A High Kinetic Energy Ion Mobility Spectrometer for Operation at Higher Pressures of up to 60 mbar

Abstract

High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) are usually operated at absolute pressures around 20 mbar in order to reach high reduced electric field strengths of up to 120 Td for influencing reaction kinetics in the reaction region. Such operating points significantly increase the linear range and limit chemical cross sensitivities. Furthermore, HiKE-IMS enables ionization of compounds normally not detectable in ambient pressure IMS, such as benzene, due to additional reaction pathways and fewer clustering reactions. However, operation at higher pressures promises increased sensitivity and smaller instrument size. In this work, we therefore study the theoretical requirements to prevent dielectric breakdown while maintaining high reduced electric field strengths at higher pressures. Furthermore, we experimentally investigate influences of the pressure, discharge currents and applied voltages on the corona ionization source. Based on these results, we present a HiKE-IMS that operates at a pressure of 60 mbar and reduced electric field strengths of up to 105 Td. The corona experiments show shark fin shaped curves for the total charge at the detector with a distinct optimum operating point in the glow discharge region at a corona discharge current of 5 μA. Here, the available charge is maximized while the generation of less-reactive ion species like NO x + is minimized. With these settings, the reactant ion population, H3O+ and O2 +, for ionizing and detecting nonpolar substances like n-hexane is still available even at 60 mbar, achieving a limit of detection of just 5 ppbV for n-hexane.

Implementation of an Open-Source Multiplexing Ion Gate Control for High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS)

“…The HiKE-IMS has been described thoroughly elsewhere, but briefly, the HiKE-IMS is a drift tube IMS with a few key differences from other DT-IMS instruments. ,, Briefly, the HiKE-IMS contains a reaction region immediately before the tristate ion gate, which allows for the formation of reactant ions via corona discharge with the background gas and ionization of analyte molecules via the formed reactant ions. , For the HiKE-IMS used in this effort, the drift region is 101.5 mm in length ending with a Faraday plate detector . The HiKE-IMS is operated at reduced pressures between 7 and 60 mbar which allows for operation at high reduced electric field strengths ( E / N ) up to 120 Td. , For these experiments, this HiKE-IMS is operated at the conditions stated in Table unless specified otherwise.…”

“…The HiKE-IMS is operated at reduced pressures between 7 and 60 mbar which allows for operation at high reduced electric field strengths ( E / N ) up to 120 Td. , For these experiments, this HiKE-IMS is operated at the conditions stated in Table unless specified otherwise. More detailed information about the construction of this HiKE-IMS is given by Schlottmann et al…”

Ultra-Fast Ion Mobility Spectrometer for High-Throughput Chromatography

“…For IMS to be operated at high drift voltages, or at high electric field strengths respectively, at least two effects must be considered: (1) avoiding dielectric breakdown between the drift ring electrodes inside the IMS and (2) the resistor network used to set the potentials of the ring electrode. Schlottmann et al discuss the first point. Although this publication deals with an IMS operated at absolute pressures of 20–60 hPa and high reduced electric field strengths of up to 120 Td, − named high kinetic energy ion mobility spectrometer (HiKE-IMS), the considerations regarding breakdown between ring electrodes are easily transferable to any other IMS.…”

“…In this work, a self-designed and self-constructed compact ESI-PCB-IMS with a rectangular shape of 20 mm × 20 mm, and a drift tube length of 34 mm with 22 electrodes with a center distance of 1.5 mm and a gap of 0.5 mm is used, the detailed description of the setup can be found elsewhere. , The ions are generated by an electrospray ion source consisting of a quartz silica emitter (FossilIonTech, MS-Wil, Aarle-Rixtel, The Netherlands) with an inner tip diameter of 50 μm and a desolvation region of 50 mm length. The ion source operated at a flow rate of 0.5 μL/min.…”

Detection of Triacetone Triperoxide by High Kinetic Energy Ion Mobility Spectrometry

“…Another method to mitigate cross-sensitivities caused by competing gas-phase reactions is to decrease the operating pressure of the instrument, leading to a lower number of collisions between ions and neutral molecules, shifting the ion population from thermodynamic equilibrium to kinetic control. This approach is used in High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS), operated at reduced pressures from 10 to 60 mbar. , In addition to the mitigation of chemical cross-sensitivities, the operation at low pressure also allows to vary the reduced electric field strength E / N in a wide range up to 120 Td in both the reaction region and the drift region. Unlike drift tube IMS for trace gas detection operated at ambient pressure, HiKE-IMS separates ions not only by their low-field ion mobility but also by utilizing the field dependence of the ion mobility. − Therefore, HiKE-IMS can help to separate ions despite similar low-field mobilities, thereby reducing false positives .…”