| Polychlorinated biphenyls (PCBs) are one of the persistent organic pollutants which the United Nations Environmental Protection Department is committed to eliminate. According to WHO statistics, there are 2×107t PCBs from industry around the world, of which about 30% were released into the environment. PCBs have widely distributed around the world as environment pollutants, which content is from ppt to ppm. So far, the most commonly used method to analyze PCBs is HPLC. This method requires complex sample pre-treatment processes, sophisticated detection equipments, good experimental environment and well-trained operators, which limit its application .Compare with HPLC, ELISA has the advantages that sample preparation is simple, sensitivity and specificity are high, cost is low and could be used to detect the PCBs in the scene. Therefore, carrying out the enzyme-linked immunosorbent assay (ELISA) study of PCBs has important practical value.Polychlorinated biphenyls are general artificial organic compounds and their hydrogens on biphenyls are replaced by chlorine atoms at differene degrees, which have 209 kinds of homologue. This research seleced representative coplanar PCB77 to study its ELISA method, chose 3,4-Dichlorophenyl acetic acid which had active group and specific structure of PCB77 as the hapten. 3, 4-Dichlorophenyl acetic acid was coupled with bovine serum albumin (BSA) by N-hydroxysuccinimide active ester method to prepare the immune antigen DCP-BSA and the coupling rate was 23:1. An anti- 3,3',4,4'-Tetrachlorobiphenyl(PCB77) polyclonal antibody was successfully obtained by immunization of rabbits with DCP-BSA. 3,4-Dichlorophenyl acetic acid conjugated with ovalbumin (OVA) to form coating antigens by mixed-anhydride method and the result was 8:1. The result of Bouble immunodiffusion exceeded 1:16 and indirect ELISA detections showed the antiserum titer reached over 1:20000,what satisfied the request of ELISA analysis technique. Then the antiserum purified by caprylic acid/ ammonium sulfate precipitation method.Working parameters of indirect ELISA technique for detection of PCB77 were optimized, including selection of coating method, optimum dilution ratio of antiserum and medium mediation. An indirect ELISA detection method for PCB77 was developed, in which inhibition ration closely relates to Ln value of PCB77 concentration and fitted into the equation,Y= -0.1370Ln(x)+ 1.043, where Y was inhibition ratio and x represents the concentration of PCB77, coefficient of determination R2=0.9930. Detect concentrations ranged from 0.75ng/L to 300ng/L.The cross-reaction of anti-DCP-BSA to their corresponding analogs was tested. The concentration of PCB77 was 82.26ng/mL when the antibody-antigen reaction was half inhibition. The same equipments were made , had the results that concentration of PCB126 was 270.43ng/mL, the cross reactivity was 30.4% , the concentration of 3,4-Dichlorophenyl acetic acid 897.84 ng/mL, the cross reactivity was 9.1%, the concentration of 2,4-D was 2222.1 ng/mL,the cross reactivity was 3.7%,the concentration of trichloroacetic acid above 8000ng/mL , the cross reactivity was below 0.1%.Recoveries of PCB77 in soil samples ranged from 109%~146% with C.V. % of 5.00~11.77. Recoveries of PCB77 in tap water ranged from 84%~98% with C.V. % of 2.84~7.75. The results above showed that the success of this study lied in the successfully prepared artificial antigen of PCB77and after animal immune, the high titer serum was obtained to establish indirect ELISA. After optimization, standard curve of PCB77 was made and the cross reaction was not obvious .This indirect ELISA detection method of PCB77 residue could satisfy the primary analysis, and provide technical basis for the establishment of ELISA kit.
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