fused-silica capillary column coated with 0.25-μm CP-SIL 8 CB low bleed (Varian Inc., Palo Alto, CA). The injector temperature was 290 °C. The flow rate of nitrogen as a carrier gas was set at 1.0 mL/min. The temperature program was set at 250 °C, followed by a 10 °C/min oven temperature ramp to 290 °C and a 20 min heating at 290 °C. The detector temperature was set at 300 °C.