High-sensitivity microwave-induced plasma mass spectrometry for trace element analysis

Abstract

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.