Toward Compact High-Performance Ion Mobility Spectrometers: Ion Gating in Ion Mobility Spectrometry

Abstract

Printed circuit board (PCB) based drift tube ion mobility spectrometers enable the use of state-of-the-art production techniques to manufacture compact devices with excellent performance at minimum cost. The new PCB ion mobility spectrometer (PCB-IMS) presented here is equipped with either a 140 MBq tritium or a 95 MBq nickel-63 ionization source and consists of a combination of horizontally arranged 6-layer PCBs for the drift and reaction regions and vertically arranged PCBs for interfacing the ionization source, ion shutter, and detector. The design allows the reproducible manufacturing and thus comparison of different IMS topologies. Here, we investigate different ion shutters, field-switching, Bradbury-Nielsen, and tristate and their effects on resolving power and limits of detection considering two different ionization region geometries and ionization sources, tritium and nickel-63. It is shown that the high resolving power of R P > 80 at low drift voltage of 3 kV and short drift length of 50 mm can be achieved independent of the used ion shutter mechanism and reaction region geometry. While the resolving power of all ion shutters is excellent, the Bradbury-Nielsen shutter shows a pronounced discrimination of slow ion species when using short shutter opening times for small initial ion cloud widths, as required for high resolving power. Thus, the intensity of the proton-bound dimer of 2-pentanone is reduced by 30% compared to the signal intensity obtained with both the field-switching and tristate shutter. The detection limits employing the Bradbury-Nielsen shutter and a 50 mm reaction region as required for nickel-63 are 58 pptv for the protonated monomer and 3.4 ppbv for the proton-bound dimer of 2-pentanone. The detection limits achieved with the tristate shutter utilizing the same reaction region are slightly higher for the protonated monomer at 68 pptv, but lower for the proton-bound dimer at 2 ppbv due to the advanced ion shutter principle not discriminating slow ions. However, the lowest detection limits of 13 pptv and 301 pptv can be achieved with the field-switching shutter and a 2 mm reaction region, sufficient for a tritium ionization source.

Multianalytical Approach for Deciphering the Specific MS/MS Transition and Overcoming the Challenge of the Separation of a Transient Intermediate, Quinonoid Dihydrobiopterin

“…No current H4Bip assay method including liquid chromatography (LC)–tandem mass spectrometry (MS/MS) methods ,,− allows this isomer to be quantified. Approaches based on ion mobility spectrometry (IMS) coupled to MS/MS which have been shown to be very efficient for separation and characterization of molecular ions, − including short-lived intermediates, could thus be interesting for improving the characterization of qH2Bip.…”

4.2 - Compact Electrospray Ionization Ion Mobility Spectrometer

“…With this manufacturing technique it is also possible to simply rescale an IMS design. A detailed description of the miniaturized, low-cost PCB-ESI-IMS presented in this work can be found in [21]. A size comparison of all systems used in this work can be seen in Fig.…”

Miniaturized Drift Tube Ion Mobility Spectrometer with Ultra-Fast Polarity Switching

“…Besides the dimensions of the square cross sections, the two PCB-IMS are identical, including their drift length of 51 mm. A detailed description is given by Bohnhorst et al 34 The total capacitances of the two different PCB-IMS and the PEEK-IMS were measured at a measurement frequency of 1 kHz using a Keysight E4980A LCR meter and a matching Keysight 16089B Kelvin measurement adapter. The total capacitances of the drift tube (Figure 1) were 2.7 pF for the 17 × 17 mm PCB-IMS (Figure 4C), 2.4 pF for the 20 × 20 mm PCB-IMS (Figure 4B), and 7.5 pF for the PEEK-IMS (Figure 4A).…”

“…Since ionization coincides with the ion mobility experiment and polarity switching, the total ionization and collection time of 25 ms (40 Hz), which is routinely used for IMS systems in our group, is higher than the required 2 Hz polarity switching rate by over an order of magnitude. 8,9,27,34 Therefore, the routine ionization and collection time is perfectly suited for ultra-fast polarity switching. 9,35,36 In IMS, the required drift time (s) can be calculated for a given reduced ion mobility K 0 (cm 2 V −1 s −1 ) using eq 1 with the length of the drift tube L (cm), the applied drift voltage U (V), the neutral number density N, and the Loschmidt constant N 0 , which is the neutral number density for a standard temperature of 273.15 K and a standard pressure of 1013.25 mbar.…”

“…40 Here, we keep the previously used time of 25 ms to both allow ultra-fast polarity switching and maintain the highest sensitivity. 34 The blocking voltage (U Block ) applied to the injection grid prevents the early entry of any ions into the drift region by compensating the field penetration of the drift voltage (U Drift ) into the ionization region. For the second switching state of the field switching ion shutter, the collected ions are transferred into the drift region by applying an injection pulse (U Inj ) to the ionization source.…”