LAUSR

Field switching ion shutters allow generating short ion packets with high ion densities by first ionizing for several milliseconds in a field-free ionization region and then quickly pushing the entire ion population out into the drift region. Thus, they are an excellent choice for compact ion mobility spectrometers with both high resolving power and low limits of detection. Here, we present an improved setup, named the extended field switching ion shutter. By generating a second field-free region between the ionization region and the drift region, shielding of the ionization region is significantly improved, even when using grids with higher optical transparency to improve ion transmission into the drift region. Furthermore, it is shown that under certain conditions, ion transmission through multiple grids in series can even surpass transmission through a single grid of the same transparency. For the studied ions, the signal intensity at low concentrations increases by approximately a factor of 7 to 9 for monomers, 10 to 14 for dimers and 25 for the 1-octanol trimer compared to the classical field switching shutter. However, due to the non-linear response for ions containing multiple analyte molecules, the limits of detection improve only by a factor of 3 to 4 for dimers and 3 for the 1-octanol trimer. Nevertheless, this still leads to single-digit pptv limits of detection for monomers and hundred pptv limits of detection for dimers measured for a series of ketones. A slight loss of resolving power by a factor of 1.1 to 1.15 was observed, most likely caused by small field inhomogeneities due to the more transparent grids.