Separation and determination of tellurium(IV) and -(VI) by electrothermal atomic absorption spectrometry using a tungsten furnace after collection as the 3-phenyl-5-mercapto-1,3,4-thiadiazole -2(3H)-thione-tellurium complex on cobalt(III) oxide

Abstract

Using cobalt(III) oxide powder as a collector of tellurium(IV) and -(VI), the latter are separated from matrix components contained in a sample solution, then determined by electrothermal atomic absorption spectrometry using a tungsten furnace. When only cobalt(III) oxide powder was used for the collection of tellurium, the recovery of tellurium(IV) and -(VI) increased as the sample solution became more basic; almost 100% recovery was obtained at pH 11.0. When 0.1% m/v 3-phenyl-5-mercapto-1,3,4-thiadiazole-2(3H)-thione potassium salt (bismuthiol II) was used as an auxiliary agent for the collection, there was difference in the collection behavior between tellurium(IV) and -(VI) depending on the pH of sample solution (100 ml): 100% recovery was obtained at pH 1-7 for tellurium(IV) and at pH 3-7 for tellurium(VI). Therefore, by collecting tellurium(IV,VI) at pH 4.0 and then tellurium(IV) at pH 1.0, fractionation and determination of tellurium(IV,VI) can be achieved. The cobalt(III) oxide powder used as a collector is also effective as a chemical modifier in the determination; by introducing cobalt(III) oxide powder in the form of a slurry (5 ml) into a furnace, the volatilization loss of tellurium could be suppressed up to a charring temperature of 1400 °C. For 1.25 µg per 5 ml (0.25 mg l ^–1 ) tellurium(IV), when this method was used the relative standard deviation (n=6) was <3%. The detection limit (3σ) was 12 µg l ^–1 (0.12 ng per 10 µl). The method applied to several water samples, experiments being performed on the fractionation and determination of tellurium(IV,VI), and 100% recovery was obtained.