Integrated guard column

We used an Agilent 7890B GC (Agilent Technologies, Wilmington, DE, USA) equipped with Pegasus HT TOF-MS (LECO, St. Joseph, MI, USA) for sample analysis. A 1 μL sample was injected into an RTX-5Sil MS column (30 m × 0.25 mm, 0.25-μm film thickness; Restek, Bellefonte, PA, USA) and an integrated guard column (10 m × 0.25 mm, 0.25-μm film thickness; Restek, Bellefonte, PA, USA) on splitless mode for separation of metabolome in samples. The oven temperature was set for 5 min at 50°C, and was then increased to 330°C at the rate of 20°C/min, where it was then held for 5 min. The mass spectra were collected at the mass range of 85 to 500 m/z at an acquisition rate of 17 spectra/s. The temperatures of ion source and transfer line were 250°C and 280°C, respectively, and the impact of electron ionization was at 70 eV.

For metabolite analysis, an Agilent 7890B BC system (Agilent Technologies, Santa Clara, CA, USA) equipped with a Pegasus HT TOF mass spectrometer (LECO, St. Joseph, MI, USA) was used. An RTX-5Sil MS capillary column (30 m × 0.25 mm, 0.25 μm film thickness; Restek, Bellefonte, PA, USA), with an additional integrated guard column (10 m × 0.25 mm, 0.25 μm film thickness; Restek, Bellefonte, PA, USA) was injected with 1 µL of derivatives and subjected to an initial temperature of 50 °C with holding for 1 min, and then increased to 330 °C at 20 °C/min and held for 5 min. The injection temperature was 250 °C and the interface temperature was 280 °C. In the mass range of 85–500 m/z, mass spectra were collected by electron impact at 70 eV.