A schematic diagram of the GC/C/IRMS system employed for the separation of VFAs and the determination of their concentration and [13C] enrichment is shown in Fig. The gas chromatograph used was an Ai model 93 (ATAS,Cambridge, UK). The column used for VFA separation was a polar ZB-FFAP column, 30 m 0.53 mm
1 mm phase(Zebron, Phenomenex, Torrance, CA, USA).