FLOW-INJECTION ANALYSIS OF CHLOROPHENOXYACID HERBICIDES USING PHOTOCHEMICALLY INDUCED FLUORESCENCE DETECTION

A flow-injection analysis (FIA) method for the determination of chloro phenoxyacid herbicides, based on photochemically induced fluorescence (PIF) detection, is described, PTFE tubing was helically coiled around a low-pressure mercury lamp located between the injection valve and t he detector. Two analytical procedures are used, either continuous or stopped-flow mode, according to the photochemical behaviour of the ana lyte. Ultraviolet (UV) photolysis in a 50% (v/v) MeOH/pH 5 buffer solu tion provoked a more or less marked increase of the fluorescence signa l depending of the herbicide structure. In the stopped-flew mode, UV i rradiation times ranged between 90 sec and 12 min. Linear dynamic grap hs were established over a concentration range of nearly two orders of magnitude. The FIA-PIF limits of detection ranged from 23 to 98 ng/ml , according to the compound. Relative standard deviations were between 0.7 and 2.7%. The proposed method has been applied to determine those herbicides in spiked river water samples, with mean recoveries rangin g from 96 to 108%. It shows the usefulness of this technique for chlor ophenoxyacid herbicides analysis.