The injector was maintained at 250 °C for 3 min. Helium was used as carrier gas with an inlet flow rate of 1 mL/min. Oven temperature programme was: from hold at 40 °C for 2 min, to 120 °C at 8 °C/min, then from 120 to 230 °C at 10 °C/ min, and finally maintained at 230 °C for 8 min, at splitless mode.