Differences in sensitivity between As(iii) and As(v) measured by inductively coupled plasma spectrometry and the factors affecting the incoherent molecular formation (IMF) effect in the plasma

Abstract

When inorganic As species [As(III) and As(V)] and Se species [Se(IV) and Se(VI)] are measured by inductively coupled plasma spectrometry, As(V) is found to be more sensitive than As(III), although Se(IV) and Se(VI) show the same sensitivity. The mechanism of the sensitivity difference between As(V) and As(III) was investigated using ICP-sector field mass spectrometry (ICP-SFMS), and it was elucidated that the amount of hydride polyatomic species of As formed in the plasma was different between As(V) and As(III). The formation of polyatomic species depends upon the oxidation state of the As atoms in the plasma, we describe this phenomenon as the incoherent molecular formation (IMF) effect. The mechanisms of the IMF effect were further investigated and techniques for removing its influence on As determination are discussed.