7890 gas chromatography system

Short-chain fatty acid concentrations in the cecal contents were quantified after carrying out water extraction (2 vol/wt) and protein precipitation [10% vol/vol phosphotungstic acid (Sigma-Aldrich)] as described elsewhere (48 (link)). Briefly, the short-chain fatty acids (SCFAs) in the acidified supernatant (0.3 μl) were separated using a 7890 Gas Chromatography System (Agilent, Les Ulis, France) equipped with a split/splitless injector (ALS7650), a flame-ionization detector, and a Nukol-SP-1000-capillary GC column (15 m × 0.53 nm, 0.5 μm; FSCAP Nukol; Supelco, Saint-Quentin-Fallavier, France). Hydrogen was the carrier gas (flow rate = 10 ml/min). The inlet, column, and detector temperatures were 200, 100, and 240°C, respectively. We used 2-ethylbutyrate (Sigma-Aldrich) as the internal standard. Samples were analyzed in duplicate. The data were collected and the peaks were characterized using OpenLab ChemStation C.01.06 software (Agilent, Les Ulis, France).

All analyses were performed using an Agilent 7890 gas chromatography system coupled with an Agilent 5975C mass spectrometer equipped with an electron impact (EI) ion source and a single quadrupole (Agilent Technologies, Santa Clara, CA, USA). Chromatographic separation was achieved with a cross-linked poly 5% diphenyl/95% dimethylsiloxane HP-5-MS capillary column (30 m × 0.25 mm i.d. × 0.25 µm film thickness) from Agilent. The oven temperature was initially set at 100 °C held for 2 min, then ramped at 30 °C min⁻¹ to 200 °C held for 1 min, then 10 °C min⁻¹ to 250 °C held for 6.5 min, and then 40 °C min⁻¹ to 280 °C held for 16 min. One microliter of each sample was injected in splitless mode using an Agilent 7693A autosampler. The solvent delay was set at 5.0 min and the run time at 35 min. The injection port and the transfer line were both heated at 280 °C. The source and the single quadripole of the mass spectrometer temperatures were set at 230 °C and 150 °C, respectively. The carrier gas was helium at a flow rate of 1.0 mL min⁻¹, and ionization with an inert EI ion source was operated at 70 eV. The software MSD Chemstation E.02.02.1431(Agilent Tech. Inc., Les Ulis, France) was used to control the instrument and was used to collect data.