Analytical Figures of Merit and Interelement Effects with Air and Nitrogen Microwave-Induced Plasmas

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Abstract
A microwave (2450 MHz)-induced plasma (MIP) with nitrogen nebulization and plasma gases was developed and compared with an air-MIP similar to that previously reported in our laboratories. These plasmas were maintained at 300 to 500 W of forward power and were stable with pneumatic nebulized aqueous solution introduction. In general, metals with high metal-oxygen bond strengths, high excitation energies, and low ionization potentials exhibited superior detection limits in the N2-MIP. Several elements with emission lines in N2 and N2+ spectral regions yielded better detection limits in the air plasma. The effects of high concentrations (2%) of calcium, potassium, sodium, and phosphate ions upon the analytical signal intensities were examined. During direct solution nebulization, the analytical signals of both plasmas exhibited significant but predictable interferences from metals of low ionization potential and plasma loading. Matrix effects were more significant in the N2-MIP.