-AAS after in-atomizer trapping. Flow-through cellswith lead wire (cell 1) and granular lead (cell 2) as the cathodematerial were fabricated. The overall efficiency of generation,transport and collection was 71 ¡ 7% for cell I, and 80 ¡ 5%for cell II. The LOD of 50 pg, obtained with cell 2, was similarto that for generation with borohydride, for which the wasLOD 30 pg. The value reported by Bolea et al.218 (17 mg L21 fora sample volume of 420 mL) would be 7000 pg; the benefits of inatomizer trapping are readily apparent.Junkova et al.220 studied the interferences of transition

metals, noble metals and hydride-forming elements on theelectrochemical generation of hydrogen selenide in a con-tinuous flow mode system.Wieteska et al.221 studied the effectiveness of L-cysteine as a

pre-reducing agent and its effect on the HG efficiency in thedetermination of As in natural materials by batch HG withborohydride in HCl solution. Not surprisingly they found thatthe L-cysteine concentration, needed for complete reduction ofAs(V) to As(III), depends on the kind of the natural materialexamined and on the appropriate dilution of the sample beforethe measurement.D’Ulivo et al.222 studied the effects of several masking agents

on the determination of Se by continuous flow HG-AAS with aminiature argon–hydrogen diffusion flame atomizer. Theeffects of masking agents (KI, NaSCN, thiourea, L-cysteine,1,1,3,3-tetramethyl-2-thiourea) were studied both in theabsence and in the presence of selected interfering species(cobalt, copper, gold, iron, nickel, palladium, platinum andsilver). Different addition strategies were investigated: in thebatch mode, either to the sample or the borohydride solution;in the on-line mode, to the sample either before or aftermerging with the borohydride. The combined effect of somemasking agents was also investigated. They found that themode of addition could play a decisive role in the control ofinterfering processes. The addition of NaSCN to the borohy-dride solution produced a moderate catalytic effect, similar tothe one obtained in the presence of KI, and improved thetolerance towards cobalt, copper, nickel and palladium. Thecombined use of KI (added to the borohydride) and 1,1,3,3-tetramethyl-2-thiourea (added on-line to the sample) producedmasking comparable, but not superior, to that of thiourea,except towards palladium and platinum, for which goodtolerance limits were achieved. In the absence of KI in theborohydride, the masking efficiency of 1,1,3,3-tetramethyl-2-thiourea was considerably lowered. The addition of somemasking agents such as thiourea, L-cysteine and 1,1,3,3-tetramethyl thiourea on-line after the merging of a mixtureof borohydride and KI was highly effective in the con-trolling interferences from copper and silver. The method wasapplied to determination of trace of selenium in pure copperSRM.Farias et al.223 investigated the effect of several inorganic

(nitric, sulfuric and hydrochloric) and organic (acetic, mer-captoacetic and tartaric) acids on the efficiency of continuousHG determination of Sn by ICP-OES and on the extent ofmatrix interferences. They found that the highest sensitivity


was obtained with 2.5 M acetic acid and that the effects ofsignal depression produced by transition and hydride-formingelements were less pronounced with acetic and mercaptoaceticacids. A significant increase in sensitivity was obtained attemperatures above 20 uC. The LOD for acetic acid was0.1 ng ml21. The method was validated by the analysis of a soilCRM (GBW 07405).Bulska et al.224 characterized the compounds of As, Sb and

Se on graphite surfaces modified with noble metals formedduring in-atomizer trapping of the hydrides by SIMS. Thesurface and sub-surface distribution of noble metals (afterelectrodeposition of 600 mg or thermal reduction of 10 mg asmodifiers), as well as of As, Sb, and Se (200 ng) as analytes aftertheir deposition on the graphite surface, were investigated. Thispermitted simultaneous observation of the depth profile dis-tribution of modifier and analyte with a depth resolution ofdown to approximately 25 nm, limited however, by the surfaceroughness. It was found that after deposition at 400 uC, allanalytes partially penetrated the graphite surface and theirdistribution overlapped that of the noble metals; however, thedegree of penetration differed for each analyte and modifier.Ribeiro et al.225 developed a quartz tube atomizer with

tungsten coil for the determination of As down to an LOD of1.5 mg L21 by FI-HG-AAS. A Nafion membrane that con-tinuously dried the gas stream removed of 4.2 mg min21 ofwater, corresponding to an efficiency of 93%.Semenova et al.226 developed a multi-syringe system for the

determination of total inorganic Se by HG-AFS in which (a)sample in the acid media (50% HCl), (b) a sodium tetrahy-droborate solution (0.18%) and (c) a solution of hydrochloricacid (50%) were simultaneously dispensed into a gas–liquidseparation cell by a multisyringe burette coupled with onemultiport selection valve. The LOD was 0.01 mg L21 and thethroughput was 28 samples per hour. The proposed methodprovides a higher sampling frequency and a significant reduc-tion of reagent and sample consumption.D’Ulivo et al.227 evaluated aminoboranes of the type L-BH3

(L~NH3, tert-BuNH2, Me2NH,Me3N) and sodium cyanotri-hydroborate(III) (NaBH3CN) as derivatization reagents in thecontinuous flow HG of volatile hydrides and elementalmercury from the ionic species of Hg(II), As(III), As(V), Sb(V),Sb(III), Bi(III), Se(IV), Se(VI), Te(IV), and Te(VI). A miniature argon–hydrogen diffusion flame atomizer was used for AAS detection.They found that all of the agents were able to reduce Hg(II) tothe elemental state, giving sensitivities comparable to NaBH4

reduction; however, under reaction conditions giving maxi-mum sensitivity for HG with NaBH4, only some aminoboraneswere able to produce volatile hydrides from all the elements.No hydride formation was observed from Se(VI) and Te(VI). Ingeneral, the generation efficiency followed the order NaBH4 w

H3N–BH3 w tert-BuNH2–BH3 w NaBH3CNLMe2HN–BH3 w Me3N–BH3. In comparison with borohydride,aminoboranes and NaBH3CN provided better control of theinterference effects of cobalt, copper nickel and iron.Matusiewicz228 reviewed the analytical methods and techni-

ques described in the literature for hydride generation as amode of slurry sample introduction into atomization cells, andwith Mroczkowska229 developed a slurry sampling method forthe determination of As(III) by continuous flow HG-ETAASwith in-atomizer trapping on an iridium modifier. Samples(slurried in HCl with addition of ozone) were prepared withultrasonic agitation. For the estimation total As (and henceAs(V) by difference) thiourea was added to reduce As(V) toAs(III). The overall efficiency of generation and trapping was89% for particle sizes less than 20 mm and the LOD was at4.8 ng g21. The procedure was validated by the analysis of anumber of environmental and biological reference materialswith calibration by standard additions.Luna et al.230 generated volatile species by the addition of

sodium borohydride to an acidified solution of Ag, Cu, Cd, and

Zn at room temperature, which were rapidly transported to apre-heated graphite tube and trapped on the interior surface,previously treated with Ir as a permanent chemical modifier.The LOD were Ag 1 mg L21, Cd, 0.6 mg L21, Cu 3 mg L21 andZn 0.1 mg L21. The overall efficiency of the generation andtrapping process for Ag was 13%. A possible improvement forAg (by ICP-OES) was reported by Matousek and Sturgeon,231

who achieved more than one order of magnitude enhancementof efficiency by the addition of a surfactant (Triton X-100) incombination with an antifoaming agent. They concluded thatthe overall efficiency of introduction of Ag to the plasma wasover 20%, and that the effect of the surfactant could not beascribed to the formation of organized media. In addition, theydeduced that the generation reaction was not a simple one-stepprocess, as is the case for Se HG, but rather a two-stepprocedure. They observed that transport of the volatile Agspecies resembled the transport of liquid aerosol rather thanthat of a simple gaseous species, such as H2Se. Ma et al.232

generated volatile gold species from the reaction of borohy-dride with an acidified solution at room temperature, whichwere subsequently trapped in-atomizer for ET-AAS. Thereaction coil and gas–liquid separator were ‘‘conditioned’’ bypassage of a liquid solution containing low concentrations ofpalladium(II), sodium DDTC and NaBH4. For 40 s trappingtime, the LOD was 0.8 ng ml21. Ore samples were analysed; therecoveries of 25 ng ml21 spikes from dilute ore digest solutionswere 90–106%. Pohl and Zyrnicki233 studied the generation ofvolatile derivatives of Au, Pd and Pt on reaction withborohydride in aqueous acid solution for determination byICP-OES. The effect of masking agents (cyanide, thiourea andEDTA) and acidity on the interferences from cadmium, cobalt,copper, iron and nickel were investigated. Smichowski et al.234

generated volatile Zn species by merging acidified aqueoussamples and sodium tetrahydroborate(III) solution in acontinuous flow system, which were subsequently introduced,via an argon carrier stream, into an ICP for quantification byOES. The effects of (a) various mineral and organic acids, and(b) interferences from transition metals and other hydride-forming elements, were studied. They found that in HCl theefficiency of the generation process was 50%, giving an LOD of4.6 ng mL21. The method was validated by the analysis ofCRM NIST 1643d, Trace Elements in Water.Zhang et al.235 devised a procedure that they call ‘‘nebulous

phase reaction’’ for the generation of a volatile Cu derivativefor FAAS. Sample solution was sprayed into a reaction tubethrough a capillary and mixed with NaBH4 solution introducedby a peristaltic pump, and pressurized air. The effects of adozen potentially interfering ions were investigated. The LODwas 6 mg L21. Evidence is presented concerning the nature ofthe volatile compound. This procedure is conceptually similarto the nebulizer-based HG generation procedures discussed insection 1.3.206–208

With regard to the simultaneous generation of hydrides ofmore than one analyte, the numbers of publications hasdecreased compared with those of previous years. Chineseworkers, Li et al.,236 claim the simultaneous determination ofAs and Se in sulfur by HG-ICP-OES, with LOD of 0.6 ng mL21

and 0.7 ng mL21, respectively. As the sample was dissolved innitric acid and perchloric acids, it is expected that the analyteswould be present as As(V) and Se(VI). However, no informationabout how these were reduced to As(III) and Se(IV) was provided.Japanese workers, Matsumoto et al.,237 report the simulta-neous determination of As, Bi and Sb in steels by HG andhigh-power, nitrogen MIP-OES. Of the several reductantsexamined, thiourea was the best to reduce As(V) and Sb(V) to thetrivalent state prior to hydride generation. A large amount ofFe(III) caused a severe interference, while Fe(II) had little orno effect. Of the several interference-releasing agents examined,L-ascorbic acid was found to be the best. They also report thesimultaneous determination of As, Bi, Sb and Se238 by the same


procedure. With Se added to the mix, they found that the bestpre-reductants were hydrochloric acid for Sb and Se, andpotassium iodide for As. To reduce Fe(III) to Fe(II), thiourea waspreferred.Sun et al.239 determined Cd and Hg simultaneously by

vapour generation non-dispersive AFS. Ascorbic acid, cobaltand thiourea were used as enhancement reagents or maskingagents to enhance the generation efficiency of the volatilespecies of Cd and Hg, which are probably a mixture of freeatoms (Hg) and unstable hydride (Cd). Oxidation state adjust-ment is not really an issue for this analysis.

1.4.2 Other volatile compounds. Sometimes the analytes arealready mobilized in the vapour phase. Clarkson et al.240

applied an ICP emission spectrometer with a modified torch toallow the introduction of flue gas directly into the plasma forcontinuous measurement of Al, As, Ca, Cd, Cu, Hg, Na, Ni, Pb,Sb, Sn, Tl and V. The LOD were in the range 0.0004 mg m23

to 0.1 mg m23. Abanades et al.241 monitored Cd, Pb, and Zn inthe fumes from a laboratory fluid-bed incinerator by ICP-OES. Following initial studies with pure mineral and organicmatrices, a more complex metal-spiked matrix, derived fromreal waste, was burned to simulate metal release duringmunicipal solid-waste incineration and the metal evaporationprocesses were successfully monitored.Guo et al.242 converted inorganic Se(IV) to volatile hydrogen

selenide, selenium carbonyl, dimethyl selenide, and diethylselenide in the presence of formic, acetic, propionic, andmalonic acids, respectively, by irradiating the mixtures withUV light. The volatile products were identified by cryotrappingGC-MS. In acetic acid solution, the generation efficiencywas 50 ¡ 10%. Cobalt and nickel at concentrations of 100 and500 mg L21, respectively, did not interfere and the QT-AASLOD was 2.5 mg L21.Scriver et al.243 described a procedure for the determination

of tributyltin (TBT) in aqueous samples and extracts based onits relatively high volatility in halide media, permitting vapourphase sampling from the headspace above such samples leadingto the technique of chloride generation FI-ETAAS with inatomizer trapping on the surface of an iridium-treated graphitetube. The solution LOD was 0.33 ng mL21 for a 4 mL sub-sample and the procedural LOD for the analysis of an NRCCCRM, PACS-2 (sediment), was 66 ng g21 as TBT in thesediment.Matsumoto et al.244 report, in Japanese, on the determina-

tion of Cu in steels by ICP-OES with chemical vapour genera-tion from citric acid solution; however, they could not identifythe nature of the volatile derivative, which was sufficientlystable to be separated in a gas–liquid separator and delivered tothe plasma in an argon gas stream. The interference from ironcould only be overcome by extraction of the Cu. The LOD was1.5 ng mL21 at the Cu I 324.754 nm line. Matsumso andNakahara245 determined C in aqueous solutions by He MIP-OES with a gas-phase sample introduction technique in whicha continuous flow of carbon dioxide was generated fromcarbonate and hydrogencarbonate ion by acidification. Of theacids and drying agents investigated, hydrochloric acid foracidification and anhydrous calcium chloride as a desiccantwere selected. The LOD at the C I 193.09 and C I 247.86 nmlines were 7.89 and 8.10 mg L21, respectively. Bromide, calcium,chloride, fluoride, iodide, potassium and rubidium did notinterfere, although many other matrix components did.Guchardi and Hauser246 were able to detect C via the C2

emission 385.2 nm in their capacitatively coupled microplasmasustained in a fused silica capillary of 250 mm id. For CO2, CH4

and ethanol (determined from the vapour) the LOD were90 ppb, 30 ppb and 33 ppb, respectively.Bermejo-Barrera and co-workers have developed an ETAAS

Cr speciation procedure based on in-atomizer chemical vapourgeneration, in which the Cr(III) was removed as a volatile chelate

with either thenoyltrifluoracetone247 or 1,1,1-trifluoro-2,4-pentadione.248 The complex was formed either by initialmixing on sonication for 5 s at 40 uC time followed by reac-tion for 210 min,247 or by heating in a 100-W microwave ovenfor 2 min.248 At temperatures above 700 uC, the Cr(III) complexwas completely volatilized from the furnace, leaving Cr(VI),which was ashed at 1600 and atomized 2400 uC, respectively.Better separation was obtained when 5 mg L21 of palladiumwas added as a modifier. The LOD was 0.7 mg L21 Cr; Cr(III)was determined by difference following the determination oftotal Cr.Haberhauer-Troyer et al.249 compared different three

chloroformates for the derivatisation of seleno-amino acidsfor determination using GC-AES: ethyl chloroformate; methylchloroformate; and menthyl chloroformate. They concludedthat methyl chloroformate was the preferred derivatisationreagent, as it gave the best derivatisation yield and reprodu-cibility, and also showed less significant conditioning effectsthan ethyl chloroformate. The overall efficiencies for the deter-mination of selenomethionine and selenoethionine fromaqueous extracts ranged from 40 to 100% for methyl chloro-formate, from 30–75% for ethyl chloroformate and from 15–70% for menthyl chloroformate, measured over a period ofmonths. The RSD of the method for the methyl and menthylchloroformate derivatisation ranged from 7 to 13% withoutinternal standard, which improved to 2% for the determinationof selenomethionine with selenoethionine as internal standard.This indicates that, despite the limited reproducibility of themethod, its repeatability is good enough to allow accuratedetermination of selenoamino acids. They applied the proce-dure to the analysis of selenium dietary supplements thatcontained selenomethionine.Khuhawar et al.250 evaluated five chelating agents including

tetradentate beta-ketoamine Schiff bases, derived from DL-stilbenediamine, and meso-stilbenediamines for the GC separa-tion of Cu, nickel, Pd(II) and V(IV) with flame ionization orMIP-OES detection.

1.4.3 Vapour generation of the individual elements.1.4.3.1 Arsenic. A number of studies featuring As havealready been described. Niedzielski et al.216 reviewed the HGdetermination of As. D’Ulivo and Dedina217 investigateddouble peak formation. Wieteska et al.221 studied the role ofL-cysteine. Bulska et al.224 examined the in-atomizer trappingof arsine. Ribiero et al.225 determined As with a W-coil quartztube atomizer. D’Ulivo et al.227 generated arsine by reactionwith aminboranes. Mroczkowska229 generated arsine fromslurries.Cava-Montesinos et al.251 determined As and Sb in milk by

HG-AFS after microwave-assisted sample digestion. Cows’milk, obtained from the Spanish market, contained 3.4–11.6 ng g21 As and 3.5 to 11.9 ng g21 Sb. They point outthat this 1 : 1 ratio contrasts with the 10 : 1 natural ratio, and ispossibly indicative of the introduction of new alloys andpolymer materials in the industrial process of milk. The LODwere 6 and 3 ng L21, respectively. They also developed252 anon-chromatographic speciation procedure to distinguishbetween the -(III) and -(V) oxidation states based on HGbefore and after reduction with KI. Surprisingly, they con-cluded, from recovery experiments on spiked commerciallyavailable samples, that neither the reduced nor the oxidizedforms of the elements under study or mixtures of the twooxidation states were modified by the room temperaturesample treatment with aqua regia. They found that As(V) andSb(V) were the main species present in the samples analysed:62 ¡ 5 and 73 ¡ 5%, respectively. Sun et al.253 developed amethod for the direct determination of trace and ultra-tracelevels of As and Sb in waters by HG derivative AAS for whichthe sensitivities were increased 36.4 and 27.6 times, respectively,compared with those of conventional HGAAS. The LOD were


15 ng L21 for As and 20 ng L21 for Sb. Ronda et al.254

determined As and Hg in white beet sugar by HG-AAS. Theydemonstrated that sample digestion could be omitted withoutany significant influence (p v 0.05) on the final results. Theyfound the concentrations in commercial samples to be notgreater than 10 mg kg21 As and 2 mg kg21 Hg. Chineseresearchers, Suo and Li,255 determined As and Hg in medicinalanimal horns by HG-AFS with LOD of 1.50 ng mL21 and0.80 ng mL21, respectively.He et al.256 investigated the distribution of As and Se in 33

Chinese coal mines by FI-HG-non dispersive AFS. Theyfound that the concentrations of As in the northeast region ofw100 mg g21 are relatively higher than the values in the east.On the other hand, the Se contents are the opposite: most ofthem from the northeast mines are v1 mg g21 and increase asthe mine location advances, south where the average contentsare w5 mg g21.Other multi-analyte HG procedures featuring As that have

already been discussed are by Bings et al.,257 Li et al.,236

Matsumoto et al.,237,238 Abranko et al.,258 and Gallignaniet al.259

There are relatively few HG-AES procedures reported in thisreview period. Apart from the work of Matsumoto et al. (seeabove) the only other report is by Guchardi and Hauser,246

who were able to detect As and Sb, via HG, as well as Hg byCV generation, in their capacitively coupled microplasmasustained in a fused silica capillary of 250 mm id.Flores et al.260 developed a batch HG-AAS method for the

determination of total As in injectable drugs containing highlevels of antimony(V) as N-methylglucamine antimonate. Toavoid the interference from the antimony(V), a delay time of 1 hwas required after the digested sample had been mixed withcitric acid. The method could also tolerate copper, nickel andlead.Ribeiro et al.225 developed a quartz tube atomizer with

tungsten coil for the determination of As down to an LOD of1.5 mg L21 by FI-HG-AAS. A Nafion membrane thatcontinuously dried the gas stream removed 4.2 mg min21 ofwater, corresponding to an efficiency of 93%. They analysedmineral water, sea-water, sediment and biological materials.Yang and Zhang261 determined As in botanical samples by

HG-ETAAS with in-atomizer trapping on palladium–zirconiumas chemical modifier. The characteristic mass was 18 pg and theLOD was 15 pg was obtained.Vieira et al.262 trapped arsine on an iridium-treated graphite

tube in the determination of As in sediments, coal and fly ashslurries after ultrasonic treatment by HG-ETAAS. After grind-ing to a particle size of less than or equal to 50 mm, the samplepowder was mixed with aqua regia and hydrofluoric acid in anultrasonic bath for 30 min. After diluting the mixture withhydrochloric acid, the slurry was allowed to stand for 48 h.They concluded that the greatest advantage of the method wasthat only a minimum of reagents and sample handling wererequired, reducing the risks of contamination and/or analyteloss. On the other hand it was necessary to calibrate with themethod of standard additions. For I ml of slurry containing1 mg of sample, the LOD were 0.54 and 0.7 mg g21 for the coaland sediment samples, respectively, obtained.Mroczkowska and Matusiewicz229 also used iridium in their

slurry sampling method for the determination of As(III) bycontinuous flow HG-ETAAS with in-atomizer trapping.Samples (slurried in HCl with addition of ozone) were preparedwith ultrasonic agitation. For the estimation of total As (andhence As(V) by difference), thiourea was added to reduce As(V)to As(III). The overall efficiency of generation and trappingwas 89% for particle sizes less than 20 mm and the LOD was of4.8 ng g21. The procedure was validated by the analysis of anumber of environmental and biological reference materialswith calibration by standard additions. The procedure was

applied to the analysis of marine sediment, soil, rock salt, wastewater, human hair, urine, lobster, liver, muscle, beer and wort.Chamsaz et al.170 determined As by ETAAS after pre-

concentration by headspace liquid-phase microextraction afterHG. The arsine generated in a reaction vessel was collected in a4 mL drop containing AgDDC dissolved in a mixture of 1 1 3pyridine and benzyl alcohol suspended in the tip of amicrosyringe. After 7 min extraction at 35 uC, the drop wastransferred to the furnace. The method was applied to theanalysis of RM, tap water, washing machine powder andspiked sea-water. The LOD was 45 pg ml21.Yin et al.263 developed a method for the determination of

total As in traditional Chinese medicines by FI-HG-AFS.Samples were digested with a mixture of nitric acid andperchloric acid and As(V) was reduced to As(III) with thiourea,which also minimized the interference from transition metalion. The interferences from copper, iron, mercury and seleniumwere studied and discussed. The LOD was 0.1 ng mL21. Tocomplement this work, Yang et al.264 also developed a HG-AFS procedure. Chinese workers, Gong et al.,265 were struckby the beneficial effects of adding magnesium carbonate to themix of rosin and magnesium nitrate for the dry ashingpretreatment prior to determination of the As by HG-AFS.Caballo-Lopez and de Castro266 developed a FI pervapora-

tion method, in which the sample was introduced as slurry, forthe determination of extractable As in soil by HG-AFS.Slurries, prepared by mixing the soil (particle size v65 mm)with 6 mol L21 HCl, were magnetically stirred for 3 min, andwhile stirring, aspirated into the loop (500 mL) of the injectionvalve. The reliability of the method was evaluated by the analysisof three CRM: Stream Sediment GBW 07311 (188 mg mL21

As); River Sediment CRM 320 (76.7 mg mL21 As); and SoilGBW 07405 (412 mg mL21 As) using calibration againstaqueous standards. The procedure was applied to the analysisof six types of soil: ‘‘industrial, sandy, clayey, slimy, limy, andorganic.’’Clarkson et al.240 determined As in flue gases by direct

introduction of the gaseous sample into a plasma spectrometer.Several non-chromatographic speciation procedures have

been devised. Gonzalez et al.267 developed approaches for thespeciation of extractable As(III) and As(V) in environmental solidsamples by FI-HGAAS. A simple two-stage sequentialextraction protocol involving deionized water and a phosphatebuffer as extractants was employed. Determination of bothoxidation states of As in the extracts was accomplished bygeneration under different reaction conditions: (a) selectivedetermination of As(III) in citric acid; (b) determination of totalAs by HG in the presence of thioglycollic acid or after pre-reduction of KI and ascorbic acid. The LOD were 0.07 mg L21

for As(III), and 0.06 mg L21 for total As. Shi and co-workers268,269 sequentially extracted soils with water,0.6 mol L21 KH2PO4 solution, 1% (v/v) HCl solution and1% (w/v) NaOH solution, and then determined As(III) by HG-AFS after the addition of 0.1 mol L21 citric acid solution.Then, the total arsenic in the extract was determined by HG-AFS using on-line reduction of arsenate with L-cysteine. Thedifference was interpreted as As(V). The LOD for As(III) andAs(V) were 0.11 and 0.07 mg L21, respectively. Yang et al.270

determined As(III) and As(V) by HG-AFS in traditional Chinesemedicines. The solution LOD was 80 ng L21.There are also several speciation studies in which HG has

been used as the interface between the HPLC separation andeither the AAS or AFS detection. These are discussed in moredetail in section 6.2. In the following paragraph procedureswith AAS detection are listed first. Heinrich-Ramm et al.271

investigated the influence of controlled consumption of marinefish on the urinary excretion of As(III), As(V), dimethylarsinicacid (DMA) and monomethylarsonic acid (MMA). Vinaset al.272 speciated As baby foods and the raw fish ingredients.Alauddin et al.273 speciated arsenic metabolite intermediates in


the urine from patients in Hajiganj, a seriously arsenic-affectedarea in Bangladesh. Chen et al.274 investigated the relationshipalong with arsenic methylation ability, cumulative As exposure(CAE), and the risk of bladder cancer in a hospital-based case-control study in south-western Taiwan. They concluded thatsubjects with a low secondary methylation index (ratio ofDMA/MMA) have a substantially increased risk of bladdercancer, especially when combined with high CAE. Hwanget al.275 speciated urinary inorganic arsenic metabolites of themaintenance engineers who disassemble machines for waferfabrication in the semiconductor industry. The remainder ofthe studies listed were performed with AFS detection. Gonget al.276 characterized the As metabolic complex excreted inhuman urine after administration of sodium 2,3-dimercapto-1-propane sulfonate, used to treat acute arsenic poisoning, as acomplex between the drug and MMA(III) (monomethylarso-nous acid, the reduced form of the more commonlyencountered MMA, monomethylarsonic acid). Nemetiet al.277 studied As(V) reduction in human erythrocytes andrats with particular reference to evaluating the role of purinenucleoside phosphorylase. Huang et al.278 measured the Asspecies in farmed mouthbreeder (Oreochromis mossambicus)and culture ponds in water in blackfoot disease hyperendemicareas in Taiwan. Tu et al.279 investigated the speciation andleachability of As in the fronds of Chinese brake (Pteris vittataL.), an As hyperaccumulator, with an emphasis on theimplications for As-rich biomass disposal. They found thatin the fronds As was primarily present as inorganic arsenite,that arsenite re-oxidation occurred in the old fronds and theexcised dried tissues and that the species in the fronds wereslightly influenced by arsenic forms added to the soil. However,they also reported that air-drying of the fronds resulted inleaching of substantial amounts of arsenic and pointed out thesignificance of this when looking at disposal options of arsenic-rich biomass from the point of view of secondary contamina-tion. He et al.280 investigated extraction procedures for thedetermination of arsenic species in plant materials. Theyanalyzed plants grown on contaminated soil near an arsenicmine and found that inorganic arsenic, especially arsenate, wasthe major component in plants, though MMA and DMA weredetected at low concentrations. Soros et al.281 evaluated thepotential of arsenic speciation in molluscs (mussels collectedaround the island of Sardinia and in the Gulf of Venice) forenvironmental monitoring. Segura et al.282 studied the stabilityof arsenic species in raw and treated urban wastewater samples.They found that the decrease in the As(III) concentration withtime was accompanied by an increase in the As(V) concentra-tion. Coelho et al.283 developed a method for the determinationof the usual four species in beer.

1.4.3.2 Bismuth. Ribeiro et al.284 developed a method forthe determination of Bi in metallurgical materials by HG andAAS with a tungsten coil quartz tube atomizer. The loweststandard was 10 mg L21, the LOD was 1.9 ng and thethroughput was of 60 h21. They accurately analyzed five metal-lurgical RM. Chinese researchers, Song et al.,285 developed aFI-HG-AAS method for the determination of Bi in ‘‘bismuthpectin’’, a pharmaceutical for protecting stomach mucousmembranes. The LOD was 0.095 ng mL21. Cava-Montesintoset al.286 devised a procedure for the determination of Bi in milkby HG-AFS. Samples were digested by microwave-assistedheating with HNO3 and H2O2. The LOD was 0.01 ng mL21,corresponding to 0.50 ng g21 in the original sample. Theyfound that, in agreement with two other methods, Spanish milkcontained 11.8–28.8 ng g21. Several studies in which Bi wasdetermined as part of a multi-analyte have already beencited.236–238,257,258 The study by D’Ulivo et al. of the possibilityof generating Bi hydride by reaction with various amino-boranes227 was described earlier.

1.4.3.3 Cadmium. Bujdos et al.287,288 investigated the deter-mination of Cd by vapour generation AAS in a continuousflow reactor and confirmed what has been already reported:thiourea and cobalt(II) ions affect the sensitivity as do chelatingagents such as EDTA. Their LOD was 0.03 ng mL21 and theyvalidated the procedure by the accurate analysis of BCRCRM. They also analyzed soil extracts, obtaining results com-parable to those of obtained by ETAAS and FAAS. Chineseresearchers, Sun et al.,239 rose to the challenge of the simul-taneous determination of trace Cd and Hg in Chinese herbalmedicine by non-dispersive AFS with an intermittent flowvapor generator. Ascorbic acid, cobalt and thiourea were usedas enhancement reagents or masking agents to enhance thegeneration efficiency of the volatile species of Cd and Hg. TheLOD were 0.010 mg L21 for Cd and 0.019 mg L21 for Hg.The study by Luna et al.,230 in which Cd was determined as partof a suite of ‘‘non-conventional’’ hydride-forming elements,has been discussed already. Clarkson et al.240 and Abanadeset al.241 determined Cd as one of the analytes present in fluegases (mentioned above).

1.4.3.4 Germanium. Li et al.289 found that L-cysteineenhanced the Ge HG-AFS signal in the analysis of geologicalsamples. They also found that it reduced or eliminated inter-ferences from chromium(VI), copper, lead, nickel, selenium(IV)

and tellurium(IV). They were also able to find tolerable limits forantimony(III), arsenic(III), bismuth(III), gold, iron(III), and plati-num(II). The method LOD was 0.38 mg L21 (equivalent to0.01 mg g21 in the solid sample). The efforts by Bings et al.257

and Abranko et al.258 to determine simultaneously a number ofhydride-forming elements, including Ge, have been citedalready.

1.4.3.5 Lead. Marrero et al.290 evaluated the effects of fouracid oxidant mixtures in the determination of Pb in foods andbeverages by HG-ICP-OES. They found that of these (acetic,citric, nitric, and tartaric), plumbane was produced with 85%efficiency in tartaric acid and there was a better control ofinterferences. They tested the effect of numerous metals andother hydride-forming elements and concluded that nickel,selenium and tellurium are the elements that most severelyaffect plumbane generation. Compared to that for conven-tional continuous nebulization, the method produced a sensi-tivity increase of approximately two orders of magnitude fora radially viewed plasma. The LOD was between 4.4 and6.8 mg L21, depending on the acid. They validated the methodby the analysis of two CRM,MURST-ISS-A2 (Antarctic Krill)and CRM 063R (Skim Milk Powder). Liang et al.291 deter-mined Pb in seasoning by HG derivative AAS. In comparisonwith those of conventional HG-AAS, the LOD and sensitivityof the proposed method were improved 8.8 times and 26 times,respectively. For a 5.0 g sample, the LOD was 0.96 ng g21.Their derivative procedure for As and Sb has already beencited.253 To complete the trilogy of techniques, Sun et al.292

determined Pb in vegetable oil by HG-AFS. They incineratedsamples with a microwave ashing system, obtaining an LOD of0.31 mg L21. Song et al.293 devised a FI-HG-AAS procedure forthe indirect determination of the 6-mercaptopurine in tabletsbased on the precipitation reaction with Pb, for which the LODwas 0.2 ng mL21.

1.4.3.6 Antimony. Nedzielski et al.216 reviewed the deter-mination of Sb by HG. Filella et al.294 discuss the maincharacteristics of the solution chemistry of Sb in relation to itsbehaviour and fate in natural waters. Their work is based on acareful and systematic examination of a comprehensive collec-tion of solution equilibrium and environmentally orientedstudies, some published more than 100 years ago. They notethat information on antimony reactivity in solution is scarceand often relatively old. Chen et al.295 developed a procedure


for the determination of Sb in plant and peat samples by HG-AFS. The analytical procedure was validated by the analysis oftwo in-house peat reference materials and five plant CRM:(BCR CRM 281 Rye Grass, CTA-VTL-2 Virginia TobaccoLeaves, GBW 07602 Bush Branches and Leaves, SRM 1547Peach Leaves and SRM 1515 Apple Leaves. The solution LODwas 8 ng L21, corresponding to a method LOD of 2 ng g21 insolid peat; they indicate that this is far lower than previouslyobtained with HG-AFS. Ancient peat, with a high sea saltcontent, from remote Scottish peat bogs was accuratelyanalysed. Three procedures in which Sb was determinedalongside As have already been discussed: Sun et al.,253

Cava-Montesinos et al.251,252 Other reports of multi-elementdeterminations that include Sb are those by Bings et al.,257

Matsumoto et al.,237,238 Abranko258 and Gallignani.259

Guchardi and Hauser246 were able to detect Sb along withAs, via HG, as well as Hg, by CV generation, in their cap-acitatively coupled microplasma sustained in a fused silicacapillary of 250 mm id. Wlodarczyk and Zyrnicki296 investi-gated the spectroscopic characteristics of a low power argonMIP sustained in a resonant TE101 rectangular cavity onintroduction of gaseous species, including SbH3, producedfrom ethanol–water solutions by continuous HG. The LOD,which were significantly influenced by the presence of ethanol,ranged from 0.5 to 11 and from 5.3 to 35 mg L21, for Sb andHg, respectively.Three groups of researchers have devised Sb(III)/Sb(V) specia-

tion procedures. Flores et al.297 developed a FI-HG-AASprocedure for the selective determination of Sb(III) in commer-cial drugs, based on Sb(V), injected for leishmaniasis treatmentin South America. The conditions for Sb(III) determinationwithout interference from Sb(V) were: 20% (m/v) citric acid and2.0% (m/v) sodium tetrahydroborate. The throughtput was60 h21 and the LOD was 0.95 ng. Fuentes et al.298 devised aHG-AFSmethod for the redox speciation analysis of Sb in soilsbased on the masking of Sb(V) by citric or oxalic acid in HClmedium. Both species were extracted from soil with H2O,0.05 mol L21 EDTA and 0.25 mol L21 H2SO4 and the totalSb in the extracts was determined after reduction withKI–ascorbic acid at room temperature. The LOD were 17and 10 ng L21 for Sb(III) and total Sb, repectively. Theyindicated (a) that the Sb recovery from the different soils bythe various extractant solutions was between less than 0.02%and approximately 10%, and (b) Sb(V) was the main speciesextracted. Niedzielski and Siepak299 determined Sb(III) andSb(V) in water samples by HG-ETAAS with in-atomizertrapping. They did not divulge the basis of the speciation intheir abstract, but did report that the LOD was 0.014 ng mL21.D’Ulivo et al.227 included Sb in the suite of elements theydetermined by HG with aminoborane reagents, Bulska et al.224

investigated the nature of the compounds formed when stibinewas trapped on the interior surface of a graphite furnaceatomizer, and Sb was among the elements determined in fluegas by Clarkson et al.240

1.4.3.7 Selenium. Researchers whose studies concerning Sehave been discussed earlier include Niedzielski et al.,216 whoreviewed the conditions used for the HG-AAS determination ofAs, Sb and Se, Bings et al.,257 who developed a multi-analyte FImethod of electrochemical HG procedure, D’Ulivo et al.,222

who studied the effects of several masking agents, Bulskaet al.224 who characterized by SIMS the compounds of As, Sband Se on graphite surfaces modified with noble metals formedduring in-atomizer trapping of the hydrides, Semenova et al.226

who developed a multisyringe system for the determination oftotal inorganic Se by HG-AFS. Chinese workers, Li et al.,236

determined As and Se in sulfur by HG-ICP-OES, but gave nohint as to how oxidation states were adjusted following oxida-tive sample pretreatement. He et al.256 analyzed Chinese coalfrom various geographic regions for As and Se. Apart from the

research already cited, the only other report of a multi-analytedetermination involving Se is that by Cava-Montesinoset al.,300 who have determined, in addition to As and Sb,251

Se and Te in milk by HG-AFS. The LOD were 0.005 and0.015 ng mL21 for Se and Te, respectively. They reported thatSpanish milk contained between 11.1 and 26.0 ng mL21 for Se,and between 1.04 and 9.7 ng mL21 for Te.Pyrzynska301 reviewed recent research on the determination

of selenium species in environmental samples such as water, air,soil and plants, and commented on the stability of seleniumspecies in solutions and storage. It was pointed out that in themetabolic pathway in the body, selenide could act as thecommon intermediate for inorganic and organic Se sources aswell as the ‘‘checkpoint’’ between further utilisation and excre-tion. Moreno et al.302 investigated the effect of the presence ofvolatile organoselenium compounds on the determinationof inorganic Se by HG. They pointed out that as a result ofmicrobiological activity, it is possible to find dimethylselenide(DMSe) and dimethyldiselenide (DMDSe) in samples such assoils, sediments, sewage sludges and plants where methylationcan take place. They showed that DMSe and DMDSe gave riseto volatile species on reaction with sodium borohydride thatwere subsequently detected by several AS techniques includingAAS, AFS and ICP-MS, causing an error dependent onthe particular technique. They proposed the coupling ofpervaporation-AFS for the identification of these speciesand pervaporation-GC-AF for their individual quantification.Korenovska303 developed a FI-HG-AAS method for the deter-mination of Se in vegetables, fruits, and dairy products. Themethod, which involved microwave digestion, had an LOD of0.06 mg kg21. The procedure was validated by the analysis ofCRM BCR 150 skim milk, which contains 0.132 mg kg21 Se.Bodo et al.304 determined the various species in a laboratory

RM prepared from Brazil nuts (Bertholletia excelsa) by HPLCwith post-column UV degradation of the separated organose-lenium compounds followed by HG-AFS. The concentrationof selenomethionine was (79.9 mg g21 (calculated as Se) andtotal Se content was 82.9 mg g21, respectively).

1.4.3.8 Tin. There appears to be little interest in determin-ing total Sn by HG, as there is only one report in the currentreview period describing such a procedure. Farias et al.223

studied the effects of various acid media on the HG-ICP-OESdetermination (see section 1.4.1). They validated the procedureby the analysis of a soil CRM GBW 07405. Abranko et al.258

and Gallignani et al.259 determined Sn as part of a multi-analyte suite (see section 1.4.1) and Clarkson et al.240 deter-mined Sn directly in flue gases. Scriver et al.243 developed aprocedure for the determination of tributyltin based on thegeneration of the chloride. The accuracy of the method wasverified by the analysis of NRCC CRM PACS-2 (sediment).

1.4.3.9 Tellurium. Aswas described above, Cava-Montesinoset al.300 measured Te (LOD 0.015 ng mL21), along with Se inSpanish milk by HG-AFS after microwave-assisted sampledigestion. D’Ulivo et al.227 included Te in the suite of elementswhose hydride activity with aminoboranes was studied. Asmight be expected, H2Te was not formed from Te(VI).

1.4.3.10 Mercury. A number of studies in which Hg wasdetermined as part of a multi-analyte suite have already beendiscussed. Bings et al.257 developed an electrochemical HG as asample introduction system, for the rapid and simultaneousdetermination of six hydride-forming elements. D’Ulivoet al.227 evaluated amineboranes as derivatization reagents inthe continuous flow HG of volatile hydrides and elementalmercury. Sun et al.,239 who determined Cd and Hg simulta-neously by vapour generation non-dispersive AFS, investigatedthe role of ascorbic acid, cobalt, and thiourea as ‘‘catalysts’’(i.e. enhancers) or masking agents. Ronda et al.254 determined


As and Hg in white beet sugar by HG-AAS. Chineseresearchers, Suo and Li255 determined As and Hg in medicinalanimal horns by HG-AFS. Wlodarczyk and Zyrnicki296

determined Hg and Sb by the emission generated from a lowpower MIP in a resonant TE101 rectangular cavity on intro-duction of gaseous species, from ethanol–water. The LOD,which were significantly influenced by the presence of ethanol,ranged between 5.3 and 35 mg L21 for Hg. Wilken et al.305

proposed that an unidentified compound with the sameretention time as ethylmercury in HPLC could, in fact, beCH3–S–Hg1. Guchardi and Hauser246 detected As, Hg and Sbin a capacitively coupled microplasma sustained in a fusedsilica capillary of 250 mm id. They noted that it was alsopossible to determine CO2, CH4 and ethanol vapour from theC2 emission at 385.2 nm. LOD of a few tens of ng mL21 werequoted for these three species, but no LOD for As, Sb or Hgwere provided. Mercury is a good element to determine byminiature plasma discharges as it can be introduced as the freeatomic vapour (in a dry gas stream if needed) relatively easily.Wlodarczyk and Zyrnicki296 determined Hg by measurementof the emission from a low power argon MIP with an LOD of0.5–11 mg L21. Schermer et al.306 constructed a modifiedcompact 2.45 GHz microstrip plasma (MSP) operated with Aras working gas at atmospheric pressure at powers of 5–40 Wand Ar flow rates of 15–60 L h21. The LOD was quoted as10 ‘‘ng Hg L21 Ar’’. Guchardi and Hauser246 created an 8 Wcapacitively coupled argon or helium microplasma in a fusedsilica capillary by applying 20 kV to two cylindrical electrodesat 20 kHz, with which they detected Hg. Other miniaturesources can also be tested with Hg: Karanassios describes198 hiscurrent research toward the conceptual goal of miniaturizingelemental analysis instrumentation, including the developmentand characterization of a portable, battery-operated instru-ment for (near) real-time Hg determination in the field fromgases and from liquid and solid micro-samples.Chen et al.307 compared the analytical figures of merit in the

determination of Hg by continuous flow CV-AFS for the tworeducing agents SnCl2 and NaBH4. They found that tetra-hydroborate can reduce Hg(II) in various environmentalsamples at a concentration as low as 10 mM (ca. 3.8 61025% w/v) and that commonly encountered transition metalsand other hydride forming elements (As, Sb, Se) did notinterfere with total Hg determination. Interferences from someother ions could be removed by dilution. Compared with thereactions with Sn(II), the borohydride chemistry was muchcleaner: no precipitates were formed. The overall benefits weresummarized as reduced memory effect, simplified analyticaloperation and six-fold decrease in chemical cost. On the otherhand, Babi et al.,308 who investigated the effects of iodine,bromine and acidity of the generation of Hg by continuousflow techniques, found that on-line alkaline pH adjustmentprior to Sn(II) reduction was the most effective for interferencecorrection. Reis et al.309 developed a multicommutation CV-AFS procedure for the analysis of waters that, although nothaving as low an LOD as the conventional AFS method, hadthroughput improved by a factor of 3.6, sample consumptionreduced by a factor of 6 and reagent consumption by a factor of8.4. In addition, the waste generation was reduced by a factorof 2.4 and the Ar consumed by a factor of 6. Arbab-Zavaret al.310 devised a procedure for electrochemical CV generationfor AAS based on reduction of Hg(II) ion on a graphite cathode,the trapping of mercury vapour and its volatilization into aquartz tube. The electrochemical cell consisted of an activatedgraphite rod graphite cathode and an anode operating withconstant direct current for the production of mercury atoms.However, the performance was not impressive: antimony, arse-nic, bismuth, cadmium, lead, selenium, silver and even lithium,potassium and sodium interfered; the LOD was 2 ng mL21.Khvostikov et al.311 developed a nondispersive AF spectrometerwhich employed a signal processing algorithm that increased

the SNR by a factor of 3 compared with that of the con-ventional procedure. The method was applied to the analysis ofsoils and semolina down to an LOD of 60 pg. A semolina SRMwas also analysed. Zachariadis et al.312 constructed a combinedpreconcentration column/gas–liquid separator for the FI-CV-AAS determination of Hg. In the lower section of the devicewas a preconcentration column packed with polytetrafluor-oethylene (PTFE) turnings for the retention of Hg(PDC)(2)and subsequent on-column reduction of mercury by SnCl2.Mercury vapour is generated within the column and expelledfrom the reaction mixture by nitrogen. The upper section of thedevice was a headspace for receiving mercury vapour andseparating residual water vapour before entering the absorp-tion cell. For 60 s preconcentration at 11.5 mL min21, theenrichment factor was 32, the LOD was 6 ng L21, andthe throughput was 30 h21. The procedure was applied to theanalysis of natural waters, urine and mussels. Krata et al.93

developed a solid-phase extraction, with two-step elution, forthe elimination of copper and iron interference. They used CV-AAS with borohydride as the generating agent. The interferingions and Hg were retained on a cation-exchanger, Dowex 50W-X-4, and, in the first elution step, copper and iron wereremoved by 0.5 mol L21 KF solution. Then, mercury waseluted with 0.1% thiourea in 8% HCl. The LOD was 27 ng L21.The procedure was validated by the analysis of a CRM, BCR-144R (sewage sludge), and by spike recovery from variousnatural waters. Lazo and Cullaj313 devised a CV-AAS pro-cedure for the determination total, inorganic, and organic Hgin sea-water. Inorganic mercury only was directly reduced bySn(II) chloride under strongly acid conditions. Organic andinorganic mercury were extracted as the bromide derivativesinto toluene and re-extracted, together, into ammoniumchloride solution. Organic mercury was converted intoinorganic mercury by thermal digestion at 80–90 uC in thepresence of strong oxidants. The process was repeated toconcentrate the Hg and the toluene dissolved in the aqueousphase after re-extraction was removed by heating for 30 minat 80–90 uC. The procedure was capable of detecting0.0001 ng mL21. Melaku et al.314 compared microwavedigestion reduction–aeration and pyrolysis combined withCV-AAS and with cold CV-AFS for the analysis of environ-mental and biological materials. Biological samples weredigested in a mixture of HNO3–H2O2, the environmentalsamples in a mixture of HNO3–HClO4. After reduction withSnCl2, the mercury was collected by two-stage gold amalgama-tion. The LOD for 250 mg of the environmental meterial forthe microwave digestion reduction–aeration methods were1.4 ng g21 and 0.6 ng g21 for AAS and AFS, respectively. For500 mg of biological material, the LOD were 0.7 ng g21

(CVAAS) and 0.4 ng g21 (CVAFS). When 10 mg of a samplewere pyrolysed, the LOD were 3.5 ng g21 and 1.6 ng g21,respectively. They analysed eight CRM. Ortiz et al.315 evalu-ated different sample pre-treatment and extraction proceduresfor Hg speciation in fish. Three different drying techniqueswere investigated: oven-drying, microwave oven-drying andfreeze-drying, and four extraction methods were investigated:HCl leaching, alkaline-methanol extraction with tetramethyl-ammonium hydroxide and with KOH, and sodium dodecyl-sulfate. Measurements were made with FI-CV-AFS and speciesintegrity after extraction was determined by GC-AFS. Theyfound that Hg was lost from microwave dried and freeze-driedmaterials, that only HCl gave leaching quantitative extraction(97%), and that artificial formation of dimethylmercuryoccurred when TMAH was used. They determined methyl-mercury in tuna fish and swordfish down to an LOD of 1.2 pg.Ramalhosa et al.316 studied the effect of organic matter on thedetermination of reactive Hg in contaminated waters. Theyfound that concentrations increased with acid dilution whichthey interpreted, on the basis of studies with model com-pounds, as being due to the release of Hg from aromatic


Hg-complexes. They suggested that natural waters frommercury contaminated ecosystems should be analysed withoutdilution. Wernert et al.317 studied the effect of ‘‘strong’’ ligandson the determination of Hg CV-AFS. The ligands in questionwere Cl2, I2, S2

2, SO322, S2O3

22, cysteine, EDTA, whichcould complex both the Hg and the Sn(II) reducing agent. Theyfound that, in agreement with theoretical calculations, the Hgsignal was depressed in the presence of I2, S22 and S2O3

22 dueto the formation of very stable complexes even at low pH(pH v 1). Zamzow et al.318 designed and tested a real-timecontinuous AA spectrometer for monitoring emissions of Hg inthe flue gas streams of combustors. The sampling system allowsthe sequential determination of elemental and total Hg. Aheated pyrolysis tube converts oxidized Hg compounds toelemental Hg for the determination of total Hg, and thepyrolysis tube is by-passed to determine elemental Hg. Theinstrument contains an echelle spectrometer that providessimultaneous detection of all of the emission lines from a Hgpen lamp, which is used as the light source for the opticalabsorptionmeasurement. This feature allows for on-line spectro-scopic correction for interferent gases such as sulfur dioxide andnitrogen dioxide, typically present in combustion stack gasstreams that also absorb at the Hg wavelength of 253.65 nm.There have been a considerable number of publications

describing studies in which the determination of Hg inmaterials of interest by CV has been the technique of choice,but little or no method development was involved.319–342

There is a continued interest in the development of pro-cedures for the determination of inorganic and organic Hgspecies, though in the latter case it is mostly methyl-Hg that isof concern. Yu and Yan343 reviewed the factors affecting thestability of inorganic and methylmercury during storage ofsamples such as distilled water, organic solutions, environ-mental samples and biological materials. The authors point outthat the loss mechanisms and the ways of preserving mercuryspecies have been the subjects of much controversy and thatmore effort should be made to solve the problems associatedwith the stability of mercury species. Segade and Tyson344

devised a FI-CV-AAS method to determine inorganic Hg andtotal Hg in biological and environmental samples based onreduction with borohydride solutions of different concentra-tions. Inorganic Hg was selectively determined after reductionwith 10–4% w/v sodium borohydride, while total Hg wasdetermined after reduction with 0.75% w/v sodium borohy-dride. The LOD were 24 and 3.9 ng L21 for total and inorganicHg, respectively. They verified the procedure by analysingalkaline and acid extracts of five biological and sedimentRM. They also applied the procedure to the analysis of fishtissue slurries345 and compared the performance with a methodin which the slurries were oxidatively digested by merging withsulfuric acid, and potassium persulfate followed by thegeneration of CV Hg by reduction with Sn(II). They foundthat the procedure without oxidation was simpler, faster andmore sensitive. The LOD were 4, 1 and 10 ng g21, referred todry weight, for total Hg, inorganic Hg and methyl-Hg,respectively. Both methods were validated by the accurateanalysis of two fish tissue CRM, NRC DOLT-2 and NRCDORM-2. Monteiro et al.346 developed a sequential quanti-fication procedure in which two gas–liquid separators wereinserted in the flow system. Prior to the first, only inorganic Hgwas reduced by 0.01% m/v sodium tetrahydroborate solutionand prior to the second methyl-Hg was converted to CV byreaction with 0.3% m/v borohydride in the presence of iron(III)

chloride. The LOD were 400 and 600 ng L21 for Hg(II) andmethyl-Hg, respectively, and the throughput was 12 h21.Dadfarnia et al.347 preconcentrated both species with 1,5-diphenylcarbazone immobilized on sodium dodecylsulfatecoated alumina. Both were eluted with 1 mol L21 of hydro-bromic acid, but CV Hg was generated from inorganic Hg onlyby reaction with Sn(II). Total Hg was determined after the

oxidation of methyl-Hg. For 1 L of sample, the enrichmentfactor was 100 and the LOD (AAS) was 100 ng L21. Yanet al.348 developed a CZE procedure for the separation of Hgspecies prior to detection by AFS. The four mercury speciesHg(II), methyl-Hg, ethyl-Hg and phenyl-Hg were separated ascysteine complexes in a 50-cm 6 100-mm-id fused-silicacapillary at 15 kV with a mixture of 100 mmol L21 boricacid and 12% v/v methanol (pH 9.1). Resolution was improvedby applying hydrostatic pressure to oppose the direction of theelectroosmotic flow. Following vapour generation, the Hg wasdetected by AFS at LOD in the range 7–17 mg L21 (as Hg).Although there would appear to be no publications in which

CV Hg determination by ETAAS with in-atomizer trappingis described, there are at least two reports of the directdetermination of Hg by ETAAS.349,350

1.5 Solid sampling

1.5.1 Electrothermal vaporization. Belarra et al.351 provide acritical review of direct solid sampling with electrothermalvaporization/atomization. The advantages and disadvant-ages of solid sampling-graphite furnace-based methods areexamined and well explained. The article is particularly usefulfor the new user of solid sampling methods and the bestapplications of the various techniques are highlighted. Theeffect of tube ageing on the quality of direct solid sampling inET-AAS is a major concern. The effect of tube ageing on thedetermination of Sb by ultrasonic slurry sampling wasexamined by Cal-Prieto et al.352 using SEM and XRD analyses.Significant variations in tube morphology were detecteddepending on the sample matrix and suggestions were madeto improve tube lifetimes.Ren et al.353 have used induction heating-ETV for sample

introduction to an ICP. The report is concerned with elimina-tion of a problem with this type of sample introduction, namelythe arcing that occurs between the graphite sample cup and thesurrounding glass chamber.

1.5.2 In-torch vaporization. Karanassion198 declares that in-torch vaporization has the potential to produce a ‘‘paradigmshift in classical elemental analysis’’. This declaration isexplained by describing the improved detection limits obtainedfor both ICP-AES and ICP-MS, thus enabling determinationsfor micro- and sub-micro sized liquid or solid samples. Thelimitation of the technique is considered to be the laboratory-based nature of current ICP technology. The paper describesresearch on miniaturizing the instrumentation using a portable,battery-operated instrument for (near) real-time Hg deter-mination in the field.

1.5.3 Slurry sampling. Silva et al.354 have evaluated thefeasibility of direct introduction of clay slurries into an ICPoptical emission spectrometer with axial view configuration.The instrument was calibrated with a CRM with a meanparticle size of 13 mm (IPT 42) and two others RM (IPT 28 andIPT 32) and four samples were analyzed. It was found that thecalibration was not completely suitable for IPT 28 and thesamples due to the differences in mineralogical phases, whichwere determined by X-ray diffraction. However, after applyinga correction it was possible to obtain results for most elementsin agreement with the certified values or with the valuesobtained by a conventional technique. A critical review byMatusiewicz228 concerns the analytical methods and techniquesused for hydride generation slurry sample introduction forAAS. A comparison of detection limits and practical applica-tions to analytical samples that utilize slurry hydride genera-tion was discussed. Chinese workers, Wei et al.,355 determinedCu, Fe and Zn in Huaiyao by FAAS with slurry sampling. Astable suspension in agar was prepared and injected into theinto air–acetylene flame.


1.5.4 Glow discharge. In a review concerning glow dischargeoptical emission spectrometry, Angeli et al.356 pay particularattention to near surface analysis and the analysis of thin films.The special requirements for thin film analysis, the require-ments of further developments to the technique and the funda-mentals are discussed.The identification of organo-Se compounds by particle beam

HC-GD-OES (PB/HC-OES) by monitoring the C and Hemission, proposed by Jin and Marcus,357 is noted. Theyconcluded that the correlation of H I and C I emission intensityvalues with the atomic H : C ratio in different organoseleniumcompounds allowed selenium speciation by means of thedetermination of empirical formulae.

1.6 ET-AAS

Fernandes et al.358 have reviewed the techniques used forinternal standardization in AAS. Selection of elements asinternal standards, limitations of the method, and applicationsof internal standardization in AAS are critically discussed.Modification of a conventional ET-AAS autosampler to

allow automated in-situ electrodeposition was described byKrenzelok.166 The original injection Teflon capillary wasreplaced by a composite Pt–Teflon capillary which served asan anode in the electrodeposition circuit. Pb detection limit (3d)of 20 pg and reproducibility of 1.0–1.4% in various matriceswas obtained using this technique. A revisit to another sampleintroduction variation for ET-AAS, namely chemical vapourgeneration, was described by Luna et al.230 Volatile species ofAg, Cu, Cd, and Zn were generated at room temperature thenrapidly transported to a Ir-coated, pre-heated graphite tube.The limits of detection (3s) were 10, 0.006, 28 and 1.1 ng forAg, Cd, Cu and Zn, respectively, and the precision of replicatemeasurements was typically approximately 10% RSD.

2 Instrumentation

The atomic absorption spectrometer revolutionized chemicalanalysis in the 1960s. Invented by Alan Walsh of the CSIRODivision of Chemical Physics, Australia, its manufacture beganwith three small Melbourne companies making the necessaryoptical, mechanical and electronic components. J B Willis,co-worker with Walsh at that time and still very active as aconsultant in the field, has written a most interesting andenlightening account359 of the birth of what since became amajor Australian scientific industry.The construction and characterization of a simple but

flexible low cost laser diode system for atomic spectroscopy wasreported360 from Hungary. Detailed electronic circuit layoutsof the diode laser current controller, supplying a maximum of1300 mA current with 1 mA resolution, and functional descrip-tions of all other components were given. Results of electronicand spectroscopic tests showed that the wavelength tuning,with a precision of about 0.01 nm, and current modulationfrequency up to 10 kHz are possible with this system. It wassuggested that the performance characteristics make theproposed set-up suitable for use in AAS and AFS with ICPs.

2.1 Spectrometers

The position of spectral lines on the two-dimensional focalplane of an echelle cross dispersion spectrometer can be variedboth horizontally and vertically by changes in ambient tem-perature and relative humidity. These effects have beencomprehensively studied by Liu and Hieftje.361 The magnitudeof such variations, Dlx in horizontal and Dly in verticaldirections, were determined for variations in temperature (T)over the range 24–34 uC and in relative humidity from 31–51%using spectral lines in the range 250–570 nm. Overall, withincreasing T , Dlx declines and Dly becomes greater. Changes in

relative humidity do not affect Dlx but raise Dly almostlinearly. Both Dlx and Dly are found to change with wave-length, though not linearly. An analysis of the results showsthat Dlx, as a function of l, is related to the grating constantand the incident angle of the echelle and, as a function of T ,Dlx is governed by l, T , the grating constant, the focal lengthof the spectrometer, the thermal expansion coefficients of thegrating and of the spectrometer, and the diffraction angle of theechelle.

2.2 Sources and atom cells

2.2.1 Sources for AES. A minifabricated ICP-on-a-chip(mICP) was described by Minayeva and Hopwood.362 Thesystem consists of a planar plasma source microfabricated on aglass wafer, with a miniature aluminium vacuum chamber. Theplasma operated from 0.1–10 Torr and required less than 4 Wof power at a frequency of 493 mHz. The device was used forthe detection of molecular SO2, detection limits improving withincreasing operating power and pressure, but with a best valueof 45ppb. The performance was compared with that of avolume averaged plasma model.Watanabe et al363 described how a barrier discharge RF He

plasma could be used to determine the halogen elements. Adischarge was induced by wrapping a borosilicate glass tube intwo films of copper foil, one being earthed, the other beingsupplied with 3.2 kV of power at a frequency of 98 kHz. Anoptical fibre connected the discharge tube to a spectrometerand a charge-coupled detector to monitor the emission linesof F, Cl, Br and I in the wavelength range 730–960 nm. Anumber of alternative wavelengths were quoted. Calibrationwas said to be linear for F and Cl in the range 1–10 mg andfor Br in the range 0.1–1 mg, relative intensity being in the orderBr w I w Cl w F.A paper from Japan364 described three advanced detection

techniques in glow discharge AES. (a) An applied voltagemodulation method for a dc powered GD emission source,where an ac component superimposed on a dc bias voltage isapplied to the excitation source. Only the emission componentcorresponding to the ac frequency can be selectively detected atlow noise levels with a lock-in amplifier, thus improving thesignal-to-noise ratio. (b) A bias current introduction method inwhich a dc current driven by the self-bias voltage is conductedthrough the plasma body. The electrons introduced by thismeans cause more active excitation processes, thus improvingemission intensities and detection limits. (c) An amplitudemodulation method for an rf powered GD emission source,where a lock-in amplifier enables measurement to be under-taken with better signal-to-noise ratios while sputtering rateand amount of sample used are reduced. This method has beensuccessfully applied to the compositional measurement indepth of nm order elemental films.A new source for AES, quaintly referred to as ‘‘boiling in a

channel’’, was claimed by Zuev et al.365 This is based on thedischarge caused by Joule heating arising in a vapour gapformed in the channel of a dielectric membrane. There were nopractical details given in the available abstract, and only Na,Mg and Ca seem to have been measured, these at the 0.01–5 mM level.

2.2.2 Atom cells for AAS. Ameans for measuring vaporizedtoxic metals in biomass and waste fuels was outlined by Oikariet al.366 A continuous flow of sample gas from a bubblingfluidized bed combustor is fed into the analyser where the hot,wet and particle laden gas is mixed into a hot plasma jet. Thisresults in substantial atomization of the toxic metallic elementspresent in the vapour phase and aerosol, and these are thenmeasured by atomic absorption spectrometry with Zeemanbackground correction.


2.3 Detectors for AES

A charge injection device (CID) was used by Prevatt andDenton367 in conjunction with an echelle spectrometer anddirect current plasma source for measuring trace elements inmunicipal sludge and high solids waste waters. The CIDprovided higher sensitivity in the far UV, overall coveragebeing in the range 175–800 nm. The ‘robustness’ of the DCPsource enabled multi-element analysis to be carried out quicklywith minimal or even no sample preparation.Haisch and Becker-Ross368 suggested that the electron

bombardment CCD camera system (EB-CCD) can be a verysensitive detector, particularly for low light imaging applica-tions such as high resolution echelle AES. The major advant-age, as compared with a microchannel plate intensified CCD, isthe superior spatial resolution, characteristic of the specialamplification system. However, part of the light focussed onthe photocathode of the EB-CCD is transmitted through itand is detected on the CCD as a diffuse spot, possibly reducingsignal-to-background ratio and leading to ghost peaks,especially when lines of very different intensities are beingmeasured.

3 Fundamentals

A number of publications have addressed the production offundamental spectroscopic data. Zheng and Wang have usedthe weakest bound electron potential model theory to calculatetransition probabilities for Ne II369 and neutral F,370 radiativelifetimes, transition probabilities and oscillator strengths of Cand O.371 Computer simulations have been used to computethe Stark broadened full line profiles and dipolar correlationfunctions for the Balmer-alpha, -beta, and -gamma lines,372

over the range ne ~ 1020–1025 m23 and Te ~ 1000–175 000 K.The authors claim that these profiles are better diagnostic toolsthan line widths in the case of non-equilibrium plasmas.A technique for radially resolving the temperatures in low-

temperature, inhomogeneous, optically thin plasmas has beenproposed.373 The method utilises the measurement of half-widths, spectral shifts and intensities of emission lines, and hasbeen modelled for an Ar atmospheric pressure plasma andatomic lines with different broadening parameters, and experi-mentally verified. Likewise, a fast Abel inversion method usingFernandez-Palop smoothing has been reported374 and evalu-ated for the estimation of the population of He I excited statesin the ICP.

3.1 Plasmas

3.1.1 Microwave induced plasmas. A microstrip MIP hasbeen evaluated for the detection of gaseous samples.306 Theplasma was formed on a sapphire substrate and operated atatmospheric pressure in Ar, with flow rates and powers ofbetween of 15–60 L h21 and 5–40 W, respectively. The Texc wasfound to be between 6000–7000 K, using Fe as the thermo-metric probe, and a LOD of 10 ng L21 for Hg in Ar wasobtained.Trot (OH,CH),Texc (Ar,H, Sb) and ne (0.57–2.56 10215 cm23;

Stark broadening) in a low power Ar MIP have beendetermined while introducing volatile species formed by thesodium borohydride reaction,296 with and without ethanolpresent, and assuming a Boltzmann distribution. Trot (OH)increased from 2970 to 3820 K, and Trot (CH) decreased from6100 to 4540 K with ethanol ranging from 10 to 90%; Texc

ranged between 5670–4800, 6190–3950, 10 500–7390 for Ar,H, and Sb, respectively over the same range of ethanolconcentration.

3.1.2 Inductively coupled plasmas. A greater number offundamental studies have appeared in the literature compared

to last year’s review. Several studies have reported on the effectof perturbing the plasma in some way. van de Sande et al.375

used Thomson and rotational Raman scattering to study thedensity and temperature of electrons and nitrogen moleculesaround the edge of the plasma, thereby gaining some insightinto the effect of air entrainment. They concluded that nitrogenconcentration at 1 mm from the plasma edge was only a fewpercent, andv0.1% in the active zones, which is not enough toaffect the plasma. They calculated that electron loss due todiffusion of nitrogen into the plasma was much slower thanpreviously observed and suggested the formation of molecularrare gas ions as an alternative reason for electron loss. In asecond, related paper376 the same authors used time-resolvedThompson scattering to study electron density during and afterpower interruption in an Ar ICP. They concluded thatambipolar diffusion, and three-particle recombination andionization, influences the temporal development of ne and Te inthe central channel. However, at the plasma edges an electronheating mechanism, other than recombination, was explainedby the formation and destruction of molecular argide ions.The effect of hydrogen addition to a He ICP has been

reported377 to increase the emission intensity of Cs, Cl and Mgby up to 4 times on addition of up to 0.09 L min21 H2. Theexcitation and rotational temperatures increased from 3500 to4800 K, and 2400 to 2900 K, respectively, and ne decreased by30%. Workers also reported, in two separate papers,378,379 thatthe introduction of ethanol into an Ar ICP reduced the gas,excitation, ionization, and electron temperature and electronnumber density.Lehn et al.380 studied the effects of placing an ICP-MS

sampler interface 13 mm above the load coil (ALC). Theyperformed optical measurements, using Thomson and Ray-leigh scattering, and observed a drop in Te and Tg at, 6, 7 and8 mm ALC in the presence of the sampler interface. Incomparison, ne increased in the outer regions and decreased inthe central channel, which the authors postulated was due tothe dominant effect of ambipolar diffusion, becoming moreefficient as Te dropped. They further concluded that the plasmadeviated more significantly from thermal equilibrium in thepresence of the sampler interface. In a related paper381 the sameauthors determined radial profiles of Ca and Sr, usingsaturated laser fluorescence at 396.5 nm and 421.55 nm, res-pectively, in the presence and absence of the sampling interfaceand at the same positions ALC as in the previous paper.380

They found that the interface could raise or lower the ionnumber density, alter its peak value, and cause a vertical shiftwith respect to the ICP axis. These effects were highlydependent on the central gas flow rate.A simulation of droplet coalescence, heating and desolvation

has been performed200 using Monte Carlo methods and theAshgriz-Poo model to compute droplet–droplet interactionsand the outcome of droplet collisions, respectively. Spatialmaps of droplet number and mass densities in an Ar ICP werecomputed for conventional, direct injection high efficiency(DIHEN), and large bore (LB) DIHEN nebulisers. The mainconclusions were linked to a consideration of the effect ofcoalescence and were: droplet collisions mainly lead to coale-scence, particularly when using DIHENs; there is a complexrelationship between gas temperature and droplet size; DIHENdroplets penetrate further into the ICP; droplets from theLB-DIHEN coalesce less frequently than those from theDIHEN.Temperature measurements in a low pressure (LP) ICP have

been made during sample introduction by nebulization andmembrane desolvation.382 Measurements of Trot(OH) yieldedtwo temperatures, ca. 800–1100 K and 1850–2800 K, whereasTrot (N2) gave a single temperature equivalent to the highTrot (OH) temperature. Increased gas flow (and presumablypressure) from 0.3 to 1.1 L min21 resulted in a decrease in Texc

(Fe II) from 10 400 to 9200 K, which is higher than normally


reported in an atmospheric ICP, perhaps indicative of the non-equilibrium nature of the low pressure plasma.Young et al.383 have determined the temperature in an ICP

operated under conditions optimised for atomic fluorescenceafter excitation with hollow cathode lamps and light emittingdiodes. They determined Texc and Trot to both be within therange 2500–3000 K, indicating that the plasma was operatingclose to LTE.Spectral lines have been classified into hard and soft cate-

gories using neural networks.384 Wavelength, excitation energy,lower level of the electronic transition, statistical weights of theupper and lower levels and transition probabilities were usedfor the classification by the methods of back-propagation andself-organising maps.A method has been proposed to estimate the continuum

background emission in the ICP for any given set of excitationconditions.385 The basis of the method is that the ratio ofbackground continuum emission at two different plasmaexcitation conditions is a constant for all wavelengths, hence,if the conditions change, the new background emission at anywavelength can be calculated from the initial backgroundemission at that wavelength and the emission at anotherconvenient wavelength. Using this methodology, the authorsutilised the ratio of differences in emission intensity, which theytermed the ‘f-factor’, to background-subtract analyte emission,and compared it to the off-peak background correctionmethod. They claimed complete agreement except in the caseof spectral interference of H on Ca 396.847 nm.

3.1.3 Glow discharges. Several papers have appeared in thelast year reporting on the characterisation of a millisecondpulsed glow discharge.386–389 Jackson and King389 studied thespatial and temporal characteristics of a 5 ms pulsed GD togain insight into the nature of the plasma at each point in space,and also during the initial breakdown, steady state andrecombining periods of the discharge cycle. At initial break-down a highly ionizing plasma is formed with over-populatedlower excited states, before reaching a steady state which is alsoionizing in nature. After the pulse a re-combining plasma isformed which exhibits population inversion, except close to thecathode where electrons are lost by diffusion so are notavailable for recombination. A second paper by the sameauthors described the effect of adding 1% N2.

386 The degree ofionization of sputtered atoms was reduced by 106 during thepower-on and steady-state periods, but had less effect on atomemission intensity, which was dominated by electron collisions.The effect on the afterpeak was more pronounced because: theadded nitrogen reduced the number of Ar ions available forrecombination; and vibrationally excited states of N2 slowedthe thermalization of electrons, thereby decreasing recombina-tion efficiency. Thus, the reduction in number of Ar metastablespecies affects the ionization of sputtered atoms in theafterpeak. In related work, a model of an Ar millisecondpulsed GD with a Cu cathode has been developed387 to accountfor the recombining nature of the post-pulse plasma. Three-body collisional radiative recombination was put forward asone plausible explanation: however, this requires a 26 rise inelectron denisty compared with the steady state, so dissociativerecombination of Ar2

1 ions cannot be ruled out. Furtherstudies of this type of plasma388 compared the temporal emis-sion of millisecond pulsed rf and dc GDs, and found negligibledifference between the two sources. Ion and atom excitationthrough electron collision, asymmetric charge exchange andPenning ionization occurred at varying distances from thecathode surface during the power pulse. The post-pulse periodwas characterised by recombination to form excited atoms andargon metastables. Other workers390 have also studied a pulsedGD and used experimentally confirmed simulations to predictthe contribution of Penning ionisation, which is significant evenafter discharge termination.

Davis and Marcus391 have studied different powering modesof a liquid sampling atmospheric pressure glow discharge.They determined temperatures in the presence of N2 and Heconcentric sheath gases, with Trot (OH) in the range 2100 to3600 K and Texc (Fe I) between 2400 to 3600 K. Rotational andexcitation temperatures were observed to increase slightly withHe compared to N2. In a futher paper of note Gamez et al.392

used Thomson and Rayleigh scattering to determine that theelectron energy distribution was non-Maxwellian in a planar-cathode GD.

3.1.4 Flames. A shearing interferometer has been used todetermine the temperature inside the flame of an AA slotburner,393,394 and good agreement with the temperature mea-sured using a thermocouple was obtained.

3.1.5 Other sources. A dc arc plasma formed in Ar atatmospheric pressure and 6 A has been studied using the powerinterruption technique, whereby the arc current was inter-rupted for periods up to 200 ms.395 This has the effect of eitherincreasing or decreasing the spectral line intensities, therebyindicating either a Saha or Boltzmann balance for the parti-cular species. Elements with high IP were observed to obey theSaha balance (i.e., excitation by three body recombination),those with medium IP the Boltzmann balance (i.e., excited byelectron collisions), and some lines of C, P, Hg with highexcited state levels seemed to obey both mechanisms, therebycancelling out both effects. Further, spectral line responses ofeasily ionised elements were found to depend on the observa-tion zone in the plasma.The temperature (Texc ~ 12 000 K) in a capacitively coupled

plasma, formed in a 250 mm id fused capillary, operated at 8 W(20 kHz and 20 kV), was determined using the He emissionspectrum and a Boltzmann plot.246 The plasma was sustainedat He or Ar flow rates of between 3–200 mL min21.

3.2 Furnaces

Ortner et al.396 provide a useful review of modifiers andcoatings in ET-AAS. The authors suggest that much of theliterature concerning the mechanisms of modification is unsub-stantiated by experimental evidence. Two basic processes aredeemed to be responsible for analyte stabilization by the twomost important groups of modifiers, namely refractory, carbideforming group IVa–VIa elements and the Pt-group metals.These concepts are based on carbide formation and intercala-tion processes. The main experimental results that have lead tothe understanding of the modifier mechanisms are described.Most graphite–analyte–modifier interactions are understood tooccur from the surface of the graphite to a depth of 10 mmbecause of the porosity of the pyrocarbon coating of commonlyused graphite tubes and platforms. The authors describe anumber of theories that they consider erroneous, and certainlythey provide compelling evidence for their criticism. This paperprovides a good guide through the complex topic of modifierselection and use in ET-AAS and should be of help to mostusers.The role of chemical modifiers in ET-AAS spectrometry was

reviewed by Volynskii.397 The mechanisms of the action of themost commonly used modifiers are discussed: namely, nitricand oxalic acids; magnesium, nickel and ammonium nitrates;high-melting carbides; organic compounds, and some otherchemical modifiers. The most appropriate applications of thesemodifiers are suggested.NaCl continues to be a troublesome matrix component in

ET-AAS determinations. Castro et al.398 investigated thethermal treatment of a matrix of NaCl alone and with nitricacid, Ni, Pd and Th, using SEM and XRD. The distribution ofNaCl appeared as relatively large particles on the platformsurface, which contrasts with other metal chlorides and nitrates


that generally appear on the surface as fine granules. The NaClwas observed to remain on the graphite surface up to tem-peratures of around 950 uC when present alone: however, whenprotons from nitric acid are present, NaCl is vaporized at muchlower temperatures. Pd was also observed to delay the thermaldegradation of NaCl. The same authors investigated theinterference of Al on the determination of As by ET-AAS399

when sampling by aerosol and liquid drop was used. The Alinterference appeared to be the result of the formation of agas phase Al oxide, which absorbed at the As analyticalwavelength. The addition of activated carbon to the furnacewas seen to reduce the Al interference.A novel use of a two-stage atomizer for AAS was described

by Nagulin et al.400 The analytical cycle used contained anadditional stage involving the fractional condensation ofanalyte atoms, resulting in an analytical cycle consisting ofvaporization–condensation–atomization stages. Separate heat-ing of the upper and lower parts of the graphite furnace permitscontrol of condensation and subsequent re-vaporization, andallows these processes to be studied.The transverse heated filter atomizer (THFA) provides

substantial advantages in trace element determination, due tosuppression of interferences. A study of vapour transport in theTHFA was reported by Ngobeni and Katskov.401,402 Theauthors used Matlab software to model the transport pro-cesses, allowing a set of optimal dimensions and conditionsfor the furnace to be selected. The THFA was successfullyevaluated for the determination of Pb and Cd in urine inanother publication.403

The tungsten coil atomizer has been in use for a number ofyears, and although the reports of its use have been scarce thisyear, some fundamental studies have been carried out. Queirozet al.404 have published data obtained from measuring thesurface and gas phase temperatures of the tungsten coil. Thedata show differences between surface and gas phase tem-peratures that can reach values higher than 1000 uC, dependingon the applied voltage and observation height.

4 Laser-based analytical atomic spectrometry

For the purposes of this review, lasers are generally used in twodifferent ways in analytical atomic spectrometry. One is as anintense energy source where wavelength is not necessarily ofprimary importance, such as in laser induced breakdownspectroscopy (LIBS). The second is as a bright radiation sourceof precise wavelength, as in laser excited atomic fluorescence,laser atomic absorption, and laser enhanced ionization. Thisreview will be divided into these two categories following asimilar format to last year’s review.405 The use of lasers forfundamental studies of the properties of atoms, atomicvapours, plasmas, and applications to studies involving thinfilms will not be covered. Also not covered by this review willthe applications where lasers are used to vaporize a solidsample for detection with an ICP-MS (laser ablation–ICP-MS).

4.1 Lasers as energy sources

A laser can be focused in a high-energy pulse onto a small areato vaporize (ablate) a small volume of sample (microsampling).Using repeated pulses can provide a depth profile of thesample. The laser energy may also be used to generate a plasmaand excite the emission spectrum of analyte atoms. The laserwavelength is not usually critical (wavelengths from 193 nm tothe infrared have been used) but matching wavelength tosample material is often advantageous. Pulse energies are of theorder of millijoules, with repetition rates optimised to matchanalytical requirements.

4.1.1 Laser induced breakdown spectroscopy (LIBS). Ina LIBS system, sometimes called laser induced plasma

spectrometry (LIPS), a laser pulse vaporizes a sample andalso excites the emission spectrum of the material. The lastdecade has shown important developments in the area, and thetechnique is slowly becoming established to the point wherethere are special issues and reviews dedicated to the topic in themajor atomic spectroscopy journals. The utilization of LIBS islikely to increase for certain applications, especially when non-contact sampling of solids is required, or for remote sensing.Although the technique features high spatial resolution, itsuffers from relatively poor detection limits compared withother elemental techniques. There was a LIBS feature issue inthe journal Applied Optics.406

4.1.1.1 Fundamental studies. There were several importantpapers in this area over the past year. Theoretical modeling wasused successfully to explain the fundamental processes that areoccurring in the laser induced plasma. Also, some noveltechniques are being developed to increase LIBS sensitivity andprecision.Babushok et al.407 reported a fundamental study for the

understanding of the physical and chemical nature of LIBSresults by kinetic modelling of the plume from metallic lead.The authors develop a computational fluid dynamics modelthat includes a set of air reactions and gas phase ion chemistryas well as the oxidization, excitation, and ionization of leadatoms. At total of 38 chemical species and 220 reactions wereincluded in the model, and comparison was made with experi-mental measurements for several lead emission lines.An algorithm has been developed and evaluated for the

approximation and automatic subtraction of continuum back-grounds in laser-induced breakdown and was also applied toRaman spectroscopy.408 The background correction algorithmwas applied to simple and complex spectra from different typesof plastics and its effect on identification accuracy was studied.A linear correlation technique was used to identify the plasticsamples using both LIBS and Raman spectra. Interestingly, forboth techniques the algorithm successfully eliminated con-tinuum background without compromising spectral integrityand improved the number of correct plastic identifications. Theapproach should be applicable to a wide range of backgroundcorrection problems in atomic and molecular spectroscopy.Aguilera and Aragon409 presented a study on laser intensity,

temperature and electron density distributions of laser-inducedplasmas with two-dimensional spatial and temporal resolution.The plasmas were generated in air at 10–1000 mbar using aniron sample. A blast wave model was used describe the intensitydistributions at initial laser sampling. By comparing two Fe Iemission lines of different energies, the temperature distribu-tions and electron density data are obtained. It is also notedthat the results were dependent on the pressure of the cell, andat higher pressures the signal intensity and temperaturedistributions are higher. The same authors410,411 took theabove work further in two similar publications by investigatingFe I lines emitted from a laser-induced plasma, generated withFe and Fe–Ni alloys in air at atmospheric pressure, lookingat the influence of plasma temporal evolution and spatialinhomogeneity. The curve of growth model predicted theradiative transfer within a plasma in local thermodynamicequilibrium, and was based on observation of spectral lineswith different energy levels and line widths emitted at differentoptical depths. Gradients in temperaure (9400–7800 K) anddensity of Fe atoms (46 1016–0.026 1016 cm23 for a 100% Fesample) between the inner and the outer plasma regions wereobserved. After the laser induced plasma expands and cools,the COG for emission lines may be described by a single regionmodel at 6700 K and with a density of 0.06 6 1016 cm23 Featoms.Carranza and Hahn412 presented a novel study of laser-

induced plasma vaporization of individual silica microspheresin an aerosolised air stream. The authors suggest that the upper


size limit for complete particle vaporization corresponds to asilica particle diameter of 2.1 mm for a laser pulse energy of320 mJ. This was determined by the deviation from a linearmass response of the silicon atomic emission signal. Also, acomparison of the measured silica particle sampling rates andtheoretical Poisson statistics, and the laser-induced plasmavolume, indicates that the mechanism of particle vaporizationis related to direct plasma–particle interactions. In a relatedpaper, the same authors413 compared conditional data proces-sing techniques as tools for analyte detection in single-shotLIBS. Both peak-to-base ratio and signal-to-noise ratios werestudied using the 288.1 nm Si I emission line provided by anaerosol stream of monodisperse 2.5-mm-sized silica micro-spheres. Both the Si emission line and a spectral regioncorresponding to continuum emission were used to evaluate thestatistical distribution of spectral noise. The authors calculatedthe probability of false hits as determined by evaluating variousconditional processing thresholds. The results showed that asthe detection threshold increased the rate of detected silicaparticle hits decreased along with the expected fraction offalse-particle hits. For threshold values the signal-to-noiseratio was found to provide a more robust technique for single-shot analyte detection compared to the peak-to-base ratio. Athird paper by Carranza and Hahn414 considered plasmavolume for the analysis of gaseous and aerosol samples usingLIBS where three distinct characteristic volumes were experi-mentally measured. Sample volume, emission-based plasmavolume, and the physical plasma volume could be dis-tinguished and measured in the range between 1.2 6 1023

and 2.4 6 1023 cm23. The variations were explained in termsof the behaviour of laser induced plasma particle interactions.The particle vaporization necessary for subsequent detectionwas limited to a plasma region somewhat smaller than theregion defined by the physical plasma volume, suggestingplasma inhomogeneity. In contrast, the emission-based plasmavolume, the largest of the three recorded volumes, reflectedanalyte emission following particle vaporization and diffusion.Casavola et al.415 presented an experimental and theoretical

investigation of laser-induced plasma spectrometry of atitanium metal target. Both the fluid dynamics and the kineticsof the laser-induced plasma were taken into account, and theresults obtained by a theoretical model were applied to thespectroscopic observation and used to calculate the initialconditions for the plume expansion. The predictions madeusing the model agreed with the experimental results.Mateo416 discussed an improvement to a LIBS microline

imaging technique to obtain uniform ablation, giving a repre-sentative spatial elemental distribution of the sample surface.To achieve this improvement, two types of Nd:YAG pulsedlasers, a Gaussian laser and a flat top laser were compared forthe effect of beam energy distribution on lateral resolution,element intensity, distribution maps and plasma electrontemperature. A homogeneous stainless steel and a composi-tionally patterned photovoltaic cell were chosen as samples.The results indicate the Gaussian laser provides the best lateralresolution, but with more redeposition at both sides of themicroline crater. The chemical maps obtained from the flat toplaser matched the distribution of the constituents of the samplesurface. The same group published a study of the performanceof line-focused laser ablation417 for the characterization ofinterfaces in layered materials by LIBS. A point-focusingmethod compared signal precision, signal-to-noise ratio, abla-tion rates and surface sensitivity with the line focussedtechnique using a pulsed Nd : YAG laser beam operating at532 nm with a homogeneous flat-top energy distribution. Theanalyte emission was detected with an iCCD detector binnedalong the slit-height direction. An advantage of the line focus-ing technique is that it permits higher laser power input whilemaintaining relatively low laser fluence, thereby yieldingincreased surface sensitivity and detection. Signal-to-noise

was improved by a factor of 6, and the ablation rate was 9 nmper pulse for the microline approach, compared with 23 nm perpulse obtained with the point-focusing method. The resultsdemonstrate that the microline-focusing approach was suitablefor the depth analysis of coated and layered materialsA laser induced plasma has been studied by means of

time and space resolved optical emission spectroscopy of ametallic titanium target at two different pressures, 1025 and3.4 6 1022 Torr, at distances up to 3 mm from the target.418

Time of flight measurements and Boltzmann plots were used tostudy the dynamic and kinetic aspects of the plasma.Also, microjoule picosecond and nanosecond KrF laser

pulses419 were compared for Si and Al targets. Differencesbetween the two lasers become significant only at very lowfluences approaching the plasma formation threshold, which issignificantly lower for 50 ps pulses than for 10 ns pulses.However, the authors state that the dominant process foremission is from expansion and cooling of the plasma plume inthe form of a blast wave in the ambient air, and this is primarilydependent on the energy deposited in the plasma and not thepulse length.

4.1.1.2 Instrumentation. Among the recent improvements inLIBS are portable field instruments, commercial laboratorysystems, and the use of fibre optics to couple sample excitationand emission to the laser source and spectrometer.Sabsabi et al.420 compared two commercial LIBS systems

with echelle spectrometers and iCCD detectors. Both systemswere used to analyse the same Al alloy samples for Be, Mg, Si,Mn, Fe, and Cu with the same conditions. Both instrumentsgave similar sensitivity and precision results. Also, bromine,chlorine, and iodine were detected using a LIBS systemequipped with a gas purged spectrometer and an intensifiedCCD (iCCD) detector.421 Emission lines down to 130 nm couldbe recorded.Vadillo et al.422 presented a remote detection system based

on optical emission spectrometry of laser-induced plasmas torecord real time spectra in the visible region from samplesplaced at remote distances from the excitation source. Unlikefibre optic based systems, light collection was performedremotely. The application would ultimately be for the non-invasive remote analysis of hot samples (y1200 uC) allowingthe dynamic monitoring of selective elemental migration.An array of Geiger photodiodes423 has been shown to

enhance the performance of LIBS. These compact, silicon-based detectors could eliminate the need for post-amplificationelectronics and allow for the detection of single photons atroom temperature. The system did not require gating circuitry,making the setup simpler. The detectors featured dark countrates of v500 Hz at room temperature and adequate responsefrom the UV to the near IR. This new approach was shown tobe more sensitive compared with standard LIBS detectionsystems.The sensitivity and overall performance of normal CCD and

iCCD detectors has been compared for LIBS.424 Themeasurements were made in a calcium-based aerosol-seededgas stream at atmospheric pressure. The signal-to-noise ratiobased on the 393.37 nm calcium emission line was calculated asa function of detector delay with respect to the plasmainitiating laser pulse. Both ensemble averaging and single shotspectral analyses were performed. As expected, under allconditions the iCCD system provided an enhanced signal-to-noise ratio compared with the normal CCD system.Palanco et al.425 have published a promising report of a

portable LIBS system with fully-automated operation andquantitative analysis capabilities. The system integrates a50 mJ per pulse Nd:YAG laser operating at 1064 nm, a 1/8 mspectrograph, and an iCCD detector with computer controlledinstrument operation, data acquisition and processing. Aspecial hand-held sampling probe delivered the laser, focusing,


and collection optics. Results obtained in the field for steelscrap sorting compare well with those obtained by XRF in thelaboratory.Detalle et al.426 studied both 1064 nm (Nd:YAG) and

2940 nm (Er:YAG) lasers for fundamental parameters and forLIBS analysis of aluminium alloy samples in air and helium atatmospheric pressure. Emission was used to calculate the spaceaveraged electron density and plasma temperature in the laser-induced plasma and the lasers were also investigated forspectrochemical analysis. The Er:YAG laser could increaselinearity by limiting the levelling in the calibration curve forsome elements in aluminium alloys. The two lasers producedifferent electron density and plasma temperatures.Zeng et al.427 presented a study of the formation of a laser-

induced plasma in a cavity and the effects of the cavity on theablation process. The cavities were constructed of fused silicawith aspect ratios (depth/diameter) of 1, 3 and 6. The plasmatemperature and electron number density of the pulsed laser-induced plasma were determined from spectroscopic measure-ments. The results suggest that reflection and confinementeffects by the cavity walls and plasma shielding could explainincreased temperature and electron number density withincreasing cavity aspect ratio. The temporal variations of theplasma temperature and electron number density sharplydecreased inside the cavity. Also, laser-induced plasma proper-ties within cavities were compared with those on a flat surface.Corsi et al.428 produced a study on the temporal and spatial

evolution of a laser-induced plasma from a steel target usingoptical time-of-flight and shadowgraphic techniques. Theresults, obtained for two distinct laser energy regimes, showtwo regions in the plume. One is characterized by air andcontinuum emissions produced by the shock wave ionizationand the other by emissions from ablated material. The data

indicate that a sufficiently high laser fluence and a short delaytime of acquisition are required to avoid inhomogeneous effectsin the plasma.Nanosecond and femtosecond laser pulses have been

combined429 in an orthogonal preablation dual-pulse LIBSsystem. Sensitivity, signal-to-noise ratio, and signal-to-back-ground ratio enhancements were observed for both copper andaluminium targets. These results have implications forexplaining the sources of dual-pulse LIBS enhancements.A low cost system was reported430 by replacing the gated

analyser normally used in laser plasma spectroscopy by asimpler system without gating. The results obtained by thislow-background technique are more sensitive than electronmicroprobe microanalysis. The system is capable of field mea-surements for geological applications. LIBS was also tested in a5 kG magnetic field431 and detection limits were improved by afactor of 2 for Mg and Mn. The enhancement in the emissionwas attributed to an increase in the plasma density.

4.1.1.3 Applications. Table 1 summarizes the varied recentapplications of LIBS found in the literature. Aragon et al.432

used LIBS for the analysis of the composition of thin filmsproduced by pulsed laser deposition. The same laser was usedto deposit the samples (under vacuum) on a slide and thenperform atmospheric LIBS analysis. Interestingly, the single-shot line intensities emitted by the laser plasma generated withthe deposited films are up to 16 times higher than those emittedby the plasma obtained with an equivalent bulk sample. Asimilar plasma temperature of about 7000 K was measuredwith both types of samples. Those results indicate that theablation process is much more efficient for the films than inbulk samples. Calibration curves showed good correlation withabout 5% RSD.

Table 1 Applications of laser-induced breakdown spectroscopy

Matrix Analyte Comments Ref.

Aluminium alloy (molten) Cr, Mg, Zn, Cu, Si, Fe, Al Probing inside a melt within a furnace for alloycomposition

438

Aluminum alloy Cu, Mg, Mn To study y10 mm precipitate impurities in commercialalloys

439

Bio aerosols Ca, Na, Mg Screening for airborne pollen and fungal spores 440Ceramics Mg, Al, Ca, Fe, Ti Quantitative method development 441Combustion exhaust C, H, O, N Process monitoring 442Electronic equipment Br, heavy metals To sort waste electronics high in brominated fire retardants

and heavy metal hazardous waste443

Flue gas Be, Hg, Cr Off line filter analysis in laboratory 444Fly ash Carbon Automated, precise analysis of unburned carbon in a boiler

furnace445

Glasses, historical Li, Be, B, Si, Na, K 266 nm laser, Si used as internal standard, 3–20% RSD 446Gunpowder residues Tape sampling for identification of gunpowder on the

hands of a shooter447

Hair Heavy metals Calibration free screening method 448High temperature industrialboilers and furnaces

Na, K, Ca, Mg, C, B, Si, Mn, Al,Fe, Rb, Cl, and Ti

Novel probes for high temperature applications 449

Iron slurries Fe, Si For online monitoring 450Liquid submerged steel Cr, Mn and Si LOD of 310, 325 and 455 ppm, respectively 451Liquids, water Mg, Cr, Mn, Re Liquid jet LOD 0.1–8 ppm lower than bulk liquid 452Nuclear materials Ce in a U matrix Ce LOD 1.4% with 2% RSD 453Paper, historical Na, Ca, V, Ti, Fe To check for cleaning of historical paper documents 454Pollen grains Classification and sorting of individual pollen grains when

used with complementary Raman method455

Pottery High success rate for identifying known artefacts 456,457Pottery, metal Various elements Rapid sorting of field samples 458Rock, ore Ca, Ag, Cu Tandem laser technique 459Rocks, ores Na, Ca Fluid inclusion work to identify palaeofluid composition 460Soil Total carbon Organic and inorganic analysis possible 461,462Steel (liquid) S, P, C, Ni, Cr For process analysis in a steel plant 463Steel slag Ca, Si, Fe-total Screening for steel production 464Water Mg, Mn, Cr Use of a Meinhard nebulizer for sampling 465Water Ca, Cr, Zn Dual laser, direct sampling of bulk solution, LOD y1 ppm 466Water Mg Single/dual pulse laser comparison. LOD 230 ppb (single)

69 ppb (double)467

Water Na 0.1 ppb LOD using dual pulse 468


An analytical method for element-specific in situ investiga-tions of biological samples with high spatial resolution usingLIBS is presented by Assion et al.433 The authors suggest thatfor high spatial resolution, precise lateral and axial micro-ablation are necessary. Both ns-LIBS and fs-LIBS were testedon an aqueous solution of CaCl2 and on the outer epidermalwall of a sunflower seedling stem. The physiology of thesunflower seedling was used in order to estimate ablationdepth. The authors suggest that high spatial resolution waspossible with the fs-LIBS, as demonstrated by in situ mea-surements of wall-associated calcium ion (Ca21). The axialresolution was on the order of 100 nm.LIBS may also be used for geochemical analysis on other

planets, as suggested by Brennetot et al.434 The technique wasfound to work well in the 5–12 mbar CO2 atmosphere of Marsfor the study of soils and rocks. The best conditions obtainedwere for a laser wavelength of 1064 nm with 40 mJ at 15 Hz,which is the maximum energy available due to space limita-tions. Other authors have combined a Raman spectrographand a LIBS system for sampling planetary surfaces from adistance of 25 cm away from the sample.435 The design is basedon the optical configuration of a telescope. Continuing in thevein, LIBS has been field-tested for remote planetary explora-tion436 on a Mars type rover for mineralogical and elementalidentification. Results were presented from remote measure-ments for representative samples (basalt, iron oxides, alteredrhyolite, and dolostone) during May 2000 rover trials at BlackRock Summit, Nevada. The remote analysis results were laterverified in a laboratory setting with conventional analysis.LIBS analysis revealed variation with depth as an alumino-silicate coating was ablated and a basaltic composition wasrevealed beneath.A microline-imaging LIPS system has been used for surface

and depth analysis of heterogeneous solid samples in air atatmospheric pressure.437 A pulsed Nd:YAG laser beamoperating at 532 nm was used with a homogeneous energydistribution (flat top laser). A microline plasma was formed onthe sample surface and subsequent light from the plasma wasresolved spectrally and spatially with an imaging spectrographand an iCCD. A patterned metal sample was used, and three-dimensional chemical maps of Ni and Cu from the edgeconnectors of a printed circuit board were obtained. The resultsillustrate the capability of microline imaging for fast mappingof large-area samples and for depth profiling purposes.

4.2 Lasers as sources of intense monochromatic radiation

4.2.1 Laser excited atomic fluorescence. Sometimes referredto as laser induced fluorescence (LIF), the technique uses anatomization or ionization technique in conjunction with a laserto produce fluorescence of the analytes. In addition to applica-tions in analytical atomic spectroscopy, laser fluorescence iswidely used as a probe technique in the study of atomic vapourgenerating systems and chemical surface coating applications.These latter applications will not be reviewed here, nor willapplications of laser fluorescence to the fundamental propertiesof atoms for astrophysical research.Two papers469,470 from the same group were published on

the use of laser induced atomic fluorescence for trace analysisof lead and aluminium in sea-water. In each case, excitationof fluorescence was performed with a pulsed Nd:Yag lasercoupled to an optical parametric oscillator. Fluorescencespectra were recorded with a spectrograph equipped with aniCCD for enhanced sensitivity. Temporal resolution wasnecessary to avoid the matrix fluorescence. Traces of alumi-nium and lead in sea-water were observed with femtogramLODs.Gottwald and Monkhouse471 have determined Ni in indus-

trial flue gas by LIF. An ArF excimer laser (193 nm) was usedfor excitation in a simulated laboratory cell with NiCl2 as the

precursor molecule. Ni atomic emission spectra were recordedin the range 300–550 nm. The LIF signals gave lifetimes longerthan the known natural lifetimes. Quenching effects wereinvestigated by measuring fluorescence signals and lifetimes innitrogen or air up to 1 atm. Detection limits for Ni incombustion applications such as power plants were of the orderof tens of ppb, sufficient for regulatory measurements.

4.2.2 Laser atomic absorption. There has been little activityin the literature for the application of lasers to atomicabsorption (AA) analysis. Modulated diode lasers were usedby Gustafsson et al.472 to improve the performance of GF-AAfor lines plagued by etalon interferences. Sulfur compounds, aselemental S, were detected by atomic absorption in CO2 bytunable diode lasers.473 The detection limits obtained satisfyrequirements for the control of sulfur compounds in CO2 usedin the food and beverage industry.Galbacs et al.360 constructed and characterized a diode laser

system for atomic spectroscopy, with detailed electronic circuitlayouts of the laser current controller supplying 1300 mA andalso a functional description of all other components, such astemperature controller and optics. Results from electronic andspectroscopic tests show that wavelength may be tuned to aprecision of 0.01 nm and current modulation frequency up to10 kHz. The system was designed for atomic fluorescence andabsorption measurements, but these were not attempted in thispaper.Diode lasers at 860.795 nm and 682.691 nm were used for

uranium measurements in a hollow cathode discharge.474

Uranium isotope analysis475 was also performed on naturalmineral and artificial solid samples with no sample preparation:however, the isotope ratios were not precise. Detection limitswere reported to be 47 ppm.

4.2.3 Laser enhanced ionisation. This technique has thecapability of being a very sensitive trace analysis tool. Itinvolves a spectrally selective laser to excite analyte atoms andthe subsequent collisional ionization and detection of theelectric charge. However, it has not been widely used for theanalysis of complex matrices, but the problems associated withthe matrix can be reduced if some form of chemical separationis performed. For example, the technique could function as adetector in a GC or HPLC system.Pb was determined at ppb levels by Gravel et al.476 in solid

samples by UV laser ablation and laser-enhanced ionizationdetection. The ablated material was transported from theablation cell to a miniature LEI flame for Pb detection.Compared to argon, helium as the carrier gas produced higherablation yields and lower pulse-to-pulse variations in LEIsignal, and therefore better analytical figures of merit. Adetection limit of 60 ng g21 was reported for the determinationof Pb in high purity aluminium.Temirov et al.477 reported laser-enhanced ionization with

avalanche amplification for the detection of caesium at fg mL21

levels in hydrogen and propane flames. The avalancheamplification detection was very sensitive and gave a signal-to-noise ratio of y104 for a 100 ppt Cs solution. Theextrapolated limit of detection was 30 fg mL21.

4.2.4 Cavity ringdown spectroscopy (CRDS). Several appli-cations of this technique appear for the detection of molecules,but few applications of this approach have been attempted forthe determination of atoms. However, the technique has thepotential for very sensitive atomic absorbance measurementsand it is therefore worthy to keep the subject under review.Inductively coupled plasma–CRDS was applied for the

isotopic measurement of uranium.478 Isotopic-resolved spectraof uranium were recorded at three different atomic/ionictransition lines, 286.57, 358.49 and 409.01 mn. Of the threelines, the largest isotope shift of approximately 9 pm was


measured at the 286.57 ionic line. Isotopically-resolved spectrawere recorded in ratio of 1 : 1 (235U/238U, 2.5 mg ml21) and atthe natural abundance ratio of 0.714% (235U/238U, 1.25 mg ml21

235U). The smallest measurable isotope shift of approximately3 pm was determined for the 409.01 nm ion spectral line. Detec-tion limits obtained were in the range of 70–150 ng ml21, exceptfor the 238U component of the 286.57 nm line (300 ng ml21) dueto a strong, previously unreported absorption interferencefrom an argon emission line.In another promising development, a group from Los

Alamos479 explored the use of CRDS with a microwaveplasma source for atomic absorption measurements of leadwith a detection limit of 0.8 ppb. The compact microwaveplasma source runs at low power and low plasma gas flow rate.The CRDS system consists of a tunable dye laser with a customsampling system for solution sample introduction. The ring-down signals were monitored using a photomultiplier tube andrecorded using a digital oscilloscope interfaced to a computer.A simple, periodically locked continuous wave CRDS

technique has been reported,480 enabling a very large numberof ringdown events to be rapidly acquired. An external cavitydiode laser is locked to a high-finesse cavity where 16 000ringdown events per second were recorded, obtained byperiodically switching off the light entering the cavity.Following each ringdown event, the light to the cavity wasswitched on and cavity lock rapidly reacquired. The systemfeatured a modest digitization rate, but still obtained a mini-mum detectable absorption loss of 4.7 6 1029 cm21. Fasterdigitization could theoretically increase sensitivity by an orderof magnitude.CRDS has been used for the detection and characterization

of a variety of laser breakdown generated aerosols,481

providing time resolved morphological information on theaerosol plume and sensitive detection. CRDS was also used tomake atmospheric aerosol measurements.482 The ambient airextinction coefficient was measured and found to be a sensitiveindicator of micrometre sized airborne particles. Scatter andabsorption of light by the airborne particles induced ameasurable decrease in the ringdown decay time. When acopper vapour laser operating at 8–10 kHz was employed and1500 individual ringdowns were averaged on an oscilloscope,minimal detectable extinction coefficients of 1026 m21 wereachieved. The ringdown instrument was used to detect acorrelation between the observed ringdown extinction coeffi-cient and particulate mass concentrations (mg m23 of air).

5 Chemometrics

A review of the application of chemometrics in spectroscopyhas been published,483 with a second part to follow. This firstpart deals with the major, classical chemometric and dataanalysis techniques.A number of papers have described the use of wavelets for

multivariate calibration in ICP-AES.484–488 Coelho and co-workers484,485 have developed a variable selection algorithm tochoose a subset of wavelet coefficients with minimal colinear-ity, allowing calibration byMLR. They successfully applied themethod for the determination of Mn, Mo, Cr, Ni and Fe insteel samples using low resolution ICP-AES. Qin and Shen486

used wavelet transformation to reduce spectral noise in ICP-AES prior to using a Kalman filter. Ma and Zhang487,488

developed a wavelet filtering method to separate the high andlow frequency signals equating to the analyte and backgroundsignals. They evaluated the approach by processing bothexperimental and simulated spectra, and achieved relativeerrors in peak height of v5% for signal-to-noise ¢2.Principal components analysis has been used489 to select

internal standards for ICP-AES by selecting appropriateanalyte and reference lines to correct for supression effects

due to mineral acids; however, certain lines could not becorrected. The method of PLS has been used to calibrate directsolid-sampling FAAS using dry aerosol sample introductioninto a quartz cell, and reduced errors from 64% to less than 4%using univariate calibration.490

As usual, there have been several papers describing theclassification of wines and other foods based on their traceelement content.491–493 One paper of note compares theapproaches of ICP-AES and 1H NMR,494 with NMR dataproviding the best predictor.A few papers address the growing issue of uncertainty

calculations.495–497 A high accuracy reference method for thedetermination of minor elements in steels by ICP-AES has beendeveloped, whereby an exact matching technique has been usedto match the signal for standard and sample as closely aspossible. Standard and sample were also matrix-matched andAu was used as an internal standard for drift-correction. Thisapproach makes it possible to easily estimate a full uncertaintybudget, without the added complication of including thecalibration curve.

6 Coupled techniques for speciation

6.1 Gas chromatography

6.1.1 GC-AES. An overview of GC-AES has been pre-sented by van Stee and co-workers.498 These authors com-mented on the fact that the number of applications of thetechnique in assorted different research areas is increasingrapidly and that this was because of its versatility andanalytical power. They also concluded that when it is used inconjunction with GC-mass spectrometry (GC-MS), veryrewarding information can be obtained.As with all GC methods, the analyte species must be volatile,

or at least easily derivatized into a volatile form. The mostcommon analytes have been organotin species. Detection isnormally by either flame photometry (FP) or AES. An exampleincludes the determination of phenyltin compounds in poly-chlorinated biphenyl (PCB)-based transformer oil samples, inwhich MS, AES and FP were all used as methods of detec-tion.499 Tetraphenyltin (TePhT) has been used as a stabilizerfor some kinds of PCB based transformer oil formulations and,after extended use, the tetraphenyltin may metabolise into tri-,di- and monophenyl Sn compounds (TrPhT, DPhT andMPhT,respectively). After propylation using a Grignard reagent, thespecies were separated by GC. It was found that although theMS was the most sensitive of the detection systems (LODs of30, 9.8, 5.5 and 0.6 ng mL21 for MPhT, DPhT, TrPhT andTePhT, respectively), it was also less selective than either FP orAES. Two samples of used transformer oil were analysed andTePhT and TrPhT were found in both. Headspace solid phasemicroextraction (SPME) has been used by two research groupsto determine organotin compounds. Butyltin compounds weredetermined in 44 commercial Chinese alcoholic beverages usingGC-FPD as a means of detection.500 It was found that concen-trations of monobutyltin (MBT) and dibutyltin (DBT) rangedfrom v0.016 to 5.687 and from v0.0022 to 33.257 mg Sn L21,respectively. The presence of DBT was confirmed by GC-MSanalysis of the samples. Low levels of tributyltin (TBT) werealso detected. The authors concluded that dry wines generallycontained more DBT than sweet ones and that liquor samplesgenerally contained less organotin species than wines. Theother paper that has used headspace SPME described thesimultaneous determination of 14 organotin compounds(namely, assorted methyl-, butyl- phenyl- and octyl- species)using GC coupled with a pulsed FPD.501 The sorption of thespecies onto the SPME fibre and the desorption of the speciesinto the GC injection port were optimised using experimentaldesigns. The LODs for the species were reported as being sub-ng Sn L21 and the technique was applied to the analysis of


spiked environmental samples. In a similar paper, the sameresearch group has also used a chemometric approach utilisingexperimental design to validate a GC-ICP-AES system fororganotin speciation.502 Four factors were considered to ensurethat the analyte species passed through the transfer line fromthe GC to the ICP. The absolute LODs were found to becomparable to those obtained using a FPD. When usingSPME, LODs are at the sub-10 ng Sn L21 level and a precisionof 3–10% RSD is typical, depending on the extraction systemused. The method was applied to a range of reference sedimentsand both fresh and waste waters. Butyltin compounds havealso been determined in retail mollusc products.503 Afterenzymatic hydrolysis of the samples, the Sn species wereextracted with 0.05% tropolone in hexane : ether (1 : 1); theethyl derivatives were prepared using a Grignard reagent andthe extracts analysed using GC-AES. It was found that MBT,DBT and TBT were present in most samples, with samplesfrom East and South East Asia having the highest concentra-tions. It was also found that gastropods tended to have lowerlevels than other molluscs. The presence of the butyltincompounds was confirmed by the use of GC-MS.Another popular analyte in this review period has been Hg.

Two groups have used chemometric approaches to optimise thespeciation of Hg compounds using GC-AES instrumenta-tion.504,505 In the first example, GC-MIP-AES was used tospeciate inorganic Hg, methylmercury and dimethylmercury.The species were ethylated using sodium tetraethylborate andthen extracted into hexane prior to their separation on an OV-1701 capillary column; and the whole process was optimisedusing factorial design, analysis of variance (ANOVA) andmulti-simplex techniques. The authors also described proce-dures for the cleaning of glass and plastic-ware and for thepurification of reagents to prevent high blank signals. Usingthe optimum conditions found, absolute LODs of 0.5, 3.0 and15 pg were obtained for dimethyl-, methyl- and inorganic Hg,respectively. The precision was reported as being better than5% (n ~ 5). In the second example,505 the simultaneouschemometric optimisation of a headspace SPME and deriva-tization procedure followed by GC-MIP-AES detection wasdescribed. The Hg species were derivatized by sodiumtetraphenylborate sorbed on a poly(dimethylsiloxane) coatedfused silica fibre and desorbed in the GC injector in splitlessmode. Experimental design methodology was used to optimisethe sample volume, tetraphenylborate volume, pH, sorptiontime, extraction–derivatization temperature and rate of stir-ring. Two papers by Grinberg and co-workers have discussedthe use of GC coupled with furnace atomization plasmaemission spectrometry (FAPES) for the speciation analysis ofHg compounds. In one, a comparison of alkyl derivatizationmethods was made.506 Biological samples were extracted withmethanolic potassium hydroxide, the pH adjusted, the Hgspecies derivatized with either tetraphenylborate or tetrapro-pylborate and then extracted using SPME. Following carefuloptimization, the tetrapropylborate was found to offer thebetter sensitivity and was more robust and faster than otherderivatizing agents. Using this reagent, LODs of 0.55, 0.34 and0.23 ng g21 for methyl-, ethyl- and inorganic Hg were achieved.Method validation was by successful analysis of the CRMsDORM-2, DOLT-2 and TORT-2. The other paper was verysimilar.507

Two papers have reported the determination of other metalanalytes by GC-AES. These include one that compared ethyl-,methyl- and menthylchloroformates for the derivatization ofthe seleno-amino acids, selenomethionine, selenoethionine andselenocysteine.249 In addition, the effects on some S containingamino acids (methionine, cysteine, cystine and methylcysteine)were also tested. It was found that methylchloroformate was thebest derivatization agent in terms of both derivatization yieldand reproducibility and that it also showed the least significantconditioning effects. Overall, the efficiency of determination of

selenomethionine and selenoethionine from aqueous extractsranged from 40–70% for methyl-, 30–75% for ethyl- and from15–70% for menthylchloroformate. Precision for the determi-nation of selenomethionine was typically 7–13%, but this couldbe improved to 2% if selenoethionine was used as an internalstandard. The authors concluded that despite the method’slimited reproducibility, the repeatability was good enough foraccurate determination of selenoamino acids. They illustratedthis by the successful analysis of supplementation tablets.Metal chelates of five tetradentate beta ketoamine Schiff basesderived from distilbenediamine and meso-stilbenediamineswere examined for the separation of Cu(II), Ni(II), Pd(II) andoxovanadium(IV).250 Detection was by either GC-FID or GC-MIP-AES. Complete separation between the analytes wasreported for all the systems tested and the LODs ranged from 6to 23 pg of metal.The high ionization capabilities of helium used to form the

MIP have been used to determine a selection of analytes thatcannot easily be detected using other atomic spectrometrictechniques. Included in these analytes are the halogens, S andP. Several applications have been reported, including thedetermination of organochlorine, organophosphorus and pyre-thrin insecticides;508 the determination of methyl tert-butylether and tert-butyl alcohols in sea-water509 and of organopho-sphorus insecticides in natural waters.98 In the last of thesepapers, stir-bar sorptive extraction was combined with thermaldesorption GC-AES for the determination of eight organo-Ppesticides. An extraction time of 50 min and a desorption timeof 6 min was sufficient to obtain LODs of between 0.8 ng L21

(ethion) and 15.4 ng L21 (fenamiphos). Recoveries for seven ofthe eight pesticides were between 62 and 88%, but fenamiphoshad only a 15% recovery. This was attributed to its high watersolubility. A prototype AES detector for GC that used aradiofrequency (rf) He plasma has been reported.510 The torchwas shielded by a flow of He to prevent atmospheric con-tamination into the plasma. A range of 16 halogenatedaromatics, aliphatics or trihalomethanes were tested usingthe system, and the emission spectra from the halogens (Br, Cl,F and I) were clearly distinguished. A linear relationshipbetween emission intensity and the elemental ratio wasachieved. An overview of the determination of volatile Scompounds in foods and beverages has been presented.511 Arange of sample preparation methods, including distillation,co-distillation, liquid–liquid extraction and sublimation, werediscussed in terms of efficiencies and potential artefactformation. In addition, the advantages and limitations ofSPME as well as purge and trap concentration techniques andother preconcentration techniques such as adsorption onmercury based solid sorbents, metal foils and impregnatedfilters were also discussed. Detection methods including flamephotometry, chemiluminescence and AES were discussed interms of the LOD, sensitivity, selectivity and cost. Other papersthat have determined S include one by Link and co-workers,who determined S compounds in aviation fuel,512 and anotherthat used a number of techniques including GC-AES andGC-ion trap-tandem MS, to determine S containing wineodorants.513

6.1.2 GC-AFS. Three of the four relevant papers in thissection determined Hg. One application described the rapid,simple and sensitive determination of inorganic Hg and methyl-Hg compounds in natural waters.514 Both MeHg and Hg21

dithizonates were extracted from the acidified water intotoluene and then back-extracted into sodium sulfide. Afterpurging with nitrogen gas to remove hydrogen sulfide, the Hgcompounds were ethylated using sodium tetraethylborate,collected at room temperature on Tenax and then separatedusing an isothermal GC program. After a pyrolysis stage, theHg species were detected by AFS. Using a water volume of300 mL, the LODs were 0.006 ng L21 for MeHg and


0.06 ng L21 for Hg21; the precision was 5 and 10% for MeHgand Hg21, respectively. Recoveries were 90–110% for bothspecies. Aqueous phase ethylation followed by headspaceGC-AFS has also been used to determine Hg compoundsin environmental samples.515 A range of sample preparationprocedures was optimised and compared for sediments, bio-logical materials and waters using both CRMs and realsamples. The methods were applied to inter-laboratory com-parison exercises for the certification of MeHg in IAEA 405Sediment and BCR 71 Oyster Tissue. The LODs for MeHgwere 0.002 ng Hg g21 in sediment and biological materials and0.01 ng Hg L21 in water. The third Hg publication also focusedon different sample pre-treatment and preparation proce-dures.315 Three drying methods were compared, namely con-ventional oven, microwave oven and freeze drying. It wasfound that conventional oven drying was best since the othertwo resulted in losses of the analyte. Four extraction methodswere also compared. These were HCl leaching, alkalinemethanol extraction using tetramethylammonium hydroxide(TMAH) and with KOH, and sodium dodecyl sulfateextraction. Extraction efficiency was determined by comparingtotal Hg (determined after microwave digestion of the samples)with the Hg content in the different extract types. The onlymethod to obtain complete leaching (97%) was with HCl.Species integrity after extraction was evaluated by analysingthe extracts using GC-AFS. It was found that TMAH causedartificial dimethyl-Hg to be formed. The HCl extraction-GC-AFS technique was applied to the determination of MeHg inswordfish and tuna samples, with concentrations of between0.75 and 1.93 mg kg21 being found, yielding an LOD of 1.2 pg.The effect of volatile organoselenium compounds on the

determination of inorganic Se by HG has been studied in apaper by Moreno et al.302 The authors have concluded thatcompounds such as dimethyl-Se (DMSe) and dimethyl-di-Se(DMDSe), which are formed by microbiological activity insoils and sediments, are capable of forming volatile species inthe presence of sodium tetrahydroborate. The coupling ofpervaporation-AFS was proposed for the identification of thesespecies and pervaporation-GC-AFS was used for their indivi-dual quantification.

6.1.3 GC-AAS. Only two papers have been published in thisarea during this review period. The first determined butyl-Snspecies in natural water samples by aqueous phase ethylationusing sodium tetraethylborate, room temperature trapping ofthe resulting species on Tenax, followed by GC-quartzfurnace(QF)-AAS detection.516 The recoveries of differentspecies spiked into water were 90–109%, the precision at aconcentration of 100 ng Sn L21 was ¡6% RSD and the LODusing 1 L of sample was v1 ng Sn L21 for all butyl-Sn species.Another advantage was that sample throughput was greaterthan 3 h21. A paper written in Chinese has described theconstruction and evaluation of a horizontal pipe mini-flameatomization and ionization synchronous detector and a tem-perature auto-controlled zero dead-volume transfer line forGC-AAS.517 The system was reported to be capable of detect-ing organometallic compounds such as diethyl-Hg with anLOD of 2.3 6 10212 g s21, as well as organic compounds suchas benzene with an LOD of 3.56 10211 g s21. The linear rangeof calibration varied considerably, however, with a range of4.2 6 102 and 4.0 6 105 being obtained for diethyl-Hg andbenzene, respectively. Precision (n ~ 11) was better than 2%RSD for both compounds.

6.2 Liquid chromatography

Several reviews or overviews of liquid chromatography coupledwith atomic spectroscopy have been published in this reviewperiod. These include a paper presented by Karthikeyanand Hirata that reviewed As speciation in environmental

samples.518 Recent analytical progress in extraction, separationand identification of the species in soils, sediments, vegetables,fruit and marine biological samples were discussed. Techniquessuch as Soxhlet, accelerated solvent, supercritical fluid andmicrowave assisted extraction were all compared in terms ofperformance, with the low power microwave extraction beingshown to be mild (i.e., it does not change the speciation), butvery fast. A total of over 20 As species have now been observed,although many of these are, as yet, unidentified. A paperentitled ‘‘Environmentally friendly sample treatment forspeciation analysis by hyphenated techniques’’ has also beenpublished.519 This too discussed modern preparation techni-ques and highlighted their improved efficiency, the reducedtime and volume of solvent required and raised the possibilitiesof miniaturisation and automation. An overview of As specia-tion in biological tissues has been presented byMcSheehy et al.,in which the role of speciation analysis in understanding theenvironmental cycle and the preparation of CRMs for qualitycontrol were discussed.520 The authors stated that in fish,crustacea and molluscs the predominant As species tend to beof the tetraalkylarsonium type, whereas in marine algae andbivalves they tend to be of the trialkylarsine oxide type. Apaper that discusses the theory, practices and examples ofspecific applications of HPLC for soil and plant analysis hasbeen presented.521 The general overview also highlights theadvantages of the technique, such as being on-line withassorted detectors, requiring only a small sample size, beingreliable, etc.In general, peristaltic pumps are used when back pressures

are very low, e.g., for FI techniques, and HPLC pumps arerequired when large back pressures exist. However, whenintermediate pressures are experienced, no really ideal pumphas been found. Ratka and Berndt have, however, used a lowcost diaphragm pump that is capable of operating at up to84 psi to achieve on-line preconcentration or matrix separa-tion.522 Although the pump produces a strong pulsation, thiscould be neutralised by using a highly flexible piece of siliconetubing, which produced a pulse free flow. A restrictor capillaryenabled flow rates of anywhere between 0.1 and 50 mL min21

to be achieved. By using this pump in conjunction withstandard HPLC pre-columns or small ion exchange columns,on-line with either AAS or ICP-AES instrumentation as adetection technique, very low LODs could be achieved, e.g.,0.05–0.9 mg L21 for Cd, Cu, Mn, Ni, Pb, Tl, etc.

6.2.1 LC-AAS. There continues to be an interest in couplingtogether several different methods in an attempt to increasesensitivity. The coupling of liquid chromatography (LC) withHG followed by AAS detection increases the sensitivity for thedetermination of metalloids by an order of magnitude. This isbecause of the improved transport efficiency of the analyte tothe atom cell. In this review period, the most commonlydetermined analyte using this methodology has been As. Areport of the monitoring of inorganic As exposure in the urineof ion implanter maintenance engineers has been published.275

These workers are potentially exposed to As during themaintenance of machinery used for fabrication in the semi-conductor industry. The first morning urine samples from 30maintenance engineers and, as a control, 12 office-basedengineers were collected and analysed over 7 consecutive days.For the exposed group, the As(III), As(V), monomethylarsonicacid (MMA), dimethylarsinic acid (DMA) and total inorganicAs levels were monitored, though the authors acknowledgedthat the results could be misleading because of the intake of Asthrough a seafood diet. They did, however, conclude that theconcentration of MMA could be used as an indicator for Asexposure. The risk of bladder cancer as a function of Asmethylation has been studied by a research group in Taiwan.274

The species As(III), As(V), DMA and MMA were determined byHPLC-HG-AAS in the urine of 49 patients with newly


diagnosed bladder cancer and 224 control patients sufferingfrom fractures and cataracts. It was found that an increasedcumulative As exposure led to an increased risk of bladdercancer. In addition, it was also reported that subjects with a lowsecondary As methylation index (i.e., a lowered ability tomethylate MMA to DMA) were substantially more at risk thanother patients. Zerovalent iron has been reported as havingtremendous potential as a remediation material for the removalof As from groundwater and drinking water.523 This study usedHPLC-HG-AAS to investigate the speciation of As(V) andAs(III) after reaction with two zerovalent iron materials. Othertechniques, such as X-ray diffraction (XRD), scanning electronmicroscopy-energy dispersive X-ray analysis (SEM-EDAX)and X-ray absorption spectroscopy, were used to characterisethe by-products. The results indicated that high As(III) and As(V)adsorption occurred for both iron materials and that some ofthe As(III) became oxidized to the marginally less toxic As(V). Inaddition, adsorption complexes were formed with the ironcorrosion products, which were identified by extended X-rayabsorption fine structure spectroscopy (EXAFS) to be innersphere bidentate As(III) and As(V) complexes.Some As species do not readily form a hydride so, to detect

them using this method, an on-line process is necessary toconvert such species into a reducible form. An example hasbeen published by Vinas and co-workers,272 who speciated Asin baby foods and raw fish ingredients. After enzymaticextraction using either trypsin or pancreatin, several speciesincluding As(III) and As(V), DMA, MMA and arsenobetaine(AsB) were separated using an anion exchange column andphosphate as a mobile phase. The AsB required an on-lineoxidation using peroxodisulfate to convert it to a reduciblespecies, prior to HG-AAS detection. In the samples, AsB wasthe only species detected. It was concluded that the As contentin the baby food came from the raw fish ingredients and thatthe highest levels were in the plaice based foods.Two other on-line papers have been produced. These include

the chromatographic separation of Pb and Sn species.205 TheSn species (tetramethyl-, tetraethyl-, tetrabutyl-, tetrapentyl-,tributyl-, di-butyl- and monobutyl) or Pb species (tetraethyl-and tetraphenyl-) were separated on an HPLC column, andthen passed through a heated electrospray interface to a quartzfurnace (QF) AAS detector. The operating conditions of theelectrospray were optimised using a full experimental designprocedure and enabled a flow rate of anywhere between 50 and1000 mL min21 to be achieved. The results were compared withthose obtained using a thermospray interface and post-columnconversion of the species to hydrides. The LODs obtained fromthe electrospray were an order of magnitude superior to thosefrom the thermospray. The system was applied to thedetermination of Sn compounds in the CRM BCR 477 andto tetraethyllead in gasoline samples. The other on-line paperinvolved the determination of methylmercury (MeHg) in fishby HPLC-ETAAS.54 In the technique, Cu was first complexedwith DDTC and the resulting complex adsorbed onto acigarette filter. Selective preconcentration of methylmercury inthe presence of ethyl-, inorganic and phenyl-Hg was achievedat pH 6.8, with the Hg compound displacing the Cu complex.The retained MeHg was then eluted with 50 mL of ethanol anddetected on-line using ETAAS. Interference effects from othertransition metals were minimal at mg L21 concentrations.Using a 3.4 mL sample volume, a preconcentration factor of 75could be achieved, yielding a LOD of 6.8 ng L21 as Hg. Samplethroughput was 30 h21, and a precision (n ~ 13) of 2.3% wasobtained. The procedure was validated by the analysis of theCRM DORM-2 and was applied to real fish samples.A number of off-line HPLC-ETAAS procedures have been

described. This is the norm when ETAAS is used as continualoperation at atomization temperatures (typically 1500–2300 uCfor a transversely heated tube) would lead to rapid tube wear.Other drawbacks include the possibility of mis-positioning one

of the collected fractions (thereby ‘‘changing’’ the retentiontime of a compound), or the simultaneous detection of twoclosely eluting peaks. The majority of procedures have des-cribed the determination of the metallic component of drugs ordrug metabolites. Examples of this type of analysis include thedetermination of Ru in the anti-metastatic drug NAMI-A524

and the determination of Pt in the anti-cancer drug AP-5280.525

Other papers that have determined Pt by HPLC-AAS includeone that has determined the reaction kinetics of cisplatin withthiols526 and another that investigated the decomposition ofcarboplatin in infusion solutions in the presence of 1,1-cyclobutanedicarboxylic acid admixture.527 Another exampleof off-line detection includes the determination of As(III), As(V),MMA and DMA in natural waters.528 This was an attempt tostudy As transformations in the aquatic ecosystem of a tailingpit in an ore-dressing industrial plant. One further applicationdescribed the ion chromatographic separation of Se specieswith a preliminary preconcentration step.59 The preconcentra-tion was achieved using an alumina microcolumn and,although most of the work was conducted using a UV detector,AAS was also used in an attempt to improve both thesensitivity and selectivity of the analysis. The method wasapplied to the determination of Se(IV) and Se(VI) in thermalwaters and extracts of pharmaceutical supplements.

6.2.2 LC-AES. There has not really been any one focus ofattention in terms of either analytes or sample matrices in thisreview period, although Se speciation has proved the singlemost popular analysis. Direct determination of Se(IV) and Se(VI)using an end-on ICP-AES instrument has been described byNam et al.,529 whereas organo-Se compounds were determinedafter retention on a porous graphitic carbon stationary phase.73

In this latter application, selenocystamine, selenoethionine,selenomethionine and selenocystine were determined afterelution with methanoic acid. Injection of the analytes innitric or trifluoroacetic acids (2.5 mL) enabled a preconcentra-tion to be achieved, yielding LODs of 2–6 mg L21. Thesimultaneous detection of As and Se in the dimethyldisele-noarsinate anion by HPLC-ICP-AES using Hamilton PRPX-100 resin and a phosphate based mobile phase has beendescribed.530 The authors propose that the compound formsfrom reactions of DMA with selenite and glutathione and, assuch, it is possible that it could interfere with the determinationof Se. The proposed method separated the anion from As(V),Se(IV), DMA, MMA and low molecular weight thiols (e.g.,glutathione).Two papers by Peters and co-workers have described the use

of a conventional ICP-AES instrument for the determinationof non-metals. One was a review in which HPLC-ICP-AESmethods for determining compounds containing C, S, P andthe halogens were discussed,531 whereas the other described thedetermination of nine amino-acids separated on a C30 columnusing a phosphate eluent through the detection of C at193.09 nm.532 The system yielded a LOD of 30 ng and precisionfor 27 measurements of different amino acids was 2.5%RSD. The authors state that the C signal was independent ofmolecular structure and hence the sensitivity is constant fordifferent compounds. The authors concluded that the presenceof a suitable internal standard made the use of a calibrationcurve unnecessary.A weakly acidic cation exchange micro-column has been

used to separate Al species present in infusions of tea leaves.74

It was demonstrated that at a pH of between 5.5 and 8.0, alllabile monomeric Al species were retained on the columnwhereas the non-labile ones passed straight through. Theretained labile species were then eluted with 1 M HCl. Analysisof the resulting fractions was achieved using fluorinationassisted ETV-ICP-AES. The hydrolysis kinetics of thetrialkoxysilane compounds (3-glycidoxypropyl)trimethoxy-silane and (3-aminopropyl)triethoxysilane in dilute aqueous


solution have been studied by Kozerski and co-workers.533 Thehydrolysis reactions were monitored by sampling the solutionsover a period of time and then analysing the aliquots using areversed phase column and a gradient acetonitrile–watermobile phase followed by direct injection nebulization andICP-AES detection using the Si 251.611 nm line. The chro-matograms were complete within 6 min. and the rate constantsof the consecutive hydrolysis reactions were obtained by non-linear regression modelling. Using a quenching scheme,hydrolysis half lives as brief as 3 min for the parent silanecould be monitored. One interesting paper used field flowfractionation (FFF) to fractionate the Fe in colloidal matterfrom the Rio Negro in Brazil followed by on-line detectionusing either ICP-AES or UV absorbance.534 The results ofthese techniques indicated that the size distributions wereconsiderably smaller than those found by tangential flowfiltration (TFF). The authors concluded that caution must betaken when using TFF to classify the size distribution oforganic colloids and associated elements. The authors alsodemonstrated that the Fe distribution was more closelycorrelated to the organic matter distribution in the colloidalfraction than in the particulate fraction, and that in bothfractions, the Fe was elevated in the higher mass portion.As well as speciation analyses, chromatography has also

been used on-line to separate analytes from the bulk matrixelements. An example has been the use of a cation exchangecolumn to separate rare earth elements (REEs) and Y from thematrix elements in samples such as zircon, ilmenite, columbite–tantalite, rutile, garnet and silliminite.535 The sample prepara-tion method was dependent on the matrix, but was either anacid digestion using hydrofluoric, hydrochloric and perchloricacids, or a fusion using either potassium bifluoride and sodiumfluoride or potassium bisulfate. The final samples had tocontain 0.1 N acidity for the cation exchange process to work.In the absence of suitable CRMs, the authors resorted tospiking mg quantities of zirconium, titanium, niobium andtantalum into Syenite rock SY-2 solution, whose REE and Ycontents were known. An alternative sample preparationprocedure using the fluoride precipitation method was com-pared with the cation exchange, and the results were found toagree within ¡5% for most of the analytes. The authorsconcluded that their matrix separation procedure was bothaccurate and precise (RSD ~ 2–7%) and was suitable for thedetermination of REEs and Y at mg levels in mg levels ofrefractory minerals.

6.2.3 LC-AFS. Digital signal acquisition and processingsoftware for AFS and its application to Cd speciation usingcation exchange HPLC has been described in a paper written inChinese.536 The programme was written in C11 and employedthree signal processing techniques, namely Savitzky–Golaysmoothing, Fourier filter and wavelet de-noising to smooth andfilter the noisy data. The most common analyte to be deter-mined by this technique has been As. Several applications havebeen published, with As speciation in molluscs,281 beer,283

plant materials279,280 and fish278 being reported. Some of theseexamples were simple applications, e.g., for the beer,283 where4 species were separated on an anion exchange column anddetected by HG-AFS within 11 min. Limits of detection were0.12, 0.20, 0.27 and 0.39 mg L21 for As(III), DMA, MMA andAs(V), respectively. Several extraction solvents were comparedfor the extraction of As species from plants, in an attempt toinvestigate the uptake, transfer and accumulation processes.280

The method was validated by the analysis of the CRM GBW82301 Peach Leaves, and was then applied to the analysis ofplants grown on contaminated soil near an As mine. The majorspecies in the plants was found to be As(V), with minor tracesof MMA and DMA also being present. The analysis of themolluscs involved the determination of six As species includingAs(III), As(V), DMA,MMA, AsB and arsenocholine (AsChol).281

Both cation and anion chromatography systems were used forspeciation purposes and total As was determined by ICP-AES. The candidate reference material BCR 710 was used tovalidate the procedures. Unsurprisingly, the authors concludedthat higher total As concentrations in the samples did notnecessarily result in higher overall toxicity. The relativestabilities of four As species have been determined byHPLC-HG-AFS in both treated and untreated waste-watersat temperatures of 4, 20 and 40 uC over a period of fourmonths.282 It was found that As(V), MMA and DMA werestable at all temperatures over this time period for both samplematrices. However, the As(III) was found to be unstable and tooxidize to As(V) in only two weeks in the untreated wastewater.It was, however, stable in the treated wastewater at a pH of7.27, but was unstable after a month at a pH of 1.6. A series ofpapers by Gregus and co-workers has concentrated on thetoxicological aspects of As speciation.277,537,538 In twopapers,277,537 the role of purine nucleoside phosphorylase onthe reduction of As(V) to As(III) was tested. In the other,538 theeffect of selenite on the disposition of As(V) and As(III) wasdetermined. In all cases anion exchange HPLC-HG-AFS wasused. The compound sodium 2,3-dimercapto-1-propane sulfo-nate (DMPS) has been used to treat acute As poisoning. It hasbeen assumed that the compound forms a complex with the As,which aids excretion from the body, but this hypothesis has hadno supporting evidence. A paper has now been published thathas used electrospray tandem mass spectrometry to identify aDMPS-MMA(III) complex.276 Using HPLC-HG-AFS, theauthors analysed urine samples of subjects that had beendosed with 300 mg DMPS for As(III), As(V), MMA(V), DMA(V),MMA(III) and the DMPS–MMA(III) complex. The DMPS–MMA(III) complex was found not to form a hydride directly, sothe authors treated the HPLC eluate on-line with 0.1 M sodiumhydroxide to decompose the complex and convert the As into areducible form. It was found that the DMPS caused a reductionin the DMA(V) concentration with a concomitant increase inMMA(V) concentration.On-line sample treatment to form reducible species of the

analyte has also been demonstrated in a paper that describedthe preparation, homogeneity and stability studies of a candi-date reference material for Se speciation.304 The material wasBrazil nuts and the usual operational steps of homogenisation,storage, checking of homogeneity, microbiological status,possible irradiation effects and the stability of the speciesover time and at different temperatures were described. Thespeciation study focussed on different forms of chromatog-raphy, including ion pairing and anion exchange, so that correctidentification of species was achieved. A UV photolysis stagewas required post-column to digest the organoselenium com-pounds. It was found that the total Se content was 82.9 mg kg21

and that the most abundant species was selenomethionine, at aconcentration of 79.9 mg Se kg21. Speciation analysis of Hgcompounds using HPLC-CV-AFS has been reported.539 Apost-column on-line chemical oxidation using potassiumpersulfate in the presence of microwave irradiation was usedto transform the species into inorganic Hg. Water vapour andmethanol introduction to the atom cell were minimised bycooling the microwave digested eluent in a water/ice bath.Inorganic Hg, MeHgCl, ethylmercury chloride (EtHgCl) andphenylmercury chloride (PhHgCl) were baseline separated on aC18 reversed phase column using a mobile phase of 50%methanol containing 10 mM tetrabutyl ammonium bromideand 0.1 M sodium chloride. As an application, seafood sampleswere analysed and the method was validated by the successfulanalysis of the CRM DORM-2.

6.3 Electrophoresis

Only one paper has been published concerning electrophoreticseparation coupled on-line with atomic spectrometric detection.


Yan and co-workers separated four Hg species (inorganic,methyl-, ethyl- and phenyl-Hg) at 15 kV using a mixture of100 mM boric acid and 12% v/v methanol as electrolyte andthen detected them using an AFS instrument.348 Traditionalelectroosmotic flow was modified by the application of hydro-static pressure opposite to the direction of the flow. Thisreportedly improved the chromatographic resolution. Thenewly developed interface allowed the formation of volatilespecies on-line, enabling separation of the analytes from theliquid mobile phase. Precisions (n~ 5) were 1.9–2.5% RSD forthe migration times, 1.8–6.3% for peak area measurements and2.3–6.1% for peak height responses. Detection limits rangedfrom 6.8 to 16.5 mg L21 and recoveries from water sampleswere 86.6–111%, depending on the species. The method wassuccessfully applied to the analysis of Hg species in the CRMDORM-2.

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