| The helium-argon mixed-gas inductively coupled plasma (ICP) was evaluated for use as an alternative ionization source for plasma spectrometric detection. Its potential as both an optical emission and mass spectrometric source was investigated. Optimal plasma conditions, for optical emission, were found with a total plasma composition of 34% helium. The mixed-gas plasma reduced the detection limit for iodine to 0.4 ppm, a sevenfold improvement over the detection limit obtained with a 100% Ar plasma. At the optimum conditions for iodine, detection limits for most other elements studied improved or stayed the same.;The production of ions is of importance for mass spectrometric detection. The addition of He to Ar produces a plasma capable of ionizing high ionization potential elements more efficiently than the pure Ar plasma. The best signal to noise ratios for metallic elements were obtained with a 20% He plasma, and for halides with a 30% plasma. The He-Ar mixed-gas plasma showed an improvement of one order of magnitude in the detection limits of several metallic elements studied and an improvement of two orders of magnitude for non-metals in comparison with Ar ICP-MS. Additionally, the effects of various matrix constituents, Cd, Co, Pb, and synthetic ocean water, on analyte ion signal were also investigated in He-Ar plasma source mass spectrometry. Analyte ion signal suppressions and enhancements were observed in the presence of varying concomitants.;Ion chromatography was combined with ICP-MS for the speciation of arsenic compounds. Ion chromatography was used to eliminate or reduce the mass spectral interference formed from chloride, namely argon chloride, by resolving chloride chromatographically from the arsenic compounds. Phthalic acid and carbonate buffer were used as mobile phases for the speciation of As in several chloride containing matrices. Detection limits in the low ppb range were obtained in urine, club soda, and wine with Ar ICP-MS detection. Further improvements were achieved by using the He-Ar ICP. Several commercially available freeze-dried urine standards were analyzed using the standard additions method. Good agreement was obtained for total arsenic content, which was calculated from the sum of the species with accepted arsenic concentration. |
