GCIRMS

GCIRMS, or gas chromatography–isotope ratio mass spectrometry, is an analytical technique that combines a gas chromatograph with an isotope ratio mass spectrometer to measure stable isotope ratios in individual organic compounds separated by GC. It enables compound-specific isotope analysis (CSIA), providing isotope data for each component in a mixture rather than bulk material.

In a typical setup, a GC separates compounds which then enter a combustion, pyrolysis, or reduction reactor that converts the analytes into simple gases (such as CO2 for carbon, H2O for hydrogen, N2 for nitrogen) compatible with IRMS. The isotope ratio mass spectrometer measures the relative abundances of heavy to light isotopes (e.g., 13C/12C, 2H/1H, 15N/14N, 18O/16O). Results are expressed as delta values relative to international standards (e.g., VPDB for carbon, VSMOW for hydrogen and oxygen, AIR for nitrogen) and are calibrated with reference materials possessing known isotope ratios.

Applications include verification of food authenticity and provenance, ecological and metabolic studies, environmental tracing, petrochemical and forensic investigations, and quality control in pharmaceuticals. CSIA can distinguish sources and pathways by analyzing isotope ratios of individual constituents such as fatty acids, amino acids, or terpenes.

Limitations and considerations include the need for volatile or derivatizable analytes, potential isotope fractionation during sample preparation and GC, instrument drift, and the requirement for rigorous calibration and standardization to ensure comparability across laboratories. Data interpretation requires an understanding of isotopic fractionation processes and reference frameworks.

GCIRMS is widely used for researchers requiring high-resolution isotopic information on specific compounds, complementing bulk isotope measurements obtained by other methodologies.