SOIL ADSORPTION COEFFICIENTS OF S-TRIAZINES ESTIMATED WITH A NEW GRADIENT HPLC METHOD

A high-performance liquid chromatography (HPLC) method employing gradi ent elution was developed to predict soil adsorption coefficients (K-o c) from HPLC capacity factors. The gradient method allows for the dete rmination 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 high er log K-oc values. Therefore, gradient HPLC is an appropriate screeni ng method for K-oc and was used to investigate s-triazine herbicides a nd 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 t hose of hydroxy-s-triazines were lower than K-oc values estimated acco rding to the fragment contribution method of Meylan et al. (1992). Acc ording to this method, the log K-oc of the keto form of hydroxy-s-tria zines was >1 log unit higher than that of the enol form.