Liquid sampling-atmospheric pressure glow discharge as a secondary excitation source: Assessment of plasma characteristics

Abstract

The liquid sampling-atmospheric pressure glow discharge (LS-APGD) has been assessed as a secondary excitation source with a parametric evaluation regarding carrier gas flow rate, applied current, and electrode distance. With this parametric evaluation, plasmaopticalemission was monitored in order to obtain a fundamental understanding with regards to rotational temperature (Trot), excitation temperature (Texc), electron number density (ne), and plasma robustness. Incentive for these studies is not only for a greater overall fundamental knowledge of the APGD, but also in instrumenting a secondary excitation/ionization source following laser ablation (LA). Rotational temperatures were determined through experimentally fitting of the N2 and OH molecular emission bandswhile atomic excitation temperatureswere calculated using a Boltzmann distribution of He andMgatomic lines. The rotational and excitation temperatureswere determined to be ~1000 K and ~2700 K respectively. Electron number density was calculated to be on the order of ~3 × 1015 cm−3 utilizing Stark broadening effects of the Hαline of the Balmer series and a He I transition. In addition, those diagnosticswere performed introducing magnesium( by solution feed and laser ablation) into the plasma in order to determine any perturbation under heavy matrix sampling. The so-called plasma robustness factor, derived bymonitoringMg II/MgI emission ratios, is also employed as a reflection of potential perturbations in microplasma energetics across the various operation conditions and sample loadings. While truly a miniaturized source (b1 mm3 volume), the LS-APGD is shown to be quite robust with plasma characteristics and temperatures being unaffected upon introduction of metal species, whether by liquid or laser ablation sample introduction.