Comparison of different types of immunoaffinity reactors in an electrochemical flow injection immunoanalysis system developed for residue analysis

A comparison of different types of immunoreactors for a flow injection immu noanalysis (FIIA) system is presented. The use of the FIIA system was demon strated here with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The hardware system centers around the immunoreactor. In the preferred reactor set-up, a column is filled with protein G-coated porous beads serving as t he affinity matrix for the antibody. In the 2,4-D assay a 2,4-D-alkaline ph osphatase conjugate competes with the analyte in the sample for binding to the anti-2,4-D antibody. Subsequently p-aminophenol, generated from the enz ymatic reaction with p-aminophenyl phosphate, is detected at +/-150 mV at a carbon working electrode versus Ag/AgCl. The immunoreactor allows for more than 150 measurements. The fully automated assay procedure needs 15 min on ly for one measurement. For 2,4-D the working range for the determination i n water samples was between 1 and 1000 mu g/L. Results obtained with the pa cked column reactor are compared to glassy capillary reactors and miniaturi zed silicon chip reactors used in previous studies.