Development of an Indirect Competitive ELISA of DDT

Abstract

Indirect competitive enzyme immunoassays of DDT based on polyclonal antibodies have been developed. The limit of detection and limit of quantification were 0.3 nmol l m 1 and 4.2 nmol l m 1 , respectively. Non-specific interaction was eliminated by the saturation of the solid phase with 2% human serum albumin. Different polystyrene microplates were tested. The cross-reactivity of the polyclonal rabbit antibody to DDT with 2,4'-DDE, 4,4'-DDD, 2,4'-DDT, 2,4'-DDD, Methoxychlor and 4,4'-DDE was 1, 9, 12, 13, 36 and 186%, respectively. No cross-reactivity of the tested antibody with 4,4'-DDA, 4,4'-DDOH, 4,4'-DBP, 4,4'-DDM, 4,4'-PCB, 2,3'-PCB, 4-PCB and 3-PCB was observed. With respect to a limited solubility of the analyte in water, the influence of different concentrations of methanol, ethanol, acetone and N,N'-dimethylformamide on the assay sensitivity were tested. A recommended concentration of the organic solvents is 5-10% (v/v) in the reaction mixture. Preliminary tests were done with a limited number of artificially contamined food samples. A background was observed in all tested food samples especially in strawberries, nectarines, and different species of pepper. False negative results were obtained when the DDT concentration was measured in beer, red wine and Pepsi-Cola.