Valence properties of tellurium in different chemical systems and its determination in refractory environmental samples using hydride generation - Atomic fluorescence spectroscopy

摘要

Using HG - AFS as a powerful tool to study valence transformations of Te, we found that, in presence of HCl and at high temperature, Te can form volatile species and be lost during sample digestion and pre-reduction steps. It was also noticed that the chemical valences of Te can be modified under different chemical and digestion conditions and even by samples themselves with certain matrices. KBr can reduce Te(VI) to Te(IV) in 3.0 M HCl at 100 degrees C, but when HNO3 was > 5% (v/v) in solution, Br-2 was formed and caused serious interference to Te measurements. HCl alone can also pre-reduce Te(VI) to Te(IV), only when its concentration was >= 6.0 M (100 degrees C for 15 min). Among 10 studied chemical elements, only Cu2+ caused severe interference. Thiourea is an effective masking agent only when Cu2+ concentration is equal or lower than 10 mg/L. Chemical reagents, chemical composition of sample, as well as the modes of digestion can greatly affect Te valences, reagent blanks and analytical precisions. A protocol of 2-step-digestion followed by an elimination of HF is proposed to minimize reagent blank and increase the signaloise ratios. It is important to perform a preliminary test to confirm whether a pre-reduction step is necessary; this is especially true for samples with complex matrices such as those with high sulfide content. The analytical detection limits of this method in a pure solution and a solid sample were 100 ng/L and 0.10 +/- 0.02 mu g/g, respectively. (C) 2015 Elsevier B.V. All rights reserved.