(5) E. S.Moyer and W. J. McCarthy, Anal. Chim. Acta, 48, 79 (1969). (6)G. G. Guilbault and T. Meisel, Anal. Chim. Acta, 50, 151 (1970). (7)E. S.Moyer and G. G. Guilbault, Anal. Chim. Acta, 52, 281 (1970). (8)G. G. Guilbault and E. S. Moyer, Anal. Lett., 3,563 (1970). (9)W. J. Brinkman and H. Freiser. Anal. Lett., 4, 513 (1971). (IO)C. P. Poole, "Electron Spin Resonance", Interscience, New York, 1967, pp 18-26. (11) M. Agerton and E. G. Janzen, Anal. Lett., 2, 457 (1969). (12) J. M. Fitzgerald and D. C. Warren, Anal. Lett., 3, 623 (1970). (13)P. 6. Ayscough, "Electron Spin Resonance in chemistry", Methuen and Go. Ltd., London, 1967. (14)H. M. Swartz, J. R. Bolton, and D. C. Borg, "Biological Application of Electron Spin Resonance", Wiley-lnterscience, New York, 1972. (15) R. B. Dean and W. J. Dixon, Anal. Chem., 23,636 (1951). (16) N. M. Downe and R. W. Heath, "Basic Statistical Methods", Harper and Row, New York, 1970,Chapter 9. (17)H. A. Laitinen, "Chemical Analysis", McGraw-Hill Book Go., inc.. New York, 1970,Chapter 26. (18) W. G. Bryson, D. P. Hubbard, 6. M. Peake, and J. Simpson, Anal. Chim. Acta,
77, 107 (1975). (19)J. E. Wertz and J. R. Bolton, "Electron Spin Resonance", McGraw-Hill, New
York, 1972,Chapters 9 and 11 and Appendix D. (20) Varian Analytical Instrument Division, E-3 EPR Spectrometer System, Technical Manual, Pub. No. 87-118-001,61 1 Hansen Way, Palo Alto, Calif. 94303. (21)S.Moore and W. H. Stein, J. Biol. Chem., 192, 660 (1951). (22)D. M. Clementz, T. J. Pinnavaia, and M. M. Mortland, J. Phys. Chem., 77, 196 (1973). (23)H. F. Walton and E. Murgia, "Ligand-Exchange Chromatography of Drugs
and Alkaloids", Abstracts, 166th National Meeting, American Chemical Society, Chicago, Ill., August 27-31, 1973,No. 65. (24)A. A. Schilt, "Analytical Applications of 1, IO-Phenanthroline and Related Compounds", Pergamon, London, 1969.
RECEIVEDfor review April 12, 1976. Accepted October 15, 1976. Financial support of Grant E-384 from the Robert A. Welch Foundation is gratefully acknowledged. The National Science Foundation and the Benjamin Clayton Foundation provided funds to the Department of Chemistry, University of Houston, for the ESR spectrometer.
Determination of Mercury in Silver or Silver Nitrate by Atomic Absorption Spectrometry W. W. White" and P. J. Murphy IndustrialLaboratory, Kodak Park Division, Eastman Kodak Company, Rochester, N. Y. 14650
A rapid method for the determination of trace quantities of mercury in silver or silver nitrate is described. Mercury Is separated from precipitatedAgBr as the HgBr4*- complex for subsequent atomic absorption analysis. The optimum condltions for the separation of mercury from silver as the bromide anionic complex have been studied. The relative standard deviation of the method is less than 10%.
The determination of submicrogram quantities of mercury in silver or silver nitrate has most often been an arduous task. Efforts to determine mercury directly by cold vapor atomic absorption have been largely unsuccessful. For example, various acidities and types of reducing agents were employed in the presence of silver ions. Because of the amalgamation characteristics of mercury with silver, none of these attempts was satisfactory ( 1 ) . A search of the literature revealed that there is presently no rapid and simple method for the determination of mercury in silver. Jackwert et al. ( 2 )have developed a colorimetric method to determine mercury in high purity silver by first concentrating the mercury in a silver iodide precipitate. However, this method is quite complex and requires 10 g of sample to detect 600 ng of mercury. The method proposed in this paper is rapid and suitable for the routine determination of mercury in silver bullion or silver nitrate. The method is based on the separation of mercury from silver as the HgBr42- complex. Insoluble silver bromide is filtered leaving the mercury complex in the filtrate. Tin(I1) chloride is added to the filtrate for subsequent atomic absorption analysis.
Mercury Stock Solution. See Coleman Analyzer Manual ( 3 ) . Silver Nitrate and Metal. 99.999% pure. All the chemicals used were reagent grade and "mercury-free". All glasswme was cleaned with concentrated "03 and rinsed thoroughly with distilled water before use. Procedure for Hg in Silver. Transfer a weighed sample (100-1000 mg) to a 100-ml beaker. Add 6 ml of 8 M nitric acid and gently warm until the sample completely dissolves. Cool the solution to room temperature and transfer it quantitatively to a 500-ml polyethylene bottle. Add 80 ml of distilled water and several drops of the Bromocresol Purple indicator to the bottle. Add ammonium hydroxide dropwise until a faint purple color is sustained (pH -6). Add 20 ml of the potassium bromide solution. Cap the bottle and shake for 1min. Allow the suspension to settle for a t least 2 min. Suction-filter the suspension onto a Gooch crucible fitted with two glass fiber filter pads. Transfer the filtrate to a BOD bottle. Add 10 ml of the tin(I1) chloride solution and determine the mercury content using a Coleman MAS-50 Analyzer (3). Procedure for Hg in Silver Nitrate. Transfer a weighed sample containing between 100-1000 mg of silver to a 500-ml polyethylene bottle. Add 80 ml of distilled watsr and 20 ml of the potassium bromide solution. Cap the bottle and continue as stated in the Procedure for Hg in Silver. (No pH adjustment should be necessary.)
RESULTS AND DISCUSSION Our experiments show that approximately 70% and 85%of the mercury is recovered from samples of silver and silver nitrate, respectively. Therefore it is recommended that a calibration curve be prepared by the analyst prior to the analysis of silver samples. Table I presents the calibration data for both silver and silver nitrate methods. It was not surprising to find that some coprecipitation of mercury occurs when the element is separated as the soluble bromide complex from insoluble silver bromide. The addition of ammonium hydroxide to adjust the pH in the silver metal method appears EXPERIMENTAL to increase the degree of coprecipitation. It was found that Reagents and Solutions. Tin(ZZ) Chloride Dihydrate. A stock total recovery of mercury is obtained at a pH of 4 to 6 using solution was prepared by dissolving 100 g of the salt in 100 ml of the appropriate correction factor that can be calculated from concentrated HC1 and diluting to 11. with distilled water. the calibration data (Table I). Likewise, no appreciable difPotassium Bromide. A stock solution was prepared by dissolving ferences in recovery were detected if precipitated samples 200 g of the salt in distilled water and diluting to 11. Bromocresol Purple ( 5 ~ 5 " - D i b r o m o - o - c r e s o l s u l ~ o n e p h t h a ~ e ~were ~ ) . allowed to stand between 2 and 120 min prior to filtration. A stock solution was prepared by grinding 200 mg of the dye in 3.5 ml of 0.1 N NaOH and then diluting to 500 ml with distilled water. The quantities of soluble silver remaining in the filtrate ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
255
Table I. Calibration Data for Silver and Silver Nitrate Methods (1 g of silver added in each case) Mercury recovered,Opg Mercury added, pg
Silver method
Silver nitrate method
0.025 0.050
0.020 0.040
0.100
0.080
0.250 0.500
0.200 0.385 0.520 0.690
0.020 0.045 0.090 0.220 0.425 0.630 0.850
0.700 1.000 a
Values represent an average of duplicate determinations.
upon the precipitation of 1-g samples of silver did not appear to have a significant effect on mercury recovery. For example, 0.250 pg of ionic mercury were determined in the presence of 200 and 400 pg of ionic silver. Virtually 100% recovery was observed when compared to determinations made without silver present. However, negative interference was observed when the same quantities of mercury were determined in the presence of 1000 pg of silver. Apparently some amalgamation occurs when higher levels of silver are present. Potassium bromide appears to be the only suitable halide capable of separating mercury from silver according to the analytical syptem proposed. Similar attempts using potassium iodide were unsuccessful because of filtration problems. The use of potassium chloride gave very low recovery for mercury in trial samples. Table I1 shows that mercury can be recovered from silver samples varying in weight from 100 to 1000 mg. Excess potassium bromide must be added to keep the HgBQ- in solution. Stoichiometric quantities of potassium bromide added to the silver resulted in almost complete coprecipitation of mercury with the silver bromide. Table I11 shows that diverse quantities of mercury can be
256
ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1 9 7 7
Table 11. Recovery of Mercury from Various Sample Weights (0.250 Mg added in each case) Silver, mg
Mercury recovered,a pg
100
0.260 0.265 0.255 0.252 0.247
250 500
750 1000
Values represent an average of duplicate determinations.
Table 111. Recovery of Diverse Quantities of Mercury in the Presence of One Gram of Silver Mercury present, pg
Mercury recovered,a pg
Re1 std dev, %
0.100
0.095 0.245 0.520 0.990
8.0
0.250 0.500 1.000
7.4
6.5 7.0
Each value is an average of five determinations.
recovered from 1-g samples of silver. No appreciable differences in recovery were detected when 0.100 to 1.000 pg of the element was added to the silver.
LITERATURE CITED (1) W. W. White and P. J. Murphy, unpublished work. (2) E. Jackwerth, E. Doring, and J. Lohmar, Fresenhs’ 2.Anal. Chem., 253, 195-201 (1971). ( 3 ) Coleman instruments, Maywood, Ill., Coleman Mercury Analyzer MAS-50, Operating Directions 50-900 (1971).
RECEIVEDfor review September 1, 1976. Accepted October 8, 1976.
