Helium gas was used as carrier gas at a flow rate of 1 ml/min; injector port and detector temperatures were maintained at 250 ◦C; oven temperature was maintained at 50 ◦C for 3 min initially, and then was increased to 250 ◦C at the rate of 2 ◦C/min and was maintained at 250 ◦C for 3 min; ionization voltage was 70 eV