Focus gas chromatograph

The concentrations of acetoin, 2,3-butanediol, 2,3-butanedione, ethyl acetate, ethyl lactate, isoamyl acetate, (iso)butyric acid, (iso)valeric acid, methyl-1-butanol, and propionic acid were measured by gas chromatography with flame ionization detection (GC-FID), applying internal standardization, as described before for ethyl acetate and acetoin (De Roos et al., 2018 (link)). Briefly, a Focus gas chromatograph (Interscience, Breda, Netherlands) equipped with a Stabilwax-DA column (Restek, Bellefonte, PA, United States) coupled to a FID-80 detector (Interscience) was used. All operating conditions were the same. All samples and standards were deproteinized, vortexed, centrifuged, and filtered as described above, before injection (1 μl; split 40) into the column.

The following equipment and materials have been used in this study: carbon dioxide (Air Liquide, Liège, Belgium); helium (Air Products, Brussels, Belgium); acetonitrile (Biosolve, Valkenswaard, Netherlands); luminometer Orion II (BRS, Drogenbos, Belgium); adenosine triphosphate (ATP), Dulbecco's modified Eagle's medium (DMEM), DMEM without red phenol, and fetal bovine serum and trypsin (Fisher Bioblock Scientific, Tournai, Belgium); Focus gas chromatograph and Polaris Q mass spectrometer (Interscience, Louvain-la-Neuve, Belgium); charcoal, dextran, o,p′-DDD, p,p′-DDD, p,p′-DDE, o,p′-DDT, p,p′-DDT, 17β-estradiol, HCB, α-HCH, β-HCH, γ-HCH, δ-HCH, nonane, PCB 80 ¹³C, PCB 138 (2,2′,3,4,4′,5′-hexachlorobiphenyl), PCB 153 (2,2′,4,4′,5,5′-hexachlorobiphenyl), and PCB 180 (2,2′,3,4,4′,5,5′-heptachlorobiphenyl) (Sigma-Aldrich, Bornem, Belgium); D-luciferin (potassium salt) (Synchem OHG, Kassel, Germany); HT8 column (VWR, Leuven, Belgium).