Soil Adsorption Coefficients of s-Triazines Estimated with a New Gradient HPLC Method

A high-performance liquid chromatography (HPLC) method employing gradient elution was developed to predict soil adsorption coefficients (K(oc)) from HPLC capacity factors. The gradient method allows for the determination of K(oc) values over a range of 4.4 orders of magnitude in a single experiment without adjustment of the solvent composition, as is required in isocratic HPLC measurements. The range of K(oc) estimated can easily be extended by using reference compounds with lower or higher log K(oc) values. Therefore, gradient HPLC is an appropriate screening method for K(oc) and was used to investigate s-triazine herbicides and their degradation products. Log K(oc) ranged from 0.8 for cyromazine to a maximum of 2.6 for anilazine and aziprotryne. HPLC-derived K(oc) values of s-triazines containing an azido group were higher than and those of hydroxy-s-triazines were lower than K(oc) values estimated according to the fragment contribution method of Meylan et al. (1992). According to this method, the log K(oc) of the keto form of hydroxy-s-triazines was >1 log unit higher than that of the enol form.