Speciation of selenium and tellurium in milk by hydride generation atomic fluorescence spectrometry

A simple, fast and highly sensitive method has been developed for the differentiation of Se and Te into their (IV) and (VI) oxidation states in milk samples by HG-AFS. This procedure involves a previous leaching of milk slurries by sonication with aqua regia for 10 min. Se(IV) and Te(IV) were determined by analysis of the samples without a pre-reduction step; being total Se and Te determined after reduction with KBr. The method provides limit of detection values (LOD) of 0.012 and 0.023 ng ml(-1) for Se(IV) and Te(IV) respectively. Average relative standard deviation values of 10.5%, 3.9%, 12% and 12.5% were found for the determination of Se(IV), Se(VI), Te(IV) and Te(VI) in milk samples containing Se from 11.1 to 32.2 ng g(-1) and Te from 1.1 to 10 ng g(-1). Recovery experiments made on actual samples spiked with Se(IV), Se(VI), Te(IV) and Te(VI) evidenced that the sonication with aqua regia does not modify the oxidation state of the elements considered.