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Cite this: J. Anal. At. Spectrom., 2012, 27, 1831
www.rsc.org/jaas TUTORIAL REVIEW
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Green chemistry in analytical atomic spectrometry: a review
C. Bendicho,*a I. Lavilla,a F. Pena-Pereiraab and V. Romeroa
Received 20th July 2012, Accepted 3rd September 2012
DOI: 10.1039/c2ja30214d
As a result of the greater consciousness within the analytical community on the impact of chemicals on
human health and environment, green issues are increasingly taken into account when choosing an
established analytical method or developing a new one. Apart from typical analytical characteristics
(e.g., sensitivity, limit of detection, repeatability, etc.), other features such as the amount of sample/
reagents, operation time, use of energy-effective apparatus, waste production, etc. should be
highlighted in order to meet the principles of Green Chemistry. Although conventional approaches for
trace element analysis by atomic spectrometry usually involve well-established sample pre-treatments
based on ‘wet chemistry’, and high consumption of gases, reagents, etc. is inherent to many techniques
in this group, there are still many avenues where green issues can be implemented. For greening atomic
spectrometry, green chemistry principles should be applied to every step of the analytical process, i.e.,
from sampling and sample pre-treatment to data processing. In this review, main pathways for greening
atomic spectrometry such as downsizing of instrumentation, use of portable instruments, solid
sampling, application of clean energies (ultrasound, microwaves, etc.) for sample pre-treatment,
development of on-site, on-line and at-line approaches vs. typical off-line methods, application of
modern extraction techniques (e.g., solid- and liquid-phase microextraction), green solvents and
derivatization agents and use of chemometric tools for method optimization, signal processing, etc. are
discussed in a critical way.
1. Introduction
In recent years, an increased interest has arisen in the analytical
community for the implementation of the principles of Green
Chemistry. Several of the twelve principles established by
Anastas and Warner1 more than 10 years ago are directly con-
nected with Analytical Chemistry, such as prevention of wastes,
safer solvents and reagents, energy efficiency, renewability,
reducing derivatives, real-time analysis and accident prevention
through implementation of safer chemistry. In the last two years,
the subject has deserved attention in several books2,3 and
reviews,4–15 and the concept ‘Green Analytical Chemistry (GAC)’
has been increasingly employed.
Several trends have driven for long the research on new
detection methods such as miniaturization, automation,
simplification and acceleration, which in turn are related to
many of those principles. Implementation of those trends in the
analytical methods has usually provided not only enhanced
analytical characteristics, but also significantly improved
greenness profile.
aDepartamento de Qu�ımica Anal�ıtica y Alimentaria, �Area de Qu�ımicaAnal�ıtica, Facultad de Qu�ımica, Universidad de Vigo, Campus AsLagoas-Marcosende s/n, 36310 Vigo, Spain. E-mail: [email protected];Fax: +34-986-812556; Tel: +34-986-812281bCESAM & Department of Chemistry, University of Aveiro, 3810-193Aveiro, Portugal
This journal is ª The Royal Society of Chemistry 2012
Although some workers have addressed the greening of
analytical techniques such as chromatography8,14 or molecular
spectroscopy12 and mainly oriented toward the determination of
organic analytes,13 to the best of our knowledge, no review or
monograph has been specifically focused on the implementation
of GAC principles in analytical atomic spectrometry.
At present, there is a growing interest in developing green
methods using atomic spectrometric techniques. Fig. 1 shows the
evolution of the publications devoted to green analytical chem-
istry in atomic spectrometry since 2000 following the subjects:
‘green’, ‘greener’, ‘clean’, ‘cleaner’ and ‘environmentally friendly’
atomic spectrometry. Fig. 2 shows the corresponding literature
sources.
The implementation of GAC principles in the analytical
atomic spectrometry field demands for a close knowledge of the
ways for greening every step of the analytical procedure,
including sampling, preservation, sample pre-treatment,
measurement and data processing. In order to establish a metric
of the greenness related to any analytical protocol, issues such as
the type of solvent, apparatus and method should be focused.
Some attempts have already been made to assign a greening
profile, e.g., National Environment Methods Index (NEMI)
database,16 according to the properties of reagents and wastes
generated. Recently, Namie�snik’s group has proposed a novel
metric approach so that new or modified analytical methods can
be compared in respect to greenness.17 Ideally, a green method in
J. Anal. At. Spectrom., 2012, 27, 1831–1857 | 1831
Fig. 1 Evolution of the publications devoted to green analytical chem-
istry in atomic spectrometry since 2000using the subjects ‘green’, ‘greener’,
‘clean’, ‘cleaner’ and ‘environmentally friendly’ atomic spectrometry
(source: ISI Web of knowledge (Web of Science) – Thomson Reuters).
Fig. 2 Evaluation of the publications devoted to green analytical
chemistry in atomic spectrometry as a function of the corresponding
literature sources since 2000 using the subjects ‘green’, ‘greener’, ‘clean’,
‘cleaner’ and ‘environmentally friendly’ atomic spectrometry (source: ISI
Web of knowledge (Web of Science) – Thomson Reuters).
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atomic spectrometry should involve small reagent/sample
consumption, energy-efficient apparatus, safe operations, short
total times for analysis and avoid the use of toxic/hazardous
reagents.
An assessment of different strategies carried out in every stage
of the analytical process according to their ‘greenness profile’ for
trace element analysis and speciation by atomic spectrometry is
provided in Table 1.
1832 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
Undoubtedly, the maximum greening profile is achieved with
methods carried out on-site using portable instrumentation.2,3 In
this case, neither preservation nor pre-treatment procedures are
required and transport to the lab is also circumvented. Unfor-
tunately, unlike other analytical techniques (e.g., photometry,
electroanalysis), the instrumentation available for atomic spec-
trometry is difficult to adapt for field analysis without any sample
pre-treatment, although some efforts have been made in this
direction (e.g., portable X-ray fluorescence spectrometers,
portable laser-induced breakdown spectrometers, miniaturized
atomizers for atomic absorption spectrometry, etc.). In the
present state of the art, portable instruments based on atomic
spectrometry principles are, in general, far from fulfilling the
outstanding analytical performance of conventional instruments
available in labs.
The solid state is perhaps the one that requires the most
stringent sample pre-treatment for determination of trace
elements by the wide-spread atomic spectrometric techniques.
Therefore, one of the most realistic options to meet GAC
requirements is direct analysis with little or no sample pre-
treatment. In this way, solid analysis including direct solid
introduction and slurry sampling into the atomization system
has been known for long as an efficient way to overcome wet
chemistry that includes non-green operations, i.e., use of corro-
sive mineral acids, potential risks inherent to the application of
high pressures and heating, high energy consumption, etc. When
no direct analysis is feasible, an enhanced greening profile can be
reached using activation of sample pre-treatment by efficient
energies such as microwaves, ultrasound, UV radiation, etc.11,15
These processes generally involve less concentrated reagents and
safer operation conditions.
As an intermediate situation, on-line and at-line analyses
represent a jump toward GAC concepts in atomic spectrom-
etry, involving automated or semi-automated operation and
generally lower consumption of reagents. On the opposite side,
off-line methods, which are typically recommended in many
official methods of analysis, do not fulfil most GAC
requirements.
Examples where pre-treatment is maintained but a drastic
decrease in the amount of reagents occurs are the group of
modern miniaturized separation techniques. Preconcentration,
matrix removal, derivatization and other typical processes
required for trace element analysis and speciation can be easily
simplified and integrated by resorting to solid and liquid-phase
microextraction approaches (e.g., Ref. 9).
Fig. 3 shows a variety of green strategies resulting from the
passage of atomic spectrometry through the optics of green
chemistry. According to this, pathways toward the achievement
of greener atomic spectrometry methods would include the
following.
(a) Development of on-site, on-line and at-line methods in
contrast to traditional off-line methods.
(b) Decreasing the use of reagents, sample consumption (use of
microsamples) and derivatizing agents, or even better, to apply
direct analysis without reagents.
(c) Replacing traditional separation methods (e.g., liquid–
liquid extraction, LLE) by other methods involving miniaturized
approaches (e.g., solid- and liquid-phase microextraction), with
the subsequent reduction of solvents.
This journal is ª The Royal Society of Chemistry 2012
Table
1Greennessprofile
ofdifferentstrategiescarriedoutfortrace
elem
entanalysisandspeciationateach
stageoftheanalyticalprocess
Greennessprofile
Preservation
Sample
dissolution
Derivatization
Separation
Measurement
Data
processing
Low
Additionofchem
icals
forpreservation
Wet
digestionwith
mineralacids
Harm
ful,unstable,toxic
derivatizationagents
Solventextractionusing
largevolumes
oftoxic
organic
solvents
(e.g.,
benzene,
CHCl 3,etc.)
Conventionalapplication
ofatomic
spectrometric
techniques
such
asFAAS,
ICP-O
ES,etc.
Univariate
approach
formethodoptimization
Open
vessel
digestion
Organic
solvents
and
multistageprocedures
forderivatization(e.g.,
Grignard
methodfor
organometals,West€ o€ o
methodforHg,etc.)
Conductiveheating
(e.g.hotplate)
Interm
ediate
—Energy-efficient
treatm
ents
(MW,
US,UV
radiation,
etc.)
Derivatizationin
aqueous
phase
(e.g.,ethylationfor
speciationoforganometals
byhyphenatedtechniques)
Miniaturizedextraction
techniques
(e.g.,SPE,
LPME,SBSE,SPME)
Applicationofsensitivetechniques
insteadofusingpreconcentration
withclassicalmethods(e.g.use
ETAASinsteadofFAAS
combined
withsolventextraction)
—
Smallvolume
digestion
Use
ofenergy-efficient
methods(focusedMWs,
ultrasound,etc.)for
extractionofspecies
Mem
braneseparations
Softextractions
(e.g.UAEinsteadof
complete
dissolution)
Surfactants
(e.g.,
cloudpointextraction)
Advancedoxidation
(e.g.,UV/H
2O
2,UV–US,
photocatalysis,etc.
insteadofchem
ical
oxidants)
New
sorbents
based
onnanomaterials
Efficientsample
introduction
system
sinsteadof
conventionalnebulizers
Modernsolid–liquid
extractiontechniques
(SFE,ASE,etc.)
Automatedon-line
system
sallowingsample
pre-treatm
ent,
separations,etc.
(FIA
,SIA
,multicommutation)
Non-chromatographic
approaches
forspeciation
analysisofsampleswith
afew
species
High
Onsite
analysis
withoutpreservation
Solidsampling:direct
solidsamplingandslurry
sampling(SS-ETAAS,
ETV-ICP-O
ES,ETV-
ICP-M
S,GD-ICP-O
ES,
TXRF,LIB
S,etc.)
Photochem
ical
vapourgeneration
Solventlessseparation
techniques
(e.g.,SPME
withthermaldesorption)
Miniatomizerswith
low
consumption
ofgases
Multivariate
approaches
formethodoptimization
(e.g.,factorialdesign)
Electrochem
ical
vapourgeneration
Miniaturizedseparations
(e.g.,microchips)
‘In-atomizer’trapping
techniques
insteadof
preconcentrationby
chem
icalprocedures
Chem
ometrictoolsfor
treatm
entoflargeamount
ofdata
inorder
toextract
hidden
inform
ation
Ultrasound-promoted
cold
vapourgeneration
Green
solvents
(e.g.,ionic
liquids)
Miniaturizedflow
system
s(lab-on-valve,lab-on-a-chip)
coupledto
atomic
detectors
Green
interfacesbetween
HPLC
andIC
P-M
S,AFS,
etc.
forspeciationbasedon
nanomaterials(e.g.
UV/nano-TiO
2)
Solventlessmethods
forspeciation(purge-and-
trap,cryotrapping,etc.)
Screeninganalysisusing
portable
instruments
(on-site)
Multivariate
calibration
approaches
Nanoflow
HPLC
for
hyphenatedtechniques
inspeciationanalysis
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Fig. 3 Relevant areas of improvement for increasing the greenness of
atomic spectrometry after filtering through the standpoint of green
chemistry.
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(d) Use of green solvents and derivatization reagents (e.g.,
ionic liquids, ILs) in the analytical methodology.
(e) Removal or simplification of the sample pre-treatment
stages, using energy-efficient procedures (e.g., application of
ultrasound, microwaves, UV light in pre-treatment operations).
(f) Extraction of the maximum information from analytical
data using chemometric tools that facilitate calibration, method
optimization, signal acquisition, etc.
(g) Development of automated analytical methods using flow-
injection, sequential injection or multicommutation approaches.
(h) Development of automated and miniaturized methods
based on lab-on-valve (LOV) approaches and micro-total
analytical systems (m-TASs).
(i) Design of new instrumentation for greening atomic
spectrometry.
The aim of this review is to show these possibilities so that
users of atomic spectroscopy techniques can acquire criteria in
order to implement green chemistry concepts in labs devoted to
trace element analysis and speciation.
2. Green sample preparation in atomic spectrometry
Sample preparation is undoubtedly considered as an essential
stage in the analytical process. The isolation and preconcentra-
tion of target analytes, as well as the performance of a clean-up
step when dealing with complex matrices, are the main objectives
pursued at this step of the analytical process. In the last few
years, many efforts have been taken towards the development of
environmentally friendly sample preparation approaches in
analytical chemistry. In this section we provide an overview of
those sample treatment approaches and related green issues that
are directly relevant to the development of sustainable analytical
procedures for total element analysis and speciation.
2.1. Green extraction techniques: different variants of solid and
liquid phase extraction
Sample preparation techniques such as solid-phase extraction
(SPE), solid-phase microextraction (SPME) and liquid-phase
microextraction (LPME) have represented a step forward in the
development of versatile treatment techniques and, in general,
1834 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
they also fulfil the requirements so as to be considered as green
sample preparation techniques.
The development of the above mentioned sample preparation
approaches has allowed the downscaling of the sample and
organic solvent volumes needed to perform a single analysis, thus
giving rise to a significant reduction in the amounts of residues
typically generated.
The SPE technique allows the preconcentration of analytes in
short extraction times for total element and speciation anal-
ysis.18 It should be highlighted that in spite of high reduction in
solvent consumption when compared with LLE, the amounts of
solvent needed to perform a single SPE are generally in the
range of 5–15 mL.19 In the last few years, the performance of
SPE systems has been improved with the introduction of novel
materials that show higher adsorption capability, selectivity
and/or lower cost of preparation, including ion-imprinted
polymers, biosorbents and nano-sized particles.20 The applica-
tion of on-line SPE procedures with green sorbents has also
been reported. Chen et al.21 proposed the employment of a
hydrophilic ionic liquid (1-chlorovinyl-3-methylimidazolium
chloride, NmimCl) immobilized onto a polyvinyl chloride
(PVC) substrate as a green SPE sorbent to carry out speciation
analysis. In this work, Cr(VI) was determined by retention via
anion exchange and electrostatic interaction with a mini-column
containing PVC–NmimCl particles. Cr(III) was pre-eliminated
by using a strong acidic styrene type cation exchange resin mini-
column, thus allowing the speciation analysis of Cr by electro-
thermal atomic absorption spectrometry (ETAAS) and induc-
tively coupled plasma-mass spectrometry (ICP-MS). The on-line
SPE system improved the sample throughput and provided an
enhancement factor of 23.4 when using 2 mL sample volumes.
Tian et al.22 employed mungbean-coat as a biodegradable
adsorbent for on line-SPE. Cadmium was retained and enriched
in the mini-column, presumably via coordinative interactions
with the carboxylic acid groups of the bean-coat. The retained
cadmium is then eluted with 70 mL of 1 mol L�1 HNO3 and
determined by ETAAS.
The inception of miniaturized sample preparation techniques
such as SPME23–25 and LPME9,26,27 has represented a break-
through in GAC. In fact, both SPME and LPME are (virtually)
solventless techniques that allow the achievement of large
enrichment factors mainly as a result of their highly reduced
extractant-to-sample volume ratio. Hence, the SPME process
can be completely carried out without the employment of organic
solvents when thermal desorption is performed after the micro-
extraction process, while LPME techniques generally use an
almost negligible volume of extractant phase (1–100 mL). Several
microextraction modes are nowadays feasible for the extraction
of a given analyte as a function of its physicochemical properties.
However, the different microextraction modes can differ signif-
icantly in terms of greenness depending on the volume and
properties of the extractant phase, additional reagents needed to
perform the extraction process, the number of steps involved
and, in the case of SPME, the desorption conditions. A deriva-
tization step is generally required to efficiently extract and pre-
concentrate target analytes by SPME or LPME when dealing
with total element and speciation analysis. Thus, both neutral
complex formation and in situ chemical vapour generation
(CVG) are mainly employed with this aim.28
This journal is ª The Royal Society of Chemistry 2012
Fig. 4 Schematic representation of relevant miniaturized sample prep-
aration techniques.
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Another sample preparation technique that has been
employed with the aim of total element determination and
speciation analysis is stir bar sorptive extraction (SBSE).29–31
Like SPME, this technique is based on the extraction of analytes
onto a polymer-based coating. As a larger mass of polymer is
involved as compared to SPME, enhanced extraction efficiency is
achieved. Like SPME, SBSE is characterized as a fully solvent-
less sample preparation technique when thermal desorption is
selected. A special thermal desorption unit is generally used when
SBSE is combined with gas chromatography (GC) due to the
non-fitting geometry of the coated stir bar and the injection port,
respectively.32
Fig. 4 shows a schematic representation of the main minia-
turized extraction techniques discussed above.
Even though the miniaturization of a conventional method
generally involves positive aspects in terms of solvent
consumption and waste reduction, we should stress that the
employment of a miniaturized sample preparation technique is
not enough to classify an analytical method as green. In fact,
several examples can be found in the literature where reagents
and/or organic solvents displaying certain toxicity are used with
microextraction approaches, as can be shown in Section 2.4.
2.2. Green methods for treatment of solid samples
Conventional sample preparation methods for decomposition of
solid samples for analysis by atomic spectrometric techniques
involve the addition of high amounts of additional reagents and
This journal is ª The Royal Society of Chemistry 2012
oxidizing acids, as well as high temperatures for matrix decom-
position. These conventional pre-treatment methods are not free
from drawbacks, including risk of contamination, analyte losses,
extended decomposition times and large energy consumption.
The use of microwave (MW) and ultrasound (US) energies, as
well as the use of organic solvents, carbon dioxide and water at
both subcritical and supercritical conditions has led to the
development of a plethora of sample preparation approaches for
solid samples that meet the greenness criteria to a lesser or
greater extent.
MW energy is commonly used for both digestion and extrac-
tion procedures. Unlike conductive heating systems typically
used, MW-assisted digestion (MAD) involves homogeneous
heating of the sample by dipole rotation and ionic conduction,
thus improving the matrix decomposition process in terms of
time and energy consumption, lower volume of acids needed, and
lower blanks obtained.19
The application of small volume polytetrafluoroethylene
(PTFE) closed vials for greener MAD of breast biopsies has been
recently proposed by Millos et al.33 The use of three vials of low
capacity (6 mL) inserted into a commonly used MW digestion
vessel allowed the simultaneous matrix decomposition of small
biological sample sizes (20–30 mg) prior to multielemental
determination by ICP-MS using reduced volumes (0.3 mL per
sample) of HNO3.
MW-assisted extraction (MAE) exploits the increased solvent
diffusion of an extractant heated by MW energy to extract and
solubilize target analytes present in a sample matrix. Both pres-
surized (PMAE) and focused (FMAE) MAE can be performed,
FMAE being recognized as highly efficient for the extraction of
organometallic compounds.19 As a proof of concept, FMAE has
been exploited for the solid–liquid extraction of organometallic
species of Hg and Sn in solid environmental samples.34 The use of
disposable MW glass vessels avoided possible contamination
risks and allowed the extraction of a batch of 10 samples in less
than 1 h using acetic acid : methanol (3 : 1) or diluted tetra-
methylammonium hydroxide as the extractant.
As pointed out above, US energy is also employed for diges-
tion and extraction purposes. Acoustic cavitation produced by
US irradiation provides unique conditions that are exploited for
improving the greenness profile of analytical methodologies,
including reduced operation times, lower energy requirements,
reduced amounts of solvents and lower risk of contamination
and/or analyte losses.15 A variety of US-based systems, namely,
US bath, US probe and cup horns/sonoreactors, are nowadays
commercially available.15,35 When applied to solid matrix
decomposition, US energy avoids the use of drastic temperature
and pressure conditions, even though the use of concentrated
acids is still mandatory. On-line MAD can be used to speed up
matrix decomposition of liquid extracts and slurries, hence
avoiding the high cooling times required before the digestion
vessels can be opened. For instance, G�omez-Ariza et al.36 per-
formed chiral speciation of selenomethionine in pre-treated
breast and formula milk samples by coupling high performance
liquid chromatography (HPLC)–hydride generation (HG)–
atomic fluorescence spectrometry (AFS) with on-line MAD.
The use of US energy in combination with enzymes (hydro-
lases) has been recently proposed for the rapid decomposition of
solid samples under mild conditions. US-assisted enzymatic
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hydrolysis has been applied for total trace element analysis and
speciation, even though further work is needed to carefully
control the effect of US irradiation on the stability and activity of
hydrolases. As an example, Moreda-Pi~neiro et al.37 have applied
ultrasound assisted-enzymatic hydrolysis of seafood samples for
As speciation. The use of pepsin as a proteolytic enzyme together
with ultrasound irradiation allowed achieving the enzymatic
process in short times.
US irradiation can also contribute to accelerate the solid–liquid
extraction of elements from solid matrices. When compared with
the related sample preparation techniques mentioned above, the
extraction time is commonly reduced with US-assisted extraction
(UAE), and moreover treatments are performed at atmospheric
pressure and room temperature. Diluted acids and soft extrac-
tants under mild conditions are employed in UAE for total trace
element analysis and speciation, respectively. Costas et al.38
employed UAE as a sample pre-treatment for extraction of rare
earth elements in seafood tissues prior to ICP-MS analysis. UAE
involved the use of diluted acids and reduced extraction times,
yieldingmuch lower volumes of acidic waste thanMAD.A clean-
up of the extracts with a C18 cartridge was mandatory to remove
organic matter prior to ICP-MS analysis.
The use of fluids in the supercritical state has also been
considered as an efficient sample preparation technique for the
extraction of target compounds from complex matrices. The
unique properties of supercritical fluids, namely, much lower
viscosity and diffusion coefficients than in the liquid state, cause
an enhancement of mass transfer and solubilisation processes.
Thus, supercritical fluid extraction (SFE) has been used in several
areas, CO2 being by far the most employed supercritical fluid due
to its non-toxicity, non-flammability, economy and availability.
Even though SFE involves short extraction times and minimal
organic solvent consumption, as well as suitability for automa-
tion, it has been superseded by alternative sample preparation
techniques, mainly due to the poor robustness of early
commercial SFE systems, the lack of standard extraction
procedures and the requirement of clean-up procedures after
SFE of certain samples.39 As for the extraction of metal species
and organometallic compounds by SFE, the use of an organic
modifier of supercritical CO2 is generally mandatory due to its
limited capability of leaching polar or ionic analytes. In addition,
ion-pair formation and complexation are usually performed in
SFE to extract charged species.40
The use of fluids at high temperature and pressure in such a
way that they are kept at subcritical conditions has also been
reported for extraction of analytes from solid samples. Pressur-
ized liquid extraction (PLE) makes use of both organic solvents
and water as extractants. The physicochemical properties of
water are highly modified when the temperature is increased
between its boiling point and critical temperature, the relative
permeability being decreased on increasing the temperature.
Extraction of metals by pressurized hot water extraction is
commonly performed by using diluted acids as modifiers.41 In
general, PLE involves the use of relatively low volumes of
extractants (10–40 mL), causing the extraction process to occur
in reduced times. However, the obtained extracts using PLE
usually require a clean-up to remove co-extracted compounds,
which extends the sample pre-treatment time before the
analysis.42
1836 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
2.3. Membrane and surfactant-based sample preparation
Membranes act as selective barriers that allow the contact of the
sample solution with an acceptor phase. They allow the enrich-
ment of target analytes and sample clean-up using lower volumes
of organic solvents than conventional sample preparation
methods, such as LLE or SPE, being also suitable for minia-
turization. Thus, membrane-based extraction techniques are
being considered as environmentally friendly sample preparation
approaches.6,43 Accordingly, membranes can contribute to
greening analytical procedures. However, the green profile of
membrane-based methods will depend to a large extent on the
reagents and solvents used.
Membranes have been used in a variety of configurations for
sample pre-treatment, including hollow fibers, flat-sheet
membranes and membrane bags, and employed for trace element
analysis and speciation.44,45
A flat sheet supported liquid membrane (SLM) was reported
for Hg separation using polyvinylidenefluoride as the supporting
material, trioctylamine as the carrier, coconut oil as the diluent,
and a diluted NaOH aqueous solution as the stripping phase.46
Peng et al.47 employed a hollow fiber (HF) SLM extraction
system in combination with ETAAS for determining Cd in
diluted seawater samples. A liquid membrane was prepared by
filling the pores of a polypropylene HF with a 1-octanol solution
containing a mixture of dithizone (used as a carrier) and oleic
acid, using a 0.05 mol L�1 HNO3 solution (20 mL) as the strip-
ping solution.
Miniaturized sample preparation techniques have been
developed with the use of polymeric HFs. Thus, HF-LPME has
been employed for preconcentration of metals and organome-
tallic compounds. For instance, HF-LPME has been used in
combination with electrothermal vaporization (ETV)-ICP-MS
for the determination of ultratrace levels of Cu, Zn, Pd, Cd, Hg,
Pb and Bi in environmental and biological samples.48HFs caused
an enhancement of the extraction efficiency, providing an
appropriate sample clean-up and improved stability of the
extractant phase in comparison with related miniaturized LPME
approaches such as single-drop microextraction.
Surfactants are characterized as being non-volatile, non-
flammable and, in general, as showing negligible toxicity. Several
analytical separation processes have been improved in terms of
greenness by using surfactants as extraction media, cloud point
extraction (CPE) being the most relevant and popular.49 CPE is
based on the formation of a turbid solution when a sample
containing a surfactant is heated over the cloud-point tempera-
ture. Above this temperature, which depends on the type of
surfactant used and its concentration, two immiscible phases are
formed, the surfactant-rich phase being the one capable of
extracting a variety of hydrophobic compounds. Thus, surfac-
tants can be used as green extractant phases in CPE for enriching
target analytes prior to their determination by atomic spectro-
metric techniques, thereby avoiding the use of volatile organic
solvents commonly used in LLE. Several methods for total
element analysis and speciation involving CPE can be found in
the literature.49
On line-CPE avoids the equilibration, cooling and centrifu-
gation procedures typically needed in batch mode, hence
providing an increase in sample throughput. Furthermore, the
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elution step can be easily performed. Ortega et al.50 employed a
flow injection (FI)-CPE method in combination with inductively
coupled plasma-optical emission spectrometry (ICP-OES) for
the determination of total Gd in previously digested urine
samples. Gd(III) was complexed with 2-(5-bromo-2-pyridylazo)-
5-diethylaminophenol and extracted with the non-ionic
surfactant poly(ethylene glycol) mono-nonylphenyl ether. A
homemade collection column was used to retain the surfactant
rich phase containing the analyte, which was finally eluted with 4
mol L�1 HNO3. Multielemental analysis has also been per-
formed by combination of on-line CPE with ICP-OES. Thus,
Yamini et al.51 performed the on-line preconcentration of Cd(II),
Co(II), Cr(III), Cu(II), Fe(III) and Mn(II) by complexation with 1-
(2-theonyl)-3,3,3-trifluoroacetone and extraction by using a non-
ionic surfactant (Triton X-114).
The use of MW irradiation in combination with surfactant-
based procedures has demonstrated to be highly efficient, thus
allowing an important reduction in the extraction time, incuba-
tion temperature and energy consumption as compared to
conventional hot plate CPE. For instance, Simitchiev et al.52
reported a MW-assisted CPE-ICP-MS method for the determi-
nation of Rh, Pd and Pt in pharmaceuticals. In addition,
Meeravali and Jiang53 determined Au and Tl in soils and water
samples by MW-assisted mixed micelle CPE-ICP-MS.
Recently, surfactants have been applied for extraction of
metals by means of admicelles and hemimicelles adsorbed onto
the surface of metallic nanoparticles. For instance, Faraji et al.54
determined Hg(II) by FI-ICP-OES after SPE of mercury–Mich-
ler’s thioketone complex by means of sodium dodecyl sulphate
(SDS)-coated magnetic nanoparticles. Furthermore, Kar-
atapanis et al.55 employed cetylpyridinium bromide-coated
Fe3O4@SiO2 nanoparticles to extract Cu(II), Ni(II), Co(II), Cd(II),
Pb(II) and Mn(II) as their complexes with 8-hydroxyquinoline,
prior to their determination by ETAAS. Specific features to be
emphasized are the low consumption of surfactant per analysis
(�30 mg), the high enrichment factors achieved and the renew-
ability of magnetite nanoparticles.
Emulsification has been exploited for the extraction of metals
and metalloids in complex samples such as lubricating oils56 or
cosmetics.57 Emulsification of oily samples with surfactants and
water can be considered as a green sample preparation technique
since it avoids the use of organic solvents and the destruction of
the organic phase, mainly performed in the literature by acid
digestion. The formation of water-in-oil emulsions has been
exploited for the development of greener methodologies
compatible with atomic spectrometry. Thus, Aranda et al.58
presented a methodology based on the combination of emulsion
formation and cold vapour (CV)-AFS for total and inorganic Hg
determination in biodiesel samples. In addition, Cassella et al.59
determined Cu, Fe, Ni and Pb by ETAAS in diesel oil samples by
the formation of a water-in-oil emulsion with Triton X-114 in
acidic media and subsequent breaking of the emulsion by
heating.
2.4. Green solvents and reagents
Green chemistry also deals with risk reduction and pollution
prevention. Risk is defined as the product of hazard and expo-
sure.60 Exposure to a given hazardous substance may be reduced,
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for instance, by using miniaturized sample preparation tech-
niques. However, exposure controls are capable of failing, then
maximizing the risk when hazardous reagents and solvents are
used. The removal of toxic solvents and reagents from the
analytical procedures is thus a challenging task that has been
faced by researchers, especially in the last two decades. In spite of
being highly desirable, the full removal of certain solvents and
reagents is not always achievable without significant worsening
of the analytical characteristics. In these cases, the replacement
of harmful solvents and reagents by greener alternatives is
advisable. For instance, volatile organic solvents have been
replaced by water,41 ILs,61 supramolecular solvents62 and carbon
dioxide63 in a variety of sample preparation techniques for total
element analysis and speciation, thus giving rise to greener
analytical methodologies. However, toxic organic solvents, such
as benzene64 or chlorinated solvents65 are being systematically
employed in certain sample preparation techniques. In general,
the selection of a given solvent for its application in atomic
spectrometry is performed by comparison of certain physico-
chemical properties, such as solubility, polarity, density, viscosity
or vapour pressure. Given the environmental, health and safety
impact of organic solvents, their toxicological features should be
seriously taken into consideration. Therefore, we should also
consider aspects such as toxicity, flammability, explosivity,
stratospheric ozone depletion and/or atmospheric ozone
production, in order to also fulfil the criterion of reduced
hazards.66 In addition to the impact on health and environment,
the energy required to manufacture the solvent and the cumu-
lative energy demand should also be evaluated for potentially
feasible solvents.67 The use of a solvent selection guide is highly
recommended for the development of green analytical methods,
such as those recently proposed by GlaxoSmithKline (GSK)68
and Pfizer,69 respectively. A quick view of green and less green
solvents commonly used in the industry and analytical labs is
shown in Table 2. Detailed information of the relevant aspects
considered to establish the greenness of organic solvents can also
be found in the literature.70
When reagents cannot be replaced by environmentally friendly
alternatives, their minimization should be considered as a viable
option. Thus, the employment of multicommutation,71,72
sequential injection,73 and lab-on-valve systems,74,75 the immo-
bilization of reagents onto a solid substrate74 or the introduction
of the necessary reagents as part of the extractant phase in
microextraction techniques76 allows an important reduction of
the mass of reagents needed to perform a single analysis and,
therefore, a drastic reduction of costs and wastes produced.
A ‘reagent free’ photo-induced CVG method was reported by
Li et al.77 for the determination of mercury in alcoholic beverages
by exploiting the reducing capacity of the ethanol present in wine
and liquor samples when exposed to UV irradiation.
The development of ligandless analytical procedures combined
with atomic spectrometry has also been reported in the literature.
Thus, formation of metal hydroxides78,79 or insoluble chlorides80
has been employed for the development of ligandless analytical
methodologies by pH adjustment and addition of NaCl,
respectively.
The application of unrefined natural reagents as greener and
cheaper reagents has also been referenced in the literature.81 For
instance, Tuzen et al.82,83 employed SPE resins containing
J. Anal. At. Spectrom., 2012, 27, 1831–1857 | 1837
Table 2 Commonly used solvent selection guides in terms of greenchemistryc
Solvent
Solvent selection guide
GSKa Pfizerb
Water Few issues (greenest option) PreferredHydrocarbonsPentane UndesirableHexane Major issues UndesirableHeptane Some issues Usable2-Methylpentane Major issuesIsooctane Some issues UsableCyclohexane Some issues UsableMethylcyclohexane UsableBenzene Major issues UndesirableToluene Some issues UsableXylenes Usablep-Xylene Some issuesAlcoholsMethanol Some issues PreferredEthanol Some issues Preferred1-Propanol Some issues Preferred2-Propanol Some issues Preferred1-Butanol Few issues Preferred2-Butanol Few issuestert-Butanol Some issues PreferredEthylene glycol Usable2-Methoxyethanol Major issuesHalogenated solventsDichloromethane Major issues UndesirableChloroform Major issues UndesirableCarbon tetrachloride Major issues Undesirable1,2-Dichloroethane Major issues UndesirableKetonesAcetone Some issues PreferredMethyl ethyl ketone Major issues PreferredMethyl isobutyl ketone Some issuesCarboxylic acidsAcetic acid UsableEthersDiethyl ether Major issues UndesirableDiisopropyl ether Major issues Undesirabletert-Butyl methyl ether Some issues UsableCyclopentyl methyl ether Some issues1,2-Dimethoxyethane Major issues Undesirable1,4-Dioxane Major issues UndesirableTetrahydrofuran Major issues Usable2-Methyl tetrahydrofuran Some issues UsableEstersMethyl acetate Some issuesEthyl acetate Some issues PreferredPropyl acetate Few issuesDimethyl acetate UndesirableIsopropyl acetate Few issues Preferredtert-Butyl acetate Few issuesNitrogen-containing solventsAcetonitrile Major issues UsablePyridine UndesirableN-Methyl formamide Major issuesN-Methyl pyrrolidone Major issues UndesirableDimethyl formamide Major issues UndesirableDimethyl acetamide Major issuesSulfur-containing solventsDimethyl sulfoxide Some issues Usable
a Ref. 68. b Ref. 69. c The GSK solvent selection guide establishes threetypes of solvents ranked from the greenest to the least green: few issues> some issues > major issues. In the same way, the Pfizer solventselection guide establishes three types of solvents ranked from thegreenest to the least green: preferred > usable > undesirable.
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Bacillus sphaericus and Streptococcus pyogenes for Cr and Hg
speciation, respectively.
Green reagents have also been employed to increase the effi-
ciency of certain analytical processes. Thus, ILs have been used in
combination with complexing agents84,85 to achieve the enhance-
ment in the CVG efficiency of transition and noble metals.
2.5. Green derivatization methods for total element analysis
and speciation
In accordance with the 8th principle of green chemistry, unnec-
essary derivatization should be avoided whenever possible in
order to limit the use of additional reagents that, in turn, can
generate wastes.43 The improvement of analytical methods for
total element analysis and speciation has also been derived from
the application of greener derivatization methods. Thus, several
strategies have been proposed in the literature in order to avoid
conventional derivatization methodologies that involve the use
of non-green reagents and/or the formation of hazardous by-
products.
Conventional methods, such as HG or CV generation, involve
the use of toxic and expensive reagents, namely, tetrahydrobor-
ate(III), tin chloride or potassium permanganate. The replace-
ment of CVG by powerful and greener derivatization alternatives
has been a hot topic in analytical chemistry in recent years.86
Photo-CVG, based on the direct conversion of non-volatile
precursors into volatile species by means of photochemical
reactions, has been studied and employed to the development of
greener alternatives to classical CVG for sample introduction in
analytical atomic spectrometry.11,87–92 The use of low molecular
weight organic acids, alcohols and aldehydes as organic precur-
sors to assist UV reduction allows the formation of volatiles of
analytical interest, being employed for the determination of a
group of elements, including Ba, Fe, Co, Rh, Ni, Pd, Cu, Ag, Au,
Cd, Hg, In, Sn, Pb, As, Sb, Bi, S, Se, Te and I.86
Ultrasound-promoted cold vapour generation has also been
successfully employed for the conversion of Hg(II) into Hg0 in the
presence of formic acid, thus avoiding the use of chemical
reducing agents.93 The mechanism is based on the decomposition
of formic acid by means of US irradiation and subsequent
reduction of Hg(II) to Hg0 by the reducing volatiles generated. It
is interesting to note that reagentless formation of Hg0 is ach-
ieved by sonication of the sample in the absence of any chemical
reagent even though the conversion efficiency is reduced in
comparison with the use of formic acid. This method has been
applied so far to the determination of Hg in waters and
ophthalmic solutions.93–96 It should be highlighted that ultra-
sound-promoted cold vapour generation is not free from inter-
ferences, since the conversion efficiency is affected by oxidants
and complexing agents.
Hydrides can be electrochemically generated, thereby avoiding
the use of sodium tetrahydroborate. Thus, electrochemical
hydride generation (EC-HG) avoids the use of an expensive
chemical reagent that can introduce contamination and is
unstable in aqueous solution. Furthermore, the generation media
for the hydride-forming elements is similar and the efficiency of
HG is not affected by the oxidation state of the analyte.
However, some drawbacks have been attributed to EC-HG,
including limited applicability, significant interferences from
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concomitant species, e.g., Cu(II) being the most severe one, and
the poor stability of the cathode material.86,97
Dielectric barrier discharge (DBD)-induced CVG has been
recently proposed for Hg determination.98 Cold vapour genera-
tion in the DBD cell was improved by using formic acid 2% (v/v)
as the reaction medium. The mechanism by which Hg0 is formed
may be attributed to the decomposition of water and/or low
weight organic compounds and formation of radicals and
reducing agents by the DBD plasma and UV irradiation. Direct
conversion (by oxidation and atomization) of thiomersal into
Hg0 has been recently demonstrated by using a DBD cell, hence
avoiding pre-treatment steps.99 The authors directly determined
thiomersal in commercial vaccine samples by combining DBD-
plasma induced vaporization with AFS without the need to use
any chemical reagent.
2.6. Advanced oxidation methods
As previously discussed in Section 2.2, conventional sample
preparation methods for organic matter removal prior to trace
element determination involve the use of concentrated mineral
acids and high temperatures. Thus, conventional methods such
as acid digestion and/or mineralization of the sample by dry
ashing are prone to contamination, being furthermore time- and
energy-consuming. Advanced oxidation processes (AOPs) have
been developed in recent years, nowadays being considered as
greener sample preparation techniques in analytical chemistry.
UV-photo-oxidation, ozonolysis and US irradiation, as well as
the combination of these three AOPs, have been exploited for
trace-element analysis and speciation.11,100 AOPs are based on
the use of clean energies and/or chemicals with oxidizing prop-
erties and in situ formation of potent oxidizing radicals, such as
the hydroxyl radical. Relatively low concentrations of well-
known chemical oxidizing agents, such as hydrogen peroxide,
potassium persulfate, or the less green potassium dichromate, are
commonly added to facilitate the oxidation process. AOPs are
used for oxidizing the organic matter of the sample prior to
elemental determination, extraction of analytes from solids
present in an aqueous medium, and for destroying organome-
tallic compounds, thereby allowing speciation analysis.
Among the benefits of AOPs, the reduced amount of chemical
reagents needed can be highlighted, with the subsequent advan-
tages in terms of reduced contamination risks, waste generation
and economy, the possibility of performing the sample pre-
treatment at room temperature, and the low cost of equipment.
In addition, AOPs can be performed on-line.
Fern�andez-Costas et al.101 reported the combination of US-
assisted extraction with ozonation for determination of As in
biological and environmental solid samples by HG-AFS.
Ozonation proved to be highly efficient in the removal of organic
matter prior to the elemental analysis, avoiding foam formation
and, as a consequence, flame instability.
Sonolysis has been proposed as an efficient oxidation method
for the conversion of organomercurials (e.g., methyl-, phenyl-
mercury) into inorganic mercury for the subsequent determina-
tion of total Hg in waters by FI-CV-AAS. Complete oxidation
can be accomplished within 3 min by ultrasound irradiation,
hence avoiding chemical oxidants and strong reaction conditions
(i.e., high temperature and pressure).102
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The combined use of focused US irradiation with ozone
(sonozone) was first proposed by Bendicho’s group103 as sample
treatment for determining reactive arsenic toward sodium
tetrahydroborate. Sonozone has been used also for oxidizing
methylmercury into inorganic Hg, aimed at determining inor-
ganic and total Hg in undiluted urine samples by FI-CV-AAS.104
A novel high-efficiency photooxidation (HEPO) reactor was
introduced by Nakazato and Tao for the efficient and expeditive
conversion of organoarsenic species into As(V) prior to the
determination of arsenic species in human urine by liquid chro-
matography (LC)-HEPO-ICP-MS.105 The use of a highly UV
transmitting reaction tube extended within a low-pressure Hg
lamp allowing irradiation at both 185 and 254 nm was key to the
rapid photooxidation of a variety of organoarsenic species. A
photooxidation time of 3.5 s was in fact enough for the efficient
conversion of organoarsenic species without the addition of any
oxidizing agent.
The combination of AOPs with green sample preparation and
derivatization procedures prior to the elemental analysis has
demonstrated to be a powerful alternative for greening analytical
methods. For instance, we reported the use of photooxidation in
the presence of H2O2 (UV/H2O2) of thiomersal (sodium ethyl-
mercurithiosalicylate) in ophthalmic solutions prior to the sono-
induced cold vapour generation technique.96 Thus, the whole
method involves the use of 0.1 mL of H2O2 and 0.35 mL of
HCOOH for degradation of thiomersal and reduction/vapor-
ization, respectively.
2.7. Thermal desorption
Desorption of the analytes once they have been preconcentrated
is generally carried out by liquid or thermal desorption. Organic
solvents and acidic aqueous solutions are commonly used when
combining the preconcentration technique with HPLC and/or
detection by atomic spectrometry. In spite of being convenient
for appropriate desorption of target analytes, the use of such
eluting agents is generally considered as a non-green process,
especially when relatively large volumes are employed and, in
consequence, large volumes of wastes are produced.
Thermal desorption is considered as a greener alternative to
liquid desorption. In fact, the use of a solventless sample prep-
aration technique with thermal desorption provides the greenest
way towards the development of sustainable analytical proce-
dures. Analytes can be thermally desorbed by insertion of the
SPME fiber into the injection port of a gas chromatograph.106,107
Thermal desorption can also be performed after SBSE by using a
modified thermal desorption unit.32
Nevertheless, certain designs have been reported in the litera-
ture that allow the thermal desorption for direct detection by
atomic spectrometric techniques. For instance, we have reported
the combination of headspace (HS)-SPME with quartz furnace
atomic absorption spectrometry (QFAAS) for the determination
of tetraethyllead in gasoline and water samples108 and methyl-
mercury in seafood samples by HG and chloride generation.109 A
variety of volatilizators were tested, the tube-shaped design being
the preferred option due to the higher sensitivity and reproduc-
ibility achieved, presumably as a result of its lower inner volume.
Dietz et al.110 employed a home-made thermal desorption unit
containing a gas chromatographic stationary phase that allowed
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the separation in less than two minutes of at least two organo-
selenium compounds by coupling SPME with QFAAS and
ICP-MS.
Metallic surfaces have also been employed for adsorption of
target analytes and subsequent thermal desorption. For instance,
Hashemi and Rahimi111 proposed the use of a gold wire for the
preconcentration of mercury by amalgamation and subsequent
determination by ETAAS. Mercury was desorbed at 600 �C by
directly inserting the gold wire in the sample introduction hole of
the ETAAS instrument. Zierhut et al.112 employed active gold
collectors for the preconcentration of mercury species in natural
water samples. Amalgamation allowed the adsorption of Hg0,
while the adsorption of Hg2+ and MeHg+ was attributed to the
catalytic activity of gold nanostructures. Mercury species were
released as Hg0 from the gold collectors by thermal desorption at
550 �C, thus allowing the analysis by AFS. More recently,
Romero et al.113 used a variety of Pd-based collectors (Pd wire,
Pd-coated stainless steel wire and Pd-coated SiO2) for micro-
extraction and preconcentration of mercury. Thermal desorption
of mercury amalgamated onto the Pd wires was performed by
insertion into a modified quartz-T cell for AAS measurement.
Fig. 5 Flow injection systems (a) FIA (flow injection analysis); (b) SIA
(sequential injection analysis); (c) MCFIA (multicommutated flow
injection analysis); (d) MSFIA (multisyringe flow injection analysis); (e)
LOV (lab-on-valve); and (f) LOC (lab-on-a-chip).
3. Flow analysis in atomic spectrometry
Although flow systems have been proposed in order to automate
many analytical methods and improve sample throughput as well
as other analytical characteristics, these systems can also be
considered from the point of view of green chemistry.1 Thus,
according to the first principle, reagent consumption and waste
generation are usually lower than in batch procedures.114 In
agreement with the fifth and the eighth principles, sample treat-
ment can be simpler and faster, thus avoiding the use of auxiliary
reagents and the generation of derivatives.115 On-line monitoring
of processes is also achievable to control and prevent pollu-
tion,116 thus fulfilling the eleventh principle. In addition,
according to the sixth and twelfth principles, automation allows
high sample throughput with lower energy consumption and a
reduction of potential risks to the analyst.
Different flow systems typically used in combination with
atomic spectrometry are shown in Fig. 5. As can be seen, these
systems extend from the FIA introduced by Ruzicka and Hansen
in 1975117 up to more recent flow-based miniaturized systems
such as the lab-on-a-chip.118 The evolution of these systems
shows a clear trend towards an increase in automation and
miniaturization levels. Sample pre-treatment, derivatization,
separation and even waste recycling or in-line waste detoxifica-
tion can be carried out in current flow systems. In addition, these
versatile systems are not particularly expensive.
In this section we consider the possibilities offered by several
flow analysis systems and their role in the development of GAC,
including flow and microflow-injection analysis, sequential
injection analysis, multicommutation, lab-on-valve and micro-
fluidics chips also named as lab-on-a-chip (LOC).
3.1. Flow and microflow-injection analysis
Flow injection systems, based on the injection of a liquid sample
into a moving, non-segmented continuous carrier stream of a
suitable liquid, can be easily coupled to continuous atomic
1840 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
spectrometric detectors, such as, flame atomic absorption spec-
trometry (FAAS), ICP-OES and ICP-MS. On the contrary, for
discontinuous techniques, such as ETAAS, the coupling of
continuous flow systems is limited. It is possible to achieve a
semi-on-line coupling allowing different interesting approaches,
i.e. on-line sample treatment.119
In the initial stage of development, single-line manifolds with
continuous flow were used. Although this configuration provides
simple procedures and certain grade of automation, it displays an
important drawback from the standpoint of GAC, i.e., reagents
are consumed even when a sample is not processed, thereby
contributing to increased reagent consumption and waste
generation. The use of merging zones with intermittent flow
systems minimized this problem, also improving automation,
sensitivity and precision. This configuration has been mainly
applied in HG or CV. For example, Shao et al.120 developed an
intermittent flow reactor for the determination of total mercury
by AFS. With this configuration, 700 mL sample, ca. 900 mL
reductant (flow rate 4.0 mL min�1 for 14 s) and 1.4 mL carrier
(flow rate 4.0 mL min�1 for 21 s) were consumed per replicate.
Compared to continuous flow systems, this intermittent config-
uration reduces the consumption significantly. For instance,
Vermier et al.121 proposed a procedure based on a continuous
flow system coupled to AFS for mercury determination in bio-
logical samples. The volume of the sample and carrier consumed
was 35 mL (flow rate 7 mL min�1 for 5 min) and that of the
reductant was 15 mL (flow rate 3 mL min�1 for 5 min) per
replicate.
Waste generation remains high in FI systems because they
involve the use of one or more carrier streams to transport the
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sample and reagents to the detector. So, new designs related to
waste recycling and/or treatments have arisen.122 However, they
are not easy to implement, because usually the waste is highly
diversified, and therefore, there are no general strategies. Thus,
waste recycling has been implemented mainly in procedures
involving solvent extraction and/or analyte preconcentration.
Generally, phase separation is used to recover solvents in order
to reuse them. For instance, a back extraction column has been
proposed for recycling benzene using an automated on-line
solvent extraction for the determination of As and Sn by
ETAAS.123
For on-line waste treatment, different strategies and reagents
are used in order to destroy or passivate the toxic species in the
effluent. Metal ions must be passivized by adding a reagent in the
waste stream. For instance, different trace heavy metals (Cr, Cd,
Ba.) were on-line deactivated by co-precipitation with NaOH
and Fe(OH)3 in a system developed for the determination of Hg
in milk by AFS.71 For the detoxification of degradable wastes,
different strategies have been suggested, such as, thermal
degradation, oxidative detoxification, photodegradation and
biodegradation.4,10
FI systems have allowed automation and acceleration of
different sample treatments such as solvent extraction,124 acid
digestion,120 SPE125 or SPME.126
On-line digestion results in greener procedures than off-line
digestion. In general, lower volumes and concentrations of acids
as well as temperatures and pressures are used. For instance,
Shao et al.120 developed an on-line acid digestion for Hg deter-
mination in mainstream cigarette smoke using 1.4 mL of 4% (v/v)
sulphuric acid. In addition, with on-line digestion, a reduced
exposure of lab staff to potential risks is achieved (e.g., risks from
explosion and emission of vapours).
The use of natural reagents and their immobilization in FI
systems is an interesting alternative for the development of
environmentally friendly procedures. Maquieira et al.127
proposed the on-line preconcentration of heavy metals using
immobilized cyanobacteria as the biosorbent and detection by
FAAS. 20 mg of cyanobacteria were immobilized on controlled
pore glass retaining the activity for 3 months.
Greening FIA by the miniaturization way has been achieved
with micro-FIA systems (mFIA). In atomic spectrometry, mFIA
is mainly coupled with ICP-MS since it can be coupled to
micronebulizers.128–131Therefore, the consumption of sample and
reagents is only a few microliters, and consequently, waste
generation is very low. For instance, the microflow injection
system proposed by Takasaki et al.131 for the determination of
metals in some mice organs consumes only 20 mL of sample with
a flow rate of 10 mL min�1 for 2 minutes.
3.2. Sequential-injection analysis
Sequential injection analysis was developed by Ruzicka et al.132
in 1990 with the aim of overcoming some disadvantages of FIA,
mainly high consumption of samples and reagents and
complexity of the manifolds. SIA has been considered as the
second generation of FIA-based techniques.
The main feature of SIA manifolds is the multiposition selec-
tion valve providing more simple and robust designs. Fluids are
manipulated within the manifold by means of a bi-directional
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pump. The process is computer-controlled and both the sampling
sequence and the volume of each aliquot are defined by software.
The sample and reagents are sequentially aspirated. Then, the
volume inserted into the analytical path is only that necessary for
reaction development. Therefore, a drastic reduction in the
consumption of reagents and sample can be achieved, of
the order of 10–20 times in relation to FIA.133 For example, the
consumption of reagents for CV can be reduced 10 times134 in
comparison with FIA methodology based on continuous reagent
addition.135
SIA is especially interesting for complete automation of
sample treatment. Thus, automation of LLE using FIA has some
drawbacks such as low extraction efficiency and limited range of
sample-extractant volume ratios.124 These drawbacks can be
overcome by SIA, because the extraction step takes place on a
thin pseudo-stationary organic film formed on the surface of the
tube. It allows a precise control of sample-to-extractant volume
ratios in a wide range with higher extraction efficiency, lower
reagent consumption and waste generation.136–138
SIA is widely used to automate SPE procedures using atomic
detectors, e.g., Wang and Hansen139 designed an automatic
sequential injection on-line solid phase extraction system for
cadmium determination by ETAAS using a microcolumn packed
with PTFE beads. The sample consumption was 3 mL per
analysis and the analyte was eluted with only 50 mL of ethanol.
After each analysis the microcolumn was washed and regen-
erated with 400 mL of a mixture of ethanol–nitric acid.
Although SIA can be considered as a greener alternative to
FIA, the choice of one or the other depends on the specific
analysis and features associated, such as sampling rate, auto-
mation grade, sample availability and cost and toxicity of
reagents.
3.3. Multicommutation
Multicommutation was developed in 1994 by Reis et al.140 as a
flow-analysis option (multicommutated flow injection analysis,
MCFIA) in order to increase the versatility of flow systems,
reduce reagent consumption, improve mixing and facilitate
automation. Multicommutation is fully computer-controlled and
utilizes multiple solenoid valves as separate switching devices to
create a more flexible flow path that is able to use significantly
less reagents than FIA since they are recirculated to their
containers when not used.141
MCFIA and FIA have recently been compared for the deter-
mination of total Se in infant formulas by HG-AAS.142 Although
the sample consumption is similar in both systems, consumption
of reagents using the multicommutated system is ca. five times
lesser than in FIA. It also provides better detection and quanti-
fication limits with higher sampling frequency (160 samples per
hour with MCFIA vs. 60 samples per hour with FIA).
Multicommutation principles have also been implemented in
modified SIA (multisyringe flow injection analysis, MSFIA).133
Conventional rotatory valves used in SIA are replaced by sole-
noid valves. Although most applications of MSFIA rely on UV-
spectrophotometry detection there are some applications for the
analysis of trace metals by atomic spectrometric detection, such
as AFS143 or ICP-OES.144
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Like FIA and SIA techniques, multicommutation systems can
incorporate on-line sample treatment. SPE is also the most
popular sample treatment, e.g., Leal et al.143 used a column for
the preconcentration of arsenic prior to the analysis by AFS. The
work demonstrated that MSFIA decreases the consumption of
reagents and sample in comparison with FIA. In addition,
compared with a SIA system, MSFIA with preconcentration
provides higher sample throughput (36 vs. 6 sample h�1) and a
detection limit 22 times better.
In spite of the advantages of MSFIA systems, it should be
noted that most of the published works do not involve treatment
steps, because solenoid pumps do not work properly under
backpressure, thus, when a sample treatment step is coupled to
the system, the sample throughput can decrease considerably.
Following the trends towards cost-effective procedures, with
lower reagent and sample consumption and waste generation as
well as fast analysis, the use of multipumping flow systems
(MPFSs) has been proposed.145 These systems are based on the
combined use of solenoid valves and pumps operated in the form
of pulses. The number of pulses defines the total injected volume,
while the frequency of pulses defines the liquid flow-rate. MPFSs
have been used for trace metal determination by atomic spec-
trometry.146–148 For example, P�erez-Sirvent et al.147 determined
Hg by AFS. When the MPFS-based procedure is compared with
conventional flow systems,135 a substantial improvement in
sample throughput is obtained (82 samples per hour, instead of
30 samples per hour with conventional peristaltic pumps). In
addition, 90% of reagent volume and 95% of sample volume are
preserved, so waste generation is considerably diminished.
3.4. Lab-on-valve
Lab-on-valve was introduced by Ruzicka149 in 2000, and has
been accepted as the third-generation of FIA. LOV has been
developed by implementation of SIA principles in a modified
system where all components are integrated on a six-port selec-
tion valve. LOV systems involve significant progress in minia-
turization, automation and integration of on-line sample
treatments. Hence, reagent consumption and effluent generation
have been drastically reduced.
LOV has been coupled with different atomic spectrometry
techniques for the determination of metal species. For instance,
CV in a LOV system has been applied for Hg determination by
AFS.150 With this configuration the sample and reagent
consumption is only 500 mL and 400 mL respectively. Also, they
achieved a high sample throughput, i.e., 90 samples per hour.
The low sample and reagent consumption, as well as low waste
generation, makes these systems suitable for achieving greener
analytical approaches.
LOV is used to automate sample treatment, e.g., SPE. There
are two strategies for performing SPE, namely, packing the solid
material in a micro-column and using the so-called bead-injec-
tion (BI) principle. The latter option is widely used in LOV
platforms for routine analysis because it avoids the main prob-
lems associated with conventional on-line column preconcen-
tration systems, such as high backpressure or deactivation of the
surface of the solid material. In LOV-BI, a micro-column is
generated in situ by aspiration of the beads. Usually, the solid
material is renewed after each analytical cycle. This is the main
1842 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
drawback of this strategy from a standpoint of GAC. In spite of
this, when the combination of LOV-BI and ETAAS is used, trace
metals can be determined without analyte elution since beads are
transferred into the graphite furnace, e.g., Ampan et al.151
developed a LOV-BI procedure for the determination of lead by
ETAAS with Sephadex G-25 impregnated with dithizone. It
must be emphasized that the lifetime of graphite tubes is short
due to the residues deposited onto the graphite tubes after
pyrolysis of the beads.
3.5. Lab-on-a-chip
Since the introduction of flow analysis in the 70s, the clearest
trend in its evolution is without doubt miniaturization. In this
sense, Manz et al.152 developed in 1990 the concept of micro-total
analytical systems. This analytical concept has led to the devel-
opment of the so-called lab-on-a-chip devices, allowing a high
miniaturization of the analytical systems.
LOC devices have been an active subject of research in the last
decade.153 The interest in these devices arises from the incorpo-
ration of sample processing steps onto a small chip, thus reducing
the required sample volumes, reagent consumption, waste
generation and time required for the analysis. Also, these
microfluidics systems can enhance the portability compared to
traditional instrumentation and they can be fabricated in a
cheaper way.
Microfluidic chips are constituted by micrometer-scale chan-
nels and reservoirs in a substrate material (usually silica, quartz
or plastic). Although the chip material depends on the applica-
tion, plastic is the most employed today because it is the
cheapest. Three different propulsion mechanisms are used in
LOC devices: electroosmotic flow, hydrodynamic and
centrifugal.154
Chips have been mainly used for metal determination by ICP-
MS.155–157 A microchip-based nanolitre sample introducing
system for ICP-MS allows designing greener procedures than
conventional sampling systems. For instance, Cheng et al.157
developed a microfluidic chip with hydrodynamic flow (20 mL
min�1) for the determination of cisplatin in human serum. With
this system the sample consumption is very low, only 1.8 nL are
needed per analysis, ca. 105 times less than that of the conven-
tional sampling systems. Also, a high sample throughput up to
112 samples per hour was achieved.
As with LOV systems, in LOC devices, different units for
sample treatment can be implemented.158–160 As an example,
Chen et al.159 developed a microfluidic device for magnetic
nanoparticle solid phase microextraction (MSPME). It was
applied to the determination of Cd, Pb and Hg by electrothermal
vaporization-inductively coupled plasma mass spectrometry
(ETV-ICP-MS). For the preparation of the magnetic solid phase
column on the chip, 25 mg of the solid phase were aspired and
introduced into the magnetic zone. The magnetic nanoparticles
were used almost 12 times. Sample consumption was 500 mL per
analysis which is lower than that required with conventional
procedures involving ETV-ICP-MS.
The use of microfluidic chips allows a great miniaturization of
the systems, in addition to a complete automation of the
procedure. The main disadvantage of LOC devices is that they
are systems of fixed structure, and therefore, it is necessary to
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Table
3Comparisonofthegreennessprofile
ofdifferentapproaches
forsolidsampling
Electrothermalvaporization/
atomization
Arc/spark
ablation
Laserablation
Glow
discharge
X-ray
Considered
techniques
ETAAS
Arc/spark-O
ES
LA-ICP-O
ES
GD-O
ES
m-X
RF
ETV-ICP-O
ES
Arc/spark-ICP-O
ES
LA-ICP-M
SGD-M
STXRF
ETV-ICP-M
SIC
P-M
SLIB
SEDXRF
WDXRF
Multielemental
capability
ETAAS/N
oYes
Yes
Yes
Yes
ETV-ICP-O
ES/Y
esETV-ICP-M
S/Y
esSample
quantity
0.1–1mga
1–10mga
0.25ng–2mgb
quasinon-destructive
10–100mga
Non-destructive
0.1
mg–500mgc
Usualsample
pretreatm
ent
Homogenization
No
No(LAM)
No
No
Tem
perature–
pressure
conditions
ETAAS/tem
perature
program
(upto
3000
� C)
inanAratm
osphere
Highpotential
difference
between
theelectrodes
inanAr
atm
osphere
10–100mJb
Highpotential
difference
inaninert
gasatm
osphere(usually
Ar)
atreducedor
atm
ospheric
pressure
Ambienttemperature.
Atm
ospheric
pressure
orvacuum
ETV-ICP/(upto
10000
� C),
transport
byanArflow
Portability
No
Yes
LA/ICP-O
ES/N
oNo
m-X
RF/Y
esLA/ICP-M
S/N
oTXRF/Sem
i-portable
LIB
S/Y
esEDXRF/Y
esWDXRF/N
oAutomation
Yes
aYes
aNoa
Noa
Certain
grade
ofautomation(sample
changer
motorized)
Sample
throughput
ETAAS/15min
per
analyte
a1–2min
per
samplea
2–5min
per
samplea
10min
per
samplea
4–120samplesper
hourc
ETV-ICP-M
S/15min
per
samplea
aRef.181.bRef.169.cRef.182.
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design specific chips for each application, hence being less
versatile than LOV systems.
4. Solid sampling by atomic spectrometry
Sample preparation typically consumes reagents, solvents,
energy and is generally labour-intensive. So, it is not surprising
that one of the paradigms of GAC is the elimination of this stage.
The ideal analytical method from the point of view of GAC is
based on direct measurements without sampling, transport,
addition of reagents and waste generation. In this sense, remote
and on-site measurements can be considered the best strategies to
approach the philosophy of GAC.3 This is not always possible,
and therefore, when a sample is analysed in the lab, replacement
of traditional ‘wet chemistry’ for sample pre-treatment is
considered an important goal.2 In fact, developments made in
order to introduce solid samples directly into analytical instru-
ments have been long pursued by analytical researchers.
Sample decomposition by acid digestion is common when
atomic spectrometric techniques are used. It implies the appli-
cation of concentrated acids and high temperatures and pres-
sures. Nowadays, microwave energy operating with closed
vessels involves an efficient way of saving energy and acids. In
spite of this, it continues to be difficult to meet the GAC prin-
ciples when acid digestion is involved. Therefore, solid sample
analysis without or with minimal sample pre-treatment should be
an interesting alternative. This includes direct solid sampling and
slurry sampling (a suspension of a finely powdered sample).
Atomic spectrometry techniques can resort to different
systems in order to cope with solid samples, such as electro-
thermal vaporization, arc/spark ablation, laser ablation (LA) or
glow discharge (GD) sources. It is important to lay emphasis on
those atomic spectrometric techniques that allow performing
green analysis in a non-destructive way due to their ability to
directly analyse solid samples such as X-ray fluorescence tech-
niques. Solid sampling using different atomic spectrometric
techniques has been thoroughly reviewed, which points out the
interest in this topic.161–180 Table 3 shows some characteristics in
order to compare the greenness of different atomic spectrome-
tries using solid sampling.181,182
The advantages of solid sampling from the perspective of GAC
over acid digestion or other sample pre-treatments (e.g., dry
ashing, fusion) can be summarized as follows.
(a) It avoids the use of corrosive and hazardous chemicals.
(b) It reduces energy consumption by elimination of heating.
(c) It minimizes waste generation.
(d) It reduces the exposure of laboratory staff to acid vapours
and improves lab safety.
(e) It reduces labour and improves sample throughput.
(f) It is possible to analyse a very small sample mass [i.e.,
analysis at micro- (10�2 to 10�3 g), submicro- (10�3 to 10�4 g) or
even ultramicro-scale (<10�4 g)].183
Solid sampling can be considered especially green for samples
that are difficult to digest even with very drastic conditions, and
for elements whose levels are usually very low. For instance, Qi
et al.184 have recently reported a digestion method for determi-
nation of the platinum group elements in geological samples by
ICP-MS. Due to their chemical characteristics and low concen-
tration, both laborious and tedious dissolution procedures are
1844 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
required. Thus, between 2 and 10 g of the sample are first
digested with 15–30 mL of HF in a PTFE beaker on a hot plate to
remove silicates up to dryness. The residue is then digested with 5
mL of HF + 15 mL of HNO3 at 190�C for about 24–48 h in a
stainless steel pressure bomb. After cooling, 2 mL of HCl are
added and evaporated to dryness on a hot plate. In order to
remove most of the residual acids, 5 mL of concentrated HCl are
added to the bomb. After drying, the residue is dissolved with
40 mL of 2 N HCl. The resultant solution is then decanted to a
50 mL tube for centrifuging at 2800 rpm for 5 min. The upper
portion is used to preconcentrate platinum group elements by
coprecipitation. The precipitate is dissolved with aqua regia, the
solution is evaporated to near dryness, redissolved again with 0.3
mL of aqua regia and diluted to 10 mL. An ion exchange resin is
necessary to remove some interfering elements, such as Cu, Ni,
Zr and Hf.
The last procedure can be compared with solid sampling by
laser ablation and ICP-MS. For instance, Boulyga and Heu-
mann185 suspended 1 g of sample in 0.2–5 mL of different
isotope spike solutions. This suspension is dried at 75 �C,homogenized by mixing with a Teflon pestle and pressed into
pellets for direct laser ablation. 3 mg of a rock sample are
ablated within one analytical run (1 min ablation time). 50–67
successive runs are performed for each rock sample. Undoubt-
edly, solid sampling provides clear advantages with regard to
the digestion procedure: it eliminates the use of HF, HNO3 and
HCl; it reduces steps, time and labour and reduces the
temperature of operation (190 vs. 75 �C).
4.1. Electrothermal vaporization/atomization for solid
sampling
Trace metals can be directly vaporized and atomized from a solid
sample introduced into an electrothermal atomizer/vaporizer,
e.g., graphite furnace. It is an interesting alternative to sample
dissolution in AAS, ICP-OES and ICP-MS. Although direct
solid insertion (DSI) into a flame or plasma is somehow possible,
ETV systems have successfully extended solid sampling to ICP-
OES and ICP-MS. The latter approach provides matrix removal
during the pyrolysis step, for which it can be considered as a
thermochemical reactor allowing in situ sample treatment.165
From 1971, the year in which the first application of solid
sampling by ETAAS with a commercial atomizer was pub-
lished,186 until today, important progress regarding instrumen-
tation for solid sampling has been achieved. Spectrometers
equipped with autosamplers that allow weighing, introduction of
the solid sample automatically and calibration with aqueous
standards as well as the addition of a matrix modifier are now
commercially available (e.g., SSA 600L-fully automated solid
sampler with a liquid dosing unit and up to 84 samples from
Analytik Jena).187
Although ETV was used for the first time in 1974,188 applica-
tions of solid sampling with this system were performed much
later. Probably, this fact can be associated with the commer-
cialization of more robust ETVs at the end of the 90s. A degree of
automation analogous to ETAAS can be achieved with ETV
systems. An autosampler and a microbalance can be coupled to
an ETV-unit for solid sampling by ICP-OES or ICP-MS (e.g.,
autosampler AWD-50 from Spectral Systems Advanced
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Technologies).189 The main green advantage of ETV-ICP-OES
and ETV-ICP-MS with respect to ETAAS for solid sampling is
their multielemental capability.
In spite of that, solid sampling with these atomic spectrometric
techniques is unusual in routine labs. Though the state-of-the-art
of the instrumentation has eliminated the difficulties related with
the insertion of the solid sample into the atomizer, i.e., the risk of
sample losses and contamination during the weighing and
transfer from the balance to the atomizer,161 important analytical
problems (e.g., precision continues to be worse than for liquid
samples and calibration with certified reference materials is still
the most reliable approach, the use of aqueous standards and the
standard addition method being only possible sometimes) and
drawbacks from the viewpoint of GAC continue to be present.
(a) Chemical modifiers interact less effectively with the analyte
occluded within the sample matrix, and hence, a higher quantity
is used in comparison with liquid samples.
(b) Additional reagents may be needed (e.g., hydrogen,
methane or oxygen in the ashing step) in order to remove
interferences.
(c) Higher atomization temperatures are required to release the
analyte in comparison with liquid samples, especially when
refractory elements are determined.
(d) Deterioration of the atomizer is a critical issue and addi-
tional cleaning-out steps can be necessary.
The expertise of the analyst is the key in the success of solid
sampling. Paradoxically, the labour increases, especially along
method development, validation and control. Every analyte and
matrix requires a complete evaluation, i.e., optimization of the
temperature program, matrix chemical modifier, establishment
of a suitable mass interval, etc. This is especially remarkable for
ETV-ICP-MS due to the large number of potential matrix
interferences. Data treatment is also relevant because outliers
frequently appear. So, in order to minimize their influence, the
number of replicates required in solid sampling is higher.190
On the other hand, the corrosion of the graphite atomizer has
been reported by Ortner et al.191 as ‘often disastrous in solid
sampling into graphite boats’ and it can be considered an
important disadvantage in GAC. In addition, release of gaseous
and aerosol products from the matrix is enhanced in solid
sampling. A series of relatively simple strategies such as the use of
modifiers and coatings in graphite atomizers can be used in order
to avoid this problem, i.e., the lifetime of carbide-modified
graphite atomizers is longer than that of standard graphite tubes
for solid sampling.191 The design of alternative atomizers for
solid sampling still continues, e.g., a recent model of an atomizer
named ‘crucible with separated zones’.192 It consists of a graphite
tube placed in the atomization zone and heated independently of
the evaporation zone so that the filtration of sample vapours
through porous walls takes place.
Tungsten based atomizers, mainly W-tubes, have been
proposed as an alternative to graphite furnaces for solid
sampling, especially for slurry sampling. Green characteristics
such as simplicity, low cost and low power requirements have
been achieved with these atomizers. Tungsten is available at low
cost, heating rates are high and a simple power supply is suffi-
cient. In addition, no water circulating system is required as a
coolant. Hou and Jones have reviewed these atomizers in
analytical atomic spectrometry, including their potential in
This journal is ª The Royal Society of Chemistry 2012
ETAAS, ETV-ICP-OES and ETV-ICP-MS with slurry
sampling.193 However, not everything is green in this type of
atomizers. These are usually purged with up to 10% of hydrogen
mixed with argon and have a relatively short life.194
Although sample pre-treatment should be avoided whenever
possible in order to retain the green advantages of solid
sampling, it is not always possible. Drying and grinding up to a
suitable particle size are usually performed to improve precision.
In those cases, slurry sampling can be considered more advan-
tageous since it shares the advantages of direct solid sampling
(minimum sample pre-treatment) and liquid sampling (better
precision, introduction with a conventional autosampler, cali-
bration with an aqueous standard, efficiency of chemical modi-
fiers, temperature programs and atomizer corrosion similar to
liquid samples). Therefore, slurry sampling is more suitable for
routine analysis than direct solid analysis.190
Miniaturization, automation and acceleration can be simul-
taneously achieved with slurry sampling (SS). For preparing
slurries, a few milligrams of the powdered sample (typically 10–
20 mg) and a volume of the liquid diluent in the range of 1–
1.5 mL are added into an autosampler cup. In general, this liquid
medium consists of a diluted solution of nitric acid (e.g., 3% v/v)
and, in some cases, a very small amount of a stabilizing agent
such as Triton X-100 or glycerol. Homogenization of the slurry is
critical and, probably, this is the weakest point of the slurry
technique from the perspective of GAC. Although it can be
carried out by magnetic stirring, ultrasound agitation can be
certainly considered as a greener option. In contrast to direct
solid sampling, additional equipment only for the ultrasonic
homogenization of the slurry is required. In this sense,
commercial systems developed in the 90’s incorporate an ultra-
sonic probe into the ETAAS autosampler for automating the
procedure, i.e., USS-100 Ultrasonic Slurry Sampler from Perkin-
Elmer. Only a few seconds of application of this energy is suffi-
cient in order to obtain a homogeneous slurry.
SS can be used with ETV for multielemental determinations by
ICP-MS and ICP-OES. For instance, Lin and Jiang194 used
ultrasonic slurry sampling (USS)-ETV-ICP-MS for determining
Cr, Mo, Pd, Cd, Pt and Pb in drug tablets. Amberger and
Broekaert195 proposed the direct determination of trace elements
in boron carbide powders by SS-ETV-ICP-OES. Slurries can be
also nebulized directly into flames and plasmas. A comparison of
SS-ETV and slurry nebulization (SN) for determination of trace
impurities in titanium dioxide powder by ICP-MS has been
carried out by Xiang et al.196 In both cases, the particle size is
critical, though SS-ETV-ICP-MS has a lower particle size effect
compared to SN-ICP-MS (particle diameter <50 vs. 1 mm
respectively). Then, it is necessary to consider the increased
operation time that reduction of particle size implies.
4.2. Arc/spark ablation
Arc/spark optical emission spectrometry has been used since long
for direct analysis of solid samples. Ablation is carried out by an
electrical discharge between an electrode and the conducting
sample. In spite of the remarkable features (e.g., a multielemental
determination could be performed in ca. 30 s), this classical
technique has not garnered interest as an investigation topic due
to the availability of more advanced techniques such as ICP-OES
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or ICP-MS, with better analytical characteristics for liquid
sampling but with more difficulties as regards solid sampling.197
In 99% of cases, this technique is used in routine labs of the
metallurgical industry. The remaining 1% corresponds mainly to
the analysis of refractories, precious metals, steel-making slags
and geological materials.198 These last samples must be powdered
and mixed with high purity graphite, which diminishes the scope
of green chemistry.
Some technological advances incorporated into instruments
can be considered as decisive in order to green this routine
technique. Nowadays, more compact and lower-cost instruments
requiring little maintenance can be acquired. In particular, this
has been achieved with the incorporation of charge-coupled
devices (CCD), gas-filled vacuum ultraviolet (VUV) optical
chambers, digitally controlled arc/spark excitation sources,
advanced electronic time-resolved spectroscopy (TRS), fiber
optics and multiple optical cells.197 Portable systems for a variety
of applications including routine sorting, positive material
identification (PMI) or metal certification can be commercially
obtained.199 New developments according to GAC principles
have been recently patented, e.g., in order to conserve argon200 or
to use low current spark generators.201
Today arc/spark ablation can be used for sample introduction
in ICP-OES and ICP-MS, although its use is limited in
comparison with lasers or glow discharge sources. A commercial
spark ablation accessory known as ‘Separate Sampling and
Excitation Accessory (SSEA)’ is used for this purpose. It
improves the analytical characteristics of arc/spark spectroscopy
and allows extending the solid sampling capability to routine
laboratories.202–204 Both cost and maintenance are lower as
compared to other systems such as laser ablation.
4.3. Laser ablation
Laser ablation is a powerful tool for solid sampling that has been
increasingly applied in several fields. In contrast to arc/spark
ablation, laser ablation has greater versatility. All types of
materials can be used for laser ablation, i.e., conducting and non-
conducting, organic and inorganic samples. In addition, LA can
be used as a spatial and depth-resolved high resolution sampling
technique.169 Very small amounts of samples, in the order of ng
or even pg, can be analysed using laser ablation microprobes
(LAMs). So it can be considered as an essentially non-destructive
or minimally destructive technique from the viewpoint of GAC.3
LA systems can be used as sampling and excitation sources
(e.g., laser induced breakdown spectroscopy, LIBS) and coupled
with ICP (LA-ICP-OES and, in particular, LA-ICP-MS). This
last technique combines the green advantages of solid sampling
discussed above with multielemental and isotopic analysis
capability and high sensitivity. The sample is ablated in an
airtight cell and the formed aerosol is carried in a continuous
flow of an inert gas to the ICP where it is excited and ionized for
quantification by MS.169 In the case of LIBS, the plasma plume
generated on the sample surface is used for optical emission
measurements. Incident laser light and emission lines are
resolved both spectrally and temporally. The instrumentation is
simple and includes an ablation laser, an optic collection system,
a monochromator or an echelle spectrometer and a multi-
element photodiode array (typically a CCD).171 In spite of the
1846 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
good characteristics of LA for solid sampling, matrix effects
must be considered in all cases.
The formed aerosol by ablation of the sample depends not
only on the sample but also on laser characteristics. First, lasers
of ruby and later lasers of neodymium:yttrium aluminium garnet
(Nd:YAG) and excimer lasers have been used for LA. There is a
relationship between laser wavelength, laser irradiance, optical
penetration depth, particle size, and analytical precision and
accuracy. In general, it is accepted that shorter UV wavelengths
improve ablation characteristics in respect to infrared and visible
wavelengths, especially for highly transparent samples. Both,
excimer and Nd:YAG lasers can produce UV light pulses. In
general, excimer lasers offer the shortest wavelength and a
precise sampling due to their spatial coherence. In contrast,
Nd:YAG lasers are simpler, more cost-effective, require little
maintenance and produce higher repetition rates.205
LA procedures can be divided according to the mass sample
and analysis goal into bulk sample analysis and microprobe
analysis. In bulk sample analysis, there is a large amount of
sample and the difficulty lies in obtaining a representative anal-
ysis. The spot diameter is generally >100 mm corresponding to
2 mg–2 mg of ablated mass and then, in many cases, samples must
be homogenized.169 Pulverization and even fusion to form a glass
might be necessary. For instance, a meta-tetraborate fusion
procedure was used with powdered rock by Leite et al.206 in LA-
ICP-MS. Obviously, when a fusion procedure is necessary, the
green advantages of LA are clearly diminished. Therefore,
homogeneous materials such as alloys retain all the advantages
of analysis by LA from the point of view of GAC.
LAM is especially interesting for applications where a spatial
resolution is necessary (lateral and in-depth in the low-mm and
nm range, respectively), i.e., microanalysis, in-depth profiling,
and surface mapping.175 Though LAMs can reduce sensitivity
since a small amount of sample is ablated, it can be considered a
green tool. The spot diameter is generally <100 mm corre-
sponding to 0.25 ng–2 mg of ablated mass. Pulsed laser energy
used in LAMs is small (few mJ) compared with that used for bulk
sampling (10–100 mJ).169 Usually, excimer lasers with short UV
wavelengths are used. Shorter pulses improve LA localization; in
particular ultra-short laser pulses (<1 ps) and more concretely
femtosecond lasers are applied in order to improve the analytical
characteristics.175
LAMs may require sample treatment only in some cases, for
instance, for bioimaging of elements in biological tissues by LA-
ICP-MS. Soft tissues are paraffin-embedded or frozen, then
samples are sliced (usual thickness: 20–200 mm) and deposited on
a glass slide. Both the thickness of the tissue and the laser
parameters should be optimized. Cooled laser ablation cells are
preferably used for this purpose.207 Usually, soft biological
tissues are easy to ablate from a glass substrate and then, a
Nd:YAG laser with a wavelength of 266 nm is sufficient to obtain
highly spatially resolved images.208
In regard to LIBS, green intrinsic characteristics can be iden-
tified in this technique, since in situ analysis and remote sensing
with no sample preparation are suitable. Fieldable laser-induced
breakdown spectrometers have been developed in recent years.
Fortes and Laserna209 have recently revised trends and applica-
tions with these instruments. Portable, remote and stand-off
spectrometers are considered. In general, portability requires
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compact lasers with portable power supply and miniaturized
spectrometers. Usually, Nd:YAG lasers are used due to size
requirements, reliability and ruggedness. A calibration procedure
without standard reference materials and based on the calcula-
tion of temperature and the electron density in the plasma
(calibration-free) can be used with portable LIBS.210 Spectral
libraries and different data processing algorithms can improve
the green characteristics of LIBS for field measurements. In
addition, automation of portable instruments is possible. A fully
automated portable LIBS instrument has been developed by
Palanco et al.211 When a fiber optic cable is used in a LIBS
system, stand-off (both the laser and the signal are transmitted
along an open path configuration) and remote (laser and/or the
signal are transmitted through a fiber optic cable) analyses of
samples for long distances can be made. It has allowed extending
LIBS application to areas contaminated by toxic or radioactive
materials without danger to the analyst. Very interesting infor-
mation about applications of these systems can be found in the
above-mentioned review.209
4.4. Glow discharge sources
Glow discharge sources with optical emission spectrometry
(OES) or mass spectrometry (MS) are considered powerful and
versatile for bulk, surface and interface analysis of different types
of materials.177 Nowadays, GDs have gained interest due to the
development of radio frequency (rf) sources, since it has allowed
extending its application to non-conductive samples such as
organic coatings, glasses, ceramics, etc. Although with very
similar performance in both depth resolution and sensitivity,
direct current (dc) sources continue to be used most frequently,
only conducting materials can be analyzed.212
In a Grimm-type GD, sputtering is used to generate atoms and
ions directly from the solid sample surface ‘layer by layer’. Low-
pressure plasmas are initiated by applying a high potential (kV)
between two electrodes, one of which is formed by the sample
(usually the cathode). Electrons and positive ions from a
discharge gas (e.g., Ar or mixtures of Ar with N2, O2, H2 or He)
are accelerated towards the cathode surface and when these have
sufficient energy, result in releasing the material (sputtering
process). This process depends strongly on the sample material
and its surface properties. On the contrary, atomization, exci-
tation and ionization processes (separated in space and time of
the sputtering process) are practically independent of the surface
sample.176 For this reason, little matrix effects have been
observed and quantification by MS or OES is usually simpler
than in other techniques for solid sampling.212 Without doubt,
this question can be considered interesting in order to achieve
greener procedures.
New developments in instrumentation have been decisive in
order to extend the application of this technique and improve
both its green and analytical characteristics. In particular, efforts
have been focused on the design of new GDs, but also on
improvements of vacuum technology and interface and on the
implementation of CCDs and ToF (time-of-flight) detectors for
OES and MS, respectively, in order to acquire spectra faster.177
For instance, pulsed rf/dc GDs have represented an important
advance in trace analysis since they allow separating elemental
and molecular excitations. This mode provides high
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instantaneous power, increasing the atomization, excitation, and
ionization processes without thermal sample degradation.
Numerous applications (e.g., polymers) are now possible with
these sources.171,213 Magnetically boosted GD sources that
incorporate a magnetic field to improve sputtering rates and
ionization/excitation efficiencies have been also proposed.213,214
Atmospheric sampling GDs with untreated atmospheric gases
were firstly introduced as an ionization source for organic
compounds, though it has been also used for metal determina-
tion.215 The miniaturization of GD sources has also been
considered, although it has been used so far for liquid and gas
samples. A small glow discharge electron source has been used
for miniaturized mass spectrometers.216 Low power require-
ments, mechanical ruggedness, and quality of the data produced
make these sources suitable with a portable handheld mass
spectrometer.
Solid sampling with GDs is not without problems. Non-flat
samples (e.g., screws and tubes) cannot directly be mounted on a
GD and special accessories are required. Porous samples (e.g.,
foams and certain ceramics) are also difficult to handle because
they are not vacuum tight since usually the sample seals the
source.212 Particulate solids can be analysed using rf-GD-OES.
For this, sol–gel thin films or glasses are synthesized by acid-
catalysed condensation. Slurries of powdered samples are
incorporated into the films and analysed for both main and trace
element components.217,218
GD-OES and GD-MS can be compared with other techniques
used for surface analysis, such as SIMS (secondary ion mass
spectrometry) and SEM (scanning electron microscopy with X-
ray analysis). GD-OES and GD-MS are considered cheaper,
faster and easier for quantification than SIMS, and faster and
with better depth resolution than SEM. For bulk analysis, GD-
OES can compete with spark/arc emission and with X-ray
techniques.3,212 Obviously, GD-OES and GD-MS have some
drawbacks such as limited lateral resolution and inability for
micro-spot analysis. Recently, the LA-GD combination has been
proposed for solid sampling. Laser ablates the sample and GD
ionizes the ablated aerosol.219,220
4.5. X-ray fluorescence spectrometry
X-ray fluorescence spectrometry (XRF) can be considered as a
quantitative and qualitative analytical tool that can fulfil GAC
principles. Different techniques are available: wavelength
dispersive X-ray fluorescence (WDXRF), energy dispersive X-
ray fluorescence (EDXRF), total reflection X-ray fluorescence
(TXRF) and micro-X-ray fluorescence (m-XRF). All offer fast
and non-destructive analysis using clean procedures that can
routinely be applied to solid samples. In general, analysis can be
carried out within a time in the range of 30–1000 s with a good
precision.221–224
In spite of this, it is not usual to consider XRF as a set of green
techniques due to risks that this energy involves. The X-ray beam
can be generated with a ceramic tube or from radionuclides.225,226
Radionuclides are more dangerous for the analyst because they
generate g rays, are always ‘‘switch on’’ and have shorter life-
times. Their use is subject to strict regulations and can only be
handled by authorized personnel.227 X-ray tubes are mostly used
in the analytical instrument since they are safe. In addition,
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miniature X-ray tubes have made possible the development of
portable instruments for in situ analysis. This can contribute to
change the negative perspective on these techniques from the
GAC standpoint.
Although X-ray instruments could potentially be dangerous,
current instruments pose few risks to users when used properly.
Themanufacture and use ofX-ray instruments is highly regulated.
In fact, the design of the instruments limits even accidental expo-
sure. Spectrometers have a lead shielded, closed design that avoids
the scattering of the X-ray beam. In addition, the surrounding of
the equipment should be frequently checked to ensure that there is
no scattering of the X-ray radiation and there is no potential risk
for the analyst by radiation exposure (the maximum permissible
whole-body dose from occupational exposure is 5 ‘Roentgen
Equivalent Man, REM’, per year. When portable equipments are
used, wearing heavy gloves is advisable.228
The main green advantage of XRF is without doubt its ability
for direct analysis of the sample without sample treatment or
with a little preparation such as grinding, cutting, etc. Bulk
materials can be layered with a thickness #0.5 mm by cutting,
sawing or shredding.229For samples such as metals or ceramics, it
is necessary to polish for creating a smooth and clean surface
when WDRXF is used. Grinding to grain sizes of lower than
75 mm is used to obtain a homogeneous powder. Then, for higher
density solids only a pressing step is necessary in most XRF
techniques. For low-density solids, the addition of a binding
agent is needed before pressing to obtain a stable and homoge-
neous pellet. Natural substances such as starch, wax or cellulose
can be used for this purpose being desirable for GAC in contrast
to others such as polyvinyl.230
These non-destructive techniques can be used directly even
with fresh samples. The fresh sample is homogenized and frozen
and then, a portion is pressed into a pellet and analysed. For
instance, the elemental content of the edible part of lobsters has
been established by EDXRF.231
When the sample available is very small, fusion is often used as
the sample treatment in EDXRF and WDXRF.232 Usually,
borate is used as the fusion reagent (above 1000 �C). Fusion melt
is a homogeneous glass with a defined matrix.
TXRF allows analysis of powdered samples without pressing
or forming pellets, only placing on a cleaned carrier, usually
quartz glass. Different strategies can be used with powdered
samples in this technique. For example, a cotton-wool tip has
been used for analysing inorganic pigments in oil paintings. For
sampling, the surface of oil paintings is wiped off by means of a
cotton-wool tip. A few micrograms of the cotton-wool tip are
sufficient for the analysis.233 Recently, the use of slurry sampling
has been proposed in TXRF. For example, biological samples224
using an ultrasonic probe for slurry homogenization have been
analysed. A 10 mL aliquot of the slurry is deposited onto the
quartz glass carrier.
m-XRF has been developed very rapidly in the last decade,
mainly due to its versatility. It uses rotatory X-ray tubes which
provide synchrotron radiation, resulting in a very sensitive
technique with limits of detection (LODs) at the ppt level.178 Not
only is the elemental composition of a sample easy to obtain, but
also the related spatial distribution without sample treatment.
Commercial portable equipments (e.g., ARTAX� equipment
from Bruker)234 are available. They allow in situ measurements
1848 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
within 30–60 s, and then, sampling and transport to the lab are
not necessary. Portable systems are mainly applied for arche-
ometry and restoration since they avoid contact and damage,
whatever the objects under investigation.235
TXRF can be applied to micro, trace, and surface analyses.
This technique can provide detection limits at the part per billion
level.236 Commercially available TXRF instruments (e.g., S2
Picofox� from Bruker)237 are considered semi-portable systems.
This technique does not need inert gases and/or a vacuum
system. Certain grade of automation can be reached using a
motorized sample changer.
EDXRF is widely used for the determination of major, minor
and trace elements (LODs at ppm level).180 An increased auto-
mation level as in TXRF is reached by using an automatic sample
changer. Commercial portable EDXRF instruments are air-
cooled systems and they can operate in vacuum or in air (e.g.,
Tracer� family from Bruker).238 This equipment has been mainly
designed for in situ measurements in art, archeometry, geological
research, environment and also for specific industrial applications,
i.e., sorting scrap, alloy analysis and sorting for alloy verification.
The use of this portable equipment can have some drawbacks since
instruments are less robust and quantitative analysis can be trou-
blesome. Forster et al.239 pointed out that surface morphology,
surface coatings and grain size of materials can cause attenuation
of incident and fluorescent X-rays, yet appropriate mathematical
corrections can provide a high level of accuracy and precision.
Qualitative analysis with portable systems has been applied for a
more efficient sampling, i.e., soil sampling,222 in order to perform a
fast general screening of the soil composition and detect the points
of contamination. It allows selecting representative points, thereby
saving time in the sampling stage.
WDXRF is mainly applied for direct solid analysis (soils,
metals, ceramics, etc.) in routine labs. WDXRF analysis splits
the characteristic wavelengths with a high resolution, which is
especially relevant for light elements (LODs at the ppm level).180
It is faster than EDXRF and TXRF (i.e., 100 s vs. 500 s). In
contrast to mXRF and EDXRF, portable systems for WDXRF
are not available. So in WDXRF analysis, sampling and trans-
port of the sample to the lab are needed. In general, sample
consumption is higher compared to other X-ray techniques, i.e.,
only a few micrograms of sample are necessary in TXRF and
EDXRF vs. 0.1–5.0 g in WDXRF.221,240–242 The analysis is
usually carried out under vacuum, and for the analysis of loose
powders, an inert atmosphere (He or N2) is needed to prevent air
from absorbing the fluorescence X-rays. As in TXRF and
EDXRF, the use of an automatic sample changer is possible.
5. Greening instrumentation for atomic spectrometry
Nowadays, remarkable greenness in atomic spectrometry has
been reached through miniaturization, automation and design of
cost-effective systems, which allow lower consumption of gases
(e.g., fuel, plasmogen, carrier), samples and reagents, and/or
simplified sample pre-treatment. Improvements made in instru-
mentation for atomic spectrometry (including inorganic mass
spectrometry) from the early prototypes to the modern instru-
ments have also contributed to reach higher levels of greenness.
As an example, implementation of efficient background correc-
tion systems in the early atomic absorption spectrometers made
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it possible to carry out many applications with a significant
saving in operations such as matrix elimination by typical
procedures, which in turn, brought about a decrease in errors.243
More recently, the development of efficient collision and reaction
cells for elimination of some interferences caused by polyatomic
ions has simplified the application of quadrupolar ICP-MS to
complex matrices.244
Undoubtedly, major developments made in most atomic
spectrometric techniques have run in parallel with improvements
of green features. For instance, automation provided by modern
autosamplers in techniques such as ETAAS, allowing intelligent
dilution, injection of sample, diluents and matrix modifiers at
any sequence, performing calibration curve from one single
standard, recalibration, etc. has dramatically changed method
development with this technique, hence saving time, efforts and
decreasing errors.
A component that is commonly used for sample introduction in
atomic spectrometry is the pneumatic nebulizer. Development of
miniaturized nebulizers that allow minimum consumption of
sample is one of the goals of GAC. In contrast to conventional
nebulizers,micronebulizers allow the generationof a stable aerosol
at liquid flow-rates on the order of several microliters per
minute.245 Additional advantages of micronebulizers are the very
low dead volumes and lesser memory effects. Micronebulizers
originate finer primary aerosols, higher solution transport rates
and higher sensitivity as compared to conventional pneumatic
nebulizers, yet some prototypes are prone to blocking.246 The
suitability of several micronebulizers for analysis of microsamples
has been shown for techniques suchas ICP-OES247andICP-MS.248
The design of efficient sample introduction systems such as
those based on thermospray interfaces has allowed an improve-
ment in LODs apart from decreasing the sample consumption. In
the thermospray technique, the liquid is pumped through a
capillary and heated uniformly along a length of a few cm. The
heating causes the liquid to partially vaporize, giving rise to a
blast of vapour that converts the remaining liquid to droplets.
This interface has been used in conjunction with several tech-
niques such as ICP-OES, ICP-MS, FAAS and ETAAS.249 As a
result of the increased sensitivity achieved with the thermospray
technique, this interface can also benefit the coupling between
HPLC and atomic spectrometry for speciation studies.250
Greening atomizers for atomic spectrometry is another area of
research. Efforts have been made in decreasing the power and gas
consumption as well as the size of atomizers in order to approach
the concept of ‘portable instrument’.
With the arrival of plasma techniques (i.e., ICP-OES, ICP-
MS), multielement analysis at a trace level has been facilitated.
However, the high operating cost represented by the Ar
consumption can limit their application in smaller labs. Thus,
conventional ICP torches have been modified so that the Ar and
power consumption can be reduced. One way to reduce Ar
consumption is the design of minitorches.251 Nevertheless, those
systems are somewhat more prone to interferences in comparison
with conventional torches.
Microplasmas for atomic emission have been described, e.g.,
high-frequency plasmas, dc-discharges, MW plasmas.252
However, the heat capacity of these systems is limited and sample
introduction in the vapour phase instead of liquid phase is
mandatory. In this way, typical derivatization techniques such as
This journal is ª The Royal Society of Chemistry 2012
hydride generation are useful. These approaches are not free from
drawbacks due to the unstabilizing effect caused by the excess
hydrogen generated during chemical hydride generation. Alter-
native HG procedures such as those based on electrochemical
hydride generation or UV reduction are promising.253,254 Other
strategies for spreading the applicability ofmicroplasmas are their
use as detectors in gas chromatography255 or the generation of dry
vapours using electrothermal vaporization.256
Miniaturized flames have been also developed for atomization
of volatile compounds.Thus,miniaturized diffusionflames suchas
Ar/H2 have found application for AFS after HG.257These systems
offer low consumption of gases, low background emission and
lesser interferences as compared with other atomizers.258 Multi-
atomizers configured inside a quartz tube allow achieving
improved sensitivity as comparedwith diffusion flames apart from
enhanced linearity and resistance against interferences in
comparison with quartz tubes.259 The multiatomizer is similar to
conventional quartz tube atomizers, but it is punctured over the
horizontal arm so that air can be dosed through the orifices to the
optical inner volume. In thisway,multiplemicroflames arise inside
the tube as a result of themultiple hydrogen radical clouds formed.
Efficient atomic fluorescence detectors have been marketed
using the hydrogen generated in the reaction with sodium tet-
rahydroborate to feed a miniaturized diffusion flame of Ar/H2
with application in total trace analysis (Hg, As, Se, Te, Sb, Bi)
and as specific detectors for speciation when interfaced with
liquid or gas chromatography.260
Miniaturization has also spread to hyphenated techniques for
speciation in biological systems. Thus, for metallome analysis in
small amounts of tissues and cells, new tools based on minia-
turized HPLC techniques (e.g., narrow bore, capillary and nano-
HPLC) coupled to ICP-MS have been developed, which are
expected to clarify the physiological and biological roles of
metalloproteins.261 The coupling between capillary and, espe-
cially, nano-flow HPLC with ICP-MS demands for the devel-
opment of suitable interfaces so that the sample uptake is
compatible with the mobile phase flow-rate. For this, micro-
nebulizers discussed above are required.262
Other green couplings between HPLC and ICP-MS for
speciation of hydride forming elements are based on on-line UV/
TiO2 photocatalysis, thus eliminating conventional hydride
generation with the NaBH4–NaOH system.263
An interesting technique avoiding time-consuming procedures
for preconcentration is the use of ‘in-atomizer’ trapping. This
approach has been tried in different ways.
First systems were based on trapping in a graphite tube for
electrothermal atomization.264 Apart from improving sensitivity,
in situ trapping eliminates the effect of kinetic interferences inHG.
Moreover, these systems can be easily automated. More recently,
trapping onto quartz surfaces in an excess oxygen and further
atomization in multiatomizers or conventional quartz tubes have
also been proposed to achieve very low detection limits.258 Trap-
ping of volatile hydrides has also been performed in miniature
electrothermal devices, e.g., tungsten coil265 and bare and modi-
fied strips with noble metals (Pt, Ir, Rh).266 W-coil devices can be
used as atomizers for ETAAS, electrothermal atomizer laser-
excited atomic fluorescence spectrometry (ETA-LEAFS) and
ETV-ICP-OES, being ideal for the design of low-cost, compact
and portable instrumentation for field environmental and clinical
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Fig. 6 Examples of miniaturized and low consumption atomizers for atomic absorption spectrometry (Ref. 250, 255, 265, 267 and 268).
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analysis.267 W-coil atomizers along with a simple CCD-based
spectrometer make the development of AAS instrumentation for
field analysis possible. A few representative examples of minia-
turized atomizers for AAS are shown in Fig. 6.
The recent implementation of fast multielemental sequential
analysis in AAS through novel instrumentation based on
continuous radiation sources (Xe-arc lamp), echelle mono-
chromators and CCD detectors can be considered a step forward
in the achievement of greener AAS methods.269 The observation
of the analytical line at high resolution facilitates method
development and helps avoiding spectral interferences.
As indicated above, most successful achievements so far
toward the achievement of portable instruments have been
reported in the miniaturization of techniques such as XRF and
LIBS. These techniques are essentially non-destructive, fast and
they provide instantaneous multi-element analysis.2
6. Chemometrics for greening atomic spectrometrymethods
Can chemometrics be a tool for greening atomic spectrometry
methods? According to Namie�snik,270 the reduction of labour-
intensive procedures, energy and reagent consumption is essential
for the implementation of GAC principles. Automation and
robotization, multianalyte determination in a single analytical
cycle and wider utilization of hyphenated techniques are consid-
ered by this author as the main ways for greening the analytical
laboratory. There is no doubt that chemometrics is of paramount
importance to achieve the aforementioned developments, hence
being an indirect way of saving time, labour, energy and reagents.
In general, chemometrics helps extracting information with a
smaller number of experiments and preventing errors in an
1850 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
environmentally friendlyway. In spite of this, chemometrics is not
usually considered from the point of view of GAC.
In this regard, Armenta et al.4 as well as Koel and Kaljurand2
recognize the importance of chemometrics in the development of
solvent free methodologies based on direct measurements
without sample pre-treatment. Particularly, this conception has
been focused on molecular spectroscopy techniques that involve
large amounts of spectral data, such as UV-vis spectrometry,
fluorescence, near infrared (NIR), mid-infrared (MIR) and
nuclear magnetic resonance (NMR). Some examples taken into
consideration by these authors are the use of calibration by
partial least squares (PLS) in NIR,MIR or Raman spectroscopy,
thereby enhancing the application of these techniques in the
analytical lab on a routine basis4 or the use of parallel factor
analysis (PARAFAC) in the resolution of mixtures using exci-
tation–emission spectroscopy (EEM).2
Chemometrics (including exploring data, optimization, cali-
bration, signal processing, pattern recognition and artificial
intelligence) can be considered also as an interesting tool for
greening atomic spectrometry methods. As mentioned above,
chemometrics become particularly significant to reduce the
number of measurements or to obtain much simpler and efficient
analytical procedures with atomic spectrometry techniques.
To a greater or lesser extent, chemometrics is involved in all
steps of analytical methods, from development and validation up
to data evaluation. For instance, principal component analysis
(PCA) and a multi-criteria target function have been used in ICP-
MS for 83 isotopes and 21 operating parameters.271 Chemo-
metrics has been also used to evaluate the combined uncertainty
for mercury speciation by GC-AFS in the validation step.272
Multivariate techniques for pattern recognition are being
increasingly applied to trace metals data in order to discriminate
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between samples. In general, well-established chemometric tools
are used, e.g., PCA, cluster analysis (CA), linear discriminant
analysis (LDA), soft independent modelling of class analogy
(SIMCA) or artificial neural networks (ANNs). Practically, we
can find applications in all fields of interest such as clinical273 and
environmental,274 but in particular in food science for estab-
lishing geographical origins, e.g., honeys,275 onions,276 alcoholic
beverages,277 coffee,278 mussels,279 etc.
Though optimization is fundamental in the development of
analytical methods, the most usual approach for this purpose in
atomic spectrometry continues to be the non-systematic way,
based on the subjective experience of the analytical chemist (trial-
and-error approach). If this experience is less, the workload in
the laboratory is large and, in addition, optimization is not
guaranteed.280 In most cases, optimization is carried out using a
univariate strategy. It implies a large number of experiments,
which increase the consumption of reagents and are labour-
intensive. In order to overcome these disadvantages, multivariate
optimization is a more desirable option from the point of view of
GAC. Different strategies have been used in atomic spectrom-
etry, in particular experimental design and response surface
methods.281 In those methods, different variables are simulta-
neously and systematically studied. In addition, they provide
more information about variables (e.g., interaction between
them) with fewer experiments, which is especially important for
optimizing sample preparation stages, e.g. microwave-assisted
digestion,282 preconcentration using different sorbents,283,284 etc.
Optimization of measurement conditions in different atomic
spectrometric techniques is also carried out with multivariate
strategies, e.g., application of the experimental design for opti-
mization of lead determination by high-resolution continuum
source hydride generation atomic absorption spectrometry.285
Experimental design for method optimization using spectro-
metric techniques has been reviewed by Bianchi and Careri.286
Hibbert and Armstrong287 have reviewed the applications of
Bayesian methods, including spectroscopy and mass spectrom-
etry. The use of response surface methodology for optimization
in analytical chemistry has been reviewed by Bezerra et al.288
Multivariate calibration methods represent a useful strategy to
fight analyte interferences, so these can be considered as impor-
tant tools from the standpoint of GAC. A tutorial review on
multivariate calibration in atomic spectrometry techniques has
been published by Andrade et al.289 These authors include among
the advantages of multivariate calibration ‘lower workloads,
increased laboratory turnarounds, economy, higher efficiency in
method development, and relatively simple ways to take account
of complex interferences’, all of which are directly related to
GAC. Application of multiple ordinary least squares regression
(MOLSR), principal components regression (PCR), PLS and
ANN on FAAS, HG-AAS, ETAAS, ICP-OES and LIBS are
presented in a practice-oriented way. These multivariate cali-
bration methods may be applied to monoelemental techniques
considering the transient signals (absorbance vs. time) as a
spectrum (absorbance at multiple wavelengths).
On the other hand, signal processing can be considered as a
simple way for improving instrumental performances without
hardware component changes and/or replacement by expensive
systems.290 Signal processing is used to enhance signal vs. noise,
to improve peak resolution, to decompose complex signals, etc.
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Undoubtedly, it allows extracting more information from
analytical data with a lower number of experiments. For
example, chemical interference correction, including separation,
can be replaced or minimized by chemometric interference
correction. Mathematical algorithms for background modelling
and correction have been designed and applied to different
atomic techniques in order to improve their analytical charac-
teristics.291–296 At present, signal processing is an active field
especially when transient signals are obtained. For instance,
Chaves et al.297 proposed the processing of fast transient signals
provided by different sample introduction systems (FI, LA, GC,
HPLC) with modern simultaneous ICP-OES instruments. Pri-
kler et al.298 compared different strategies as convolution with
Gaussian distribution curves, Fourier transform, and wavelet
transform for improving the detection power in HPLC-ICP-MS.
A total signal integration method has been proposed as an
alternative to quantify transient signals with LA and ICP-MS.299
In general, application of artificial intelligence (AI), especially
expert systems (ES), intelligent analysers and robot systems,
constitutes an efficient way so as to turn the analytical lab green,
since lab efficiency is increased and the occupational exposure of
the personnel and reagent consumption are decreased.280,300 An
intelligentized analytical lab results in a more cost-effective use of
staff and resources. AI can be used from the selection and opti-
mization of an analytical method up to the final report, including
detection of malfunctions and validation. During the 90s, a large
number of ESs were developed for different atomic spectrometry
applications. ESs are programs with a heuristic knowledge based
on the experience of experts. ESs have been included in FAAS
spectrometers for full automation (in particular for error detec-
tion and correction).301 In ICP-OES, ESs are used for prediction
and correction of spectral interferences,302,303 spectral line simu-
lation and selection,304,305 system diagnosis306 or as a hybrid
expert-database system for sample preparation by microwave-
assisted dissolution.307,308 ES has been also used in ICP-MS for
controlling the spectrometer,309,310 the whole sample pre-treat-
ment process311 and developing a simple diagnostic procedure to
automatically ensure the quality of results.312 In XRF, it has been
applied for the evaluation of different possibilities in the reso-
lution of a given analytical problem.313,314 Intelligent analysers
have also been designed with different atomic spectometers,315–317
i.e., an intelligent flow system has been proposed for the on-line
speciation of metal ions at a wide range of concentrations
without requiring manifold reconfiguration.316
7. Conclusions
A remarkable greenness can be achieved when GAC principles
are applied to Atomic Spectrometry. For this, every stage of the
analytical process should be focused. Advances in instrumenta-
tion, sample preparation techniques, chemometric treatment of
data, etc. can drive significant improvements not only in
analytical characteristics but also in green issues of the whole
methodology. Labs involved in trace metal analysis can benefit
from the concepts of green chemistry, since apart from advan-
tages inherent to the implementation of automated, simplified,
accelerated and miniaturized systems, there is also a great
conservation of reagents, solvents and energy, less risks to the
analyst, and less production of wastes. More progress is expected
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over the next years concerning this topic with the downsizing of
instruments, implementation of new materials (e.g., nano-
materials) and development of analytical devices for on-site
determination.
List of abbreviations
AAS
1852 | J. Anal. At.
Atomic absorption spectrometry
AFS
Atomic fluorescence spectrometryAI
Artificial intelligenceANNs
Artificial neural networksAOPs
Advanced oxidation processesASE
Accelerated solvent extractionBI
Bead-injectionCA
Cluster analysisCCD
Charge-coupled devicesCPE
Cloud point extractionCV
Cold vapourCVG
Chemical vapour generationDBD
Dielectric barrier dischargedc
Direct currentDSI
Direct solid insertionEC-HG
Electrochemical hydride generationEDXRF
Energy dispersive X-ray fluorescenceEEM
Excitation-emission spectroscopyES
Expert systemsETAAS
Electrothermal atomic absorptionspectrometry
ETA-LEAFS
Electrothermal atomizer laser-excited atomicfluorescence spectrometry
ETV
Electrothermal vaporizationFAAS
Flame atomic absorption spectrometryFI
Flow injectionFIA
Flow injection analysisFMAE
Focused microwave-assisted extractionGAC
Green analytical chemistryGC
Gas chromatographyGD
Glow dischargeGSK
GlaxoSmithKlineHEPO
High-efficiency photooxidationHF
Hollow fiberHG
Hydride generationHIFU
High-intensity focused ultrasoundHPLC
High performance liquid chromatographyHS
HeadspaceICP-MS
Inductively coupled plasma-massspectrometry
ICP-OES
Inductively coupled plasma-optical emissionspectrometry
IL
Ionic liquidLA
Laser ablationLAM
Laser ablation microprobeLC
Liquid chromatographyLDA
Linear discriminant analysisLIBS
Laser induced breakdown spectroscopyLLE
Liquid–liquid extractionLOC
Lab-on-a-chipLODs
Limits of detectionSpectrom., 2012, 27, 1831–1857
LOV
This
Lab-on-valve
LPME
Liquid-phase microextractionMAD
Microwave-assisted digestionMAE
Microwave-assisted extractionMCFIA
Multicommutated flow injection analysism-FIA
Micro-flow injection analysism-TAS
Micro-total analytical systemm-XRF
Micro-X-ray fluorescenceMIR
Mid-infraredMOLSR
Multiple ordinary least squares regressionMPFS
Multipumping flow systemMS
Mass spectrometryMSFIA
Multisyringe flow injection analysisMSPME
Magnetic nanoparticle solid phasemicroextraction
MW
MicrowaveNd:YAG
Neodymium:yttrium aluminium garnetNEMI
National environment methods indexNIR
Near infraredNmimCl
1-Chlorovinyl-3-methylimidazolium chlorideNMR
Nuclear magnetic resonanceOES
Optical emission spectrometryPARAFAC
Parallel factor analysisPCA
Principal component analysisPCR
Principal components regressionPLE
Pressurized liquid extractionPLS
Partial least squaresPMAE
Pressurized microwave-assisted extractionPMI
Positive material identificationPTFE
PolytetrafluoroethylenePVC
Polyvinyl chlorideQFAAS
Quartz furnace atomic absorptionspectrometry
REM
Roentgen Equivalent Manrf
Radio frequencySBSE
Stir bar sorptive extractionSDS
Sodium dodecyl sulphateSEM
Scanning electron microscopySFE
Supercritical fluid extractionSIA
Sequential injection analysisSIMCA
Soft independent modelling of class analogySIMS
Secondary ion mass spectrometrySLM
Supported liquid membraneSN
Slurry nebulizationSPE
Solid-phase extractionSPME
Solid-phase microextractionSS
Slurry samplingSSEA
Separate sampling and excitation accessoryToF
Time-of-flightTRS
Time-resolved spectroscopyTXRF
Total reflection X-ray fluorescenceUAE
Ultrasound-assisted extractionUS
UltrasoundUSAED
Ultrasound-assisted enzymatic digestionUSS
Ultrasonic slurry samplingVUV
Vacuum ultravioletWDXRF
Wavelength dispersive X-ray fluorescenceXRF
X-ray fluorescencejournal is ª The Royal Society of Chemistry 2012
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Acknowledgements
Financial support from the Spanish Ministry of Economy and
Competitiveness (Project CTQ2009-06956/BQU), the Xunta de
Galicia (project 10PXIB 314030 PR) and the Vigo University
(Contract for Reference Research Groups 09VIA08) is gratefully
acknowledged. The Spanish Ministry of Education, Culture and
Sport is acknowledged for financial support through a FPU pre-
doctoral grant to Vanesa Romero. The Portuguese Foundation
for Science andTechnology is acknowledged for financial support
through a Post-Doctoral grant to Francisco Pena-Pereira.
References
1 P. T. Anastas and J. C. Warner, Green Chemistry: Theory andPractice, Oxford University Press, New York, 1998.
2 M. Koel and M. Kaljurand, Green Analytical Chemistry, RoyalSociety of Chemistry, Cambridge, 2010.
3 M. de la Guardia and S. Garriges, Challenges in Green AnalyticalChemistry, Royal Society of Chemistry, Cambridge, 2011.
4 S. Armenta, S. Garrigues and M. de la Guardia, TrAC, Trends Anal.Chem., 2008, 27, 497–511.
5 M. Tobiszewski, A. Mechli�nska, B. Zygmunt and J. Namie�snik,TrAC, Trends Anal. Chem., 2009, 28, 943–951.
6 M. Tobiszewski, A. Mechlinska and J. Namie�snik, Chem. Soc. Rev.,2010, 39, 2869–2878.
7 M. de la Guardia, TrAC, Trends Anal. Chem., 2010, 29, 577.8 C. J. Welch, M. Biba, R. Hartman, T. Brkovic, X. Gong, R. Helmy,W. Schafer, J. Cuff, Z. Pirzada and L. Zhou, TrAC, Trends Anal.Chem., 2010, 29, 667–680.
9 F. Pena-Pereira, I. Lavilla and C. Bendicho, TrAC, Trends Anal.Chem., 2010, 29, 617–628.
10 S. Garrigues, S. Armenta and M. de la Guardia, TrAC, Trends Anal.Chem., 2010, 29, 592–601.
11 C. Bendicho, F. Pena, M. Costas, S. Gil and I. Lavilla, TrAC, TrendsAnal. Chem., 2010, 29, 681–691.
12 A. Molina-Diaz, J. F. Garc�ıa-Reyes and B. Gilbert-L�opez, TrAC,Trends Anal. Chem., 2010, 29, 654–666.
13 M. Farr�e, S. P�erez, C. Goncalves, M. F. Alpendurada andD. Barcel�o, TrAC, Trends Anal. Chem., 2010, 29, 1347–1362.
14 M. Tobiszewski and J. Namie�snik, TrAC, Trends Anal. Chem., 2012,25, 67–73.
15 C. Bendicho, I. de La Calle, F. Pena, N. Cabaleiro and I. Lavilla,TrAC, Trends Anal. Chem., 2012, 31, 50–60.
16 http://www.nemi.gov, last accessed, June 2012.17 A. Galuszka, P. Konieczka, Z. M. Migaszewski and J. Namie�snik,
TrAC, Trends Anal. Chem., 2012, 37, 61–72.18 V. Camel, Spectrochim. Acta, Part B, 2003, 58, 1177–1233.19 C. Bendicho, I. Lavilla, F. Pena and M. Costas, in Challenges in
Green Analytical Chemistry, ed. M. de la Guardia and S.Garrigues, Royal Society of chemistry, Cambridge, 2011, pp. 63–99.
20 V. A. Lemos, L. S. G. Teixeira, M. A. Bezerra, A. C. S. Costa,J. T. Castro, L. A. M. Cardoso, D. S. de Jesus, E. S. Santos,P. X. Baliza and L. N. Santos, Appl. Spectrosc. Rev., 2008, 43,303–334.
21 M. L. Chen, Y. N. Zhao, D. W. Zhang, Y. Tian and J. H. Wang, J.Anal. At. Spectrom., 2010, 25, 1688–1694.
22 Y. Tian, Z. M. Xie, M. L. Chen and J. H. Wang, J. Anal. At.Spectrom., 2011, 26, 1408–1413.
23 Z. Mester, R. Sturgeon and J. Pawliszyn, Spectrochim. Acta, Part B,2001, 56, 233–260.
24 Z. Mester and R. Sturgeon, Spectrochim. Acta, Part B, 2005, 60,1243–1269.
25 S. Risticevic, V. H. Niri, D. Vuckovic and J. Pawliszyn, Anal.Bioanal. Chem., 2009, 393, 781–785.
26 F. Pena-Pereira, I. Lavilla and C. Bendicho, Spectrochim. Acta, PartB, 2009, 64, 1–15.
27 S. Dadfarnia and A. M. Haji Shabani, Anal. Chim. Acta, 2010, 658,107–119.
28 F. Pena-Pereira, I. Lavilla and C. Bendicho, Anal. Chim. Acta, 2010,669, 1–16.
This journal is ª The Royal Society of Chemistry 2012
29 E. Baltussen, P. Sandra, F. David and C. Cramers, J. MicrocolumnSep., 1999, 11, 737–747.
30 F. David and P. Sandra, J. Chromatogr., A, 2007, 1152, 54–69.31 A. Prieto, O. Basauri, R. Rodil, A. Usobiaga, L. A. Fern�andez,
N. Etxebarr�ıa and O. Zuloaga, J. Chromatogr., A, 2010, 1217,2642–2666.
32 J. Vercauteren, C. P�er�es, C. Devos, P. Sandra, F. Vanhaecke andL. Moens, Anal. Chem., 2001, 73, 1509–1514.
33 J. Millos, M. Costas-Rodr�ıguez, I. Lavilla and C. Bendicho, Anal.Chim. Acta, 2008, 622, 77–84.
34 J. Pacheco-Arjona, P. Rodriguez-Gonzalez, M. Valiente, D. Barclayand O. F. X. Donard, Int. J. Environ. Anal. Chem., 2008, 88, 923–932.
35 I. de la Calle, N. Cabaleiro, I. Lavilla and C. Bendicho, Spectrochim.Acta, Part B, 2009, 64, 874–883.
36 J. L. G�omez-Ariza, V. Bernal-Daza and M. J. Villegas-Portero,Anal. Chim. Acta, 2004, 520, 229–235.
37 A. Moreda-Pi~neiro, J. Moreda-Pi~neiro, P. Herbello-Hermelo,P. Bermejo-Barrera, S. Muniategui-Lorenzo, P. L�opez-Mah�ıa andD. Prada-Rodr�ıguez, J. Chromatogr., A, 2011, 1218, 6970–6980.
38 M. Costas, I. Lavilla, S. Gil, F. Pena, I. de la Calle, N. Cabaleiro andC. Bendicho, Anal. Chim. Acta, 2010, 679, 49–55.
39 M. Zougagh, M. Valc�arcel and A. R�ıos, TrAC, Trends Anal. Chem.,2004, 23, 399–405.
40 M. D. Luque de Castro and M. T. Tena, TrAC, Trends Anal. Chem.,1996, 15, 32–37.
41 J. Kronholm, K. Hartonen andM. L. Riekkola, TrAC, Trends Anal.Chem., 2007, 26, 396–412.
42 V. Camel, Analyst, 2001, 126, 1182–1193.43 L. H. Keith, L. U. Gron and J. L. Young, Chem. Rev., 2007, 107,
2695–2708.44 L. Chimuka and R. Majors, LC$GC Eur., 2004, 17, 396–401.45 J. A. L�opez-L�opez, C. Mendiguch�ıa, J. J. Pinto and C. Moreno,
TrAC, Trends Anal. Chem., 2010, 29, 645–653.46 K. Chakrabarty, P. Saha and A. K. Ghoshal, J. Membr. Sci., 2010,
350, 395–401.47 J. F. Peng, R. Liu, J. F. Liu, B. He, X. L. Hu and G. B. Jiang,
Spectrochim. Acta, Part B, 2007, 62, 499–503.48 L. Xia, Y. Wu and B. Hu, J. Mass Spectrom., 2007, 42, 803–810.49 C. Bosch Ojeda and F. S�anchez Rojas, Anal. Bioanal. Chem., 2009,
394, 759–782.50 C. Ortega, M. R. Gomez, R. A. Olsina, M. F. Silva and
L. D. Martinez, J. Anal. At. Spectrom., 2002, 17, 530–533.51 Y. Yamini, M. Faraji, S. Shariati, R. Hassani and M. Ghambarian,
Anal. Chim. Acta, 2008, 612, 144–151.52 K. Simitchiev, V. Stefanova, V. Kmetov, G. Andreev, N. Kovachev
and A. Canals, J. Anal. At. Spectrom., 2008, 23, 717–726.53 N. N. Meeravali and S. J. Jiang, J. Anal. At. Spectrom., 2008, 23,
1365–1371.54 M. Faraji, Y. Yamini and M. Rezaee, Talanta, 2010, 81, 831–836.55 A. E. Karatapanis, Y. Fiamegos and C. D. Stalikas, Talanta, 2011,
84, 834–839.56 R. Q. Auc�elio, R. M. de Souza, R. C. de Campos, N. Miekeley and
C. L. P. da Silveira, Spectrochim. Acta, Part B, 2007, 62, 952–961.57 I. Lavilla, N. Cabaleiro, M. Costas, I. de la Calle and C. Bendicho,
Talanta, 2009, 80, 109–116.58 P. R. Aranda, P. H. Pacheco, R. A. Olsina, L. D. Martinez and
R. A. Gil, J. Anal. At. Spectrom., 2009, 24, 1441–1445.59 R. J. Cassella, D. M. Brum, C. E. R. de Paula and C. F. Lima, J.
Anal. At. Spectrom., 2010, 25, 1704–1711.60 P. Tundo, P. Anastas, D. StC. Black, J. Breen, T. Collins, S. Memoli,
J. Miyamoto, M. Polyakoff and W. Tumas, Pure Appl. Chem., 2000,72, 1207–1228.
61 E. M. Martinis, P. Berton, R. P. Monasterio and R. G. Wuilloud,TrAC, Trends Anal. Chem., 2010, 29, 1184–1201.
62 S. Jafarvand and F. Shemirani, Microchim. Acta, 2011, 173, 353–359.
63 C. Erkey, J. Supercrit. Fluids, 2000, 17, 259–287.64 L. Xia, B. Hu, Z. Jiang, Y. Wu and Y. Liang, Anal. Chem., 2004, 76,
2910–2915.65 X. Jia, Y. Han, X. Liu, T. Duan and H. Chen, Spectrochim. Acta,
Part B, 2011, 66, 88–92.66 P. T. Anastas, in Clean Solvents: Alternative Media for Chemical
Reactions and Processing, ed. M.A. Abraham and L. Moens,American Chemical Society, Washington, DC, 2002, pp. 1–9.
J. Anal. At. Spectrom., 2012, 27, 1831–1857 | 1853
Publ
ishe
d on
04
Sept
embe
r 20
12. D
ownl
oade
d on
18/
06/2
015
14:2
9:54
. View Article Online
67 P. G. Jessop, Green Chem., 2011, 13, 1391–1398.68 R. K. Henderson, C. Jim�enez-Gonz�alez, D. J. C. Constable,
S. R. Alston, G. G. A. Inglis, G. Fisher, J. Sherwood, S. P. Binksand A. D. Curzons, Green Chem., 2011, 13, 854–862.
69 K. Alfonsi, J. Colberg, P. J. Dunn, T. Fevig, S. Jennings,T. A. Johnson, H. P. Kleine, C. Knight, M. A. Nagy, D. A. Perryand M. Stefaniak, Green Chem., 2008, 10, 31–36.
70 http://www.rsc.org/suppdata/gc/c0/c0gc00918k/c0gc00918k.pdf, lastaccessed June 2012.
71 P. Cava-Montesinos, E. R�odenas-Torralba, A. Morales-Rubio,M. L. Cervera and M. de la Guardia, Anal. Chim. Acta, 2004, 506,145–153.
72 E. R�odenas-Torralba, P. Cava-Montesinos, A. Morales-Rubio,M. L. Cervera and M. de la Guardia, Anal. Bioanal. Chem., 2004,379, 83–89.
73 R. B. R. Mesquita and A. O. S. S. Rangel, Anal. Chim. Acta, 2009,648, 7–22.
74 Y. L. Yu, Z. Du, M. L. Chen and J. H. Wang, J. Anal. At. Spectrom.,2007, 22, 800–806.
75 Y. L. Yu, Y. Jiang, M. L. Chen and J. H. Wang, TrAC, Trends Anal.Chem., 2011, 30, 1649–1658.
76 L. Xia, X. Li, Y. Wu, B. Hu and R. Chen, Spectrochim. Acta, Part B,2008, 63, 1290–1296.
77 Y. Li, C. Zheng, Q. Ma, L. Wu, C. Hu and X. Hou, J. Anal. At.Spectrom., 2006, 21, 82–85.
78 S. Z. Mohammadi, D. Afzali and Y. M. Baghelani, Anal. Chim.Acta, 2009, 653, 173–177.
79 H. Sereshti, V. Khojeh, M. Karimi and S. Samadi, Anal. Methods,2012, 4, 236–241.
80 S. Z. Mohammadi, D. Afzali, M. A. Taher and Y. M. Baghelani,Talanta, 2009, 80, 875–879.
81 K. Grudpan, S. K. Hartwell, S. Lapanantnoppakhuna andI. McKelvie, Anal. Methods, 2010, 2, 1651–1661.
82 M. Tuzen, O. D. Uluozlu and M. Soylak, J. Hazard. Mater., 2007,144, 549–555.
83 M. Tuzen, O. D. Uluozlu, I. Karaman and M. Soylak, J. Hazard.Mater., 2009, 169, 345–350.
84 C. Zhang, Y. Li, X. Y. Cui, Y. Jiang and X. P. Yan, J. Anal. At.Spectrom., 2008, 23, 1372–1377.
85 C. Zeng, N. Zhou and J. Luo, J. Anal. At. Spectrom., 2012, 27, 120–125.86 P. Wu, L. He, C. Zheng, X. Hou and R. E. Sturgeon, J. Anal. At.
Spectrom., 2010, 25, 1217–1246.87 X. Guo, R. E. Sturgeon, Z. Mester and G. J. Gardner, Anal. Chem.,
2003, 75, 2092–2099.88 C. Zheng, Y. Li, Y. He, Q. Ma and X. Hou, J. Anal. At. Spectrom.,
2005, 20, 746–750.89 Y. He, X. Hou, C. Zheng and R. E. Sturgeon, Anal. Bioanal. Chem.,
2007, 388, 769–774.90 M. A. Vieira, A. S. Ribeiro, A. J. Curtius and R. E. Sturgeon, Anal.
Bioanal. Chem., 2007, 388, 837–847.91 C. Zheng, R. E. Sturgeon and X. Hou, J. Anal. At. Spectrom., 2009,
24, 1452–1458.92 C. Han, C. Zheng, J. Wang, G. Cheng, Y. Lv and X. Hou, Anal.
Bioanal. Chem., 2007, 388, 825–830.93 S. Gil, I. Lavilla and C. Bendicho, Anal. Chem., 2006, 78, 6260–6264.94 S. Gil, I. Lavilla and C. Bendicho, Spectrochim. Acta, Part B, 2007,
62, 69–75.95 A. S. Ribeiro, M. A. Vieira, S. Willie and R. E. Sturgeon, Anal.
Bioanal. Chem., 2007, 388, 849–857.96 S. Gil, I. Lavilla and C. Bendicho, J. Anal. At. Spectrom., 2007, 22,
569–572.97 F. Laborda, E. Bolea and J. R. Castillo, Anal. Bioanal. Chem., 2007,
388, 743–751.98 X. Wu, W. Yang, M. Liu, X. Hou and C. Zheng, J. Anal. At.
Spectrom., 2011, 26, 1204–1209.99 Q. Wu, Z. Zhu, Z. Liu, H. Zheng, S. Hu and L. Li, J. Anal. At.
Spectrom., 2012, 27, 496–500.100 J. L. Capelo-Mart�ınez, P. Xim�enez-Emb�un, Y. Madrid and
C. C�amara, TrAC, Trends Anal. Chem., 2004, 23, 331–340.101 F. Fern�andez-Costas, I. Lavilla and C. Bendicho, Spectrosc. Lett.,
2006, 39, 713–725.102 J. L. Capelo, I. Lavilla and C. Bendicho, Anal. Chem., 2000, 72,
4979–4984.103 J. L. Capelo, I. Lavilla and C. Bendicho, Anal. Chem., 2001, 73,
3732–3736.
1854 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
104 J. L. Capelo, C. Maduro and A. M. Mota, J. Anal. At. Spectrom.,2004, 19, 414–416.
105 T. Nakazato and H. Tao, Anal. Chem., 2006, 78, 1665–1672.106 L. Abrank�o, L. Yang, R. E. Sturgeon, P. Fodor and Z. Mester, J.
Anal. At. Spectrom., 2004, 19, 1098–1103.107 R. Pe~nalver, N. Campillo and M. Hern�andez-C�ordoba, Talanta,
2011, 87, 268–275.108 M. S. Fragueiro, F. Alava-Moreno, I. Lavilla and C. Bendicho, J.
Anal. At. Spectrom., 2000, 15, 705–709.109 S. Fragueiro, I. Lavilla and C. Bendicho, J. Anal. At. Spectrom.,
2004, 19, 250–254.110 C. Dietz, T. P�erez-Corona, Y. Madrid-Albarr�an and C. C�amara, J.
Anal. At. Spectrom., 2003, 18, 467–473.111 P. Hashemi and A. Rahimi, Spectrochim. Acta, Part B, 2007, 62,
423–428.112 A. Zierhut, K. Leopold, L. Harwardt, P. Worsfold and M. Schuster,
J. Anal. At. Spectrom., 2009, 24, 767–774.113 V. Romero, I. Costas-Mora, I. Lavilla and C. Bendicho,
Spectrochim. Acta, Part B, 2011, 66, 156–162.114 C. Pons, R. Forteza, A. O. S. S. Rangel and V. Cerd�a, TrAC, Trends
Anal. Chem., 2006, 25, 583–588.115 A. Economou, TrAC, Trends Anal. Chem., 2005, 24, 416–425.116 W. C. Tseng, P. H. Chen, T. S. Tsay, B. H. Chen and Y. L. Huang,
Anal. Chim. Acta, 2006, 576, 2–8.117 J. Ruzicka and E. H. Hansen, Anal. Chim. Acta, 1975, 78, 145–157.118 M. Tokeshi and T. Kitamori, in Advances in Flow Analysis, ed. M.
Trojanowicz, Wiley VCH, Weinheim, 2008, pp. 149–165.119 R. Pereiro, in Flow Analysis with Atomic Spectrometric Detectors, ed.
A. Sanz-Medel, Elsevier, Amsterdam, 1999, pp. 34–61.120 L. J. Shao, W. E. Gan, W. B. Zhang and Q. D Su, J. Anal. At.
Spectrom., 2005, 20, 1296–1298.121 G. Vermeir, C. Vandecasteele and R. Dams, Anal. Chim. Acta, 1991,
242, 203–208.122 S. Armenta and M. de la Guardia, in Challenges in Green Analytical
Chemistry, ed. M. de la Guardia and S. Garrigues, Royal Society ofChemistry, Cambridge 2011, pp. 286–298.
123 T. Taniai, A. Sakuragawa and A. Uzawa, ISIJ Int., 2004, 44, 1852–1858.
124 G. Tao and Z. Fang, Spectrochim. Acta, Part B, 1995, 50, 1747–1755.125 R. M. Cresp�on-Romero and M. C. Yebra-Biurrun, Anal. Chim.
Acta, 2008, 609, 184–191.126 C. Cui, M. He and B. Hu, J. Hazard. Mater., 2011, 187, 379–385.127 A. Maquieira, H. A. M. Elmahadi and R. Puchades, Anal. Chem.,
1994, 66, 3632–3638.128 P. Giusti, Y. N. Ordo~nez, C. P. Lienemann, D. Schauml€offel,
B. Bouyssiere and R. qobi�nski, J. Anal. At. Spectrom., 2007, 22,88–92.
129 N. Homazava, A. Ulrich and U. Kr€ahenb€uhl, Spectrochim. Acta,Part B, 2008, 63, 777–783.
130 N. Homazava, T. Suter, P. Schmutz, S. Toggweiler, A. Grimberg,U. Kr€ahenb€uhl and A. Ulrich, J. Anal. At. Spectrom., 2009, 24,1161–1169.
131 Y. Takasaki, M. Watanabe, H. Yukawa, A. Sabarudin, K. Inagaki,N. Kaji, Y. Okamoto, M. Tokeshi, Y. Miyamoto, H. Noguchi,T. Umemura, S. Hayashi, Y. Baba and H. Haraguchi, Anal.Chem., 2011, 83, 8552–8558.
132 J. Ruzicka, G. D. Marshall and G. D. Christian, Anal. Chem., 1990,62, 1861–1866.
133 M. Mir�o, V. Cerd�a and J. M. Estela, TrAC, Trends Anal. Chem.,2002, 21, 199–210.
134 W. E. Doering, R. R. James and R. T. Echols, Fresenius’ J. Anal.Chem., 2000, 368, 475–479.
135 G. Tao, S. N. Willie and R. E. Sturgeon, Analyst, 1998, 123, 1215–1218.
136 R. C. D. Costa and A. N. Ara�ujo, Anal. Chim. Acta, 2001, 438, 227–233.
137 A. N. Anthemidis, Talanta, 2008, 77, 541–545.138 A. N. Anthemidis and K. I. G. Ioannou, Anal. Chim. Acta, 2010,
668, 35–40.139 J. Wang and E. H. Hansen, J. Anal. At. Spectrom., 2002, 17, 248–
252.140 B. F. Reis, M. F. Gin�e, E. A. G. Zagatto, J. L. F. C. Lima and
R. A. S. Lapa, Anal. Chim. Acta, 1994, 293, 129–138.141 V. Cerd�a, R. Forteza and J. M. Estela, Anal. Chim. Acta, 2007, 600,
35–45.
This journal is ª The Royal Society of Chemistry 2012
Publ
ishe
d on
04
Sept
embe
r 20
12. D
ownl
oade
d on
18/
06/2
015
14:2
9:54
. View Article Online
142 M. Pist�on andM. Knochen, Int. J. Anal. Chem., 2012, DOI: 10.1155/2012/918292.
143 L. O. Leal, N. V. Semenova, R. Forteza and V. Cerd�a, Talanta, 2004,64, 1335–1342.
144 Y. Fajardo, E. G�omez, F. Garcias, V. Cerd�a and M. Casas, Anal.Chim. Acta, 2005, 539, 189–194.
145 R. A. S. Lapa, J. L. F. C. Lima, B. F. Reis, J. L. M. Santos andE. A. G. Zagatto, Anal. Chim. Acta, 2002, 466, 125–132.
146 C. M. P. V. Lopes, A. A. Almeida, J. L. M. Santos andJ. L. F. C. Lima, Anal. Chim. Acta, 2006, 555, 370–376.
147 C. P�erez-Sirvent, M. J. Mart�ınez-S�anchez, M. Garc�ıa-Lorenzo,I. L�opez-Garc�ıa and M. Hern�andez-C�ordoba, Anal. Bioanal.Chem., 2007, 388, 495–498.
148 I. L�opez-Garc�ıa, J. Arroyo-Cortez and M. Hern�andez-C�ordoba,Talanta, 2008, 75, 480–485.
149 J. Ruzicka, Analyst, 2000, 125, 1053–1060.150 Y. L. Yu, Z. Du and J. H. Wang, J. Anal. At. Spectrom., 2007, 22,
650–656.151 P. Ampan, J. Ruzicka, R. Atallah, G. D. Christian, J. Jakmunee and
K. Grudpan, Anal. Chim. Acta, 2003, 499, 167–172.152 A.Manz, N. Graber andH.M.Widmer, Sens. Actuators, B, 1990, 1–
6, 244–248.153 T. Vilkner, D. Janasek andA.Manz,Anal. Chem., 2004, 76, 3373–3386.154 R. D. Johnson, V. G. Gavalas, S. Daunert and L. G. Bachas, Anal.
Chim. Acta, 2008, 613, 20–30.155 Q. J. Song, G. M. Greenway and T. McGreedy, J. Anal. At.
Spectrom., 2004, 19, 883–887.156 G. Pearson and G. Greenway, J. Anal. At. Spectrom., 2007, 22, 657–
662.157 H. Cheng, Z. Xu, J. Liu, X.Wang andX. Yin, J. Anal. At. Spectrom.,
2012, 27, 346–353.158 J. P. Lafleur and E. D. Salin, J. Anal. At. Spectrom., 2009, 24, 1511–
1516.159 B. Chen, S. Heng, H. Peng, B. Hu, X. Yu, Z. Zhang, D. Pang, X. Yue
and Y. Zhu, J. Anal. At. Spectrom., 2010, 25, 1931–1938.160 B. Chen, B. Hu, P. Jiang, M. He, H. Peng and X. Zhang, Analyst,
2011, 136, 3934–3942.161 C. Bendicho and M. T. C. de Loos-Vollebregt, J. Anal. At.
Spectrom., 1991, 6, 353–374.162 A. Martin-Esteban and B. Slowikowski, Crit. Rev. Anal. Chem.,
2003, 33, 43–55.163 M. G. R. Vale, N. Oleszczuk and W. N. L. dos Santos, Appl.
Spectrosc. Rev., 2006, 41, 377–400.164 B. Welz, M. G. R. Vale, D. L. G. Borges and U. Heitmann, Anal.
Bioanal. Chem., 2007, 389, 2085–2095.165 M. Resano, F. Vanhaecke andM. T. C. de Loos-Vollebregt, J. Anal.
At. Spectrom., 2008, 23, 1450–1475.166 M. Aramend�ıa, M. Resano and F. Vanhaecke, Anal. Chim. Acta,
2009, 648, 23–44.167 Z. Zaide, Z. Kaizhong, H. Xiandeng and L. Hong, Appl. Spectrosc.
Rev., 2005, 40, 165–184.168 F. L. King, J. Teng and R. E. Steiner, J. Mass Spectrom., 1995, 30,
1061–1075.169 D. G€unther, S. E. Jackson and H. P. Longerich, Spectrochim. Acta,
Part B, 1999, 54, 381–409.170 J. D. Winefordner, I. B. Gornushkin, D. Pappas, O. I. Matveev and
B. W. Smith, J. Anal. At. Spectrom., 2000, 15, 1161–1189.171 J. M. Vadillo and J. J. Laserna, Spectrochim. Acta, Part B, 2004, 59,
147–161.172 J. D. Winefordner, I. B. Gornushkin, T. Correll, E. Gibb,
B. W. Smith and N. Omenetto, J. Anal. At. Spectrom., 2004, 19,1061–1083.
173 D. G€unther and B. Hattendorf, TrAC, Trends Anal. Chem., 2005, 24,255–265.
174 C. Pickhardt, H. J. Dietze and J. S. Becker, Int. J. Mass Spectrom.,2005, 242, 273–280.
175 B. Fernandez, F. Claverie, C. Pecheyran and O. F. X. Donard,TrAC, Trends Anal. Chem., 2007, 26, 951–966.
176 J. Pisonero, B. Fernandez and D. G€unther, J. Anal. At. Spectrom.,2009, 24, 1145–1160.
177 B. Fern�andez, R. Pereiro and A. Sanz-Medel, Anal. Chim. Acta,2010, 679, 7–16.
178 K. Janssens, W. D. Nolf, G. V. D. Snickt, L. Vincze, B. Vekemans,R. Terzano and F. E. Brenker, TrAC Trends Anal. Chem., 2010, 29,464–478.
This journal is ª The Royal Society of Chemistry 2012
179 U. E. A. Fittschen and G. Falkenberg, Spectrochim. Acta, Part B,2011, 66, 567–580.
180 M. West, A. T. Ellis, P. J. Potts, C. Streli, C. Vanhoof,D. Wergrzynek and P. Wobrauschek, J. Anal. At. Spectrom., 2011,26, 1919–1963.
181 M. Resano, E. Garc�ıa-Ruiz, M. A. Belarra, F. Vanhaecke andK. S. McIntosh, TrAC, Trends Anal. Chem., 2007, 26, 385–395.
182 B. Bekhoff, B. Kanngießer, N. Langhoff, R. Wedell and H. Wolff,Handbook of Practical X-Ray Fluorescence Analysis, Springer, NewYork, 2006.
183 M. A. Zezzi Arruda, Trends in Sample Preparation, Nova SciencePublishers, New York, 2007.
184 L. Qi, J. Gao, X. Huang, J. Hu, M. F. Zhou and H. Zhong, J. Anal.At. Spectrom., 2011, 26, 1900–1904.
185 S. F. Boulyga and K. G. Heumann, Anal. Bioanal. Chem., 2005, 383,442–447.
186 J. D. Kerber, At. Absorpt. Newsl., 1971, 10, 104–105.187 www.analytik-jena.de/en/solid-AA/Systems-4400, last accessed June
2012.188 D. E. Nixon, V. A. Fassel and R. N. Kniseley,Anal. Chem., 1974, 46,
210–213.189 www.spectral-systems.de/english/autosamp.htm, last accessed June
2012.190 M. A. Belarra, M. Resano, F. Vanhaecke and L. Moens, TrAC,
Trends Anal. Chem., 2002, 21, 828–839.191 H. M. Ortner, E. Bulskab, U. Rohra, G. Schlemmerc,
S. Weinbruchd and B. Welz, Spectrochim. Acta, Part B, 2002, 57,1835–1853.
192 V. N. Oreshkin and G. I. Tsizin, J. Anal. Chem., 2011, 66, 951–954.193 X. Hou and B. T. Jones, Spectrochim. Acta, Part B, 2002, 57, 659–
688.194 M. L. Lin and S. J. Jiang, J. Anal. At. Spectrom., 2011, 26, 1813–
1818.195 M. A. Amberger and J. A. C. Broekaert, J. Anal. At. Spectrom.,
2010, 25, 1308–1315.196 G. Xiang, B. Hu and Z. Jiang, J. Mass Spectrom., 2006, 41, 1378–
1385.197 V. Thomsen and J. L. Spencer, Spectroscopy, 2011, 26, 18–21.198 V. Thomsen, Spectroscopy, 2010, 25, 44–45.199 www.angstrom-inc.com/spectrometers.html, last accessed June
2012.200 P. D. Pant, PCT Int. Appl., WO 2011114340 A2 20110922, 2011.201 F. Vincent, J. P. Sola and G. Wuethrich, Brit. UK Pat. Appl., GB
2466198 A 20100616, 2010.202 https://www.thermo.com/eThermo/CMA/PDFs/./productPDF_
57273.PDF, last accessed June 2012.203 A. F. Kiera, S. Schmidt-Lehr, M. Song, N. Bings and
J. A. C. Broekaert, Spectrochim. Acta, Part B, 2008, 63, 287–292.204 G. Buchbinder, N. Verblyudov and A. Clavering, Spectroscopy,
2009.205 J. Roy and L. Neufeld, Spectroscopy, 2004, 19, 16–28.206 T. D. F. Leite, R. Escalfoni Jr., T. C. O. da Fonseca and
N. Miekeley, Spectrochim. Acta, Part B, 2011, 66, 314–320.207 I. Konz, B. Fern�andez, M. L. Fern�andez, R. Pereiro and A. Sanz-
Medel, Anal. Bioanal. Chem., 2012, 403, 2113–2125.208 J. S. Becker, Int. J. Mass Spectrom., 2010, 289, 65–75.209 F. J. Fortes and J. J. Laserna, Spectrochim. Acta, Part B, 2010, 65,
975–990.210 A. Ciucci, V. Palleschi, S. Rastelli, A. Salvetti, D. P. Singh and
E. Tognoni, Laser Part. Beams, 1999, 17, 793–797.211 S. Palanco, A. Alises, J. Cu~nat, J. Baena and J. J. Laserna, J. Anal.
At. Spectrom., 2003, 18, 933–938.212 T. Nelis and J. Pallosi, Appl. Spectrosc. Rev., 2006, 41, 227–258.213 R. Pereiro, A. Sol�a-V�azquez, L. Lobo, J. Pisonero, N. Bordel,
J. M. Costa and A. Sanz-Medel, Spectrochim. Acta, Part B, 2011,66, 399–412.
214 M. J. Heintz and G. M. Hieftje, Spectrochim. Acta, Part B, 1995, 50,1109–1124.
215 G. P. Jackson, R. G. Haire and C. Duckworth, J. Anal. At.Spectrom., 2003, 18, 665–669.
216 L. Gao, Q. Song, R. J. Noll, J. Duncan, R. G. Cooks and Z. Ouyang,J. Mass Spectrom., 2007, 42, 675–680.
217 W. C. Davis, B. C. Knippel, J. E. Cooper, B. K. Spraul, J. K. Rice,D. W. Smith, Jr and R. K. Marcus, Anal. Chem., 2003, 75, 2243–2250.
J. Anal. At. Spectrom., 2012, 27, 1831–1857 | 1855
Publ
ishe
d on
04
Sept
embe
r 20
12. D
ownl
oade
d on
18/
06/2
015
14:2
9:54
. View Article Online
218 T. M. Brewer, W. Clay Davis and R. K. Marcus, J. Anal. At.Spectrom., 2006, 21, 126–133.
219 D. Fliegel and D. G€unther, Spectrochim. Acta, Part B, 2009, 64, 399–407.
220 M. Tarik and D. G€unther, J. Anal. At. Spectrom., 2010, 25, 1416–1423.
221 E. Margu�ı, M. Hidalgo and I. Queralt, Spectrochim. Acta, Part B,2005, 60, 1363–1372.
222 G. Custo, S. Boeykens, L. Dawidowski, L. Fox, D. Gomez, F. Lunaand C. Vazquez, Anal. Sci., 2005, 21, 751–756.
223 N. Bukowiecki, P. Lienemann, C. N. Zwicky, M. Furger,A. Richard, G. Falkenberg, K. Rickers, D. Grolimund, C. Borca,M. Hill, R. Gehrig and U. Baltensperger, Spectrochim. Acta, PartB, 2008, 63, 929–938.
224 I. de la Calle, M. Costas, N. Cabaleiro, I. Lavilla and C. Bendicho,Spectrochim. Acta, Part B, 2012, 67, 43–49.
225 R. E. A. Jim�enez, Spectrochim. Acta, Part B, 2001, 56, 2331–2336.226 http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c¼ecfr&sid¼e29fdcb9d
258d1ed8c80f521ef9801a4&rgn¼div6&view¼text&node ¼ 42:5.0.1.1.5.3&idno ¼ 42, last accessed June 2012.
227 http://epswww.unm.edu/xrd/xrd_haz.pdf, last accessed June 2012.228 Environmental Protection Agency, USA, Environmental Technology
Verification Report: Field Portable X-Ray Fluorescence Analyzer,Spectrace TN 9000 and TN Pb Field Portable X-Ray FluorescenceAnalyzers, EPA/600/R-97/145, Washington DC, 1998.
229 J. Injuk, R. Van Grieken, A. Blank, L. Eksperiandova andV. Buhrke, in Handbook of Practical X-Ray Fluorescence Analysis,ed. B. Bekhoff, B. Kanngießer, N. Langhoff, R. Wedell and H.Wolff, Springer, New York, 2006, pp. 415–424.
230 R. B. Hallet and P. R. Kyle, Geostand. Newsl., 1993, 17, 127–133.231 S. Barrento, A. Marques, B. Teixeira, P. Vaz-Pires, M. L. Carvalho
and M. L. Nunes, Food Chem., 2008, 111, 862–867.232 M. F. Galluza, S. Vicente, M. Ordu~na and M. J. Ventura, X-Ray
Spectrom., 2012, 41, 176–185.233 C. Vazquez, G. Custo, N. Barrio, J. Bur�ucua, S. Boeykens and
F. Marte, Spectrochim. Acta, Part B, 2010, 65, 852–858.234 http://www.bruker-axs.com/artax.html, last accessed June 2012.235 G. Buzanich, P. Wobrauscheck, C. Streli, A. Markowicz,
D. Wegrzynek, E. Chine-Cano and S. Bamford, Spectrochim.Acta, Part B, 2007, 62, 1252–1256.
236 A. von Bohlen, Spectrochim. Acta, Part B, 2009, 64, 821–832.237 http://www.bruker-axs.com/s2picofox.html, last accessed June
2012\.238 http://www.bruker-axs.com/traceriiiv.html, last accessed June 2012.239 N. Forster, P. Grave, N. Vickery and L. Kealhofer, X-Ray
Spectrom., 2011, 40, 389–398.240 Y. Shibata, J. Suyama, M. Kitano and T. Nakamura, X-Ray
Spectrom., 2008, 38, 410–416.241 E. Margu�ı, C. Font�as, A. Buend�ıa, M. Hidalgo and I. Queralt, J.
Anal. At. Spectrom., 2009, 24, 1253–1257.242 A. A. Shaltout, B. Welz andM. A. Ibrahim,Microchem. J., 2011, 99,
356–363.243 A. J. Aller, Espectroscopia at�omica electrot�ermica anal�ıtica,
Secretariado de Publicaciones y Medios Audiovisuales de laUniversidad de Le�on, Le�on, 2003.
244 H. E. Taylor, Inductively Coupled Plasma-Mass SpectrometryPractices and Techniques, Academic Press, San Diego, 2001.
245 S. E. Maestre, J. L. Todol�ı and J. M. Mermet, Anal. Bioanal. Chem.,2004, 379, 888–899.
246 J. L. Todoli, V. Hernandis, A. Canals and J. M. Mermet, J. Anal. At.Spectrom., 1999, 14, 1289–1295.
247 F. Vanhaecke, M. V. Holderbeke, L. Moens and R. Dams, J. Anal.At. Spectrom., 1996, 11, 543–548.
248 S. F. Boulyga and J. S. Becker, Fresenius’ J. Anal. Chem., 2001, 370,612–617.
249 J. A. Koropchak and M. Veber, Crit. Rev. Anal. Chem., 1992, 23,113–141.
250 X. Zhang, D. Chen, R. Marquardt and J. A. Koropchak,Microchem. J., 2000, 66, 17–53.
251 N. Praphairaksit, D. R. Wiederin and R. S. Houk, Spectrochim.Acta, Part B, 2000, 55, 1279–1293.
252 J. A. C. Broekaert and V. Siemens, Anal. Bioanal. Chem., 2004, 380,185–189.
253 B. €Ozmen, F. M. Matysik, N. H. Bings and J. A. C. Broekaert,Spectrochim. Acta, Part B, 2004, 59, 941–950.
1856 | J. Anal. At. Spectrom., 2012, 27, 1831–1857
254 X. Guo, R. E. Sturgeon, Z. Mester and G. J. Gardner, Anal. Chem.,2004, 76, 2401–2405.
255 F. G. Bessoth, O. P. Naji, J. C. T. Eijkel and A. Manz, J. Anal. At.Spectrom., 2002, 17, 794–799.
256 J. A. C. Broekaert and U. Engel, in Encyclopedia of AnalyticalChemistry, ed. R. A. Meyer, John Wiley & Sons, Chichester, 2000,pp. 9613–9667.
257 J. Cai, in Encyclopedia of Analytical Chemistry, ed. R. A. Meyer,John Wiley & Sons, Chichester, 2000, pp. 2270–2292.
258 J. D�edina, Spectrochim. Acta, Part B, 2007, 62, 846–872.259 J. D�edina and T. Matou�sek, J. Anal. At. Spectrom., 2000, 15, 301–
304.260 W. T. Corns, P. B. Stockwell, L. E. Ebdon and S. J. Hill, J. Anal. At.
Spectrom., 1993, 8, 71–77.261 Y. Ogra, Biomed. Res. Trace Elem., 2008, 19, 34–42.262 R. Lobinski, D. Schauml€offel and J. Szpunar,Mass Spectrom. Rev.,
2006, 25, 255–289.263 Y. C. Sun, Y. C. Chang and C. K. Su, Anal. Chem., 2006, 78, 2640–
2645.264 H. Matusiewicz and R. E. Sturgeon, Spectrochim. Acta, Part B,
1996, 51, 377–397.265 O. Y. Ataman, Spectrochim. Acta, Part B, 2008, 63, 825–834.266 B. Doc�ekal, S. Gucer and A. Seleck�a, Spectrochim. Acta, Part B,
2004, 59, 487–495.267 X. D. Hou, K. E. Levine, A. Salido, B. T. Jones, M. Ezer, S. Elwood
and J. B. Simeonsson, Anal. Sci., 2001, 17, 175–180.268 B. Welz and M. Sperling, Atomic Absorption Spectrometry, Wiley-
VCH, Weinheim, 1999.269 B. Welz, S. Mor�es, E. Casarek, M. G. R. Vale, M. Okruss and
H. Becker-Ross, Appl. Spectrosc. Rev., 2010, 45, 327–354.270 J. Namie�snik, J. Sep. Sci., 2001, 24, 151–153.271 E. Marengo, M. Aceto, E. Robotti, M. Oddone and M. Bobba,
Talanta, 2008, 76, 1224–1232.272 Z. Jokai and P. Fodor, J. Anal. At. Spectrom., 2009, 24, 1229–1236.273 G. R. Lloyd, S. Ahmad, M. Wasim and R. G. Brereton, Anal. Chim.
Acta, 2009, 649, 33–42.274 K. Schaefer, J. W. Einax, V. Simeonov and S. Tsakovski, Anal.
Bioanal. Chem., 2010, 396, 2675–2683.275 M. J. Latorre, R. Pe~na, S. Garc�ıa and C. Herrero,Analyst, 2000, 125,
307–312.276 K. Ariyama, H. Horita and A. Yasui, Anal. Sci., 2004, 20, 871–877.277 R. Iglesias Rodr�ıguez, M. Fern�andez Delgado, J. Barciela Garc�ıa,
R. M. Pe~na Crecente, S. Garc�ıa Mart�ın and C. Herrero Latorre,Anal. Bioanal. Chem., 2010, 397, 2603–2614.
278 A. P. Fernandes, M. C. Santos, S. G. Lemos, M. M. C. Ferreira,A. R. A. Nogueira and J. A. Nobrega, Spectrochim. Acta, Part B,2005, 60, 717–724.
279 M. Costas-Rodriguez, I. Lavilla and C. Bendicho, Anal. Chim. Acta,2010, 664, 121–128.
280 M. Otto, Chemometrics. Statistical and Computer Application inAnalytical Chemistry, Wiley-VCH, Weinheim, 2007.
281 X. T. Morer, L. Gonzalez-Sabat�e, L. Fernandez-Ruano andM. P. Gomez-Carracedo, in Basic Chemometric Techniques inAtomic Spectroscopy, ed. J. M. Andrade, Royal Society ofChemistry, Cambridge, 2009, pp. 51–141.
282 M. Cocchi, C. Durante, A. Marchetti, M. Li Vigni, C. Baschieri,L. Bertacchini, S. Sighinolfi, L. Tassi and S. Totaro, inMicrowaves: Theoretical Aspects and Practical Applications inChemistry, ed. A. Marcheti and S. Sighinolfi, Transworld ResearchNetwork, T. C., Kerala, 2011, pp. 203–226.
283 J. M. O. Souza and C. R. T. Tarley, Int. J. Environ. Anal. Chem.,2009, 89, 489–502.
284 E. Kend€uzler, S. Baytak, €O. Yalcinkaya and A. R. T€urker, Can. J.Anal. Sci. Spectrosc., 2007, 52, 91–100.
285 S. L. C. Ferreira, S. M. Macedo, D. C. dos Santos, R. M. de Jesus,W. N. L. dos Santos, A. F. S. Queiroz and J. B. de Andrade, J. Anal.At. Spectrom., 2011, 26, 1887–1891.
286 F. Bianchi and M. Careri, Curr. Anal. Chem., 2008, 4, 142–151.287 D. B. Hibbert and N. Armstrong, Chemom. Intell. Lab. Syst., 2009,
97, 211–220.288 M. A. Bezerra, R. E. Santelli, E. P. Oliveira, L. S. Villar and
L. A. Escaleira, Talanta, 2008, 76, 965–977.289 J. M. Andrade, M. J. Cal-Prieto, M. P. G�omez-Carracedo,
A. Carlosena and D. Prada, J. Anal. At. Spectrom., 2008, 23, 15–28.
This journal is ª The Royal Society of Chemistry 2012
Publ
ishe
d on
04
Sept
embe
r 20
12. D
ownl
oade
d on
18/
06/2
015
14:2
9:54
. View Article Online
290 C. Y. Fu, L. I. Petrich, P. F. Daley, A. K. Burnham and K. Alan,Anal. Chem., 2005, 77, 4051–4057.
291 T. Pettke, C. A. Heinrich, A. C. Ciocan and D. Gunther, J. Anal. At.Spectrom., 2000, 15, 1149–1155.
292 T. Nomizu, H. Hayashi, N. Hoshino, T. Tanaka, H. Kawaguchi,K. Kitagawa, K. Kuniyuki and S. Kaneco, J. Anal. At. Spectrom.,2002, 17, 592–595.
293 D. Q. Zhang, C.M. Li, L. L. Yang andH.W. Sun,Anal. Chim. Acta,2000, 405, 185–190.
294 I. Lopez-Garc�ıa, M. S�anchez-Merlos, P. Vi~nas and M. Hern�andez-Cordoba, J. Anal. At. Spectrom., 2001, 16, 1185–1189.
295 M. Felipe-Sotelo, J. M. Andrade, A. Carlosena and D. Prada, Anal.Chem., 2003, 75, 5254–5261.
296 X. Ma and Z. Zhang, J. Anal. At. Spectrom., 2004, 19, 738–742.297 E. S. Chaves, S. Compernolle, M. Aramendia, E. Javierre,
E. Tresaco, M. T. C. de Loos-Vollebregt, A. J. Curtius andF. Vanhaecke, J. Anal. At. Spectrom., 2011, 26, 1833–1840.
298 S. Prikler, D. Pick and J. W. Einax, Anal. Bioanal. Chem., 2012, 403,1109–1116.
299 J. M. Cottle, M. S. A. Horstwood and R. R. Parrish, J. Anal. At.Spectrom., 2009, 24, 1355–1363.
300 H. Yihua, T. Li, W. Xi, H. Xiandeng and L. Yong-Ill, Appl.Spectrosc. Rev., 2007, 42, 119–138.
301 S. Lahiri and M. J. Stillman, Anal. Chem., 1992, 64, 283A–291A.302 H. Ying, P. Yang, X. Wang and B. Huang, Spectrochim. Acta, Part
B, 1996, 51, 877–886.303 Z. Zhang and X. Ma, Curr. Top. Anal. Chem., 2002, 3, 105–123.
This journal is ª The Royal Society of Chemistry 2012
304 D. P. Webb and E. D. Salin, J. Anal. At. Spectrom., 1989, 4, 793–796.
305 P. Yang, H. Ying, X. Wang and B. Huang, Spectrochim. Acta, PartB, 1996, 51, 889–896.
306 C. Sartoros, J. F. Alary, E. D. Salina and J. M. Mermet,Spectrochim. Acta, Part B, 1997, 52, 1923–1927.
307 F. A. Settle Jr, B. I. Diamondstone, H. M. Kingston andM. A. Pleva, J. Chem. Inf. Model., 1989, 29, 11–17.
308 F. A. Settle Jr, P. J. Walter, H. M. Kingston, M. A. Pleva, T. Sniderand W. Boute, J. Chem. Inf. Model., 1992, 32, 349–353.
309 F. Klages and G. Wuensch, J. Prakt. Chem./Chem.-Ztg., 1996, 338,16–22.
310 G. Wuensch and F. Klages, J. Prakt. Chem./Chem.-Ztg., 1996, 338,593–597.
311 C. C. Huang, M. H. Yang and T. S. Shih, Anal. Chem., 1997, 69,3930–3939.
312 H. Ying, J. Murphy, J. W. Trompa, J. M. Mermet and E. D. Salina,Spectrochim. Acta, Part B, 2000, 55, 311–326.
313 B. van den Bogaert, J. B. W. Morsink and H. C. Smit, Anal. Chim.Acta, 1992, 270, 107–113.
314 B. van den Bogaert, J. B. W. Morsink and H. C. Smit, Anal. Chim.Acta, 1992, 270, 115–130.
315 D. Wienke, T. Vijn and L. Buydens, Anal. Chem., 1994, 66, 841–849.316 C. Pons, M. Mir�o, E. Becerra, J. M. Estela and V. Cerda, Talanta,
2004, 62, 887–895.317 M. I. G. S. Almeida, M. A. Segundo, J. L. F. C. Lima and
A. O. S. S. Rangel, J. Anal. At. Spectrom., 2009, 24, 340–346.
J. Anal. At. Spectrom., 2012, 27, 1831–1857 | 1857