REDUCTION OF POLYATOMIC INTERFERENCES IN INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY BY SELECTION OF INSTRUMENTAL PARAMETERS AND USING AN ARGON-NITROGEN PLASMA - EFFECT ON MULTIELEMENT ANALYSES

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 I min-1) instead of the default flow rate (0.755 I min-1), or by adding nitrogen (8%) to the aerosol carrier flow. The ArCl+ interference produced by 0.05% CI (the maximum concentration expected in digested food stuff samples) was effectively removed by both methods and CIO+ and CIO2+ 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 detrimental to multi-element 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.