Capillary Zone Electrophoresis of two Cationic Herbicides, Paraquat and Diquat

Abstract

Capillary zone electrophoresis with untreated fused-silica capillaries was evaluated in the separation and determination of paraquat and diquat, both are double quaternary ammonium ion herbicides. As high as 200,000–300,000 theoretical plates per meter were obtained for the separation of the two closely related herbicides over the pH range 3.5–9.5. At relatively high ionic strength in the running electrolyte, electrostatic interactions between the cationic herbicides and the negatively charged surface of the separation capillary were minimized. Under these conditions, the plot of average plate height versus the electroosmotic flow velocity indicated that longitudinal molecular diffusion is the major contributor to band broadening. The detection limits for paraquat and diquat were 15.4 and 16.8 femtomoles, respectively, with a UV detector.