Negative Reagent Ions for Real Time Detection Using SIFT-MS

Direct analysis techniques have greatly simplified analytical methods used to monitor analytes at trace levels in air samples. One of these methods, Selected Ion Flow Tube-Mass Spectrometry (SIFT-MS), has proven to be particularly effective because of its speed and ease of use. The range of analytes accessible using the SIFT-MS technique has been extended by this work as it introduces five new negatively charged reagent ions (O−, OH−, O2−, NO2−, and NO3−) from the same microwave powered ion source of moist air used to generate the reagent ions traditionally used (H3O+, NO+, and O2+). Results are presented using a nitrogen carrier gas showing the linearity with concentration of a number of analytes not readily accessible to positive reagent ions (CO2 from ppbv to 40,000 ppmv, sulfuryl fluoride and HCl). The range of analytes open to the SIFT-MS technique has been extended and selectivity enhanced using negative reagent ions to include CCl3NO2, SO2F2, HCN, CH3Cl, PH3, C2H4Br2, HF, HCl, SO2, SO3, and NO2