MSACL 2016 US Abstract

Ion Mobility Mass Spectrometry: Alternative Drift Gas Selection for Improved Separation of Isomers in Clinical Analysis

Christopher Chouinard (Presenter)
University of Florida

Bio: Chris graduated from the University of North Carolina at Chapel Hill in 2010, with degrees in both chemistry and biology. Following a couple years working in industry, Chris began his research at the University of Florida under advisor Richard Yost. His research focuses on using ion mobility-mass spectrometry for improvement of isomer separation in metabolomics applications.

Authorship: Christopher D. Chouinard (1), Robin H.J. Kemperman (1), Harrison King (1), Richard A. Yost (1,2)
(1) Department of Chemistry, University of Florida, Gainesville, FL; (2) Southeast Center for Integrated Metabolomics (SECIM), University of Florida, Gainesville, FL

Short Abstract Ion mobility spectrometry (IMS) has been coupled with mass spectrometry to improve isomer separation capabilities without sacrificing time. To improve this potential, several strategies have been employed, including varying the drift gas environment. Although helium and nitrogen have been the traditional options, other drift gases have shown promise in improving resolution between isomers. This study will compare the most common drift gases, helium and nitrogen, to gases such as carbon dioxide, sulfur hexafluoride, and argon for their individual merits in improving separation of targeted clinical compounds, especially for Vitamin D metabolite epimers and steroid diastereomers such as testosterone and dehydroepiandrosterone.

Long Abstract

Ion mobility spectrometry (IMS) coupled with mass spectrometry (IM-MS) has seen increased usage for separation of isomers in metabolomics studies. Recently, classical drift tube IMS has been shown to improve separation within several metabolite classes, including steroids and lipids. Our group has shown that drift time can vary dramatically based on the specific cation species (e.g., [M+H]+ vs. [M+Na]+) and multimer complexes (i.e., dimers, trimers, etc.) identified. These changes in drift time have been shown to improve separation of isomers in many cases. This research aims to utilize a different experimental variable, the drift gas environment, as an additional strategy to improve separation capabilities especially for use in targeted clinically-relevant assays.

Results were obtained with an Agilent 6560 IM-QTOF instrument (Santa Clara, CA) with dual Agilent Jet Stream (AJS) source and atmospheric pressure chemical ionization (APCI) source. Initially, standards of target compounds (1-10 μg/mL in methanol) were direct infused and drift time spectra were collected. Clinically relevant standard compounds included 25-hydroxyvitamin D3 and D2 epimers, steroid structural isomers and diastereomers, and hydroxywarfarin positional isomers. For control experiments in nitrogen drift gas, the 78 cm drift tube was maintained at a constant field strength over the range from 10-19 V/cm, with a nitrogen drift gas pressure of 4 torr and temperature of 30 °C. Drift time values were plotted against the inverse of drift tube field strength to calculate collision cross sections. Reported drift time values were obtained at 19 V/cm due to optimal peak resolution. Data processing was performed using Agilent IM-MS Browser B.07.00 software. Alternative drift gases were also employed, including helium, carbon dioxide, argon, and sulfur hexafluoride.

In comparison to control experiments utilizing nitrogen, other drift gases were shown to improve separation for targeted compounds. Specifically, dehydroepiandrosterone (DHEA) and epitestosterone, an endogenous epimer of testosterone, have very similar measured CCS of 251.3 and 250.7 Å2, respectively, for the sodiated dimer [2M+Na]+ species. Conversely, these same compounds have measured CCS of 252.6 and 246.8 Å2, respectively, when analyzed with carbon dioxide. This yields an improvement in resolution between these sodiated dimer drift peaks from RS = 0.05 (with nitrogen drift gas) to RS = 0.56 (for carbon dioxide).

Following these preliminary experiments, studies are underway to investigate the use of alternative drift gases in LC-IM-MS methods. The aforementioned standards will be spiked into plasma at a range of physiologically relevant concentrations and investigated with different drift gases for comparison of relative separation. Furthermore, existing LC methods will be shortened (<3 minutes) to display the improved time scale of separation achievable with LC-IM-MS. Finally, direct infusion nanospray ionization with flow rates of ≤10 nL/min will be investigated, in the absence of chromatography, for targeted analysis of the above compounds.

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