Gas-phase ion dynamics in a periodic-focusing DC ion guide

In this work, we provide a comprehensive understanding of the radial ion focusing mechanism in the periodic-focusing DC ion guide (PDC IG). The PDC IG was developed in our laboratory to improve the sensitivity and throughput of ion mobility spectrometry (IMS) with respect to conventional uniform field IMS. Radial ion focusing, which is responsible for the sensitivity improvement, is attributed to the presence of effective potentials created by the fringing electric fields of thick ring electrodes and collisional cooling of the ions with the neutral buffer gas. The ion focusing mechanism is affirmed by investigating the variations in the effective ion temperature (Teff) which are dependent upon axial position in the device. The concepts derived herein outline guidelines for the design of high performance PDC IG ion mobility instruments and other ion optical devices such as periodic-focusing DC ion funnels.

Radial ion confinement during ion mobility separation in the PDC IG is attributed to the presence of effective potentials at the edges of thick periodic-focusing electrodes.Figure optionsDownload high-quality image (136 K)Download as PowerPoint slideResearch highlights▶ The PDC IG is an ion mobility spectrometer that yields high ion transmission via suppression of radial diffusion. ▶ Ions are confined in the radial dimension by effective potentials which are present at the electrode edges. ▶ The axial electric field, assisted by collisional cooling, dampens ion kinetic energy near the back edge of electrodes to allow effective potentials to direct ion motion.