Browsing by Author "Latif, Mohsen"

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    Enhancing Separation and Constriction of Ion Mobility Distributions in Drift Tubes at Atmospheric Pressure Using Varying Fields
    (American Chemical Society, 2022-03-31) Chen, Xi; Latif, Mohsen; Gandhi, Viraj D.; Chen, Xuemeng; Hua, Leyan; Fukushima, Nobuhiko; Larriba-Andaluz, Carlos; Mechanical and Energy Engineering, School of Engineering and Technology
    A linearly decreasing electric field has been previously proven to be effective for diffusional correction of ions in a varying field drift tube (VFDT) system, leading to higher resolving powers compared to a conventional drift tube due to its capacity to narrow distributions midflight. However, the theoretical predictions in resolving power of the VFDT were much higher than what was observed experimentally. The reason behind this discrepancy has been identified as the difference between the theoretically calculated resolving power (spatial) and the experimental one (time). To match the high spatial resolving power experimentally, a secondary high voltage pulse (HVP) at a properly adjusted time is used to provide the ions with enough momentum to increase their drift velocity and hence their time-resolving power. A series of systematic numerical simulations and experimental tests have been designed to corroborate our theoretical findings. The HVP-VFDT atmospheric pressure portable system improves the resolving power from the maximum expected of 60–80 for a regular drift tube to 250 in just 21 cm in length and 7kV, an unprecedent accomplishment.
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    Field-Switching Repeller Flowing Atmospheric-Pressure Afterglow Drift Tube Ion Mobility Spectrometry
    (American Chemical Society, 2022-03-02) Latif, Mohsen; Chen, Xi; Gandhi, Viraj D.; Larriba-Andaluz, Carlos; Gamez, Gerardo; Mechanical and Energy Engineering, School of Engineering and Technology
    In this work, a field-switching (FS) technique is employed with a flowing atmospheric pressure afterglow (FAPA) source in drift tube ion mobility spectrometry (DTIMS). The premise is to incorporate a tip-repeller electrode as a substitute for the Bradbury–Nielsen gate (BNG) so as to overcome corresponding disadvantages of the BNG, including the gate depletion effect (GDE). The DTIMS spectra were optimized in terms of peak shape and full width by inserting an aperture at the DTIMS inlet that was used to control the neutral molecules’ penetration into the separation region, thus preventing neutral-ion reactions inside. The FAPA and repeller’s experimental operating conditions including drift and plasma gas flow rates, pulse injection times, repeller positioning and voltage, FAPA current, and effluent angle were optimized. Ion mobility spectra of selected compounds were captured, and the corresponding reduced mobility values were calculated and compared with the literature. The 6-fold improvements in limit of detection (LOD) compared with previous work were obtained for 2,6-DTBP and acetaminophen. The enhanced performance of the FS-FAPA-DTIMS was also investigated as a function of the GDE when compared with FAPA-DTIMS containing BNG.