pH-effect on photochemical degradation of imazapyr in aqueous solution

Depending on pH, imazapyr can exist in cationic, neutral and anionic forms. We investigated in this work the pH effect on the photodegradation of imazapyr under simulated sunlight experiments. As the molecule of imazapyr had two pKa values, pKa(1) = 1.9 and pKa(2) = 3.6, pH = 1 and pH = 3 were chosen for this study. Irradiation was carried gut with polychromatic light using Heraeus apparatus equipped with Xenon lamp. The concentration of remaining herbicide was followed using a high perrformance liquid chromatograph (HPLC) equipped with UV detector at 230 nm. The efficiency of pH on the photodegradation of imazapyr was evaluated by the quantum yield determination. Kinetics show a first order dependence of concentration of imazapyr on time. The decrease of pH in the photolysis medium lowers the rate of photodegradation.