DETERMINATION OF THALLIUM IN TELLURIDE THERMOELECTRIC-MATERIAL BY CHEMICAL MODIFICATION AND ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

Interferences encountered in the determination of Tl as a dopant in layered monocrystals of Bi2Te3 were investigated. The atomic absorption signal for Tl was found to be influenced by a great excess of H2TeO3 and Bi(NO3)(3) obtained by dissolving milligram samples of the crystal in dilute HNO3. Interpretation of the influence of the pyrolysis temperature on the Tl signal and independent chemical examination indicated that the losses of Tl were caused by the volatility of TlNO3 above 300 degrees C. The sensitivity and reproducibility of the determination of Tl were also negatively influenced by a molten matrix and the volatility of Tl2O and TeO2, which probably participate in recombination reactions at the start of the atomization. These interfering effects were removed with the use of a chemical modifier consisting of an optimized mixture of tartaric acid, ascorbic acid and Mg(NO3)(2). The resulting changes in the thermal reactions were interpreted. For optimum conditions and, e.g., the peak-height absorbance, a linear calibration between 5 and 35 ng ml(-1) of Tl was obtained, allowing reliable determinations of 10-400 ppm of Tl. Estimates of the relative standard deviation were 1-3% and that of the 3s detection limit 0.6 ng ml(-1) or 12 pg per injection.