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

• HG–AFS is a powerful tool in studies of chemical valences and forms of Te in different conditions.
• Te can be lost in form of volatile species in presence of HCl at high temperature.
• Metal ions can be classified into 3 categories of interference; thiourea can effectively mask Cu2+.
• A 2-step digestion allows to eliminate HF, reduce background and improve analytical precision.
• Matrix of sample can strongly influence Te chemical valence of Te and a pre-reduction is necessary.

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 °C, but when HNO3 was >5% (v/v) in solution, Br2 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 °C for 15min). 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 signal/noise 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 μg/g, respectively.

Figure optionsDownload as PowerPoint slide