Potentiometric Investigations of Nickel, Iron and Cobalt Interferences in the Generation of Selenium Hydride by Sodium Tetrahydroborate(III)

Abstract

The products of the reactions of Fe^II, Ni^II and Co^II with sodium tetrahydroborate(^III), which interfere with the determination of selenium by hydride generation, were precipitated by different methods and investigated by potentiometric titration accompanied by monitoring of hydrogen evolution, direct current plasma atomic emission spectrometry and positive ion FAB mass spectrometry. Boron was found in the precipitates of Ni^II and Co^II but not Fe^II obtained from the acid solutions under the conditions of hydride generation. Several sections on the potentiometric titration curves were found, which indicated the formation of several boride-like compounds with different compositions depending on the sequence of mixing reagents, pH, reactant concentrations and ratios, speed of mixing and the presence of oxygen. A hypothesis was formulated about the reduction of boron^III from sodium tetrahydroborate(III) to lower oxidation states of boron in boride-like species which is used to explain the properties of the potentiometric titration curves and the suppression of the selenium hydride signal in hydride generation.