Determination of deltamethrin residue in Chinese cabbage by direct competitive enzyme-linked immunosorbent assay

The deltamethrin polyclonal antibody and the horseradish peroxidase labeled hapten was employed to establish the direct competitive enzyme-linked immunosorbent assay(DC-ELISA) for the determination of deltamethrin residue in Chinese cabbage. After ultrasonic extraction, concentration and dissolution with 10% methanol, the samples were determined by DC-ELISA and verified by HPLC. The results showed that the optimized concentration for antibody immobilization was 2.0 mg/L, and for HRP-hapten was 2×105 times diluted. The optimized coating medium was pH 7.2 PB and the optimized reaction medium was pH 6.8 PB containing 0.125 mol/L NaCl. Under the optimized conditions, the linear concentration range for the deltamethrin determination method using DC-ELISA was from 0.10 mg/L to 10 mg/L. The half maximal inhibitory concentration(IC50) of deltamethrin to antibody HRP-hapten reaction was 1.68 mg/L with relative standard deviation(RSD) of 2.11%(n=5). And the IC10 was 0.16 mg/L. The average recoveries of deltamethrin from Chinese cabbage determined by DC-ELISA were 97%, 106% and 95% with RSDs of 8.5%, 8.1% and 8.1%(n=5) at the spiked levels of 5 mg/kg, 1 mg/kg and 0.2 mg/kg respectively. The recovery of deltamethrin from Chinese cabbage determined by HPLC was 107% at the spiked level of 0.2 mg/kg. The DC-ELISA could be used for the rapid determination of deltamethrin residue in Chinese cabbage.