Enhancing the sensitivity of ion mobility spectrometry using the ion enrichment effect of non-uniform electrostatic field

The diversified applications of ion mobility spectrometry (IMS) frequently pose challenges to the sensitivity of IMS measurements. In this work, the ion density evolution profiles of a continuous flow of ions travelling in nonuniform electrostatic fields were studied. Based on that, an ion enrichment method was proposed for enhancing the sensitivity of IMS. It employed a gradually weakening electrostatic field in the ionization region of IMS and achieved ion density enhancement for the ion flow migrating from the ion source to the ion shutter. Using that method, the ion density of the ion flow produced by the ion source was increased by 180% when approaching the ion shutter. With the increased ion density, the limit of detection (LOD) for DMMP dimer peak was lowered from 425 to 200 pptv. Meanwhile, there was a slight reduction in the resolving power, which was tentatively assigned to the enhanced coulomb repulsion along with the increased ion density. The resolving power of the IMS with a drift length of 60mm was still maintained around 80 at 100 degrees Celsius. The ion enrichment method needs no radial-confining radio frequency voltage. Also, it does not affect the response speed of IMS.