High resolution Varying Field Drift Tube Ion Mobility Spectrometer with diffusion autocorrection

Drift tubes (DT) are prominent tools to classify small ions in the gas phase. This is in contrast with its limited use in the aerosol field at atmospheric pressures where the differential mobility analyzer (DMA) has been the tool of choice. While the DMA has been successful, it does not normally achieve the resolution of a common DT. On the other hand, the size range of the DT is limited as well as its sensitivity. Here we propose a variation of the DT where a varying linearly decreasing field is used instead of the constant field commonly used in DT. The Varying Field Drift Tube (VFDT) has the advantage that it allows for diffusion constriction in the axial direction and thus a larger package of ions can be allowed into the system increasing its sensitivity without hampering its resolution. The VFDT also generally outperforms the DT in resolution and this is demonstrated theoretically and empirically reaching resolutions of over 90 in our data although higher resolutions are expected. The diffusion constriction capabilities are also proven theoretically and experimentally by using a mixture of tetraalkylammonium salts while injecting broad packets of ions into the system. The transformation from the raw variable arrival time distribution to Collision Cross Section or mobility diameter is linear making the transformation as simple as with a DMA. •The Varying Field Drift Tube (VFDT), an IMS for the classification of nanoparticles at atmospheric pressure, has been tested.•A linearly decreasing electric field has been proven to provide diffusion constriction in the axial direction.•Resolutions of up to 100 have been proven experimentally while higher resolutions are expected from theoretical analysis.•The VFDT system is fast and has a high resolution which is necessary to study fast changing aerosols.