Investigation of spectrochemical matrix effects in the liquid sampling-atmospheric pressure glow discharge source

Abstract

The liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma was evaluated with regard to its spectrochemical robustness in its application as a miniaturized optical emission spectroscopy (OES) source for liquid samples. The susceptibility to perturbations in excitation/ionization conditions was probed across a wide range test species, including transition metals, easily ionized elements (group I), and elements with low second ionization potentials (group II). Spectrochemical metrics included the plasma excitation temperature (Texc), ionization temperatures (Tion), and magnesium (Mg) ionic:atomic (Mg II:Mg I) ratios. The introduction of the 11 different matrix elements into the LS-APGD at concentrations of 500μgmL−1 yielded no significant changes in the optically-determined plasma characteristics, indicating a relative immunity to spectrochemical matrix effects. Texe values for the plasma, using He I as the spectrometric species averaged 2769±79K across the test matrix, with Mg-based ionization temperature values centered at 6665±151K. Typical Mg II:Mg I ratios (the so-called robustness parameter) were 0.95±0.3. The lack of appreciable perturbation in excitation/ionization conditions observed here is also manifested in virtually no changes in the probe Mg II and I species' intensities, even at matrix loadings of up to 1000μgmL−1 of Ba. These observations indicate that the LS-APGD could serve as an OES source for the analysis of diverse aqueous samples without appreciable spectroscopic matrix effects, though potential physical matrix effects including vaporization effects must be evaluated.