In atmospheric pressure Ion Mobility Spectrometry (IMS), ions are injected into the drift region of the IMS using an electrostatic gate. These gates provide perpendicular fields within the tube which prevent ion passage. The gate is opened briefly (0.05 to 0.2 ms pulses) to pass ions into the drift region for separation. The gating process itself decreases overall IMS signal as ions must transit a ion-depleted region before they are detected. Prior efforts have attempted pulsed ionization sources in lieu of an ion gate. These include both Corona Discharge Ionization (CDI) and Electrospray Ionization (ESI). These efforts utilized significant shifts in electric field in order pulse the ionization source. In this work, an ESI source is pulsed with a 100 V amplitude, from 50 V below onset of ESI to 50 V above onset of ESI. This pulsing is demonstrated to be reproducible and provide minimal perturbation to the electric field of the IMS cell; comparable with a traditional IMS gate. This modification comes through using IMS pulsing electronics already available to the community and uses a modular PCB IMS cell for direct comparison between gated and pulsed IMS experiments. In this work, we demonstrate the initial results of a low amplitude pulsed ESI source on an IMS separation in direct comparison to gated operation using the same cell. Pulsed ESI-IMS has been demonstrated in the positive mode with comparable resolving power and reduced mobility accuracy to gated IMS for a series of electrosprayed IMS standards.

Low amplitude pulsed electrospray ionization gateless ion mobility spectrometry

ACS Spring Meeting 2021

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