Determination of pesticides in water by capillary gas chromatography with splitless injection of large sample volumes

Abstract

A large-volume injection for a capillary gas chromatograph equipped with an electron-capture, nitrogen—phosphorus-selective (NPD) or flame photometric detector is proposed for the determination of pesticides. The cold-trap column, a deactivated fused-silica column (3 m × 0.53 mm I.D.), was attached to the analytical column (30 m) and the regulation column (3 cm), DB-5, both of 0.25 mm I.D. with film thickness 0.25 μm, with a dual-outlet splitter. The regulation column was connected with the solvent-diversion column, a deactivated fused-silica column (2 m × 0.53 mm I.D.), which was led out of the column oven and attached to an electromagnetic valve. By opening the valve in the splitless mode, the pesticides slowly injected in n-hexane in a volume from 25 to 150, μl were trapped in the cold-trap column, and a large volume of n-hexane was almost all diverted from the gas chromatograph through the diversion column. The trapped pesticides were introduced to the analytical column by closing the valve. Twenty-five pesticides, scattered on a golf course in Japan, were determined at concentrations from 1 to 100 ng/ml in n-hexane. The reproducibility of separation of the pesticides by the proposed method was similar to that of normal splitiess (1-μl) injection. The proposed method was applied to the screening of the pesticides in groundwater after liquid—liquid extraction with dichloromethane; the pesticides could be determined at levels lower than 1 μg/l in a 20-ml water sample.