Systematic Optimization of Ambient Ionization Ion Mobility Mass Spectrometry for Rapid Separation of Isomers

Abstract

Current methods typically used for metabolite screening and disease diagnosis often require extensive sample preparation, which increases analysis time and associated costs. While ambient ionization techniques enable the analysis of various samples in complex matrices with little or no sample preparation in a short time (typically within a minute), their reduced selectivity, even when coupled with high-resolution mass spectrometers, limits their application in certain fields. In this study, we have optimized the coupling of paper spray (PS) and leaf spray (LS) ambient ionization techniques with a commercially available ion mobility mass spectrometer (IM−MS) and demonstrated the separation of geometric and constitutional isomers. Ambient ionization techniques allow simultaneous introduction and ionization of samples, while background noise and matrix interference from paper and leaf substrates are filtered out by IM separation, resulting in high sensitivity and selectivity of the PS−IM−MS and LS−IM−MS workflows. In addition, we introduced a novel approach to perform single-field collision cross section (CCS) measurements, which resulted in CCS values that differ by 0.15% and 0.25% from traditional stepped-field and single-field methods, respectively. In addition, we used advanced computational tools to confidently identify analyte structures by comparing CCS values from experimental IM measurements and theoretical calculations. These results suggest that the coupling of ambient ionization methods with ion mobility techniques enables rapid, sensitive, and highly selective analysis that can be used in different fields, such as agrochemical screening and disease diagnostics.

Strain-Level Discrimination of Bacteria by Liquid Chromatography and Paper Spray Ion Mobility Mass Spectrometry

“…The effluent from the RPLC separation was directed to the ESI source of the Agilent 6560 IM-QTOF MS. The instrument has been described in detail elsewhere, and the conditions for the ESI source were as follows: Drying gas temperature and flow rate, 325 °C, and 5 L/min; nebulizer gas pressure, 30 psi; sheath gas temperature and flow rate, 275 °C, and 12 L/min; capillary voltage, 3500 V; nozzle voltage, 1000 V; fragmentor, 400 V; octopole RF, 750 V. The instrument was operated in all-ion IM-MS/MS mode, with ion mobility spectra acquired using a pseudorandom 5-bit sequence (multiplexing mode). In the multiplexing mode, several ion packets are pulsed into the drift tube during each data acquisition cycle, increasing the efficiency of ion utilization within the same dwell time .…”

“…Then, the filter papers were cut into several triangles of approximately 8 mm base width and 10 mm height and placed at an optimal distance (∼6 mm) from the IM-MS inlet. Spray solvent and high voltage were then applied to generate an electrospray-like plume . Forty microliters of the spray solvent were added, which enabled the extraction of various analytes and efficient paper spray ionization.…”

Ion Mobility Mass Spectrometry for the Separation and Characterization of Small Molecules

“…188 The additional separation technology can significantly improve the selectivity by effectively reducing the background noise, thus increasing the detection limit by 5−10 times. Olajide et al 197 optimized the ionization and transmission parameters of PSI-IM-MS, demonstrated the separation of geometric isomers and structural isomers, and developed a leaf spray ionization IM-MS platform, which can quickly analyze pesticide isomers in leaf matrix. In addition, they introduced a new method to measure the single-field CCS, and the difference between CCS and traditional steped-field and single-field methods was only 0.15% and 0.25%, respectively, which improved the reliability of compound identification.…”

Applications of ambient ionization mass spectrometry in 2022: An annual review

“…In comparison to other techniques, such as LTP‐MS and ESI‐IMS, similar LODs could be achieved for a number of target analytes, including codeine, papaverine, and caffeine. In a similar vein, PS and leaf spray ionization techniques were also coupled with ion mobility and MS 197 . In coupling these techniques, the authors demonstrated the ability to separate isomeric pesticides and lipids, reduce the effects of matrix effects, and improve the signal‐to‐noise of target analytes.…”