A Simple Analytical Model for Predicting the Detectable Ion Current in Ion Mobility Spectrometry Using Corona Discharge Ionization Sources

Kirk, Ansgar T.; Kobelt, Tim; Spehlbrink, H.; Zimmermann, Stefan

doi:10.1007/s13361-018-1970-6

Cited by 17 publications

(25 citation statements)

References 17 publications

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“…As shown in the center panel of Figure , the ion transmission only depends on the ratio between the field before and after the injection grid, not on absolute field strengths. This is what we previously predicted, ,, as the ion loss is caused by the number of field lines ending at the grid and thus guiding the ions toward the grid. As scaling all potentials by the same factor does not change the shape of the field lines, only the ratio of the potentials and thus the ratio of the electric fields is affecting the ion transmission.…”

Section: Resultssupporting

confidence: 83%

Improving Ion Mobility Spectrometer Sensitivity through the Extended Field Switching Ion Shutter

et al. 2020

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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 protonated monomers, 10 to 14 for proton-bound dimers, and 25 for the proton-bound 1-octanol trimer compared to the classical field switching shutter. However, due to the nonlinear response for ions containing multiple analyte molecules, the limits of detection improve only by a factor of 3 to 4 for proton-bound dimers and 3 for the proton-bound 1-octanol trimer. Nevertheless, this still leads to single-digit pptv limits of detection for protonated monomers and hundred pptv limits of detection for proton-bound dimers measured for a series of ketones. However, for the most intense peaks such as the reactant ion peak, a significant loss of resolving power by a factor of up to 1.4 was observed due to Coulomb repulsion.

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Section: Resultssupporting

confidence: 83%

Improving Ion Mobility Spectrometer Sensitivity through the Extended Field Switching Ion Shutter

et al. 2020

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“…Afterwards, the pressure mainly affects the ion current. Stated in [35] the ion current is proportional to the reciprocal of the pressure, which resembles the results. A small periodic signal is visible that is caused by our zero air generator (pressure swing system).…”

Section: Resultssupporting

confidence: 73%

“…Here the minimum reduced electric DC field strength is raised to 44 Td due to the minimum voltage output of the DC sources. Although, the initial ion amount decreases with decreasing pressure, as shown in [35], the maximum ion current through the exit aperture can be raised to 1280 pA for 190 V RF voltage amplitude and 62 Td, as shown in Figure 8 b). At 100 Td, ion currents up to 740 pA are possible with maximum RF voltage.…”

Section: Resultsmentioning

confidence: 84%

A Simple Printed Circuit Board–Based Ion Funnel for Focusing Lowm/zRatio Ions with High Kinetic Energies at Elevated Pressure

Schlottmann

Allers

Kirk

et al. 2019

J. Am. Soc. Mass Spectrom.

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Ion funnels are one of the key components for transferring ions from higher pressure into vacuum. Typically, ion funnels are constructed of several different plate ring electrodes with a decreasing inner diameter where radio frequency (RF) voltages and electric DC fields are applied to the electrodes to focus and transport ion clouds. In this work, we developed and investigated a simple and low-cost ion funnel design that is based on standard printed circuit boards (PCB) with integrated planar electrodes including the signal distribution network. This ion funnel is capable of withstanding high electric fields with superimposed RF voltages due to its buried capacitors. To evaluate the ion focusing efficiency of the ion funnel, we simulated the movement of ions inside this funnel and experimentally evaluated the ion transfer. Our simulations show that a rectangular ion funnel like the PCB ion funnel has similar performance compared to conventional stacked ring-funnels. Due to the hundredfold lower parasitic capacitance between the planar electrodes compared to conventional ion funnels, high RF voltage amplitudes up to 195 V and reduced electric DC field strengths up to 100 Td can be reached at a frequency of about 5 MHz. Thus, the funnel is appropriate to focus light ions at elevated pressures up to 20 mbar.

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“…In previous works, the ion species underlying these peaks have been identified as NO + (H 2 O) n , H 3 O + (H 2 O) n , and O 2 + (H 2 O) n . 21,22 Increasing the reduced electric field strength in the reaction region, the total charge in the spectrum increases due to reduced Coulomb repulsion 58 . However, when investigating chemical reactions leading to the conversion of ion species, it is more useful to consider relative abundances instead of absolute abundances.…”

Section: Resultsmentioning

confidence: 99%

Formation of positive product ions from substances with low proton affinity in high kinetic energy ion mobility spectrometry

Allers

Kirk

Schaefer

et al. 2021

Rapid Comm Mass Spectrometry

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Rationale: Ion mobility spectrometry (IMS) instruments are typically equipped with atmospheric pressure chemical ionization (APCI) sources operated at ambient pressure. However, classical APCI-IMS suffers from a limited ionization yield for nonpolar substances with low proton affinity (PA). This is mainly due to ion clustering processes, especially those that involve water molecules, inhibiting the ionization of these substances. Methods: High Kinetic Energy (HiKE)-IMS instruments are operated at decreased pressures and high reduced electric field strengths. As most clustering reactions are inhibited under these conditions, the ionization yield for nonpolar substances with low PA in HiKE-IMS should differ from that in classical APCI-IMS. To gain first insights into the ionization capabilities and limitations of HiKE-IMS, we investigated the ionization of four model substances with low PA in HiKE-IMS using HiKE-IMS-MS as a function of the reduced electric field strength. Results: The four model substances all have proton affinities between those of H 2 O and (H 2 O) 2 but exhibit different ionization energies, dipole moments, and polarizabilities. As expected, the results show that the ionization yield for these substances differs considerably at low reduced electric field strengths due to ion cluster formation. In contrast, at high reduced electric field strengths, all substances can be ionized via charge and/or proton transfer in HiKE-IMS. Conclusions: Considering the detection of polar substances with high PAs, classical ambient pressure IMS should reach better detection limits than HiKE-IMS. However, considering the detection of nonpolar substances with low PA that are not detected, or only difficult to detect, at ambient pressure, HiKE-IMS would be beneficial. 1 | INTRODUCTION Due to their high sensitivity, fast response times, and compact design, ion mobility spectrometers are commonly used in safety and security applications such as the detection of chemical warfare agents, 1,2 toxic industrial chemicals, 3,4 drugs, 5,6 and explosives. 7-9 Basically, ion mobility spectrometry (IMS) instruments can be divided by their principle of ion separation. In this work, a drift tube (DT) ion mobility spectrometer is used. In DT-IMS, ions are separated by their motion along the axis of a drift tube driven by a homogeneous static electric field. To initiate the measurement, an ion packet is injected into the drift tube. During their motion, the ions are separated based on the absolute value of their ion mobility in the present drift gas. At the end of the drift tube, the ions are captured by a detector that converts

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A Simple Analytical Model for Predicting the Detectable Ion Current in Ion Mobility Spectrometry Using Corona Discharge Ionization Sources

Cited by 17 publications

References 17 publications

Improving Ion Mobility Spectrometer Sensitivity through the Extended Field Switching Ion Shutter

Improving Ion Mobility Spectrometer Sensitivity through the Extended Field Switching Ion Shutter

A Simple Printed Circuit Board–Based Ion Funnel for Focusing Lowm/zRatio Ions with High Kinetic Energies at Elevated Pressure

Formation of positive product ions from substances with low proton affinity in high kinetic energy ion mobility spectrometry

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