Patent ID: 7838823
Filing Date: 2010-11-23
Classification: G01N

Abstract:
1. An ion mobility spectrometer, comprising: an ionizing region for ionizing a sample vapor to form ions, a drift tube comprising a drift region in which the ions drift under the influence of an electric field, established by a plurality of stacked electrodes, against a counter-flowing drift gas and are separated into at least one single ion swarm therein, a gate for pulsing the ions into the drift region, an ion collector for detecting the at least one single ion swarm at the end of the drift region to provide an ion mobility spectrum, and wherein at least two of the stacked electrodes adjacent to the ion collector have an electrode pitch that less than the width of an ion swarm and each of the adjacent electrodes is connected to a source of free charge, thereby providing a virtual aperture grid at the end of the drift region that shields the ion collector from the mirror current of the ion swarm.