Determination of Residues of 2,4-D and Benazone in Water Body by Gas Chromatography with Solid Phase Extraction

A method for the determination of residues of 2,4-D and benazone in water body by gas chromatography with solid phase extraction was proposed. The acidity of the water sample (1.0 L) was adjusted to pH less than 2 with nitric acid, and then the water sample was passed through activated HLB pro solid phase extraction cartridge at flow rate of 6.0 mL·min^-1, with rinsing by 10.0 mL of water, and eluting by 10.0 mL of ethyl acetate. The eluent was collected, and blown to nearly dryness by nitrogen, and 500 μL of N,N-dimethylformamide dimethyl acetal and 1.0 mL of n-hexane were added for derivation at 160 ℃ for 50 min. After derivative, the solution was taken and cooled to room temperature, and 2.0 mL of saturated sodium chloride solution was added. After stratification, 0.8 mL of upper organic phase was taken and filtrated through 0.22 μm organic phase filter membrane. The filtrate was determined according to the working conditions of the instrument. It was shown that the derivatives of 2,4-D and benzoate were 2,4-D-methyl ester and benzoate-methyl, respectively. The mass concentrations of 2,4-D and benzoate were linearly related with the corresponding peak areas of derivatives in the range of 0.01-0.50 mg·L^-1, with detection limits (3.143s) in the range of 0.003-0.010 μg·L^-1. Test for precision was made on the actual samples, and RSDs (n=6) of the determined values were less than 7.0%. In the spiked samples of drinking water, surface water, urban sewage and sea water, the recoveries of the targets were in the range of 81.3%-95.4%.