Analyses were performed using an Agilent Technologies 6890N network gas chromatograph system coupled to an Agilent Technologies 5975 inert mass selective detector. Furan in the model systems was separated using a HP-PLOT Q fused silica capillary column (15 m × 0.32 mm I. D., 20 μm film thickness, J & W Scientific, Folsom, CA, USA). The injector port was heated to 250 °C, and the splitless injection mode was used. The GC oven temperature program was set to 50 °C (held for 5 min) and increased to 230 °C at 25 °C/min (held for 2 min). The mass spectrometer was operated in positive electron impact ionisation mode using automatic gain control with 70 eV of electron energy and selective-ion monitoring mode by recording the current following ions: m/z 68 [M]+ and m/z 72 [M]+ for furan and d4-furan determinations, respectively. The ions m/z 39 [M-CHO]+ and m/z 42 [M-CDO]+ were monitored to confirm detection of furan and d4-furan.