High-sensitivity microwave-induced plasma mass spectrometry for trace element analysis
A high power (⩽ 1.5 kW, 2.45 GHz) atmospheric pressure nitrogen microwave-induced plasma mass spectrometer is described for trace element analysis. The plasma, which has an annular shape, was produced by an ‘Okamoto cavity’ operated in a surface-wave mode. The background mass spectrum was dominated by 30NO+, 14N+ and 16O+, and argon related ions such as 39Ar+, 40Ar+, 52ArC+, 56ArO+ and 80Ar2+, were not observed. Preliminary detection limits for 39K+, 40Ca+, 52Cr+ and 56Fe+ obtained directly were less than 5 ppt, which are lower than those for argon inductively coupled plasma mass spectrometry. Analytical curves for the elements of interest were linear over five orders of magnitude of concentration.