7890b plus gc system

Short-chain fatty acids (SCFAs) concentration in feces was measured by gas chromatography spectrometer (GCS) (7890B Plus GC System, Agilent, California). SCFAs were extracted from stool samples as follows: 100 mg of a dry fecal sample was put in a 10-ml centrifuge tube and gently suspended in 1.6-ml deionized water. About 0.4-ml 50% H₂SO₄ and 2-ml diethyl ether were then mixed with an orbital shaker for 45 min before centrifuging at 3,000 rpm for 5 min at room temperature. About 10-mg anhydrous CaCl2 was added to remove residual water for collecting a supernatant. Finally, a 2-μL supernatant was injected into the GCS. Gas chromatography analysis was carried out using Agilent 7890B GCS fitted with a flame ionization detector (FID). A GCS column (ZB-FFAP, Phenomenex, California) of 30 m × 0.32 mm × 0.25 μm was used. Nitrogen was supplied as the carrier gas at a flow rate of 1.69 ml/min in a non-split mode (injector temperature at 250°C). The initial oven temperature was 1006C for 2 min, and then rose at a rate of 8°C/min to 240°C before upholding there for 10 min. The temperatures of the FID and the injection port were 350°C. SCFAs were quantified by an external standard method using the mix standard solution of acetic, propionic, butyric, and valeric acids.