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Determination of indium by hydride generation and atomic-absorption spectrometry
CO39-9140/82/06OS19-02$03.00/O Copyright 0 1982Pergamon Press Ltd
Talanta. Vol. 29. pp. 519 to 520. 1982 Printed in Great Britain. All rights reserved
DETERMINATION OF INDIUM BY HYDRIDE GENERATION AND ATOMIC-ABSORPTION SPECTROMETRY I. S. BUSHEMAand J. B. HEADRIDGE Department of Chemistry, The University, Sheffield, England (Receioed 14 October 1981. Accepted 1 November 1981) Summary--Conditions are presented for the determination of indium by atomic-absorption spectrometry following hydride generation. Indium hydride produced by addition of sodium borohydride to a solution of indium in 3M hydrochloric acid is flushed with argon into an electrically heated silica tube. The mass of indium giving 1% absorption is 0.3 pg.
ution, onto the flat bottom. Then inject 2 ml of sodium borohydride solution,. Measure the absorbance of the exit argon gas within the silica tube at 1200”. Repeat the measurements for 40, 60, 80 and 100 ~1 volumes of indium solution. Construct a calibration graph of peak height or peak area us. mass of indium.
generation coupled with atomic-absorption spectrometry is a most useful technique for the determination of elements in the middle and towards the bottom of Groups IV, V and VI of the Periodic Table. namely germanium, tin, lead, arsenic, antimony, bismuth, selenium and tellurium.‘** During an attempt to extend the method to neighbouring elements, it was found that indium can be determined by atomicabsorption spectroscopy after generation of indium hydride from aqueous solution. The appropriate conditions are now presented. Hydride
RESULTS AND DISCUSSION
EXPERIMENTAL Apparatus and reagents
The hydride was generated in a cylindrical tube of 22 mm internal diameter, sealed with a flat bottom and fitted with a detachable top. Its total capacity was 70 ml. It was constructed with a side-arm fitted with a “Suba-seal” through which sodium borohydride solution could be injected. The inlet tube for argon was centrally situated and terminated 10 mm from the bottom of the tube, i.e., just above the surface of the liquid during the generation of hydride. The exit tube for argon was situated at the top of the vessel and contained a plug of glass wool to prevent any spray being carried forward. The vessel is like a Drechse1 bottle with a side-arm for injection of solutions. The exit tube was connected to a siliFti tube (8 mm bore x 17.5 cm long) with a short length of PVC tubing. The silica tube was heated electrically and positioned within a PerkinElmer 300s atomic-absorption spectrometer fitted with an indium hollow-cathode lamp. The resonance line at 303.9 nm was employed. Standard indium solution (1 mg/mf). Dissolve 0.1 g of indium metal in about 54 ml of hydrochloric acid (1 + 1) with warming. Dilute the solution to volume in a lOO-ml standard flask to produce a solution 3M in hydrochloric acid. Sodium borohydride solution, 2%. Prepared freshly each day. The solution was not stabilized with sodium hydroxide, because the acid concentration is an important factor in the hydride generation. Preparation of the calibration graph
Into the dry generating vessel through which argon is flowing at 2 I./min, inject 20 ~1 of standard indium sol-
Useful indium signals were obtained at silica-tube temperatures above 700”, with an optimum temperature range of 950-1250”. The optimum flow-rate of argon was 2 l./min. The optimum hydrochloric acid concentration of the indium solution for hydride generation was 3M for area measurements, but wellshaped peaks were produced within the acid concentration range 2-6M. When larger volumes (0.55 ml) of 3M hydrochloric acid containing 20-100 pg of indium were injected into the generating vessel, followed by sodium borohydride, much smaller absorbances were obtained and success in obtaining useful absorbances required the injection of volumes of indium solution smaller than or equal to 100 ~1. With peak height measurements the calibration graph for 20-100 pg of indium was slightly convex but that of peak area LX mass was a straight line through the origin. The mass of indium giving 1% absorption was 0.3 pg and for peak area (absorbance x time in seconds) measurements the slope of the calibration graph was 0.033 sec/pg of indium. Compared with atomic-absorption spectrometric methods involving hydride generation for germanium, tin, arsenic, antimony, bismuth, selenium and tellurium,‘.* the method for indium has poor sensitivity. However, the characteristic mass for indium by hydride generation is not appreciably greater than that for lead.‘.2 It may be possible to improve upon the sensitivity .by a detailed study of generating conditions. Previous information on the existence of indium hydride is scanty and the compound does not appear
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to have been well characterized.3*4 Not all the indium(III) is converted into indium hydride, because, in all cases, a black precipitate (presumably of metallic indium) was also produced on addition of sodium borohydride. The signal was definitely due to atomic absorption and not molecular absorption because no absorbance signal resulted when the indium hollowcathode lamp was replaced by a hydrogen lamp. With the reported reciprocal sensitivity of 0.3 pg of indium for 1% absorption, the method involving hydride production has little to commend it in comparison with nebulizing an indium solution into an airacetylene flame, for which the characteristic concentration is 0.5 pg/ml.’ Pulse nebulization of 100 ~1 of indium solution into a flame should produce a greater absorbance than the hydride method with a similar volume of solution6 but any future improvement in
the hydride method will make it more competitive with methods involving nebulization into flames. Acknowledgement-We thank the University of El-Fateh, Libya, for a studentship (for I.S.B.). REFERENCES
1. W. B. Robbins and J. A. Caruso, Anal. Chem., 1979, 51, 889A. 2. R. G. Godden and D. R. Thomerson, Analyst, 1980, 105, 1137. 3. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 4th Ed., p. 339. Wiley, New York, 1980. 4. K. M. Mackay, Hydrogen Compounds of the Metallic Elements, pp. 116 and 181. Spon, London, 1966. 5. W. J. Price, Spectrochemical Analysis by Atomic Absorption, p. 311. Heyden, London, 1979. 6. D. C. Manning, At. Abs. Newslett., 1975, 14, 99.
Talanta. Vol. 29. pp. 519 to 520. 1982 Printed in Great Britain. All rights reserved
DETERMINATION OF INDIUM BY HYDRIDE GENERATION AND ATOMIC-ABSORPTION SPECTROMETRY I. S. BUSHEMAand J. B. HEADRIDGE Department of Chemistry, The University, Sheffield, England (Receioed 14 October 1981. Accepted 1 November 1981) Summary--Conditions are presented for the determination of indium by atomic-absorption spectrometry following hydride generation. Indium hydride produced by addition of sodium borohydride to a solution of indium in 3M hydrochloric acid is flushed with argon into an electrically heated silica tube. The mass of indium giving 1% absorption is 0.3 pg.
ution, onto the flat bottom. Then inject 2 ml of sodium borohydride solution,. Measure the absorbance of the exit argon gas within the silica tube at 1200”. Repeat the measurements for 40, 60, 80 and 100 ~1 volumes of indium solution. Construct a calibration graph of peak height or peak area us. mass of indium.
generation coupled with atomic-absorption spectrometry is a most useful technique for the determination of elements in the middle and towards the bottom of Groups IV, V and VI of the Periodic Table. namely germanium, tin, lead, arsenic, antimony, bismuth, selenium and tellurium.‘** During an attempt to extend the method to neighbouring elements, it was found that indium can be determined by atomicabsorption spectroscopy after generation of indium hydride from aqueous solution. The appropriate conditions are now presented. Hydride
RESULTS AND DISCUSSION
EXPERIMENTAL Apparatus and reagents
The hydride was generated in a cylindrical tube of 22 mm internal diameter, sealed with a flat bottom and fitted with a detachable top. Its total capacity was 70 ml. It was constructed with a side-arm fitted with a “Suba-seal” through which sodium borohydride solution could be injected. The inlet tube for argon was centrally situated and terminated 10 mm from the bottom of the tube, i.e., just above the surface of the liquid during the generation of hydride. The exit tube for argon was situated at the top of the vessel and contained a plug of glass wool to prevent any spray being carried forward. The vessel is like a Drechse1 bottle with a side-arm for injection of solutions. The exit tube was connected to a siliFti tube (8 mm bore x 17.5 cm long) with a short length of PVC tubing. The silica tube was heated electrically and positioned within a PerkinElmer 300s atomic-absorption spectrometer fitted with an indium hollow-cathode lamp. The resonance line at 303.9 nm was employed. Standard indium solution (1 mg/mf). Dissolve 0.1 g of indium metal in about 54 ml of hydrochloric acid (1 + 1) with warming. Dilute the solution to volume in a lOO-ml standard flask to produce a solution 3M in hydrochloric acid. Sodium borohydride solution, 2%. Prepared freshly each day. The solution was not stabilized with sodium hydroxide, because the acid concentration is an important factor in the hydride generation. Preparation of the calibration graph
Into the dry generating vessel through which argon is flowing at 2 I./min, inject 20 ~1 of standard indium sol-
Useful indium signals were obtained at silica-tube temperatures above 700”, with an optimum temperature range of 950-1250”. The optimum flow-rate of argon was 2 l./min. The optimum hydrochloric acid concentration of the indium solution for hydride generation was 3M for area measurements, but wellshaped peaks were produced within the acid concentration range 2-6M. When larger volumes (0.55 ml) of 3M hydrochloric acid containing 20-100 pg of indium were injected into the generating vessel, followed by sodium borohydride, much smaller absorbances were obtained and success in obtaining useful absorbances required the injection of volumes of indium solution smaller than or equal to 100 ~1. With peak height measurements the calibration graph for 20-100 pg of indium was slightly convex but that of peak area LX mass was a straight line through the origin. The mass of indium giving 1% absorption was 0.3 pg and for peak area (absorbance x time in seconds) measurements the slope of the calibration graph was 0.033 sec/pg of indium. Compared with atomic-absorption spectrometric methods involving hydride generation for germanium, tin, arsenic, antimony, bismuth, selenium and tellurium,‘.* the method for indium has poor sensitivity. However, the characteristic mass for indium by hydride generation is not appreciably greater than that for lead.‘.2 It may be possible to improve upon the sensitivity .by a detailed study of generating conditions. Previous information on the existence of indium hydride is scanty and the compound does not appear
519
520
SHORT
COMMUNICATIONS
to have been well characterized.3*4 Not all the indium(III) is converted into indium hydride, because, in all cases, a black precipitate (presumably of metallic indium) was also produced on addition of sodium borohydride. The signal was definitely due to atomic absorption and not molecular absorption because no absorbance signal resulted when the indium hollowcathode lamp was replaced by a hydrogen lamp. With the reported reciprocal sensitivity of 0.3 pg of indium for 1% absorption, the method involving hydride production has little to commend it in comparison with nebulizing an indium solution into an airacetylene flame, for which the characteristic concentration is 0.5 pg/ml.’ Pulse nebulization of 100 ~1 of indium solution into a flame should produce a greater absorbance than the hydride method with a similar volume of solution6 but any future improvement in
the hydride method will make it more competitive with methods involving nebulization into flames. Acknowledgement-We thank the University of El-Fateh, Libya, for a studentship (for I.S.B.). REFERENCES
1. W. B. Robbins and J. A. Caruso, Anal. Chem., 1979, 51, 889A. 2. R. G. Godden and D. R. Thomerson, Analyst, 1980, 105, 1137. 3. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 4th Ed., p. 339. Wiley, New York, 1980. 4. K. M. Mackay, Hydrogen Compounds of the Metallic Elements, pp. 116 and 181. Spon, London, 1966. 5. W. J. Price, Spectrochemical Analysis by Atomic Absorption, p. 311. Heyden, London, 1979. 6. D. C. Manning, At. Abs. Newslett., 1975, 14, 99.