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Extraction and spectrophotometric determination of copper with thiobenzoylacetone (3-mercapto-1-phenylbut-2-en-1-one)
SHORT
2. V. G. Torgov, V. N. Andrievskii, E. N. Gil’bert, I. L. Kotlyarevskii, V. A. Mikhailov, A. V. Nikolaev, V. N. Pronin and D. D. Trotsenko, ibid., 1969, (5), 148. 3. A. V. Nikolaev, V. G. Torgov, V. A. Mikhailov, V. N. Andrievskii, K. A. Bakovets, M. F. Bondarenko, E. N. Gilbert, I. L. Kotlyarevskii, G. A. Mardezhova and S. S. Shatskava. ibid.. 1970. (4). 54. V. A. Mikha%v, S. .S. Shatskaya, D. D. Bogdanova and V. G. Torgov, ibid., 1976, (3), 34. V. A. Mikhailov. N. A. Korol and D. D. Bogdanova, ibid., 1975, (6), 29. 0. S. Shelovnikova, A. V. Nikolaev and R. J. Novoselov, ibid., 1976, (3), 44. M. F. Bondarenko, N. K. Lyapina, Yu. E. Nikitin, A. Kh. Sharipov, L. M. Zagryatskaya, V. S. Nikitina and M. A. Pais, ibid., 1973, (3), 16.
Tafanta, Vol. 25, pp. 161-166.
Pergamon
EXTRACTION
Press, 1978. Pnnted
165
COMMUNICATIONS
8. D. M. Chizhikov, B. P. Kreingauz and G. M. Denisova, ibid., 1970, (4), 120. 9. P. A. Lewis, D. F. C. Morris, E. L. Short and D. N. Waters, J. Less-Common Metals, 1976, 45, 193. 10. Z. Marczenko, Spectrophotometric Determination of Elements, Horwood, Chichester, 1976. 11. R. G. Pearson, J. Am. Chem. Sot., 1963, 85, 3533. 12. S. E. Livingstone, Quart. Rev., 1965, 19, 386. 13. A. G. Sillen and A. E. Martell, Stability Constants of Metal-Ion Complexes, The Chemical Society, London, 1964 14. L. V. Companys, X. T. Morer and A. T. Carbonell, Ajnidad 1974, 31, 559.
in Great Britain
AND SPECTROPHOTOMETRIC DETERMINATION COPPER WITH THIOBENZOYLACETONE (3-MERCAPTO-l-PHENYLBUT-2-EN-l-ONE)
OF
M. V. R. MURTI and S. M. KHOPKAR Department of Chemistry, Indian Institute of Technology, Bombay-400 076, India (Received 11 March 1977. Revised 4 October 1977. Accepted 20 October 1977)
Summary-The copper(H)-thiobenzoylacetone complex, extracted into benzene, is used for photometric determination of copper at 410nm after excess of reagent has been removed by scrubbing with a buffer at pH12. The extraction is quantitative over a broad pH range (3.5-9.5). The method is highly sensitive for the determination of copper.
The spectrophotometric determination of copper with l,l,l-trifluoro-3-(2-thenoylacetone) has been recently reported by Akaiwa et al.’ They claim advantages of this method over previous methods for solvent extraction of copper with various B-diketonesz4 It is now shown that the solvent extraction of copper with thiobenzoylacetone (HSBA) followed by removal of the excess of reagent by scrubbing with a buffer solution of pH 12.0, without decomposing the Cu(SBA), complex in benzene as a diluent, provides a more selective and fairly sensitive method.
General procedure
Transfer a sample solution containing l-20 pg of copper to a separatory funnel. Add 10ml of pH 6.0 buffer, dilute with distilled water to 25ml and shake the mixture with 10ml of 10e3M thiobenzoylacetone in benzene for about 10min. After settling, run off the aqueous phase, then shake the greenish yellow organic phase twice (for 2 min) with 10ml of pH 12 buffer to remove excess of reagent. Measure the absorbance of the copper complex at 410nm against a reagent blank prepared similarly. Compute the amount of copper from the calibration curve.
EXPERIMENTAL
A stock solution of copper sulphate was prepared by dissolving 3.935 g of the analytical grade reagent in 500 ml of water containing 1% sulphuric acid, and standardized complexometrically with EDTA, PAN being used as indicator. Solutions of lower concentration were prepared by appropriate dilution. Acetate buffer of pH 6.0 was prepared by dissolving 16g of sodium acetate in 1 litre of distilled water and acidifying with acetic acid to pH 6.0. For scrubbing, buffer solution of pH 12.0 was prepared by mixing 10 ml of 0.05M borax with 12.6 ml of O.lM sodium hydroxide. Thiobenzoylacetone was prepared from benzoylacetone as described earlier.’ A 10-3M solution in benzene was used. The reagent is preferably preserved in the refrigerator.
RESULTS
AND
DISCUSSION
E@ct of organic solvent
Various organic solvents such as benzene, toluene, xylene, chloroform, carbon tetrachloride, n-butanol, amyl alcohol and amyl acetate were tried. The absorbance of the complex was highest when benzene was used as the solvent. Absorption characteristics
Figure 1 shows the absorption spectrum of the copperthiobenzoylacetone complex measured against the reagent blank obtained by the procedure described, showing almost complete removal of residual HSBA from the organic phase. The spectrum of the reagent blank measured against benzene is also shown. The complex has
166
SHORT COMMUNICATIONS
Table 1. Tolerance for various ions in determination pH 6.0. Tolerance limit, /47
of 1Opg of Cu(I1) by extraction at
Foreign ion
5 x lo4 1 x 104
Rb+, Cs+ Mg’+, Ca’+, ST’+, Ba”, MI?+, Cl-, Br-, NO;, NO;, SO:-, tit”-, acetate-, Zn*+* Cd’+*, Pt4+, Be’+, I-, SO:-, PO:-, F-, tart3-, malonate*-, ReO;, CrO:Tl+, Sb”+, Rh3+, Fe3+*, Th4+, UO:‘, Ce4+, Zr4+, WO:-, Mo,O$;, AsO:-, VO; Co’+ Ni*+, thiourea-, ClO; Bi3+,‘Ir3+, A13+, SCN0s6+ Ru3+, Cr3+, Pbz+* Ag+, ‘Hg’+, Pd2+ , SaO:-, EDTA4-, CN-, ascorbate-
5 x 103 2 x lo3 1 x 103 5 x lo2 1 x lo2 None
* Cu(I1) was extracted at pH 4.0, to avoid co-extraction of these ions. Varying the volume from 2.5 to 15 ml of 10m3M reagent showed that 1Oml of reagent is adequate for complete extraction. The extraction is incomplete with a lower reagent concentration (5 x 10e4Jvf). Use of a higher reagent concentration (2 x 10e3M) does not improve the results. Varying the shaking time showed that the extraction was complete if the equilibration time exceeded 4-5 min. Interference
450
400
350 -
Wavelength
(nm) -c
Fig. 1. Absorption spectra of (A) reagent blank us. benzene (SBA 1 x 10w3M; pH 6.0; scrubbed with pH-12 buffer) and (B) copper-SBA complex (Cu 1.56 x lo-‘M; SBA 1 x lo-‘M; pH 6.0; scrubbed with pH-12 buffer). maximum absorbance at 4lOnm. The molar absorptivity of the complex is 3.46 x lo4 l.mole-’ cm-‘. The removal of the excess of reagent with buffer solution of pH 12 gave maximum difference in absorbance between the complex and the reagent blank. A similar technique was utilized by Uhlman et ~1.~ The calibration curve obtained at pH 6.0 is linear over the range 0.12-2.0 gg/ml at 410 nm. The sensitivity is comparable to that of earlier methods,6 and in those methods a large excess of reagent was generally used, especially with dithizone7 and cupral.’ The absorbance remains constant for 48 hr, or even longer if the complex is stored in the dark or diffused light. Reaction conditions The extraction was found to be quantitative at pH 3.5-9.5. When copper was extracted with different volumes and concentrations of reagent it was found that a single extraction with 10ml of 10-“&f reagent was quantitative.
Various ions were tested for possible interference (Table 1). The tolerance limit was set as the amount of foreign ion needed to cause f 2% error in the recovery of copper. Mercury(H), palladium(II), thiosulphate, cyanide, ascorbate and EDTA interfere seriously. The interference of bismuth and aluminium is eliminated by masking them with citric and malonic acids respectively. The reagent provides a good method for separation of copper from nickel, cobalt(II), iron(III), cadmium and zinc, which are generally associated with it. Copper is selectively extracted with thiobenzoylacetone, followed by extraction and photometric determination of nickel with dimethylglyoxime, cobalt with 1-nitroso-2-napthol, iron with l,lO-phenanthroline, cadmium with 4-(2-pyridylazo)resorcinol and zinc with trioctylamine6. REFERENCES
1. H. Akaiwa, H. Kawamoto and F. Izumi, Talanta, 1976, 23, 403. 2. S. M. Khopkar and A. K. De, Z. Anal. Chem., 1959, 171, 241. 3. V. M. Shinde and S. M. Khopkar, Anal. Chem., 1969, 41, 342. 4. E. Uhleman, B. Schuknecht, K. D. Busse, and V. Pohl, Anal. Chim. Acta, 1971, 56, 185. 5. M. V. R. Murti and S. M. Khopkar, Indian J. Chem., 1976, 14A, 455. 6. A. K. De, S. M. Khopkar and R. A. Chalmers, Solvent Extraction of Metals, Van Nostrand-Reinhold, London, 1970. 7. R. W. Geiger and E. B. Sandell, Anal. Chim. Acta, 1953, 8, 157. 8. G. Gottschalk, Z. Anal. Chem., 1963, 194, 321.
2. V. G. Torgov, V. N. Andrievskii, E. N. Gil’bert, I. L. Kotlyarevskii, V. A. Mikhailov, A. V. Nikolaev, V. N. Pronin and D. D. Trotsenko, ibid., 1969, (5), 148. 3. A. V. Nikolaev, V. G. Torgov, V. A. Mikhailov, V. N. Andrievskii, K. A. Bakovets, M. F. Bondarenko, E. N. Gilbert, I. L. Kotlyarevskii, G. A. Mardezhova and S. S. Shatskava. ibid.. 1970. (4). 54. V. A. Mikha%v, S. .S. Shatskaya, D. D. Bogdanova and V. G. Torgov, ibid., 1976, (3), 34. V. A. Mikhailov. N. A. Korol and D. D. Bogdanova, ibid., 1975, (6), 29. 0. S. Shelovnikova, A. V. Nikolaev and R. J. Novoselov, ibid., 1976, (3), 44. M. F. Bondarenko, N. K. Lyapina, Yu. E. Nikitin, A. Kh. Sharipov, L. M. Zagryatskaya, V. S. Nikitina and M. A. Pais, ibid., 1973, (3), 16.
Tafanta, Vol. 25, pp. 161-166.
Pergamon
EXTRACTION
Press, 1978. Pnnted
165
COMMUNICATIONS
8. D. M. Chizhikov, B. P. Kreingauz and G. M. Denisova, ibid., 1970, (4), 120. 9. P. A. Lewis, D. F. C. Morris, E. L. Short and D. N. Waters, J. Less-Common Metals, 1976, 45, 193. 10. Z. Marczenko, Spectrophotometric Determination of Elements, Horwood, Chichester, 1976. 11. R. G. Pearson, J. Am. Chem. Sot., 1963, 85, 3533. 12. S. E. Livingstone, Quart. Rev., 1965, 19, 386. 13. A. G. Sillen and A. E. Martell, Stability Constants of Metal-Ion Complexes, The Chemical Society, London, 1964 14. L. V. Companys, X. T. Morer and A. T. Carbonell, Ajnidad 1974, 31, 559.
in Great Britain
AND SPECTROPHOTOMETRIC DETERMINATION COPPER WITH THIOBENZOYLACETONE (3-MERCAPTO-l-PHENYLBUT-2-EN-l-ONE)
OF
M. V. R. MURTI and S. M. KHOPKAR Department of Chemistry, Indian Institute of Technology, Bombay-400 076, India (Received 11 March 1977. Revised 4 October 1977. Accepted 20 October 1977)
Summary-The copper(H)-thiobenzoylacetone complex, extracted into benzene, is used for photometric determination of copper at 410nm after excess of reagent has been removed by scrubbing with a buffer at pH12. The extraction is quantitative over a broad pH range (3.5-9.5). The method is highly sensitive for the determination of copper.
The spectrophotometric determination of copper with l,l,l-trifluoro-3-(2-thenoylacetone) has been recently reported by Akaiwa et al.’ They claim advantages of this method over previous methods for solvent extraction of copper with various B-diketonesz4 It is now shown that the solvent extraction of copper with thiobenzoylacetone (HSBA) followed by removal of the excess of reagent by scrubbing with a buffer solution of pH 12.0, without decomposing the Cu(SBA), complex in benzene as a diluent, provides a more selective and fairly sensitive method.
General procedure
Transfer a sample solution containing l-20 pg of copper to a separatory funnel. Add 10ml of pH 6.0 buffer, dilute with distilled water to 25ml and shake the mixture with 10ml of 10e3M thiobenzoylacetone in benzene for about 10min. After settling, run off the aqueous phase, then shake the greenish yellow organic phase twice (for 2 min) with 10ml of pH 12 buffer to remove excess of reagent. Measure the absorbance of the copper complex at 410nm against a reagent blank prepared similarly. Compute the amount of copper from the calibration curve.
EXPERIMENTAL
A stock solution of copper sulphate was prepared by dissolving 3.935 g of the analytical grade reagent in 500 ml of water containing 1% sulphuric acid, and standardized complexometrically with EDTA, PAN being used as indicator. Solutions of lower concentration were prepared by appropriate dilution. Acetate buffer of pH 6.0 was prepared by dissolving 16g of sodium acetate in 1 litre of distilled water and acidifying with acetic acid to pH 6.0. For scrubbing, buffer solution of pH 12.0 was prepared by mixing 10 ml of 0.05M borax with 12.6 ml of O.lM sodium hydroxide. Thiobenzoylacetone was prepared from benzoylacetone as described earlier.’ A 10-3M solution in benzene was used. The reagent is preferably preserved in the refrigerator.
RESULTS
AND
DISCUSSION
E@ct of organic solvent
Various organic solvents such as benzene, toluene, xylene, chloroform, carbon tetrachloride, n-butanol, amyl alcohol and amyl acetate were tried. The absorbance of the complex was highest when benzene was used as the solvent. Absorption characteristics
Figure 1 shows the absorption spectrum of the copperthiobenzoylacetone complex measured against the reagent blank obtained by the procedure described, showing almost complete removal of residual HSBA from the organic phase. The spectrum of the reagent blank measured against benzene is also shown. The complex has
166
SHORT COMMUNICATIONS
Table 1. Tolerance for various ions in determination pH 6.0. Tolerance limit, /47
of 1Opg of Cu(I1) by extraction at
Foreign ion
5 x lo4 1 x 104
Rb+, Cs+ Mg’+, Ca’+, ST’+, Ba”, MI?+, Cl-, Br-, NO;, NO;, SO:-, tit”-, acetate-, Zn*+* Cd’+*, Pt4+, Be’+, I-, SO:-, PO:-, F-, tart3-, malonate*-, ReO;, CrO:Tl+, Sb”+, Rh3+, Fe3+*, Th4+, UO:‘, Ce4+, Zr4+, WO:-, Mo,O$;, AsO:-, VO; Co’+ Ni*+, thiourea-, ClO; Bi3+,‘Ir3+, A13+, SCN0s6+ Ru3+, Cr3+, Pbz+* Ag+, ‘Hg’+, Pd2+ , SaO:-, EDTA4-, CN-, ascorbate-
5 x 103 2 x lo3 1 x 103 5 x lo2 1 x lo2 None
* Cu(I1) was extracted at pH 4.0, to avoid co-extraction of these ions. Varying the volume from 2.5 to 15 ml of 10m3M reagent showed that 1Oml of reagent is adequate for complete extraction. The extraction is incomplete with a lower reagent concentration (5 x 10e4Jvf). Use of a higher reagent concentration (2 x 10e3M) does not improve the results. Varying the shaking time showed that the extraction was complete if the equilibration time exceeded 4-5 min. Interference
450
400
350 -
Wavelength
(nm) -c
Fig. 1. Absorption spectra of (A) reagent blank us. benzene (SBA 1 x 10w3M; pH 6.0; scrubbed with pH-12 buffer) and (B) copper-SBA complex (Cu 1.56 x lo-‘M; SBA 1 x lo-‘M; pH 6.0; scrubbed with pH-12 buffer). maximum absorbance at 4lOnm. The molar absorptivity of the complex is 3.46 x lo4 l.mole-’ cm-‘. The removal of the excess of reagent with buffer solution of pH 12 gave maximum difference in absorbance between the complex and the reagent blank. A similar technique was utilized by Uhlman et ~1.~ The calibration curve obtained at pH 6.0 is linear over the range 0.12-2.0 gg/ml at 410 nm. The sensitivity is comparable to that of earlier methods,6 and in those methods a large excess of reagent was generally used, especially with dithizone7 and cupral.’ The absorbance remains constant for 48 hr, or even longer if the complex is stored in the dark or diffused light. Reaction conditions The extraction was found to be quantitative at pH 3.5-9.5. When copper was extracted with different volumes and concentrations of reagent it was found that a single extraction with 10ml of 10-“&f reagent was quantitative.
Various ions were tested for possible interference (Table 1). The tolerance limit was set as the amount of foreign ion needed to cause f 2% error in the recovery of copper. Mercury(H), palladium(II), thiosulphate, cyanide, ascorbate and EDTA interfere seriously. The interference of bismuth and aluminium is eliminated by masking them with citric and malonic acids respectively. The reagent provides a good method for separation of copper from nickel, cobalt(II), iron(III), cadmium and zinc, which are generally associated with it. Copper is selectively extracted with thiobenzoylacetone, followed by extraction and photometric determination of nickel with dimethylglyoxime, cobalt with 1-nitroso-2-napthol, iron with l,lO-phenanthroline, cadmium with 4-(2-pyridylazo)resorcinol and zinc with trioctylamine6. REFERENCES
1. H. Akaiwa, H. Kawamoto and F. Izumi, Talanta, 1976, 23, 403. 2. S. M. Khopkar and A. K. De, Z. Anal. Chem., 1959, 171, 241. 3. V. M. Shinde and S. M. Khopkar, Anal. Chem., 1969, 41, 342. 4. E. Uhleman, B. Schuknecht, K. D. Busse, and V. Pohl, Anal. Chim. Acta, 1971, 56, 185. 5. M. V. R. Murti and S. M. Khopkar, Indian J. Chem., 1976, 14A, 455. 6. A. K. De, S. M. Khopkar and R. A. Chalmers, Solvent Extraction of Metals, Van Nostrand-Reinhold, London, 1970. 7. R. W. Geiger and E. B. Sandell, Anal. Chim. Acta, 1953, 8, 157. 8. G. Gottschalk, Z. Anal. Chem., 1963, 194, 321.