Fast determination of paraquat residues in water by an optical immunosensor and validation using capillary electrophoresis-ultraviolet detection Original Research Article

A solid-phase fluoroimmunoassay combined with an optical transducer chemically modified with an analyte derivative coupled to a FIA system was used [A. Brecht, A. Klotz, C. Barzen, G. Gauglitz, R. Harris, G. Quigley, J. Wilkinson, P. Sztajnbok, R. Abuknesha, J. Gascón, A. Oubiña, D. Barceló, Anal. Chim. Acta 362 (1998) 69]. Excitation and collection of fluorescence from fluorescently labelled anti-paraquat antibodies locally bound at the planar interface allows the measurement of the fluorescent signal which is indirectly related to the paraquat concentration of the sample. Matrix effects on the immunosensor response were observed, thus leading to the following detection limits, 0.01 and 0.06 μg l−1, when analyzing paraquat in MilliQ and in river water, respectively. The validation of the biosensor was carried out analyzing paraquat samples by capillary zone electrophoresis with ultraviolet detection (CZE-UV) at 214 nm. Preconcentration of the samples prior to their injection in the capillary electrophoresis were performed using the automated solid-phase extraction system (ASPEC-XL). Paraquat samples were adjusted at pH 9 and were percolated through a silica cartridge, subsequent elution was carried out using a mixture of hydrochloric acid and methanol and afterwards samples were evaporated and injected.