TRACE ANALYSIS OF FLUORESCEIN-DERIVATIZED PHENOXY ACID HERBICIDES BY MICELLAR ELECTROKINETIC CHROMATOGRAPHY WITH LASER-INDUCED FLUORESCENCE DETECTION

Micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence (LIF) detection was used for the trace analysis of phenoxy acid herbicides. Capillary electrophoresis (CE) with LIF detection, which has not previously been used for pesticide analysis, overcomes the poor sensitivity of on-column UV detection. A novel derivatization procedure was developed which is suitable for nanogram amounts of organic acids. In this procedure, the acids are activated by hydroxybenzotriazol (HOBT) and diisopropylcarbodiimide (DIG) and reacted with 5-(aminoacetamido)fluorescein in dimethylformamide at ambient temperature. The fluorescent derivatives of all relevant phenoxy acid herbicides were separated in a single run by MEKC. A 488 nm Ar laser line was used for excitation. The reproducibility and reliability of the method were evaluated. The detection limit was 2 fg for a 4-nl injection, but for practical reasons, a minimum of 1 ng per compound should be subjected to the derivatization. The applicability of the described method to the extract of an aqueous sample was demonstrated.