Patent ID: 7026612

Claim:
An apparatus for selectively transmitting ions comprising: a high field asymmetric waveform ion mobility spectrometer comprising two electrodes defining an analyzer region therebetween, the two electrodes disposed in a spaced apart arrangement for allowing ions to propagate therebetween and for providing an electric field within the analyzer region resulting from the application of an asymmetric waveform voltage to at least one of the two electrodes and from the application of a compensation voltage to at least one of the two electrodes, for selectively transmitting an ion of interest at a given combination of asymmetric waveform voltage and compensation voltage; and, a doping portion for receiving a flow of a carrier gas from a gas source and for controllably mixing a dopant gas with the flow of a carrier gas to produce a doped carrier gas stream containing a predetermined concentration of the dopant gas, the doping portion also in fluid communication with the analyzer region for providing the doped carrier gas stream thereto, wherein during use the doped carrier gas stream that is provided to the analyzer region contains less than 1% dopant gas by volume.