We routinely support CSIA of ¹³C in fatty acid methyl esters (FAMEs).  FAMEs dissolved in hexane are injected in splitless mode and separated on a Varian factorFOUR VF-5ms column (30m X 0.25mm ID, 0.25 micron film thickness). Once separated, FAMEs are quantitatively converted to CO₂ in an oxidation reactor at 950°C. Following water removal through a nafion dryer, CO₂ enters the IRMS. δ¹³values are corrected using working standards composed of several FAMEs calibrated against NIST standard reference materials.

Column Selection: the VF-5ms is suitable for most FAME mixtures. The highly polar SGE BPX70 column has better separation of cis- and trans- isomers, which is useful for analysis of methyl oleate (18:1n9c) and methyl linoleate (C18:2n6c). These are separated by less than 15 seconds on the VF-5ms. However, BPX70 is not suitable for samples that include C19:0 internal standards, because it does not sufficiently separate C19:0 from C18:2n6c.