High Resolution\nGC-Orbitrap-MS Metabolomics Using\nBoth Electron Ionization and Chemical Ionization for Analysis of Human\nPlasma

Gas\nchromatography–mass spectrometry (GC-MS) platforms are\ntypically run in electron ionization (EI) mode for mass spectral matching\nand metabolite annotation. With the advent of high resolution mass\nspectrometry (HRMS), soft ionization techniques such as chemical ionization\n(CI) may provide additional coverage for compound identification.\nWe evaluated NIST SRM 1950 pooled plasma reference sample using a\nHRGC-MS instrument [GC-Orbitrap-MS with electron ionization (EI),\npositive chemical ionization (PCI), and negative CI (NCI) capabilities]\nfor metabolite annotation and quantification to assess the suitability\nof the platform for routine discovery metabolomics. Using both open\nsource and vendor workflows, we validated the spectral matches with\nan in-house spectral library (Wake Forest CPM GC-MS spectral and retention\ntime libraries) of EI-MS and CI-MS/MS spectra obtained from chemical\nstandards. We confidently [metabolomics standards initiative (MSI)\nconfidence level 2] identified 263, 93, and 65 metabolites using EI,\nPCI, and NCI modes, respectively, of which 270 metabolites (64%) were\nvalidated using our Wake Forest CPM GC-MS spectral libraries. When\ncompared to published LC-MS-based efforts using the same NIST SRM\n1950 plasma sample, there was only 17% overlap between the two platforms.\nIn addition, the metabolomics analysis of community approved standard\nhuman plasma demonstrated the ability of EI- and CI-MS modes of analysis\nusing a HRGC-MS platform to enable reproducible and interoperable\nspectral matching.