Determination of thallium in telluride thermoelectric material by chemical modification and electrothermal atomic absorption spectrometry

Abstract

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 °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.