Studies on Mixed-Gas Plasmas and Segmented Flow Injection for Use with Inductively Coupled Plasma Mass Spectrometry.
In this thesis, mixed gas plasmas and flow injection into air bubbles were investigated for use with inductively coupled plasma mass spectrometry (ICP-MS), in order to improve the technique's analytical capabilities. The mixed gas plasmas were created in two different ways: (i) by adding another gas, either argon, nitrogen, or hydrogen, to the nebulizer gas flow using a sheathing device or (ii) by adding nitrogen to the plasma gas flow. The introduction of each sheathing gas led to degraded analyte sensitivity but generally improved plasma stability, resulting in improved detection limits for a few elements. Introduction of nitrogen into the plasma gas, under the same operating conditions used for an all-argon plasma, resulted in degraded sensitivity but improved signal-to-noise and signal-to-background ratios for Cr, Fe, and Se. The tolerance of ICP-MS to effects caused by the concomitant elements Na and K was improved by addition of nitrogen to the plasma gas flow. Flow injection using a segmented air/water carrier resulted in improved precision, sensitivity, and detection limits compared to those obtained using an all-water carrier. The enhancement in sensitivity was found to be mass dependent and was attributable to more than simply a reduction in dispersion. Under optimized operating conditions, using segmented flow injection resulted in similar or improved detection limits for all analytes except Se when compared to those obtained using continuous nebulization. Changing the gas used to segment the carrier stream did not result in appreciable changes in analyte signals or positions of maximum ionization within the plasma, indicating that the fundamental properties of the plasma did not change. The tolerance of ICP-MS to effects caused by the concomitant elements Na and Ca was not improved by using a segmented carrier compared to that experienced using an all-water carrier.
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- Chemistry: Analytical; Physics: Fluid and Plasma