A COMPARISON OF ARGON AND MIXED GAS PLASMAS FOR INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

The effects of adding N2 to the outer gas flow of an Ar plasma in inductively coupled plasma mass spectrometry (ICP-MS) are illustrated. With 5% N2 added to the outer gas flow and provided the central (nebulizer) gas flow is increased, modest signal enhancements (up to a factor of 4) are observed. The degree of enhancement depends on the extent to which an element forms a strong metal oxide bond and also, to some extent, on ionization potential. An important feature of N2 mixed gas plasmas for ICP-MS is that the signals for analyte oxide species (MO+) and certain background species (ArO+, ArOH+, Ar2+, ClO+, and ArCl+) are significantly reduced (an order of magnitude) by the addition of N2 to the outer gas flow. In addition to these observations, some results are also presented for O2 and air (outer gas) mixed gas plasmas and N2 (central gas) mixed gas plasmas. © 1990.