Patent ID: 6639214
Filing Date: 2003-10-28
Classification: G01N

Abstract:
A method for operating an ion mobility spectrometer that uses a bulk inert gas and a drift gas, said spectrometer comprising an analyzer cell having an ionization as region, an interaction region, and a drift region, said ionization region having an ionization source, said spectrometer further comprising a shutter grid separating said interaction region and said drift region, said drift region having an ion current detector for detecting ions transiting said drift region, and means for measuring transit times through said drift region of ions generated in said ionization region and released into said drift region through said shutter grid, said method comprising the steps of:a) applying a drift gas stream to an inlet in said drift region; b) mixing a selected reagent gas comprised of argon with a bulk inert gas to create a doped bulk inert gas stream; c) applying said doped bulk inert gas stream to an inlet in said ionization region, to carry a test sample of said doped bulk inert gas stream into said interaction region to form ions of the doped bulk inert gas; d) measuring an ion current at said ion current detector, at a time corresponding to a transit time through said drift region, of ions generated by said test sample in said interaction region; and e) said reagent gas comprised of argon causing ions generated by said test sample in said interaction region to have transit times through said drift region different from transit times through said drift region of ions generated by a trace impurity of interest in said test sample, said reagent gas selected for its capacity to alter the nature of the ions formed by the bulk inert gas to shift the location of a bulk inert gas mobility peak such that the bulk inert gas mobility peak does not overlap with an impurity mobility peak of the ions of the trace impurity of interest, whereby bulk inert gas ions are quenched and a cluster of the reagent comprised of argon and the bulk inert gas is formed.