Separation of quaternary ammonium herbicides by capillary electrophoresis with indirect UV detection

Suitability of various absorbent carrier electrolytes for the determination of quaternary ammonium ion herbicides ('quats') with indirect UV detection in capillary electrophoresis was investigated. Consideration of the electrophoretic mobility and the molar absorptivity of the chromophore, and the effective separation achieved, suggested that 1-(4-pyridyl)pyridinium chloride hydrochloride (PP) was the best electrolyte for the simultaneous detection of quats. The influence of pH, chromophore concentration, organic modifier, detection wavelength and ionic strength was investigated. The optimal conditions for separation were: 10 mM PP (pH 2.5), 10% methanol as carrier electrolyte, applied potential +20 kV, hydrodynamic injection 5 s and UV detection at 205 nm. Figures of merit such as detection limits and run-to-run and day-to-day reproducibility were established. The detection limits for the non-absorbent herbicides were 0.8 mu g ml(-1). The method was successfully applied to the determination of chlormequat and mepiquat in spiked tap water although the dependence of the detection limits on the sample matrix was observed. (C) 1997 Elsevier Science B.V.