The GC–MS analyses were conducted on a Shimadzu GC-17A/QP-5000 (Japan) instrument using a fused silica HP-5 MS capillary column (5% phenyl/95% dimethylpolysiloxane) (30 m × 0.25 mm i.d. × 0.25 μm of film thickness) from J&W Scientific (USA). The instrumental parameters used were as follows: injector, splitless mode for 1.0 min at 250 °C; stripping gas, helium at 1.0 mL.min− 1; oven, 40 °C, increased to 240 °C at 3 °C min− 1 and remained at this temperature for 4 min; interface temperature, 240 °C; electronic ionization at 70 eV; quadrupole mass analyzer; and mass range 35–350 m/z.