Optimization of lens size and ion source parameters for gas chromatography/mass spectrometry-based metabolomics using hydrogen as a carrier gas.

Gas chromatography/mass spectrometry (GC/MS) is widely employed in metabolomics owing to its high resolution, reproducibility, and compatibility with volatile and semi-volatile compounds. While helium has traditionally been used as the carrier gas, increasing costs and global shortages have prompted the exploration of hydrogen gas as an alternative. Hydrogen offers faster analysis times and reduced ion source contamination but presents challenges, including ion source reactions, which can change compound fragmentation patterns. To address this, a hydrogen-deactivated electron ionization (EI) source has been developed to minimize undesired chemical interactions and improve spectral integrity. In this study, we systematically evaluated the effect of extraction lens sizes (3, 6, and 9 mm) under hydrogen carrier gas conditions using n-alkane and human metabolomic standard solutions. The hydrogen-deactivated ion source equipped with a 3 mm extraction lens provided superior peak symmetry and the highest signal intensities, with acceptable relative standard deviation (RSD) values (i.e., below 30%). In addition, the reproducible fragmentation patterns as those observed with helium carrier gas were obtained for phosphorylated metabolites. Using this optimized configuration, we applied hydrogen gas-based GC/MS to metabolomic profiling of the human colon cancer cell line HCT116 with mutant isocitrate dehydrogenase 1 (IDH1). Key metabolic alterations, including increased levels of the known biomarker 2-hydroxyglutaric acid, were detected in IDH1-mutant cells compared with wild-type cells. These findings establish hydrogen gas-based GC/MS with a hydrogen-deactivated ion source as a robust and reliable platform for metabolomics, offering an effective alternative to helium-based systems.