Micellar-enhanced photochemically induced fluorescence detection of chlorophenoxyacid herbicides. Flow injection analysis of mecoprop and 2,4-dichlorophenoxyacetic acid

In this paper, a combination of a flow injection analysis (FIA) system with micellar-enhanced photochemically induced fluorescence (MEPIF) detection is presented as a powerful alternative for the rapid and sensitive analysis of chlorophenoxyacid herbicides. These compounds do not show native fluorescence but they can be photolysed into strongly fluorescence photoproducts after direct irradiation with ultraviolet light. The use of a cationic surfactant such as cetyltrimethylammonium chloride (CTAC) provides a considerable enhancement of photochemically induced fluorescence intensity and the nature of the technique allows a possible and easy adaptation to a FIA system. In this sense, parameters related to the nature of the analytical signal (pH, irradiation times, surfactant concentration) and to the FIA manifold (injection volume, flow rate and reactor length) have been optimised. Linear calibration graphs, with three replicates for each concentration value were established in the range of 0.2–5.0 μg ml−1 for 2,4-Dichlorophenoxyacetic acid (2,4-D) and 0.1–5.0 μg ml−1 for Mecoprop (MCPP). The IUPAC detection limits were 73.2 and 33.5 ng ml−1 for 2,4-D and MCPP, respectively. Satisfactory recoveries were obtained in the analysis of these herbicides in spiked waters.