BACKGROUND SPECTRAL FEATURES FOR MODERATE-POWER NITROGEN MICROWAVE-INDUCED PLASMA MASS-SPECTROMETRY

The mass spectral background features of a moderate-power nitrogen microwave-induced plasma are presented. In general, the mass spectral background obtained from a nitrogen plasma is less congested at low mass than is the case with argon ICP-MS. In addition, there are no significant (less than 20 counts per second) background species above mass 60. At normal multiplier voltage, the major background species found in a dry nitrogen plasma include 14N+, 14NH+, 14N2+, 14N2H+, 14N16O+, 14N16OH+, 14N3+ and 14N4+. This background is unchanged by the nebulization of deionized water, 5% (v/v) acids (nitric, hydrochloric, and sulfuric acids), and 5% (v/v) methanol solutions. These background species do not interfere with the determination of K, Ca, and Se at their major isotopes, which commonly have interfering background species in Ar ICP-MS. On the basis of the nebulization of 5% HCl and methanol in the nitrogen plasma, As and Cr do not have isobaric interferences at their major isotope masses 75 and 52.