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The extraction and determination of thiocyanate complexes by use of polyurethane foam
Tdanra, Vol. 30, No. 8, pp. 62&622, 1983 Printed in Great Britain. All rights reserved
Copyright 0
0039.9140/83 %3.00+0.00 1983 Pergamon Press Ltd
THE EXTRACTION AND DETERMINATION OF THIOCYANATE COMPLEXES BY USE OF POLYURETHANE FOAM A. CHOW and S. L. Department
of Chemistry,
University
GINSBERG
of Manitoba,
Winnipeg,
Manitoba,
Canada
(Received 27 August 1982. Revised 8 January 1983. Accepted 4 February 1983) Summary-Metal thiocyanate metal contents determined by collectively from 3.OM NH&I simultaneously extracted from
solutions were extracted with polyether-type polyurethane foam and the X-ray fluorescence. Iron, cobalt and zinc were extracted individually and and I .OM NH.$CN solutions. Similarly platinum and palladium could be 0.12M NH,SCN and 5.OM NH&I for subsequent determination. The metal
extractions were more than 95% complete and the determination presence of the others.
The direct determination of preconcentrated metal complexes may offer the advantages of higher metal concentrations, lower amounts of matrix and interferents, and faster analyses. Metal complexes extracted into polyurethane foam can be determined non-destructively by use of neutron activation,’ radiochemical tracers,2m5 visual colorimetry,6,7 and by X-ray fluorescence.’ The extraction of several metal thiocyanates by polyurethane has been described,9m’7 and it appears that multielement extractions and determinations might be possible for a variety of species. The present paper describes the extraction of platinum and palladium, or of iron, cobalt and zinc, from thiocyanate solutions with polyether-type polyurethane foam, and the subsequent determination of these metals on the polymer by X-ray fluorescence. EXPERIMENTAL
of one metal was not affected by the
Extraction of iron, cobalt and zinc
Previous work with the thiocyanate system8 has shown that the extraction of cobalt is most efficient from high ionic strength solutions. For the present experiments, 50 ml of a solution of an appropriate amount of the test metal in 3.OM ammonium chloride/l.OM ammonium thiocyanate medium were extracted with a single 0.127 k 0.001 g foam disc, by manual squeezing with a flat-bottomed plunger in a glass cell. The extractions were repeated to establish the minimum extraction time for the individual complexes. For l-5 ppm solutions of iron, cobalt or zinc, 10 min were sufficient but for 5-10 ppm solutions 20 min were required. After the extraction the solutions contained less than 0.05 ppm of the metals, even though equilibrium was not obtained. This corresponds to an extraction coefficient of 8 x 103-8 x IO4 for cobalt thiocyanate, which may be compared with the > IO6 reported previously. R” The use of non-equilibrium conditions makes this method more practical since only a small amount of the test element is left unextracted, and the time needed is far less than the minimum of 6 hr required to establish equilibrium. Extraction of platinum and palladium
Apparatus Atomic-absorption spectrometry was used to evaluate the efficiency of metal extraction as reported previously.* An energy-dispersive X-ray fluorescence system* was used with a polyurethane-foam sample-holder held at a fixed distance from the source and detector by 4-pm thick Mylar film. Uniform foam discs (2.0 cm diameter, 1.6cm thick) were cut from commercial, polyether-type polyurethane foam sheet by compressing it with a large brass block and rotating a sharpened brass tube (2.0 cm diameter) in a corresponding hole drilled through the block. The discs were thoroughly cleaned* before use. Cobalt and zinc solutions were made by dissolving the metals in hydrochloric acid and diluting to produce a lOOO-ppm standard in lo/, v/v acid. A lOOO-ppm iron solution was prepared similarly in 5% v/v nitric acid. Platinum and palladium solutions were prepared from PtCI, and PdCI, in 0.12M hydrochloric acid. Solutions (5.OM) of ammonium chloride and ammonium thiocyanate were prepared from the reagent-grade salts in water. Because it contained trace amounts of iron, the 5M thiocyanate solution was filtered through polyurethane foam to remove this background contaminant. All water used was distilled and demineralized. 620
Low thiocyanate concentrations provide the most efficient extraction of platinum and palladium.‘6~‘7 For the present studies of the extraction of palladium alone, 0.006M ammonium thiocyanate/2M ammonium chloride medium was used, and for platinum alone or with palladium, 0.12M ammonium thiocyanate/5M ammonium chloride medium. The extraction of platinum with or without palladium required the samples to be heated at 90” for 10 min before extraction. Samples (100 ml) were extracted for 30 min with 0.128 + 0.001 g foam discs, with an automatic squeezer.” The extraction efficiency for l-10 ppm platinum or palladium solution was at least 95%. Analysis Before X-ray fluorescence analysis, the foams were squeezed dry and then air-dried overnight. The sample foam was placed in the hole cut in the polyurethane-foam sampleholder attached to the X-ray fluorescence exciter/detector unit. The fluorescence spectrum was accumulated for 100 set and the peak areas for each metal were integrated individually. Each foam was counted at least three times on each side. The results indicate that repeated counting of the same side had a variation of less than & 3% and that the two sides agreed within + 5%.
SHORT
0
20
40 METAL
60
CONCENTRATION
80
621
COMMUNEATIONS
100
(ppml
PALLADIUM
CONCENTRATION
,ppml
Fig. I. X-Ray fluorescence intensity for iron, cobalt and zinc. Conditions: 50 ml of solution containing l-10 ppm of metal in 3.OM NH,CI and l.OM NH&N, extracted with 0.127g of polyurethane foam; x---x iron; A-----n zinc; 0-O cobalt.
Fig. 3. The effect of varying palladium concentration on the X-ray fluorescence of platinum. Conditions as for Fig. 2 but 1 ppm of platinum and I-10 ppm of palladium: l palladium; 0 platinum.
Several variations in the sample-holder arrangement were evaluated such as distance of the sample above the detector, change in sample-holder design, and confinement of the sample to a smaller volume but none provided significantly better precision or sensitivity than the method outlined and all were less convenient. Regular commercial foam was adequate for use in the procedure, but Hypol’” foam appeared more free from metals than the others tested. Polyester foam does not give large distribution coefficients and does not provide rapid extraction. The average X-ray fluorescence values obtained for individual iron, cobalt and zinc samples were a reasonably linear function of the metal concentrations (Fig. 1). Mixtures of iron, cobalt and zinc in concentration combinations ofl+l+l, l+l+O, 1+5+5,0+5+5and5+5+5 ppm were also extracted, and the number of counts obtained by X-ray fluorescence were compared with those obtained for the corresponding concentrations of the individual elements. The results indicated that there is little or no mutual interference between these elements in either the extraction or the X-ray fluorescence determination. The values for zinc and cobalt were within + 5% of those obtained in the absence of the other metals. The values for iron were not as
accurate, owing to some effect of the other elements on the X-ray fluorescence background for iron. This difficulty causes inaccuracy in determination of iron at the 1-ppm level, but reasonably correct values are obtained at the 5-ppm level. A higher count rate would significantly increase the precision of the analysis and permit a more sensitive determination. The individual X-ray fluorescence calibration curves for platinum and palladium were linear up to at least 8 ppm. The extraction and determination of 1 ppm palladium in the presence of up to 10 ppm platinum and of 1 ppm platinum in the presence of up to IO ppm palladium are completely unaffected by the second metal. The fluorescence count rate for the metal determined remained constant within +4.5x in the presence of l-10 ppm of the other metal. The higher sensitivity for platinum and palladium than for iron, cobalt and zinc allows more precise determination. In addition the rapid equilibration with the polyurethane foam gives a more consistent and quantitative extraction of platinum and palladium.
CONCLUSION The ements
0 80 -
60 -
; 8
Fig. 2. The effect of varying platinum concentration on the X-ray fluorescence of palladium. Conditions: 100 ml of solution containing 1 ppm of palladium and I-10 ppm of platinum in 5.OM NH&l and 0.12M NH,SCN, extracted with 0.128 g of polyurethane foam: 0 platinum; l palladium.
simultaneous at
low
determination
concentrations
of
is possible
several by
elcom-
bining polyurethane foam extraction with X-ray fluorescence analysis. Longer extraction times and larger sample volumes would extend the methods to lower concentrations and more sophisticated X-ray equipment could extend the lower limit of analysis by one or two orders of magnitude. The major limiting factor is the background which depends on freedom from overlap of the peaks for the extracted elements with each other or with those of the elements already present in the polyurethane foam. These procedures require the simultaneous quantitative extraction of the metal complexes and are therefore dependent on the solution chemistry of the system. The thiocyanate system is a particularly useful one, but many complexing agents can be used for the simultaneous extraction of a variety of metals. Acknowledgements-This work was financially supported by the Natural Sciences and Engineering Research Council
622 of Canada Manitoba.
SHORT
and
by the
Research
Board,
University
COMMlJNlCATlONS
of
REFERENCES
1. P. Schiller and G. B. Cook, Anal. Chim. Acta, 1971,54, 364. 2. S. Palagyi and T. Braun, J. Radioanal. Chem., 1979,51, 267. 3. S. Palagyi and E. Bila, Radiochem. Radioanal. Lett., 1978, 32, 87. 4. T. Braun and S. Palagyi, Anal. Chem., 1979, 51, 1697. 5. S. Palagyi and R. Markusova, Radiochem. Radioanal. Lett., 1978, 32, 103. 6. T. Tanaka, K. Hiiro and A. Kawahara, Buns&i Kagaku, 1973, 22, 523; Chem. Abstr., 1973, 79, 87234.
7. T. Braun and A. B. Farag, Anal. Chim. Acta, 1974, 73, 301. 8. A. Chow, G. T. Yamashita and R. F. Hamon, Talanta, 1981, 28, 437. 9. T. Braun, A. B. Farag and M. P. Maloney, Anal. Chim. Acta, 1977, 93, 191. 10. T. Braun and A. B. Farag, ibid., 1978, 98, 133. 11. T. Braun and M. N. Abbas, ibid., 1980, 119, 113. 12. R. F. Hamon, Ph.D. Thesis, University of Manitoba, 1981. 13. R. F. Hamon and A. Chow, Abstracts 60th CIC Conference, Montreal, Canada, 1977. 14. M. P. Maloney, G. J. Moody and J. D. R. Thomas, Proc. Chem. Sot. Anal. Div., 1977, 14, 244. 15. T. Braun and M. N. Abbas, Anal. Chim. Acra, 1982, 134, 321. 16. S. J. Al-Bazi and A. Chow, Anal. Chem., 198 1,53, 1073. 17. Idem, ibid., in the press.
Copyright 0
0039.9140/83 %3.00+0.00 1983 Pergamon Press Ltd
THE EXTRACTION AND DETERMINATION OF THIOCYANATE COMPLEXES BY USE OF POLYURETHANE FOAM A. CHOW and S. L. Department
of Chemistry,
University
GINSBERG
of Manitoba,
Winnipeg,
Manitoba,
Canada
(Received 27 August 1982. Revised 8 January 1983. Accepted 4 February 1983) Summary-Metal thiocyanate metal contents determined by collectively from 3.OM NH&I simultaneously extracted from
solutions were extracted with polyether-type polyurethane foam and the X-ray fluorescence. Iron, cobalt and zinc were extracted individually and and I .OM NH.$CN solutions. Similarly platinum and palladium could be 0.12M NH,SCN and 5.OM NH&I for subsequent determination. The metal
extractions were more than 95% complete and the determination presence of the others.
The direct determination of preconcentrated metal complexes may offer the advantages of higher metal concentrations, lower amounts of matrix and interferents, and faster analyses. Metal complexes extracted into polyurethane foam can be determined non-destructively by use of neutron activation,’ radiochemical tracers,2m5 visual colorimetry,6,7 and by X-ray fluorescence.’ The extraction of several metal thiocyanates by polyurethane has been described,9m’7 and it appears that multielement extractions and determinations might be possible for a variety of species. The present paper describes the extraction of platinum and palladium, or of iron, cobalt and zinc, from thiocyanate solutions with polyether-type polyurethane foam, and the subsequent determination of these metals on the polymer by X-ray fluorescence. EXPERIMENTAL
of one metal was not affected by the
Extraction of iron, cobalt and zinc
Previous work with the thiocyanate system8 has shown that the extraction of cobalt is most efficient from high ionic strength solutions. For the present experiments, 50 ml of a solution of an appropriate amount of the test metal in 3.OM ammonium chloride/l.OM ammonium thiocyanate medium were extracted with a single 0.127 k 0.001 g foam disc, by manual squeezing with a flat-bottomed plunger in a glass cell. The extractions were repeated to establish the minimum extraction time for the individual complexes. For l-5 ppm solutions of iron, cobalt or zinc, 10 min were sufficient but for 5-10 ppm solutions 20 min were required. After the extraction the solutions contained less than 0.05 ppm of the metals, even though equilibrium was not obtained. This corresponds to an extraction coefficient of 8 x 103-8 x IO4 for cobalt thiocyanate, which may be compared with the > IO6 reported previously. R” The use of non-equilibrium conditions makes this method more practical since only a small amount of the test element is left unextracted, and the time needed is far less than the minimum of 6 hr required to establish equilibrium. Extraction of platinum and palladium
Apparatus Atomic-absorption spectrometry was used to evaluate the efficiency of metal extraction as reported previously.* An energy-dispersive X-ray fluorescence system* was used with a polyurethane-foam sample-holder held at a fixed distance from the source and detector by 4-pm thick Mylar film. Uniform foam discs (2.0 cm diameter, 1.6cm thick) were cut from commercial, polyether-type polyurethane foam sheet by compressing it with a large brass block and rotating a sharpened brass tube (2.0 cm diameter) in a corresponding hole drilled through the block. The discs were thoroughly cleaned* before use. Cobalt and zinc solutions were made by dissolving the metals in hydrochloric acid and diluting to produce a lOOO-ppm standard in lo/, v/v acid. A lOOO-ppm iron solution was prepared similarly in 5% v/v nitric acid. Platinum and palladium solutions were prepared from PtCI, and PdCI, in 0.12M hydrochloric acid. Solutions (5.OM) of ammonium chloride and ammonium thiocyanate were prepared from the reagent-grade salts in water. Because it contained trace amounts of iron, the 5M thiocyanate solution was filtered through polyurethane foam to remove this background contaminant. All water used was distilled and demineralized. 620
Low thiocyanate concentrations provide the most efficient extraction of platinum and palladium.‘6~‘7 For the present studies of the extraction of palladium alone, 0.006M ammonium thiocyanate/2M ammonium chloride medium was used, and for platinum alone or with palladium, 0.12M ammonium thiocyanate/5M ammonium chloride medium. The extraction of platinum with or without palladium required the samples to be heated at 90” for 10 min before extraction. Samples (100 ml) were extracted for 30 min with 0.128 + 0.001 g foam discs, with an automatic squeezer.” The extraction efficiency for l-10 ppm platinum or palladium solution was at least 95%. Analysis Before X-ray fluorescence analysis, the foams were squeezed dry and then air-dried overnight. The sample foam was placed in the hole cut in the polyurethane-foam sampleholder attached to the X-ray fluorescence exciter/detector unit. The fluorescence spectrum was accumulated for 100 set and the peak areas for each metal were integrated individually. Each foam was counted at least three times on each side. The results indicate that repeated counting of the same side had a variation of less than & 3% and that the two sides agreed within + 5%.
SHORT
0
20
40 METAL
60
CONCENTRATION
80
621
COMMUNEATIONS
100
(ppml
PALLADIUM
CONCENTRATION
,ppml
Fig. I. X-Ray fluorescence intensity for iron, cobalt and zinc. Conditions: 50 ml of solution containing l-10 ppm of metal in 3.OM NH,CI and l.OM NH&N, extracted with 0.127g of polyurethane foam; x---x iron; A-----n zinc; 0-O cobalt.
Fig. 3. The effect of varying palladium concentration on the X-ray fluorescence of platinum. Conditions as for Fig. 2 but 1 ppm of platinum and I-10 ppm of palladium: l palladium; 0 platinum.
Several variations in the sample-holder arrangement were evaluated such as distance of the sample above the detector, change in sample-holder design, and confinement of the sample to a smaller volume but none provided significantly better precision or sensitivity than the method outlined and all were less convenient. Regular commercial foam was adequate for use in the procedure, but Hypol’” foam appeared more free from metals than the others tested. Polyester foam does not give large distribution coefficients and does not provide rapid extraction. The average X-ray fluorescence values obtained for individual iron, cobalt and zinc samples were a reasonably linear function of the metal concentrations (Fig. 1). Mixtures of iron, cobalt and zinc in concentration combinations ofl+l+l, l+l+O, 1+5+5,0+5+5and5+5+5 ppm were also extracted, and the number of counts obtained by X-ray fluorescence were compared with those obtained for the corresponding concentrations of the individual elements. The results indicated that there is little or no mutual interference between these elements in either the extraction or the X-ray fluorescence determination. The values for zinc and cobalt were within + 5% of those obtained in the absence of the other metals. The values for iron were not as
accurate, owing to some effect of the other elements on the X-ray fluorescence background for iron. This difficulty causes inaccuracy in determination of iron at the 1-ppm level, but reasonably correct values are obtained at the 5-ppm level. A higher count rate would significantly increase the precision of the analysis and permit a more sensitive determination. The individual X-ray fluorescence calibration curves for platinum and palladium were linear up to at least 8 ppm. The extraction and determination of 1 ppm palladium in the presence of up to 10 ppm platinum and of 1 ppm platinum in the presence of up to IO ppm palladium are completely unaffected by the second metal. The fluorescence count rate for the metal determined remained constant within +4.5x in the presence of l-10 ppm of the other metal. The higher sensitivity for platinum and palladium than for iron, cobalt and zinc allows more precise determination. In addition the rapid equilibration with the polyurethane foam gives a more consistent and quantitative extraction of platinum and palladium.
CONCLUSION The ements
0 80 -
60 -
; 8
Fig. 2. The effect of varying platinum concentration on the X-ray fluorescence of palladium. Conditions: 100 ml of solution containing 1 ppm of palladium and I-10 ppm of platinum in 5.OM NH&l and 0.12M NH,SCN, extracted with 0.128 g of polyurethane foam: 0 platinum; l palladium.
simultaneous at
low
determination
concentrations
of
is possible
several by
elcom-
bining polyurethane foam extraction with X-ray fluorescence analysis. Longer extraction times and larger sample volumes would extend the methods to lower concentrations and more sophisticated X-ray equipment could extend the lower limit of analysis by one or two orders of magnitude. The major limiting factor is the background which depends on freedom from overlap of the peaks for the extracted elements with each other or with those of the elements already present in the polyurethane foam. These procedures require the simultaneous quantitative extraction of the metal complexes and are therefore dependent on the solution chemistry of the system. The thiocyanate system is a particularly useful one, but many complexing agents can be used for the simultaneous extraction of a variety of metals. Acknowledgements-This work was financially supported by the Natural Sciences and Engineering Research Council
622 of Canada Manitoba.
SHORT
and
by the
Research
Board,
University
COMMlJNlCATlONS
of
REFERENCES
1. P. Schiller and G. B. Cook, Anal. Chim. Acta, 1971,54, 364. 2. S. Palagyi and T. Braun, J. Radioanal. Chem., 1979,51, 267. 3. S. Palagyi and E. Bila, Radiochem. Radioanal. Lett., 1978, 32, 87. 4. T. Braun and S. Palagyi, Anal. Chem., 1979, 51, 1697. 5. S. Palagyi and R. Markusova, Radiochem. Radioanal. Lett., 1978, 32, 103. 6. T. Tanaka, K. Hiiro and A. Kawahara, Buns&i Kagaku, 1973, 22, 523; Chem. Abstr., 1973, 79, 87234.
7. T. Braun and A. B. Farag, Anal. Chim. Acta, 1974, 73, 301. 8. A. Chow, G. T. Yamashita and R. F. Hamon, Talanta, 1981, 28, 437. 9. T. Braun, A. B. Farag and M. P. Maloney, Anal. Chim. Acta, 1977, 93, 191. 10. T. Braun and A. B. Farag, ibid., 1978, 98, 133. 11. T. Braun and M. N. Abbas, ibid., 1980, 119, 113. 12. R. F. Hamon, Ph.D. Thesis, University of Manitoba, 1981. 13. R. F. Hamon and A. Chow, Abstracts 60th CIC Conference, Montreal, Canada, 1977. 14. M. P. Maloney, G. J. Moody and J. D. R. Thomas, Proc. Chem. Sot. Anal. Div., 1977, 14, 244. 15. T. Braun and M. N. Abbas, Anal. Chim. Acra, 1982, 134, 321. 16. S. J. Al-Bazi and A. Chow, Anal. Chem., 198 1,53, 1073. 17. Idem, ibid., in the press.