Essential oil was diluted with the oil to ethanol ratio of 1:100 by volume (HPLC grade, RCI Labscan, Thailand) and analyzed by a Finnigan Trace GC ultra-equipped with a Finnigan DSQ quadrupole mass spectrometric detector (MSD). The BPX5 (Phenyl: Dimethylpolysiloxane 5:95) capillary column (30 m in length, 0.25 mm i.d., and 0.25 m in thickness) was used as stationary phase