Characterization studies of a He high-efficiency microwave-induced plasma, He-HEMIP, utilizing direct sample introduction with pneumatic nebulization for atomic emission and atomic fluorescence spectrometry are presented. These studies include diagnostic measurements and analytical characterization of the 150-W He-HEMIP. Diagnostic measurements include excitation temperatures with the use of aqueous and organic nebulized thermometric species, electron number densities, and ionization temperatures for the plasma. The effect of sample uptake rate on the emission intensity is investigated. Ionization interferences are minimal, and phosphate interferences were found not to occur. In addition, the He-HEMIP is characterized as an atom source for metals and nonmetals with the use of atomic emission spectrometry and atomic fluorescence spectrometry. With AES, detection limits for metals and nonmetals are in the sub-ppm range. With AFS, detection limits for metals were determined to be in the low to sub-ppb range and were found to be not statistically different from those reported for HCL-ICP-AFS. Linear ranges for AES and AFS ranged from four up to five and one-half orders of concentrative magnitude.
The direct introduction of aqueous samples into a low-power microwave plasma is achieved with the use of a highly efficient TM010 microwave plasma. A toroidal plasma is sustained in the cavity solely by the Ar gas output of the nebulizer. Samples from a concentric glass nebulizer/Scott type spray chamber are fed directly into the cavity with no desolvation apparatus. A toroidal plasma can be sustained from the output of the nebulizer while 1 mL/min water is being aspirated at power levels of 36 W. This plasma is characterized as an atom cell by the study of emission profiles, working curves, and limits of detection. Also, ionization and vaporization interferences that occur with the use of this plasma are discussed.
An atomic fluorescence spectrometry system employing a low-powered, highly efficient MIP as the atom cell (MIP-AFS) has been developed and is evaluated with the use of direct aqueous nebulization. The MIP-AFS system employs hollow cathode lamp and Xe-arc lamp excitation sources. Detection limits of 14 elements were studied and compared to results for ICP-AFS. Linear working ranges of at least 5 orders of concentration magnitude were found. Interelement effects (i.e., vaporization, ionization, and scatter interferences) were also investigated.
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