High-Pressure Ion Mobility Spectrometry

Abstract

The effects of above-ambient pressure on ion mobility on resolving power, resolution, and ion current were investigated using a small, stand-alone ion mobility spectrometer (IMS). This work demonstrates the first example of ion mobility spectrometry at pressures above ambient. Ion mobility spectra of chemical warfare agent (CWA) stimulant dimethyl methylphosphonate (DMMP) and several other standard compounds are shown for superambient conditions. The IMS was operated at pressures from 700 to 4560 Torr. An optimal resolving power was obtained at a specific voltage as a function of pressure, with higher optimal resolving powers obtained at higher voltages, as predicted from standard IMS theory. At high pressures, however, resolving power did not increase as much as theory predicted, presumably due to ion clustering. Nevertheless, an increase in pressure was found to improve resolution in IMS. One example where high pressure improved resolution was the separation of cyclohexylamine (K0 = 1.83) and 2-hexanone (K0 = 1.86) (where K0 is the reduced mobility value). The product ions of these two compounds could not be separated at ambient pressure but could be nearly baseline separated when the pressure of the buffer gas was raised to 2280 Torr. Total ion current was also examined at pressures from ambient up to 4560 Torr. Total ion current, when investigated with pressure, was found to reach a maximum, initially rising with increased pressure.

Simulation of Electric Potentials and Ion Motion in Planar Electrode Structures for Lossless Ion Manipulations (SLIM)

“…The resulting value was used to then compute the diffusion limited resolving power $false(R_d=\sqrt{\frac{LEq}{16k_{B}T\text{ln}2}}=true(\sqrt{\frac{63.2}{7.3}}true)r_{d}false)$ of the 63.2 cm design used for experimental measurements. The net resolving power achievable is a combination of the diffusion limited resolving power ( R d ) and the gate limiting resolving power $false(R_g=\frac{T}{\mathrm{normal\Delta }{T}_{\mathit{\text{gate}}}}false)$ [38]. FWHM (Δ T FWHM ) of the IMS peak determined the diffusion limited resolving power for all mobilities after a certain ion drift time ( T ), and the experimental gate opening time (Δ T gate ) of 162 µs determined the gate limited resolving power, specific to mobility of the ion of interest.…”

Quantification and remote detection of nitro explosives by helium plasma ionization mass spectrometry (HePI‐MS) on a modified atmospheric pressure source designed for electrospray ionization

“…Ion mobility spectrometry is one of the most widely used techniques for explosives detection . Although this is a low‐cost, high‐throughput technique, its low resolution leads to many false results, both positive and negative.…”

High pressure effects in high-field asymmetric waveform ion mobility spectrometry

“…Thus, applying high pressure is an obviously efficient method to enhance FAIMS performance with no additional cost of design or power consumption. Some teams have clarified pressure effects and the underlying physics on Differential Mobility Spectrometry (DMS) and Ion Mobility Spectrometry (IMS) . This paper focuses specially on higher pressure and aims to investigate the effect of high pressure on ion peak position, peak width, resolving power, and peak intensity to determine the possibility of using above‐ambient pressure for enhanced performance of a FAIMS analyzer.…”