DETERMINATION OF HALOGENATED HYDROCARBONS BY HELIUM MICROWAVE PLASMA TORCH TIME-OF-FLIGHT MASS-SPECTROMETRY COUPLED TO GAS-CHROMATOGRAPHY

A helium microwave plasma torch (MPT) was coupled to time-of-flight ma ss spectrometry (TOFMS) for the detection of halogenated hydrocarbons separated by capillary gas chromatography(GC), The GC-MPT-TOFMS system offered excellent stability over the course of the experiments and av oided mass spectral peak distortions caused by spectral skew. In the i nitial studies, empirical formulas based on the halogen-to-carbon rati o were predicted utilizing a now cell apparatus. The MPT proved to be very robust and could handle large amounts of organic vapor. Results f rom this study indicate that, for both aromatic and aliphatic halogena ted hydrocarbons, the ratios of carbon to chlorine signals correlate w ell (r = 0.994) with the ones expected from their chemical composition . This study was later extended to include chromatographic separation. For a series of homologous aliphatic halogenated hydrocarbons, a corr elation coefficient of 0.999 was obtained for both peak heights and pe ak areas obtained from a single chromatogram, A novel Nichrome wire-he ated transfer line was developed to ensure that the capillary column w as heated efficiently from the GC oven to the MPT and then through the length of the MPT up to the microwave plasma itself. No appreciable p eak broadening and no detectable memory effects were associated with t he heated transfer line. The GC-MPT-TOFMS system offered equal sensiti vity for I, Br, and Cl, Absolute detection limits for the halogenated hydrocarbons ranged from 160 to 330 fg, constituting an improvement by a factor of 5-35 over earlier results obtained with MIPs supported in a TM010 cavity and combined with quadrupole-based mass spectrometry, In addition, the effect of molecular gases on the MPT performance was investigated. Up to about 1% (v/v) of either oxygen or hydrogen in the central channel helium now attenuated the signal levels for both carb on and chlorine, with the larger loss seen in the chlorine signal.