Micellar electrokinetic capillary chromatography as a method for determination of n-octanol/water partition coefficients of pesticides.

Micellar electrokinetic capillary chromatography (MEKC) was used to determine the n-octanol/water partition coefficient (Kow) of nonionic and ionic organic chemicals, mainly herbicides. Three electrolyte buffer systems with different organic modifiers were tested to evaluate their effect on the linear relationship between log Kow and log k'. The effect of the pH value of injected samples on linear log Kow/log k' relationship of ionic chemicals was also evaluated. Since a good correlation was found between log Kow values and the logarithms of the capacity factor (k') of each tested organic solvent, other parameters were considered to evaluate the efficacy of the method, such as the rate of electroosmotic flow, the efficiency and reproducibility of the separation, and the separation number (n). The method was found to be applicable over a range of log Kow values from 0.72 to 5.1 and demonstrated a good predictive capability giving similar results to direct experimental measures, at least within classes of compounds with similar physico-chemical properties.