nalyses were performed using an HP 6890 GC coupled to a HP 5973 mass spectrometer.An autosamplerunit(HP7673–8positions) was used to perform 1 μL injections. Separation was accomplished with a Phenomenex ZB-5 MS column (30 m 0.25 mm i.d.,0.25 μm phase thickness ) . Operating conditions were as follows : Injector :split ratio 25:1;Temperature:250 1 C; carrier gas:helium,1.0 mL/min,
constant flow; column temperature,60 1℃ (no hold),3 ℃ per min then at 280 hold 10 min. MS was acquired at -70 eV using a mass scan range of 45–350 m/z.