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 la yered monocrystals of Bi2Te3 were investigated. The atomic absorption signal for Tl was found to be influenced by a great excess of H2TeO3 a nd Bi(NO3)(3) obtained by dissolving milligram samples of the crystal in dilute HNO3. Interpretation of the influence of the pyrolysis tempe rature on the Tl signal and independent chemical examination indicated that the losses of Tl were caused by the volatility of TlNO3 above 30 0 degrees C. The sensitivity and reproducibility of the determination of Tl were also negatively influenced by a molten matrix and the volat ility of Tl2O and TeO2, which probably participate in recombination re actions at the start of the atomization. These interfering effects wer e removed with the use of a chemical modifier consisting of an optimiz ed mixture of tartaric acid, ascorbic acid and Mg(NO3)(2). The resulti ng changes in the thermal reactions were interpreted. For optimum cond itions and, e.g., the peak-height absorbance, a linear calibration bet ween 5 and 35 ng ml(-1) of Tl was obtained, allowing reliable determin ations of 10-400 ppm of Tl. Estimates of the relative standard deviati on were 1-3% and that of the 3s detection limit 0.6 ng ml(-1) or 12 pg per injection.