Annular-Shaped Microwave-Induced Nitrogen Plasma at Atmospheric Pressure for Emission Spectrometry of Solutions

Abstract

A high-power high-efficiency microwave-induced nitrogen and air plasma (N2 and air MIP) for trace element analysis is presented using a new simple surface wave excitor. The plasma is annular-shaped at atmospheric pressure. The excitor consists of two parts: one part is a flat rectangular waveguide with a reduced height, and the other part is a mode transfer consisting of an inner conductor and an outer cylindrical conductor terminated by a front plate. The surface wave is excited in the gap between the front edge of the inner conductor and the front plate. The microwave power (2.45 GHz, 1 kW) is coupled to new concentric quartz tubes placed inside the gap. The preliminary analytical performance of the N2 MIP was examined by measuring the line intensities of Call (393.4 nm), Zr II (343.8 nm) and N₂⁺ (391.4 nm). The plasma is a sensitive ionization source.