Stopped-flow and kinetic-fluorimetric determination of quinalphos in water samples.

The hydrolysis of the pesticide quinalphos in basic medium was kinetically followed and the measurement of the reaction rates allowed us to develop two kinetic-fluorimetric methods. In one of them the mixing of the reagents was directly performed in the measurement cell and, in the another one, the stopped-flow mixing technique was used. The reaction was completed in 100 s after the reactants were mixed and it allowed the simple application of the proposed methods to routine analyses of the pesticide. The sensitivity of the methods was very high, being the detection limits 50 and 140 ng mL(-1) for the manual procedure and the stopped-flow mixing technique, respectively. Both methods were compared using regression with uncertainties in both axes. The effect of the presence of several pesticides in the determination was tested. A solid-phase extraction process was also developed for the application of the methods to diverse waters samples. The proposed kinetic-fluorimetric methods were applied to the determination of quinalphos in drinking water, well water and river water, with very satisfactory results.