A flowing afterglow selected ion flow tube (FA/SIFT) comparison of SIFT injector flanges and H-3(+)+N revisited

The performances of two different but interchangeable Venturi injectors (an annulus and a hole injector) have been compared in a new flowing afterglow source-selected ion flow tube (FA/SIFT) instrument built at the University of Canterbury. The tests applied compared the relative "pumping efficienci es" of the two injectors; their ion transmission using (O-2(+)); the relati ve ease of injecting cluster ions subject to collision induced dissociation (H3O.+H2O); and the extent of isomerization of ions sensitive to structura l changes during the injection process (C3H5+). The annulus injector was cl early superior to the hole injector in pumping efficiency. Thereafter the i mprovement in performance was only marginal. The greater difficulty of cons truction and maintenance of the annulus injector needs to be balanced again st the slightly less versatile hole injector. It was necessary to direct a significant fraction of the total helium buffer gas flow through an outer, noncritical orifice to maintain satisfactory performance in the hole inject or when injecting ions susceptible to collision induced dissociation. Final ly, the new instrument was used to reexamine the reaction of H-3(+) and N a toms, which was found to be a nonreactive system, k < 5 x 10(-11) cm(3) s(- 1). (Int J Mass Spectrom 202 (2000) 351-361) (C) 2000 Elsevier Science B.V.