Use of stopped-flow fluoroimmunoassay in pesticide determination

Stopped-flow fluoroimmunoassay was applied to pesticide detection in foods. For this purpose, a homogeneous immunoassay was developed for the determination of 2,4-dichlorophenoxyacetic acid (2,4-D) in orange and grape juice which is based on the measurement of the initial rate of the reaction between the tracer (fluorescein-labelled 2,4-D) and the antibody. Kinetic methodology avoids the potential interference of the sample matrix, which affects the fluorescence signal obtained at or close to equilibrium. The use of the stopped-flow mixing technique allows analytical data to be obtained automatically and in a few seconds so that the method can be easily applied to routine analysis. The dynamic range of the calibration graph-is 10-400 ng ml(-1) and the relative standard deviation is less than 3%. The analytical recoveries obtained by applying the method to orange and grape juice samples ranged from 91.3 to 102.5%.