Valence Discrimination Effects with Thermospray Sample Introduction: Characterization and Prevention

With thermospray sample introduction for atomic spectrometry, sensitivity for certain elements can be valence-dependent (valence discrimination effect). To this point, this effect appears to be significant only for nonmetals with easily reducible lower oxidation states, such as arsenic, antimony, and selenium. In this work, the valence discrimination effects for these elements were studied in detail with inductively coupled plasma atomic emission spectrometry detection. The sensitivities for As(III), Sb(III), and Se(IV) were found to be significantly lower than those for As(V), Sb(V), and Se(VI), respectively. In general, the sensitivity difference between the low- and high-valence species increases with thermospray temperature but decreases with an increase in HCl or HNO3 concentration in solution. The low sensitivity for the low-valence species proved to arise from their reduction to corresponding metals within the thermospray process, after which the metals were trapped on the vaporizer and desolvation system. An effective way to prevent the valence discrimination effect is by means of the addition of a suitable oxidant into the solution.