Expanding the Capabilities of Inductively Coupled Plasma Optical Emission Spectrometry and Mass Spectrometry: Optimization of Plasma and Sample Introduction Conditions
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This thesis aims to explore simple methods to improve the analytical performance of inductively coupled plasma (ICP) optical emission spectrometry (OES) and mass spectrometry (MS). 1. An argon-nitrogen mixed-gas plasma with a hydrogen sheath gas was developed in order to improve plasma robustness for the analysis of geological/environmental samples by ICP-MS and ICP OES. Nitrogen was added to the outer plasma gas, to reduce matrix effects, while hydrogen was added as a sheath, around the nebulizer flow, to improve energy transfer to the central channel. Increased robustness allowed for the direct quantitative multi-element analysis of certified soil, ore and seawater reference materials by ICP-MS and ICP OES, without using any matrix matching or internal standardization. 2. An IR-heated sample introduction system with a conventional pneumatic nebulizer was investigated in order to improve the analytical performance of ICP OES. The aerosol generated by a pneumatic nebulizer, coupled to various spray chambers, was heated to 230 °C using an IR heater. Under optimum conditions and compared to conventional pneumatic nebulization at room temperature, a 6-fold improvement in sensitivity and a 4 to 7-fold improvement in detection limit was obtained for 38 elements using the IR-heated sample introduction setups. Another IR-heated sample introduction system was also investigated for both aqueous and organic (metals-in-oil) solutions. Under optimum conditions and compared to conventional pneumatic nebulization at room temperature, a 3-fold improvement in sensitivity and a 6 to 9-fold improvement in detection limit was obtained for 22 elements using the IR-heated sample introduction system, for both aqueous and organic solutions. 3. A measure of robustness in ICP-MS was investigated. The Be II/Li I intensity ratio was directly related to the Mg II/Mg I ratio in OES. Moreover, the 9Be+/7Li+ ratio was inversely related to the CeO+/Ce+ and LaO+/La+ oxide ratios in MS. The suppression effect of sample matrices was significantly reduced, if not eliminated in the case of 0.01 M Na, when the 9Be+/7Li+ ratio was around 0.30. To the best of our knowledge, this is the first report on using a simple analyte intensity ratio, 9Be+/7Li+, to gauge plasma robustness in ICP-MS.