Ultra-Fast Polarity Switching, Non-Radioactive Drift Tube for the Miniaturization of Drift-Time Ion Mobility Spectrometer

Drift-time ion mobility spectrometer (DT-IMS) is a promising technology for gas detection and analysis in the form of miniaturized instrument. Analytes may exist in the form of positively or negatively charged ions according to their chemical composition and ionization condition, and therefore require both polarity of electric field for the detection. In this work the polarity switching of a drift-time ion mobility spectrometer based on a direct current (DC) corona discharge ionization source was investigated, with novel solutions for both the control of ion shutter and the stabilization of aperture grid. The drift field is established by employing a switchable high voltage power supply and a serial of voltage regulator diode, with optocouplers to drive the ion shutter when the polarity is switched. The potential of aperture grid is stabilized during the polarity switching by the use of four diodes to avoid unnecessary charging cycle of the aperture grid capacitor. Based on the proposed techniques, the developed DT-IMS with 50 mm drift path is able to switch its polarity in 10 ms and acquire mobility spectrum after 10 ms of stabilization. Coupled with a thermal desorption sampler, limit of detection (LoD) of 0.1 ng was achieved for ketamine and TNT. Extra benefits include single calibration substance for both polarities and largely simplified pneumatic design, together with the reduction of second drift tube and its accessories. This work paved the way towards further miniaturization of DT-IMS without compromise of performance.

Automated summary

Drift-time ion mobility spectrometer (DT-IMS) is a promising technology for gas detection and analysis in a miniaturized instrument. This study investigated the polarity switching of a DT-IMS based on a direct current (DC) corona discharge ionization source and proposed novel solutions for ion shutter control and aperture grid stabilization. By using a switchable high voltage power supply, voltage regulator diodes, optocouplers, and diodes, the developed DT-IMS was able to switch polarity within 10 ms and acquire mobility spectrum after 10 ms of stabilization. The system achieved a limit of detection (LoD) of 0.1 ng for ketamine and TNT when combined with a thermal desorption sampler. The work also led to simplified pneumatic design and reduction of necessary components. This research opens up possibilities for further miniaturization of DT-IMS without compromising its performance.