Selective extraction-photometric redox determination of low concentrations of sulfur(IV), selenium(IV), tellurium(IV), and arsenic(III)

A procedure is proposed for the selective extraction-photometric determination of the acid-forming elements S(IV), Se(IV), Te(IV), and As(III) in their mixtures containing molecular forms or anions with different electron densities on donor atoms. The procedure is based on the difference in the oxidizability of analytes with the [SbCl6]− complex. The analytical ranges are found at different pHs of the medium, affecting the potential of the two-phase redox systems. The detection limits for sulfite, selenite, tellurite, and arsenite are 1 × 10−3, 5 × 10−5, 7 × 10−5, and 1 μg/mL, respectively. The procedure is applied to the determination of selenium in H2SO4 of high-purity grade, which is used in the production of microelectronics items and in some agricultural samples. The error of analysis is no worse than 20%.