Spatial ion density change in the electrostatic field and sensitivity improvement of ion mobility spectrometer

Abstract

Many designs have been proposed to improve the sensitivity of ion mobility spectrometry (IMS) by modifying its electric field in recent years. However, most of them have shown severe differences between the theoretical predictions and the experimental results. In this work, the effect of electric field on the drifting process was studied from the perspective of spatial ion density. Theoretical derivation illustrated that the nonuniform electric field has no direct influence on the spatial ion density in free space, and the mean spatial ion density was difficult to increase but easy to decrease when crossing grids. Therefore, to improve the sensitivity, a denser ion swarm should be produced in the reaction zone and dilution should be prevented when crossing the ion shutter. Based on this principle, an optimized design was proposed to improve the sensitivity of IMS equipping a UV radiation ionization source. A denser ion swarm was produced by reducing the electric field strength of the reaction zone, and a tri-grid ion shutter was adopted to realize the anti-dilution function. Experimental results showed an impressive improvement, and the SNR of dimethyl methylphosphonate (DMMP) dimer peak increased by 22.6 times without any loss in the resolving power.

Kaitai Guo

Assistant Professor

My research interests include broad-spectrum substance identification, microwave and infrared imaging, and system simulation and evaluation.