Near-Infrared Nonmetal Atomic Emission from a Helium Microwave-Induced Plasma. Element Ratio Determinations

摘要

The utility of near-infrared atomic emission lines of C, F, S, Cl and Br for the determination of element ratios in organic compounds is evaluated. An atmospheric-pressure helium microwave-induced plasma is used to fragment sample molecules and excite their constituent atoms. The effects of plasma operating parameters such as power and flow rate, as well as the effects of spatial viewing position and plasma length are also investigated. The results reported here offer only a qualified recommendation for the general application of this new technique to chromatography. Measured intensity ratios have been shown to vary significantly with changes in plasma operating parameters. Careful control of these variables and frequent calibration with a reference compound are desirable. The tandem plasma results suggest that fragmentation and excitation efficiencies might depend on the structure of sample molecules. Although the work reported here was restricted to near-infrared spectral region, the aspects of tandem-phase observations that deal with sample fragmentation would obviously apply also to other more commonly used regions. Finally, the dynamic range of the technique appears to be limited to perhaps two or three orders of magnitude. The ratio determinations for the molecules studied here indicate that magnitude. The ratio determinations for the molecules studied here indicate that the available precision (1-3% r.s.d.) is probably adequate for many applications if the appropriate care is exercised to avoid sources of systematic error discussed in this paper. (Reprints)