Gas chromatograph mass spectrometer

Gas chromatograph–mass spectrometer: Shimadzu Corporation, Japan; solid‐phase microextraction device: Merck, USA.

The chromatographic analyses of essential oils obtained from of O. vulgare and T. vulgaris were carried out in a GCMS-QP2010 (SHIMADZU Gas Chromatograph-Mass Spectrometer, Japan), equipped with a capillary column Rtx-5MS (30 m, 0.25 mm internal diameter, 0.25 µm film thickness) and a 5971 A mass spectrometer detector. Helium was used as carrier gas, at a flow rate of 1.61 mL/min. The column temperature was initially set to 60 °C for 5 min, and gradually increased to 160 °C (5 °C/min), and finally increased to 280 °C (15 °C/min). The injector and detector temperatures were set at 250 and 280 °C, respectively. For detection by GC-MS, an electron ionization system with an ionization energy of 70 eV was used. EOs were diluted with dichloromethane (1:1000 v/v), and 1.0 µL of diluted samples were automatically injected into no division mode. The results were obtained by comparing the mass spectra of each peak with the NIST11.lib database provided by the instrument’s software. Identification was given to those peaks exceeding the 93–95% coincidence. Additionally, calibration curves of standard compounds (Thymol) were performed and used for quantification.

The SCFA levels in mouse faecal samples were measured according to a previously reported method [19 ]. An appropriate amount of the sample was added to 0.3 mL of water, 100 μL of 50% sulfuric acid, 25 μL of 500 mg/L internal standard (cyclohexanone) solution and 0.5 mL of ether, after which the mixed solution were homogenated for 1 min and centrifuged at 12,000 rpm at 4 °C for 10 min. The supernatant was placed on the instrument for testing (Gas Chromatograph-Mass Spectrometer, Shimadzu GCMS QP2010-Ultra, Japan). The chromatographic system was as follows: Agilent DB-WAX capillary column (30 m × 0.25 mm × 0.25 μm). The carrier gas was high purity helium (≥ 99.9%), and the flow rate was 1.0 mL/min. The inlet temperature was 220 °C, the injection volume was 1 μL, and the solvent delay time was 2.5 min for splitless injection. For the mass spectrometry system, an electron bombardment ion source (EI) was used, the ion source temperature was 230 °C, and the interface temperature was 220 °C. The chromatograph was connected to a microcomputer with a detector for collecting the results of the chromatographic analysis with the GC Solution program (Shimadzu, Japan).