Alternate gas kit

The IMS/MS studies were executed with two different drift tube IMS (DTIMS)/MS platforms. The first was an in-house home-built DTIMS/MS instrument that coupled a 1 m IMS drift tube with an Agilent 6224 TOF MS upgraded to a 1.5 m flight tube (providing MS resolution of ~25 000),^{23 (link)} and the second was the Agilent 6560 IM-QTOF MS platform (Agilent Technologies).^{24 (link)–26 (link)} The Agilent 6560 was outfitted with the commercial gas kit (Alternate Gas Kit, Agilent) and a precision flow controller (640B, MKS Instruments) to allow for real-time pressure adjustment based on absolute readings of the drift tube pressure using a capacitance manometer (CDG 500, Agilent). For the DTIMS measurements on both instruments, ions were passed through an inlet capillary, focused by a high-pressure ion funnel, and accumulated in an ion funnel trap. Ions were then pulsed into the drift tubes filled with ~3.95 Torr of nitrogen gas, where they traveled under the influence of a weak electric field (10 to 20 V/cm). Ions exiting the drift tube were refocused by a rear ion funnel prior to TOF or QTOF MS detection, and their arrival times were recorded.

For the 191 human lipidomic extracted plasma samples, the Agilent 6560 IM-QTOF MS platform (Santa Clara, CA) outfitted with the commercial gas kit (Alternate Gas Kit, Agilent) and a precision flow controller (640B, MKS Instruments) was utilized. IMS-MS data were collected in both positive and negative mode from 50–1700 m/z with a cycle time of 1 sec/spectra to increase the signal of low abundance species. For the LC analyses, a Waters Aquity UPLC H class system was used. 10 μL of each sample was injected onto a reversed phase Waters CSH column (3.0 mm x 150 mm x 1.7 μm particle size). The lipids in the mixture were separated over a 34 min gradient (mobile phase A: acetonitrile/water (40:60) containing 10 mM ammonium acetate; mobile phase B: acetonitrile/ isopropyl alcohol (10:90) containing 10 mM ammonium acetate) at a flow rate of 250 μL min⁻¹. The gradient and column wash are provided in Table S2. The resolution of isomeric lipid species noted herein (A and B pairs) were largely resolved due to retention time using this LC method, while IMS collision cross section values were utilized to increase confidence of the identified lipids.