Hp innowax ms capillary column

GC-MS analysis was performed on an Agilent Technologies apparatus 7890A-5975C with HP-INNOWAX MS capillary column (30 m × 250 μm × 0.25 μm). The following oven temperature program was initiated at 60°C, held for 5 min, then increased at the rate of 10°C min^{− 1}–120°C, held for 0 min, next increased at the rate of 2°C min^{− 1}–185°C, held for 3 min, and finally increased at the rate of 8°C·min^{− 1}–250°C. The carrier gas was helium (He) at a constant flow of 1 ml min^{− 1}. The ion source was kept at 230°C. The splitting ratio was 10:1. The spectrometer operated at 70 eV with the scan from (m/z) 35–550 Da.

The quantitative analysis of fecal SCFAs was determined by a trace ultra gas chromatograph coupled with an ISQ mass spectrometer (TRACE 1310-ISQ, Thermo, MA, United States). Briefly, fecal samples were homogenized with 50 μl of 15% phosphoric acid, 100 mg of glass beads, and 100 μl of isocaproic acid as the internal standard for 10 min using a vortex mixer. After acidification, 400 μl of diethyl ether was added to each sample for SCFAs extraction, and then centrifuged the mix for 10 min at 12,000 rpm (4°C). The levels of SCFAs were quantitatively determined by the GC-MS (gas chromatography–mass spectrometry). The GC-MS analysis was performed by a trace ultra GC equipped with an HP-Innowax MS capillary column (30 m × 0.25 mm × 0.5 µm film thickness, Agilent Technologies). Temperature of injector, ion source quadrupole, the GC-MS interface was 250°C, 230°C, 150°C, and 250°C, respectively. The flow rate of helium carrier gas was kept at 1.0 ml/min. Samples were injected (1 µl) with a split injection (split ratio: 10:1). The initial column temperature was 90°C, increased to 120°C at the rate of 10°C/min, then elevated at a rate of 5°C/min to 150°C, and finally increased to 250°C at a rate of 25°C/min and held for 2 min. The mass spectrometer was used in electron impact (EI) ionization mode (70 eV).