GC-MS detection

The derivatized sample of 1 μL was injected into an HP-5 MS column (Agilent Technologies, 30 m × 250 μm × i.d. 0.25 μm) using splitless injection and analysis was carried out by Agilent 7890A GC equipped with an Agilent 5975 C VL MSD detector (Agilent Technologies). The initial temperature of the GC oven was held at 85°C for 5 min followed by an increase to 280°C at a rate of 15°C per min holding for 5 min and then increased to 310°C at a rate of 20°C per min. The solvent delay time was set as 5 min before data collection. High purity helium (purity not less than 99.999%) was used as a carrier gas and flow was kept constant at 1 mL per min. The scanning mode is full scan (SCAN), and MS was operated in a range of 50–600 m/z.