ABSTRACT
A measurement of the mobility for an ion swarm is initiated when ions from a source or reaction region are introduced into an electric eld continuously, as in eld asymmetric ion mobility spectrometry (FAIMS), differential mobility spectrometry (DMS), differential mobility analysis (DMA), or aspiration IMS (aIMS) or periodically, as in traditional congurations of ion mobility spectrometry (IMS) or in traveling wave methods. In conventional drift tubes, peak separation in a mobility spectrum is dened by differences in drift times and peak widths whose minimum value is established by pulse width of ion injection with the ion shutter. Resolving power in continuous ion §ow methods is dened by these same terms, although minimum peak width is established by the dimensions of the inlet aperture for such an analyzer. The methods and practices of ion introduction regardless of ion mobility method are essential in establishing the best possible performance; consequently, this should have received intense scrutiny and development of IMS. Strangely, interest in ion shutters and in the dynamics of ion §ow at ambient pressure has grown only in the past decade, resulting in new descriptions on the limits of shutter performance, alternative methods of ion injection, and improved analytical results. These portend further improvements in resolving power, precision of measurements, and drift tube designs.
