SEPARATION OF QUATERNARY AMMONIUM HERBICIDES BY CAPILLARY ELECTROPHORESIS WITH INDIRECT UV DETECTION

Suitability of various absorbent carrier electrolytes for the determin ation of quaternary ammonium ion herbicides ('quats') with indirect UV detection in capillary electrophoresis was investigated. Consideratio n of the electrophoretic mobility and the molar absorptivity of the ch romophore, and the effective separation achieved, suggested that 1-(4- pyridyl)pyridinium chloride hydrochloride (PP) was the best electrolyt e for the simultaneous detection of quats. The influence of pH, chromo phore 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 poten tial +20 kV, hydrodynamic injection 5 s and UV detection at 205 nm. Fi gures of merit such as detection limits and run-to-run and day-to-day reproducibility were established. The detection limits for the non-abs orbent herbicides were 0.8 mu g ml(-1). The method was successfully ap plied to the determination of chlormequat and mepiquat in spiked tap w ater although the dependence of the detection limits on the sample mat rix was observed. (C) 1997 Elsevier Science B.V.