Extending the concentration and linear dynamic range of ion mobility spectrometry with a sheath flow inlet

Recent methods used to extend the linear dynamic range of ion mobility spec trometers are reviewed and an alternative approach, arising from observatio ns of the operation of a gas chromatography inlet to an ion mobility spectr ometer, is proposed. The design, construction and preliminary testing of a variable sheath flow inlet are described. The responses obtained from dichloromethane and ethyl acetate indicate that the sheath flow inlet enabled the sensitivity of the ion mobility spectrometer to vary from the virtual shut out of the analyte to instrument saturation. The effect was reproducible and operated in less than 2 s. Preliminary analysis indicates that linear dynamic ranges may be extended to over three orders of magnitude at concentrations significantly greater, in the region of g m(-3) at ambient temperature and pressure, than have previously been reported with ion mobility spectrometry. (C) 1999 Pub lished by Elsevier Science B.V.