SENSITIVE AND SELECTIVE FLUORESCENCE DETECTION OF PHENOXYACID HERBICIDES BY LIQUID-CHROMATOGRAPHY WITH ONLINE ION-PAIR EXTRACTION

Fluorescent probes, especially a newly synthesized N-substituted l-cyanobenz[f]-isoindole quaternary ammonium fluorophore, were used as counter ions in a reaction detector for on-line ion-pair extraction of phenoxyacid herbicides. The probe was used in an on-line post-column set-up coupled to a reversed - phase chromatographic system. After separation on an C-8-bonded silica column using an aqueous methanol (pH 2.5) mobile phase, the herbicides were on-line deprotonated by post-column addition of a 10mM sodium phosphate buffer (pH 8.0), in which the probe was dissolved. Subsequently, the ion-pairs were extracted on-line with chloroform-1-butanol (80:20, v/v) and were monitored by fluorescence detection. Using this system, at least seven herbicides could be separated. The detection limits of 2,4-dichlorophe xyacetic acid and 2,4,5-trichlorophenoxyacetic acid were 400 pg (S/N = =3). The repeatability, based on peak height measurements, for 100 ng injections was about 0.5%. Calibration curves were linear over the investigated range of 1–100 ng, with correlation coefficients of 0.999 for the two analytes. Application to a drinking water sample is presented. © 1991, Taylor & Francis Group, LLC. All rights reserved.