Reduction of polyatomic interferences in inductively coupled plasma mass spectrometry by selection of instrumental parameters and using an argon–nitrogen plasma: effect on multi-element analyses

Abstract

The effect of instrumental parameters and argon-nitrogen plasmas on polyatomic ion formation has been studied in order to reduce their magnitude in routine multi-element analysis without losing detection capability. Special emphasis was placed on the chlorine based polyatomic interferences on V, Cr, Zn, As and Se. A significant reduction in signals from polyatomic ions was attained by using a high aerosol carrier gas flow rate (0.955 l min^–1) instead of the default flow rate (0.755 l min^–1), or by adding nitrogen (8%) to the aerosol carrier flow. The ArCl⁺ interference produced by 0.05% Cl (the maximum concentration expected in digested food stuff samples) was effectively removed by both methods and ClO⁺ and ClO₂⁺ by addition of nitrogen. Detection limits for elements along the mass range (from Li to U) were, on average, 2–3 times higher with the mixed gas plasma. This slight degradation of detection limits was not judged to be deterimental to multielement determinations in five reference materials when the results from using an argon-only plasma (with low and high aerosol carrier flow rates) were compared with the results from the argon–nitrogen plasma.