Comparison of the analytical performance of high-powered, microwave-induced air plasma and nitrogen plasma atomic emission spectrometry

Abstract

A high-powered, microwave-induced air plasma (air-MIP) generated by an Okamoto cavity at atmospheric pressure was investigated and compared with a nitrogen plasma (N₂-MIP) generated by the same cavity under the same conditions. The analytical performance of the plasmas was evaluated and compared with regard to excitation temperatures, electron-number densities, detection limits and tolerance to direct organic solvent introduction. The excitation temperature of the air-MIP was in the range of 4150–4750 K when the microwave power varied from 0.8 to 1.3 kW, which was 300–400 K lower than those of the N₂-MIP. The electron number densities in the air-MIP ranged from 1 to 6 × 10¹⁴ cm⁻³, which was about one order of magnitude higher than those of the N₂-MIP. The detection limits for 17 elements with a total of 38 atomic and ionic lines were determined. For most of the spectral lines with lower excitation energies, the detection limits obtained from the air-MIP were comparable with those obtained from the N₂-MIP, whereas for those spectral lines with higher excitation energies, the detection limits in the air-MIP were much poorer than those in the N₂-MIP. Preliminary experiments showed that the air-MIP was highly tolerant to direct organic solvent introduction.