Gas chromatography with electron ionization and mass spectrometry (GC–EI-MS) detection is a workhorse among analytical techniques in metabolomics. A major challenge in the utilization of GC–EI-MS in metabolomics is the identification of unknowns. The recent availability of high resolution, accurate mass, time-of-flight mass spectrometry (TOF-MS) systems provides great potential for identifying unknowns by reducing uncertainty in possible formulas and enhancing detection continuity between sample sets. A workflow using GC–EI-MS spectra for library identification, with molecular formula information for unknowns provided by chemical ionization-mass spectrometry (CI-MS) and accurate mass analysis was used for the analysis of blood plasma.
Metabolomics provides a foundation for quantitative, comparative biology and is indispensable for the comprehensive characterization of molecules and differential analysis of populations. It entails instrumental detection, characterization, and quantification of small molecules (molecular weight < 1500 Da) produced, or transformed in the cells of living organisms (1,2). Although no single instrument is capable of fully profiling the metabolome, the unique capabilities of time-of-flight mass spectrometry (TOF-MS) make it an ideal tool for metabolomic studies. Gas chromatography–time-of-fight-mass spectrometry (GC–TOF-MS) is a powerful approach for unbiased metabolic profiling and quantitation of a diverse array of metabolites (3,4). High-resolution TOF-MS provides additional benefits such as mass accuracies below 1 ppm for robust formula determinations and resolving power in excess of 50,000 for resolution of isobars and minimization of background interferences. A workflow that combines accurate mass electron ionization (EI) and chemical ionization (CI) high-resolution TOF-MS for confident characterization of different compound classes was used for the analysis of human blood plasma. It includes recommendations for sample preparation, analytical conditions, and data analysis.