Determination of trace amounts of thallium and tellurium in nickel-base alloys by electrothermal atomic absorption spectrometry

Abstract

A method is described for determining trace amounts of Tl in nickel-base alloys using pre-treatment with ammonia solution and electrothermal atomic absorption spectrometry. Thallium was coprecipitated when the sample solution of a nickel-base alloy was treated with ammonia solution. Background absorption was effectively eliminated in the new matrix. Nickel worked effectively as a chemical modifier for Te, and raised the charring temperature from 500 to 1000 °C. Therefore, it was possible to determine sub-nanogram levels of Te without any complicated pre-treatment. The accuracy and precision of the proposed method were elucidated through the analysis of two nickel-base alloys: spectroscopic standard certified reference material 346A IN100 Alloy and Standard Reference Material 899 Tracealloy C. There was good agreement between the expected values and the results obtained. For Tl, the results found for IN 100 and Tracealloy C were 1.94 ± 0.09 µg g^–1(s_r= 5%) and 0.251 ± 0.005 µg g^–1(s_r= 2%), respectively, the reference value for IN100 being 2 and certified value for Tracealloy C being 0.252 ± 0.003 µg g^–1. The recoveries for these alloys were 100 ± 4 and 102 ± 3%, respectively. The detection limit was 15 pg g^–1. For Te, the certified values for IN100 and Tracealloy C were 9 ± 1 and 5.9 ± 0.6 µg g^–1, respectively. The Te contents determined by the proposed procedure were 9.03 ± 0.09 µg g^–1(s_r= 1%) and 5.93 ± 0.26 µg g^–1(s_r= 4%), with recoveries of 98 ± 4 and 97 ± 4%, respectively. The detection limit was 35 pg g^–1. Although the addition of Pd modifier gave a better detection limit (18 pg g^–1), it led to poorer results in terms of accuracy, precision and recovery.