Development of a non-competitive immunoassay for monitoring DDT, its metabolites and analogues in water samples

This report highlights the characteristics of a general method of performing non-competitive immunoassays for low-molecular-mass analytes, which was developed and applied to 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) determination in aqueous samples. The method is based on the separation of the analyte-bound antibody from the excess of the free antibody by a chromatographic step, followed by the dissociation of the complex and the capture of the previously bound antibody on a solid phase. The measured signal is linearly correlated to the concentration of the complex and, consequently, to the analyte concentration. The 3(sigma) limit of detection (LOD, 8 ng l^-1) obtained by the above method enabled us to decidedly improve the sensitivity of the corresponding enzyme-linked immunosorbant assay (ELISA) and of all reported immunoassays for DDT. In addition, by applying this new format, even if a very selective antibody was used, a broad selectivity was observed, which allowed DDT + DDD + DDE to be determined instead of only p,pʹ-DDT as in the ELISA performed with the same antibody. In addition, real water samples were validated in a percentage recovery test. Very good recovery rates were obtained, highlighting the validity of the proposed method to accurately determine the total DDT content in water.