Similarly,   H (including H3 + correction) and   O can be measured from H2 and CO, respectively, when the GC is interfaced with the IRMS via a pyrolysis reactor (GC-Py-IRMS; preconditioned with solvent) and operated at around 1420°C. Only recently has the GC-Py-IRMS   H measurement of FAMEs been reported . Carbon fractional isotopic abundance ( 13 F; Eq 1), carbon isotope ratio ( 13 R; Eq 2) and the representation of isotope values using the delta notation ( 13 C) can be calculated from isotope measurements (Eq 3). An adjustment is made for the isotopic contribution of the chemical derivatisation (usually methyl-) group (Eq 4; .