High Resolution GC-Orbitrap-MS Metabolomics Using Both Electron Ionization and Chemical Ionization for Analysis of Human Plasma

Gas
chromatography–mass spectrometry (GC-MS) platforms are
typically run in electron ionization (EI) mode for mass spectral matching
and metabolite annotation. With the advent of high resolution mass
spectrometry (HRMS), soft ionization techniques such as chemical ionization
(CI) may provide additional coverage for compound identification.
We evaluated NIST SRM 1950 pooled plasma reference sample using a
HRGC-MS instrument [GC-Orbitrap-MS with electron ionization (EI),
positive chemical ionization (PCI), and negative CI (NCI) capabilities]
for metabolite annotation and quantification to assess the suitability
of the platform for routine discovery metabolomics. Using both open
source and vendor workflows, we validated the spectral matches with
an in-house spectral library (Wake Forest CPM GC-MS spectral and retention
time libraries) of EI-MS and CI-MS/MS spectra obtained from chemical
standards. We confidently [metabolomics standards initiative (MSI)
confidence level 2] identified 263, 93, and 65 metabolites using EI,
PCI, and NCI modes, respectively, of which 270 metabolites (64%) were
validated using our Wake Forest CPM GC-MS spectral libraries. When
compared to published LC-MS-based efforts using the same NIST SRM
1950 plasma sample, there was only 17% overlap between the two platforms.
In addition, the metabolomics analysis of community approved standard
human plasma demonstrated the ability of EI- and CI-MS modes of analysis
using a HRGC-MS platform to enable reproducible and interoperable
spectral matching.