Article ID Journal Published Year Pages File Type
1245762 Talanta 2006 7 Pages PDF
Abstract
Numerous commonly used analytical methods allow only determination of a total amount of selenium in a given sample. Electroanalytical methods as well as those based on hydride generation or on formation of piazselenol allow only determination of Se(IV). To determine Se(VI) by these procedures, present alone or in mixtures with Se(IV), it is first necessary to convert Se(VI) to Se(IV). Such conversion is effective in the presence of excess of halides in acidic media or by photoreduction. In the often used conversion of Se(VI) in the presence of chlorides or less frequently of that of bromides, it has been assumed that the halide ion acts as a reducing agent. Kinetic studies of conversion of Se(VI) in acidic solutions containing an excess of bromide ions indicated that the rate determining first step of the reaction with Se(VI) is a nucleophilic substitution of the OH2+ group in the protonated form of H2SeO4 by bromide ions. For the overall reaction with rate −d[Se(VI)]/dt = k1[H+][Br−]1.15[Se(IV)] the rate constant 1 × 10−3 L2 mol−2 s−1 was found. The following formation of Se(IV) from the bromo derivative is a fast reaction probably resulting in elimination of HBrO.
Related Topics
Physical Sciences and Engineering Chemistry Analytical Chemistry
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