Ai?alyst March 1983 VoZ. 108 $9. 305-309 305 Determination of Tellurium by Atomic-absorption Spectroscopy with Elect rother ma1 Atom isat ion after Pre-concentration by Hydride Generation and Trapping William A. Maher" Departvnent of Oceanography University of Southampton Southampton SO9 5NH A procedure for the determination of tellurium a t sub-microgram levels bv atomic-absorption spectroscopy with electrothermal atomisation after the evolution and trapping of hydrogen telluride is described. Interferences are observed in the presence of silver(I) copper(II) mercury(I1) and selenium(1V) but can be overcome by suitable pre-treatment procedures. The detection limit (based on four times the standard deviation of six blank measurements) is 0.006 pg and the coefficient of variation is 4% at the 0.3-pg level.Keywords Tellurium ; Jlydride generation and trapping ; atornic-absorption spectroscopy ; electrothermal atomisation ; interferences Tellurium is used extensively in the electronics industry and is a potentially toxic environ-mental pollutant .l Hence sensitive methods of determination are required for monitoring tellurium concentrations in the environment and to allow the biochemical role and toxico-logical effects of tellurium to be assessed. Many techniques are available for the determination of tellurium.2-6 A widely reported technique has been hydride generation - atomic-absorption spectroscopy. The prior con-version of tellurium into hydrogen telluride is used to increase sensitivity and the hydride has been flushed directly into a flame'-9 and a variety of heated silica tubes.l0V1l At present, methods incorporating hydride generation have mainly been used to analyse standard solution^^-^^ with limited application to complex or environmental samples.8t11 In this paper the optimisation of a hydride generation and trapping system for the isolation and concentration of tellurium? prior to atomic-absorption spectroscopy with electrothermal atomisation is described.The advantage of using a trapping system is in the elimination of the effects of interferents causing variable rates of hydride evolution. Interferences have been investigated and procedures developed for the removal of severe interferences. Experimental Equipment The hydride generation and trapping system used is illustrated in Fig.1. Nitrogen was used to flush hydrogen telluride from the generator into the centrifuge tube. Sodium tetra-hydroborate(II1) solution was injected using a plastic syringe connected to a small length of narrow-bore plastic tubing leading to the bottom of the flask. All atomic-absorption measurements were made with a Varian Techtron AA5 background-corrected atomic-absorption spectrometer fitted with a Perkin-Elmer HGA 72 carbon furnace. The following spectrometer conditions were used throughout the work lamp current 8 mA ; wavelength? 214.3 nm; and spectral band pass 0.2 nm. Reagents and Glassware (2 + S ) rinsed with distilled water and dried before use. in 100 ml of 3 M hydrochloric acid. in 100 ml of 3 M hydrochloric acid. 5000 Australia.All chemicals were of analytical-reagent grade. Glassware was soaked in sulphuric acid TeZZurium(IV) standard solution 1000 pg ml-l. Dissolve 0.1264 g of tellurium(1V) oxide Tellurium( V I ) standard solution 1000 pg ml-l. Dissolve 0.1802 g of ammonium tellurate * Present address Department of Physical and Inorganic Chemistry University of Adelaide Adelaide 306 Analyst Vol. 108 Dissolve 2.5 g of sodium tetrahydro-borate(II1) in 25 ml of 0.1 M sodium hydroxide solution. This solution is filtered through a 0.4-pm membrane filter to remove inhomogeneities and increase solution stability to at least 5 h. Prepare a trapping solution by dissolving 0.8 g of potassium iodide and 0.5 g of iodine in 100 ml of distilled water. Dissolve 5 g of lanthanum(II1) chloride in 100 nil of distilled water.Dissolve 0.2 g of DAN in 100 ml of 0.1 M hydrochloric acid containing 0.5 g of hydroxylammonium chloride. This solution is purified after heating at 50 "C for 25 min by extraction with cyclohexane. EDTA - hydroxylamine solution 10% m/V. Prepare by dissolving 5 g of disodium ethylenediaminetetraacqtate (EDTA) and 5 g of hydroxylammonium chloride in 50 ml of distilled water . Dissolve 0.5 g of diphenylthiourea in 50 ml of chloro-form. MAHER DETERMINATION OF T E BY AAS WITH Sodium tetrahydroborate(III) solution 10% m/V. Potassium iodide (0.8% m/V) - iodine (0.5% m/V) solution. Lanthan.um(III) solution 5o/b m/V. 2,3-Diaminonaphthalene (DAN) solution 0.2% m/V. Diphenylthiouurea ureagent 1% m/V. Nz Ball-ioint Rubber 1 septum Syringe (1 rnl) Mod if i ed Drechsel head Pasteur pipette 100-ml flask-,) Centrifuge tube Fig.1. Hydride generation and trapping system. Procedure Solutions are initially diluted to 50 ml with hydrochloric acid (final concentration 6 M) and heated at 100 "C for 40 min to reduce any tellurium(V1) present to tellurium(1V). A hydrochloric acid solution is transferred into the hydride-generation flask and the apparatus assembled as in Fig. 1 with 2 ml of potassium iodide - iodine solution in the centrifuge tube. The nitrogen flow-rate is adjusted to 300 ml min-l 1 ml of sodium tetrahydroborate(II1) solution is injected and the hydrogen telluride that evolves is collected over a 4-min period. Aliquots (20 pl) of the potassium iodide - iodine solution are injected into the carbon furnace and the tellurium atomic absorption is measured using the optimum conditions established for the removal of the potassium iodide - iodine solution (Table I).TABLE I OPTIMUM CARBON FURNACE PROGRAMME FOR THE DETERMINATION OF TELLURIUM BY ATOMIC-ABSORPTION SPECTROSCOPY WITH ELECTROTHERMAL ATOMISATION Stage r 1 Parameter Dry Ash 1 Ash 2 Atomise* Temperature setting . . . . . . 18 35 90 600 Temperature/"C . . . . 39 98 370 2213 Time/s . . . . 40 60 10 5 * Atomisation temperatures quoted are manufacturer's temperatures March 2983 ELECTROTHERMAL ATOMISATION BY HYDRIDE GENERATION Results Optimisation of Hydride Generation and Trapping 307 To optimise the conditions for hydride generation and trapping the effects of sodium tetrahydroborate( 111) concentration hydrochloric acid concentration gas flow-rate and trapping-solution composition on the evolution and trapping of hydrogen telluride were investigated.Sample solutions containing 0.75 pg of tellurium(1V) in 50 ml of 5 M hydro-chloric acid and 2 ml of a 1% m/V potassium iodide - iodine solution were used for the optimisation of flow-rate and sodium tetrahydroborate( 111) concentration. The optimum gas flow-rate was 300 ml min-l and solutions containing 10% m/V sodium tetrahydroborate-(111) in 0.1 M sodium hydroxide quantitatively reduced up to 0.75 pg of tellurium to hydrogen telluride. Variation of the hydrochloric acid concentration was found to have a pronounced effect on hydride generation (Table 11) the optimum hydrochloric acid concentration being 6 M.Under these optimum conditions the collection of hydrogen telluride was complete within 4 min. A trapping solution containing 0.8% m/V of potassium iodide and 0.5% rn/V of iodine quantitatively trapped up to 0.75 pg of tellurium as the hydride. TABLE I1 EFFECT OF HYDROCHLORIC ACID CONCENTRATION ON HYDRIDE GENERATION AND TRAPPING The conditions were as follows trapping solution composition 1 yo m/ V potassium iodide 1 m/ V iodine ; flow-rate 300 ml min-l; collection time 10 min ; and all solutions contained 0.75 p g of tellurium(1V) and were injected with 1 ml of 10% m/V sodium tetrahydroborate(II1) solution. Hydrochloric acid concentrationlM . . . . 2.4 3.6 4.8 6.0 7.2 8.4 Tellurium recovered % . . . . . . . . 33 78 94 100 97 84 Preliminary experiments showed that only tellurium( IV) will form hydrogen telluride.Therefore any tellurium( VI) present initially in extracts or produced during preparation of extracts must be reduced to tellurium(1V). The method selected to reduce tellurium was to heat extracts with hydrochloric acid i . e . Te(V1) + 2C1- + Te(1V) + Cl,. The optimum heating time was 40 min at 100 "C when a hydrochloric acid concentration of 6 M was used (Table 111). H+ TABLE I11 EFFECT OF HEATING TIME ON THE REDUCTION OF TELLURIUM(VI) TO TELLURIUM(IV) All solutions contained 0.75 p g of tellurium(V1) in 50 ml of 6 M hydrochloric acid; a temperature of 100 "C ant1 optimised hydride generation trapping conditions were used. . . 10 20 30 40 50 60 lime of heating/min .. Reduction 7; . . . . . . 45 87 98 100 100 100 Precision and Detection Limit carried tlirougli the entire procedure. was 40/ (five determinations). deviation of the blank analyses was 0.006 pg (six determinations). The precision was estimated from replicate analyses of a 0.3-pg tellurium(V1) standard The relative standard deviation at this concentration The detection limit corresponding to four times the standard Interferences IdentiJicatiofz Possible interference by other elements was investigated by measuring the hydrogen telluride generated and trapped in the presence of elevated concentrations of other elements 308 MAHER DETERMINATION OF TE BY AAS WITH Analyst Vol. 108 The concentrations at which certain elements interfere are shown in Table IV.Various other elements [Al(III) B(III) Ca(II) Cr(VI) K(I) Li(I) Mg(II) Mn(II) Na(I) Pb(II), S2- Si(IV) Zn(II)] showed no significant interference up to the 5000 pg (100 pg ml-l) level. TABLE IV EFFECT OF INORGANIC IONS ON THE GENERATION AND TRAPPING OF HYDROGEN TELLURIDE All solutions contained 0.5 pg of telluriuni(1V) in 50 ml of 6 M hydrochloric acid and optimised hydride generation and trapping conditions were used. Species A m As(II1) Cd(I1) Co( 111) Cu(I1) Fe (I 11) Hg(I1) Mo(V1) Ni(I1) Sb (111) Se(IV) Sn(1V) V(V) Suppression and elimination Concentration/pg per 50 ml Tellurium recovered yo 10 0 1 100 100 52 50 100 1 000 100 2 500 75 1000 90 500 100 100 71 50 100 2 500 87 1000 93 500 100 10 0 1 100 500 67 250 105 100 100 1000 76 500 100 50 19 10 98 1 100 50 18 0.1 90 250 66 100 100 1000 100 Although several elements cause significant interference when present at the 1000 pg (20 pg ml-l) level only silver(I) copper(II) mercury(I1) and selenium(1V) are likely to be found at concentrations in environmental materials (excluding sediments) that will cause significant interference.Initially four complexing agents thiosemicarbazide l,l0-phenanthroline S-hydroxy-quinoline and disodium ethylenediaminetetraacetate were tested in an attempt to suppress interferences by complexation before generation of hydrogen telluride. These reagents were not effective in suppressing interferences.Interferences were removed by a combination of co-precipitation and sequential extraction. After reduction of tellurium(V1) to teliurium(1V) 1 ml of lanthanum(II1) chloride solution and one drop of phenolphthalein solution were added with stirring followed by the addition of 25% V/V ammonia solution until a pink colouration occurred (pH 9-10). The lanthanum precipitate containing tellurium but not copper( 11) and mercury(I1) was separated by centrifugation and washed twice with 20 ml of 3 M ammonia solution. The precipitated lanthanum hydroxide was dissolved in 10 ml of DAN solution 1 ml of EDTA - hydroxylamine solution was added and the mixture was heated in a water-bath at 50 "C for 50 min. The piazselenol formed was extracted into cyclohesane (2 x 10 ml) and discarded.The previous solution was extracted with 20 ml of diphenylthiourea reagent and the chloroform phase was discarded. Copper(l1) and mercury(l1). SeZenium(lV). Tellurium remained in the aqueous phase. SiZver(1) March 1983 ELECTROTHERMAL ATOMISATION BY HYDRIDE GENERATION 309 The efficiency of the co-precipitation and sequential extraction procedure to remove interferences was assessed by the analysis of solutions containing 0.5 pg of tellurium( IV) together with 1000 pg of copper(II1) and mercury(I1) and 10 pg of silver(1) and selenium(1V). The percentage deviation from interference-free determinations of tellurium was less than 7%. Average recoveries of 93 4% (five determinations) were achieved. Discussion and Conclusion A simple system for the generation and trapping of hydrogen telluride prior to the deter-mination of tellurium by atomic-absorption spectroscopy with electrothermal atomisation has been developed and optimised.Interferences from copper( 11) mercury( 11) silver( I) and selenium( IV) have been identified. Suppression of these interferences by complexing agents was unsuccessful probably owing to the instability of complexes in concentrated acid solution. However the use of a co-precipitation - sequential extraction procedure prior to hydride generation overcomes all identified severe interferences. The technique should allow the sensitive measurement of tellurium concentrations in extracts. Investigation of interferences to the method also demonstrated that the use of hydrogen telluride generation to isolate and concentrate tellurium from extracts is in general of limited use unless potential interfering elements are identified and removed. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Cerwenka E. A. and Cooper W. C. Arch. Environ. Health 1961 3 189. Corbett J . A. and Godbeer W. C . Anal. Chim. Acta 1977 91 211. Kapel M. and Komaitis M. E. Analyst 1979 104 124. Beaty R. D. A t . Absorpt. Newsl. 1974 13 38. Kraehenbuehl Ti. and Wegmueller F. Radiochem. Radioanal. Lett. 1978 36 31. Sighinolfi G. P. and Santos A. M. Talanta 1979 26 143. Fiorino J . A. Jones J. W. and Capar S. G. Anal. Chem. 1976 48 120. BCdard M. and Kerbyson J . D. Can. J . Spectrosc. 1976 21 64. Smith A. E. Analyst 1975 100 300. Thompson K. C. and Thomerson D. R. Analyst 1974 99 595. Greenland L. P. and Campbell E. Y . Anal. Chim. Acta 1976 87 323. Received July 27th 1982 Accepted September 6th 198