Mechanisms of transition metal interferences in hydride generation atomic absorption spectrometry. Part 4. Influence of acid and tetrahydroborate concentrations on interferences in arsenic and selenium determinations

Abstract

An increase in the hydrochloric acid concentration from 0.5 to 5 mol l^–1 improves the range of interference-free determination for arsenic and selenium in the presence of cobalt, copper or nickel by factors of 5–100. Decreasing the sodium tetrahydroborate(III) concentration from 3 to 0.5%m/V increases the range of interference-free determination for both elements further by factors of 4–50. The only exception is the interference of copper on selenium, which is slightly more pronounced with the less concentrated tetrahydroborate(III) solution. The proposed mechanism is that both in higher acid and with lower tetrahydroborate(III) concentrations the interferent is reduced to a lesser extent to the metal (the interfering species) owing to (i) better solubility of the metal in the more concentrated acid, (ii) the formation of chloro complexes, thus reducing the concentration of free ions, and (iii) a larger percentage of the tetrahydroborate(III) being consumed by the acid. Copper, however, interferes with selenium in the ionic form.