ENHANCED SELECTIVITY IN ION MOBILITY SPECTROMETRY ANALYSIS OF COMPLEX-MIXTURES BY ALTERNATE REAGENT GAS CHEMISTRY

Ion mobility spectrometry (IMS) analysis of a complex mixture of volat ile organic compounds (VOCs) and organophosphorus compounds (OPCs) at vapor levels of 10-40 mg/m(3) produced mobility spectra with broad pro files illustrating limitations of ion mobility spectrometry (IMS) for screening such mixtures. Preseparation of this mixture with a gas chro matograph inlet to an ion mobility spectrometer enhanced analytical se lectivity although OPC detection was complicated by co-elution with ot her VOCs. Water reagent gas in the ion source of the ion mobility spec trometer yielded 46 gas chromatographic peaks in a mixture of 45 VOCs and 19 OPCs. Co-elution of two materials was observed in eight of the chromatographic peaks and co-elution of three materials occurred in fo ur instances. Further selectivity was gained using reagent gases of el evated proton affinity in the ion source. Reagent gas chemistry for ac etone and dimethylsulfoxide reduced the number of GC peaks to 26 and 2 0, respectively. Moreover, spectral integrity and quantitative respons e for OPCs were retained at 50 to 1000 pg levels with these reagent ga ses. For OPCs, analyte ions were shown to be of the type M(2)H(+) unde r these conditions of analysis and the mobilities of the product ions were independent of reagent gas. Reduced mobility values were assigned to OPC spectra using a well-characterized OPC ion as the reference. S pectral profiles and reduced mobilities suggested that the OPC product ions were not clustered with reagent gas molecules at 100 degrees C.