Overview

GC-MS metabolomics couples gas chromatography with mass spectrometry for the analysis of volatile and semi-volatile metabolites. Because most metabolites are not volatile at GC-compatible temperatures, chemical derivatization is required — typically a two-step process of methoximation followed by silylation — to convert polar functional groups into volatile, thermally stable derivatives. GC-MS offers several advantages for metabolomics: highly reproducible retention times, well-characterized fragmentation patterns, and extensive commercial and public spectral libraries (such as NIST and Golm Metabolome Database) that facilitate metabolite identification.

Methods

Derivatization proceeds in two steps. Methoximation with methoxyamine hydrochloride protects carbonyl groups and reduces the number of tautomeric forms. Silylation with N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) replaces active hydrogens on hydroxyl, amine, and carboxyl groups with trimethylsilyl groups, increasing volatility. Separation is performed on fused-silica capillary columns with non-polar stationary phases, using programmed temperature gradients to elute metabolites across a wide volatility range. Electron ionization at 70 eV produces highly reproducible fragmentation spectra that are searchable against reference libraries. Deconvolution algorithms such as AMDIS resolve co-eluting compounds by extracting pure component spectra from the total ion chromatogram.

Applications

GC-MS metabolomics is a mature platform used extensively in plant metabolomics, microbial metabolomics, and clinical diagnostics for inborn errors of metabolism. It is the method of choice for organic acid profiling in urine and for analyzing central carbon metabolism intermediates. The technique complements gas chromatography theory with mass spectrometry detection. Careful sample preparation techniques are essential for reproducible derivatization and accurate quantification.