Isotope ratio mass spectrometry (IRMS) is a type of mass spectrometry measuring precise differences in abundances of stable isotopes such as 2H/1H, 13C/12C, 15N/14N, and 18O/16O. The ratios of these elements are locally enriched or depleted by thermodynamic and/or kinetic processes. In addition to measuring naturally occurring isotopic ratios, IRMS can be used for tracer studies for research in metabolism. For a sample to be analyzed it must first be converted into simple gases such as H2, CO2, and N2 depending on the sample type and the isotopes of interest.
There are several ways to introduce the sample to the IRMS. lemental analysis (EA-IRMS) gives a bulk measurement of the average isotopic ratio in a sample. Sample preparation is straightforward with the sample weighed into a capsule followed by combustion in a furnace to the simple gases mentioned above. In general, the contribution of individual species to the average ratio cannot be determined by EA-IRMS. To measure the isotopic ratios of individual species, they must first be separated; gas chromatography (GC-IRMS) is ideally suited for this purpose. The sample is separated by GC then as the individual components elute off the column they are combusted to simple gases and detected by the mass spectrometer. For samples already in the gas phase the GasBench is used. The GasBench works by drawing the gaseous sample from the headspace of the sample vial. The sample is separated on a packed column prior to detection by the mass spectrometer.
At the AFBM we are able to measure carbon and nitrogen ratios by EA-IRMS, carbon ratios by GC-IRMS, and hydrogen, carbon, nitrogen, and oxygen ratios using the GasBench. Please contact us if you have questions or would like to get started with your project.