Experimental All solvents used were of HPLC grade. The pesticide standards used are listed in Table 1. They were prepared in ethyl acetate with concentration of 100 ppb. An Agilent 6890N gas chromatograph was used. Samples were injected onto an HP-5MS capillary column (10 x 0.18 mm, 0.18 μm film thickness) with splitless injection mode. Helium was used as the carrier gas and set at 0.6 mL/min. The injector temperature was set at 200°C. The oven temperature was held at 40°C for 1 min and then increased to 300°C at a rate of 50°C/min.