ANALYST, DECEMBER 1984, VOL. 109 1581

Extraction - Fluorimetric Determination of Mercury With 2-Phenylbenzo[8,9]quinolizino[4,5,6,7-fe~phenanthridinylium Perchlorate

Tomas Perez-Ruiz, Joaquin A. Ortufio and Concepcion Sanchez-Pedreiio" Department of Analytical Chemistry, Faculty of Sciences, University of Murcia, Murcia, Spain

The characteristics of 2-phenylbenzo[8,9]quinolizino[4,5,6,7-fe~phenanthridinylium perchlorate (PQPP) as a reagent for the formation of ion-association complexes with metal - bromide anions and its application to the fluorimetric determination of mercury are described. This reagent forms a 1 : 1 complex with HgBr3- that is slightly soluble in water and can be extracted with butyl acetate. The influence of the acidity, bromide ion concentration and foreign ions were investigated. Mercury can be determined in the range 1.5-15 ng ml-1. The stoicheiometry and apparent stability constant of the complex were determined. The method is applicable to the determination of mercury in sphalerites and organomercurials in cleaning solutions for contact lenses.

Keywords : 2- Phen ylbenzo[8,9]quinolizino[4,5,6,7-f edlp h en an th ridin ylium perch lo rate; spectro fluo rim e try; mercury determination; organomercurials determination; sphalerite

The determination of small amounts of mercury, present in both organic and inorganic combinations, is of interest in contamination analysis and geochemical prospecting. Many methods have been developed for the determination of

but there is still a need for more simple, sensitive and selective methods that will allow samples to be analysed without removing interferences.

A recent fluorimetric reagent, 2-phenylbenzo[8,9]- quinolizino[4,5,6,7-fed]phenanthridinylium perchlorate (PQPP) forms ion-association complexes with a small number of metal - halogen ions. These complexes may be used for the fluorimetric determination of the metal after extraction with the appropriate solvents. The formation and extraction of metal - chloride complexes and its application to the fluori- metric determination of gold(II1) and thallium(II1) have been reported.6-7

Q A

PQPP

This paper discusses the formation and extraction of metal - bromide complexes with PQPP and a selective fluorimetric method for the determination of trace amounts of mercury is proposed. This method is more sensitive than other fluori- m e t r i ~ , ~ spectrophot~metric~ and conventional atomic- absorption1 methods for the determination of mercury.

Experimental Apparatus

Fluorescence spectra and quantitative spectrofluorimetric measurements were obtained with a Perkin-Elmer Model

* To whom correspondence should be addressed.

3000 spectrofluorimeter, equipped with a quantum counter. Excitation spectra were corrected, but emission spectra were not. A Perkin-Elmer Model 240B elemental analyser, a Perkin-Elmer 177 grating infrared spectrophotometer , a Hewlett-Packard 5980A mass spectrometer and a Varian FT-80 nuclear magnetic resonance spectrometer were used for identification of PQPP.

Reagents

All inorganic chemicals used were of analytical-reagent grade. Acetophenone, benzaldehyde (Aldrich) and butyl acetate (Merck) were used as received. Doubly distilled water was used exclusively.

2-Phenylbenzo[8,9]quinolizino[4,5,6,7-fed~henanthridin- ylium perchlorate. This was synthesised from 1,2,4,6- tetraphenylpyridinium perchlorate (TPPP) by dissolution in methanol and irradiation with a UV lamp, as described previously. 6

2-Phenylbenzo[8,9]quinolizino[4,5,6,7-fedlphenanthridin- ylium perchlorate solution, 5 x 10-5 M. Prepared by dissolving 0.012 g of the reagent in 500 ml of ethanol. The solution is stable for several weeks. Mercury(II) standard solution, 0.01 M. Prepared by dis-

solving mercury(I1) nitrate in 0.1 M nitric acid and standardi- sed by titration with EDTA.8 Working standards were prepared from this solution as required.

Procedure for Determination of Mercury(I1)

To a volume of sample solution in a separating funnel containing up to 750 ng of mercury(I1) add 1 ml of 1 0 ~ sulphuric acid, 1 ml of 0.4 M sodium bromide solution and 3 ml of 5 X 10-5 M PQPP solution. Dilute to 50 ml with doubly distilled water and extract the mixture with 5 ml of butyl acetate. Shake the funnel vigorously for 2 min, allow the phases to separate for 10 min, then transfer the organic layer into a centrifuge tube and centrifuge it to give a water-free organic layer. Activate at 300 nm and read the fluorescence of the complex at 460 nm. Under the recommended conditions, the calibration graph is linear over the range 64-640 ng of mercury per 5 ml of butyl acetate.

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1582 ANALYST, DECEMBER 1984, VOL. 109

Table 1. Extraction efficiencies of metal - bromide complexes with PQPP in butyl acetate. Conditions: sodium bromide concentration, 0.008 M ; sulphuric acid concentration, 0.2 N ; PQPPconcentration, 3 X

M ; ratio of aqueous phase to butyl acetate, 10 + 1 (VIV)

Extraction, Extraction, Metal ion Y O Metal ion YO

Au(II1) . . . , 100 Bi(II1) . . . . 0.4 TI(II1) . . . . 100 Pb(I1) . . . . 0.08 Hg(1I) . . . , 85.5 Cu(I1) . . . . 0.007 Ag(1) . . . . 14.0 Cd(I1) . . . . 0.003 In(II1) . . . . 1.3 Fe(II1) . . . . 0.001

).

C a,

C

.- - 75

4-

.- 8 50 C a,

v)

F 0 25 - LL

751 A C

300 400 450 500 Wavelengthinm

Fig. 1. Excitation (A and B) and emission (C and D) spectra of A and C, mercury complex ( P a p + HgBrs--) in butyl acetate, and B and D. reagent in ethanol

Results and Discussion Preliminary Studies

PQPP reacts with some metal ions in an acidic medium containing an excess of bromide ion to form ion-association complexes that can be extracted into butyl acetate. The extraction efficiencies of these complexes under the selected conditions are shown in Table 1. Gold(III), mercury(I1) and thallium( 111) have high extraction efficiencies whereas other metal ions are only slightly extracted.

The extraction efficiencies of the corresponding metal - chloride complexes with PQPP are also high for gold(II1) and thallium(II1) and low for mercury.6.7 Therefore, the study of the bromide - mercury(I1) system seems to be interesting for the determination of mercury whereas there is no advantage with respect to sensitivity with the use of bromide - thal- lium(II1) and gold(II1) complexes over chloride - metal complexes for the determination of these two ions.

Fluorescence Spectra

The excitation and emission spectra of the reagent (in ethanol) and PQP+ HgBr3- (in butyl acetate) are shown in Fig. 1. The excitation spectra have maxima at 300,346 and 428 nm and the emission spectra have maxima at 460 nm.

Effect of Acidity

The effect of acidity on the formation of the PQP+ HgBr3- complex and its extraction into butyl acetate was studied using fixed concentrations of mercury(II) (12 ng mi-I), sodium

b

I I

1 8 Ratio of [POPPI 20 to [Hgl 32

Fig. 2. Stoicheiometr of mercury - PQPP complex determined by the molar ratio me tho2 Mercury(I1) concentration, 7.13 x 10-8 M

.I-

.- .<I 5 15 25

[Hgzt1/ng ml-

Fig. 3. Calibration graph for mercury

bromide (0.008 M) and PQPP (3 x 10-6 M) and varying the sulphuric acid concentration from 0.001 to 2 N. The maximum fluorescence intensity was obtained with a 0.2 N sulphuric acid concentration.

Effect of Bromide Ion Concentration

The influence of the bromide ion concentration was studied using 12 ng ml-1 of mercury(I1) solution in 0.2 N sulphuric acid and sodium bromide solutions ranging from 0.001 to 0.015 M. Increasing the bromide ion concentration in this range caused an increase in fluorescence intensity with a maximum at 0.008 M , the intensities decreasing again at higher bromide concentrations.

Composition of the Complex

To establish the composition of the complex, the continuous variationgJ0 and molar ratio" methods were applied. The molar ratio of mercury to PQPP was found to be 1 : 1 by these two methods. Fig. 2 shows that a molar ratio of [PQPP] to [Hg(II)] of higher than 16 is necessary for the complete formation and extraction of the complex. The apparent stability constant of the complex was calculated from the results of the molar ratio and continuous variation methods by the procedures of Momoki et d.'* and Likussar and Boltz13 and an average value of log K = 7.9 k 0.1 at 20 "C "as obtained.

Extraction Efficiency and Stability

The selected ratio of aqueous phase to butyl acetate was 10 + 1 (V/V) and the extraction efficiency was 85.5%.

The fluorescence intensities of the complex extracted into butyl acetate remained constant for 24 h.

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ANALYST. DECEMBER 1984. VOL. 109 1583

Table 2. Interference of other ions in the determination of mercury. Concentration of mercury(I1). 15 ng ml-1

Molar ratio, Molar ratio. [ion added]/ [ion added]/

Ion added [Hg(II)I Ion added [Hg(II) 1 Bi(II1) Cd(I1) Cr(II1)

Au(II1) In(II1) Fe(II1) Pb(I1) Mn(I1)

Cu(I1)

. . . .

. . . .

. . . .

. . . .

. . . ,

. . . .

. . . .

10 1000

500 0.02 2

5000 50 50

104

* Maximum molar ratio tested.

Pt(IV) . . A g o ) . ’ TI(II1) . . Zn(I1) . . Chloride . . Nitrate . . Perchlorate Sulphate . .

. . 1

. . 0.2

. . 0.02

. . 105*

. . 105

. . 1000

. . 100

. . 1 Oh ‘

Table 3. Determination of mercury and organomercurials in sphalerite and cleaning solutions for contact lenses

Sample Content Found, % Sphalerite . . . . 0.064% of mercury‘ 0.067 Cleaning solutions

for contact lenses: 1 . . . . . . 0.004°/0 of sodium 0.0045

ethylmercurithiosalicylate? (thiomersal)

nitrate? Value obtained by atomic-absorption spectrometry.

2 . . . . . . 0.0033% of phenylmercury 0.0031

t Certified by Laboratory Pharmaceuticals.

Effect of Shaking Time

The extraction of the complex into butyl acetate was rapid and no change was observed when the shaking time was varied from 1 to 4 min.

Calibration Graphs, Sensitivity and Precision

The slope of the calibration graphs increases with increase in mercury concentration and, under the recommended condi- tions, the calibration graph was linear over the concentration range 1.5-15 ng ml-1 (Fig. 3).

The standard deviations for 15 and 8 ng ml-1 of mercury(I1) (ten determinations each) were 0.65 and 0.51 ng ml-1, respectively, and the relative errors were 3.1 and 4.5%, respectively.

Effect of Other Ions

In the determination of 15 ng ml-1 of mercury(II), extraneous ions can be tolerated at the levels given in Table 2. The limiting value of the concentration for each ion was taken as that value which caused an error of not more than 4% in the fluorescence intensity. Cations were added as chlorides, nitrates or sulphates, and anions in the form of sodium or potassium salts.

Positive interferences are attributed to the fact that the elements concerned also form ion-pair compounds with the reagent in sodium bromide media and so are slightly extracted into the organic solvent. Thallium, gold and silver cause the largest interferences.

Applications

The method has been applied satisfactorily to the determina- tion of mercury in different materials that contain trace amounts of mercury present in organic or inorganic combina- tions.

Determination of Mercury in Sphalerites

A suitable amount (0.1 g) of sample was dissolved in aqua regia, then sulphuric acid was added and the solution was boiled until white fumes were evolved. After transferring the solution into a 200-ml calibrated flask and diluting to volume with doubly distilled water, a suitable volume (2 ml) of solution was treated following the recommended procedure. The results are given in Table 3.

Determination of Organomercurials in Cleaning Solutions for Contact Lenses

A suitable volume (1 ml) of sample was taken in a 200-ml calibrated flask, 20 ml of 10 N sulphuric acid were added and the solution was diluted to volume with doubly distilled water. Bromine vapour was added, the mixture was allowed to stand for 2 min then an air current was passed through the solution for 5 min to remove the bromine. A suitable volume ( 5 ml) of solution was treated following the recommended procedure. The results are given in Table 3.

Conclusions PQPP was found to be satisfactory for the fluorimetric determination of mercury by the formation of an ion- association complex that is extracted into butyl acetate. This method could be particularly useful in routine analytical work for the determination of mercury without a prior separation procedure.

1. 2.

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12.

13.

References Chilov, S . , Talanta. 1975, 22. 205. Mercury Analysis Working Party of BITC, Anal. Chim. Acta, 1974, 72, 37; 1976, 84, 231. Analytical Methods Committee, Analyst, 1965, 90, 515. Lopez-Rivadulla. M., and Fernandez, E., Quim. Anal., 1976, 30, 251. Snell, F. D., “Photometric and Fiuorimetric Methods of Analysis, Part 1,’. Wiley, New York, 1978, p. 101. Perez-Ruiz, T., Sanchez-Pedreno. C. , Ortuno, J. A . , and Molina-Buendia, P. , Analyst, 1983, 108, 733. Perez-Ruiz, T., Ortuno, J . A. , and Molina, P., iMicrochem. J., in the press. Piibil, R . , Koros, E., and Barcza, L., Acta Pharm. Hung., 1957, 27, 145. Job, P., Justus Liebigs Ann. Chem., 1928, 9, 113. Irving, H., and Pierce, T. B., J. Chem. SOC., 1959, 2565.

Ind. Eng. Chem., Anal. Ed . , Y o e , J . H. , and Jones, A . L.. 1944, 16, 111. Momoki, K., Sekino, J.. Sato, Chem., 1969, 41. 1286. Likussar, W., and Boltz, C. F.

I . , and Yamaguchi, N., Anal.

Anal. Chem., 1971, 43, 1265.

Paper A41164 Received April 25th, I984

Accepted June 5th) 1984

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