Db ffap gas phase capillary column

The concentrations of total VFA (TVFA) and individual VFA were detected by gas chromatography (Agilent 7890A, NYSE: A, Palo Alto, CL, United States), referring to the method of Wang et al. (2020b) (link). A total of 0.15 ml of 25% metaphosphoric acid was added into 1.5 ml of rumen fluid samples and was properly mixed. Subsequently, the mixed samples were stored at −20°C for more than 24 h and then centrifuged at 15,000 × g for 10 min at 4°C to take 1.0 ml of supernatant to filter with a 0.45-μm membrane. Then, filter liquor was injected into a special gas-phase vial, in which 1 μl of the sample was injected into an Agilent DB-FFAP gas-phase capillary column (30 m × 0.25 mm × 0.25 μm) automatically. The injector and detector temperatures were respectively set at 250 and 280°C, with the split ratio set at 50:1. The column was heated from 60 to 220°C at a rate of 20°C/min.

The VFA concentration was determined by gas chromatography (Agilent 7890A, NYSE: A, Palo Alto, America) according to the method of Wang, et al. (2017). The processing of rumen fluid has been described in Supplementary Material S1 (Section S1.1). Processed samples were automatically injected into an Agilent DB‐FFAP gas‐phase capillary column (30 m × 0.25 mm × 0.25 µm). The injector temperature was set at 250°C and the detector temperature at 280°C. The split ratio of all samples was set at 50:1. The column temperature was heated by programing from 60°C to 220°C with a rate of 20°C/min and followed by holding for a 5 min.