Influence of operating conditions on the effects of acids in inductively coupled plasma atomic emission spectrometry

Abstract

The influence of the operating conditions on interferences from HCl, HNO₃ and H₂SO₄ in inductively coupled plasma atomic emission spectrometry was studied. The acid concentration was in the 0–2 mol l^–1 range. It was found that the acid interferences were strongly dependent on the operating conditions. Several different plasma excitation conditions were obtained by modifying the aerosol carrier gas and the intermediate gas flow rates. The test element was vanadium. Plasma diagnostics were performed by measuring the excitation temperature, the electron number density and the ionic-to-atomic line intensity ratio. In each instance, it was found that the excitation temperature was not modified as a function of the acid concentration. For long residence time and efficient energy transfer, the electron number density and the ionic-to-atomic line intensity ratio were not modified. Only a minor depressing effect was observed for ionic lines, which was attributed to the aerosol formation and transport. In contrast, for short residence time and inefficient energy transfer, both the electron number density and the ionic-to-atomic line intensity ratio were depressed. The significant depressing effect for ionic lines was attributed to a change in the excitation conditions. It is, therefore, possible to separate the acid effects originating from the sample introduction system from those originating in the plasma by carefully selecting the operating conditions of the plasma.