Selected ion flow drift tube mass spectrometry with negative ions and nitrogen carrier gas
The technique of selected ion flow tube mass spectrometry, SIFT-MS has become a valuable analytical tool for real-time monitoring of environments, industrial processes and in health and safety. Methods based on this technique are finding also use in medical research, biology and food science due to high sample throughput in comparison with GC-MS. Chemical ionisation proceeds in carrier gas in flow tube by ion molecule reactions of the selected reagent ions H3O+, NO+, O2+, O-, O2-, OH- and NO2- with molecules of trace gas analytes (or VOC vapours). So far SIFT-MS used helium carrier gas, that is becoming prohibitively expensive and it seems feasible to use nitrogen, N2, as a replacement medium, in-spite of the more complicated chemistry. Thus the ion-molecule reactions of these ions with analyte molecules in presence of N2 need to be investigated. Also methods relevant to promising areas of use of SIFT-MS with and its drift tube variant SIFDT-MS in clinical breath tests with N2, in food science and industrial air contamination monitoring need to be developed and optimised.