Quantification of 2,4-dichlorophenoxyacetic acid in oranges and mandarins by chemiluminescent ELISA

Direct competitive enzyme-linked immunosorbent assay (ELISA) for 2,4-dichlorophenoxyacetic acid (2,4-D) was developed. Varying the concentrations of monoclonal anti-2,4-D-antibody and the conjugate of soybean peroxidase and 2,4-D the conditions of ELISA performance were optimised. The chemiluminescent method based on peroxidase-catalysed oxidation of luminol was applied to measure the enzyme activity of the conjugate. A mixture of 3-(10'-phenothiazinyl)propane-1-sulfonate and 4-morpholinopyridine was used as potent enhancer of chemiluminescence signal. It was shown that the values of the lower detection limit, IC50 and the working range were 1.5, 64.0, and 6.5-545 ng/mL, respectively. The recovery values of CL-ELISA from 10 spiked samples of oranges (n = 5) and mandarins (n = 5) cultivated in green house without use of 2,4-D and containing different 2,4-D concentrations (10-300 ng/mL) were ranged from 92% to 104% that indicated on the absence of matrix effect for the fruit extracts of interest. Determination of 2,4-D in peel of five oranges and five mandarins purchased from stores in Vietnam showed that 2,4-D content in oranges fruits (79-104 mu g/kg) was significantly higher than that in mandarins (1.66-2.82 mu g/kg). (C) 2013 Elsevier Ltd. All rights reserved.