Photophysical and photochemical studies of thifensulfuron-methyl herbicide in aqueous solution

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• 作者：Saâ ; dia Aziz ; Sté ; phane Dumas ; Mohammed El Azzouzi ; Mohamed Sarakha ; Jean-Marc Chovelon
• 关键词：Photodegradation ; Sulfonylurea ; Thifensulfuron-methyl ; Laser flash photolysis
• 刊名：Journal of Photochemistry and Photobiology A: Chemistry
• 出版年：2010
• 出版时间：25 January 2010
• 年：2010
• 卷：209
• 期：2-3
• 页码：210-218
• 全文大小：908 K

文摘

The photophysical and photochemical studies of a sulfonylurea herbicide, thifensulfuron-methyl (THM), have been investigated in a buffered aqueous solution. In the first part, the influence of pH on the spectroscopic properties was studied. This allowed the determination of the ground and excited state acidity constants, pK_a = 4 and 4.4, respectively, thus exhibiting the potential existence of a photoinduced protonation in the singlet state. In the second part, the photolysis kinetics was studied at different pH and varying oxygen concentrations, using an HPK 125 W lamp and followed up by the identification of photoproducts formed under continuous photo-irradiation. The kinetics results suggest that the photolysis process is faster in acidic (k = 3 × 10⁻⁴ s⁻¹) than in basic medium (k = 9.8 × 10⁻⁵ s⁻¹). The photolysis products were identified by high performance liquid chromatography HPLC-DAD, HPLC–MS and HPLC–MS–MS. In order to obtain a better understanding of the photodegradation mechanism, a laser flash photolysis study was performed. By comparing the quenching rate constant (k_q = 9.64 × 10⁸ mol⁻¹ l s⁻¹) obtained from triplet state quenching by molecular oxygen and from the Stern–Volmer relation (k_q = 0.41 × 10⁸ mol⁻¹ l s⁻¹), the role of the singlet state in the photodegradation process was demonstrated. The photoproducts originating from both singlet and triplet excited states have been identified and hypothetical photodegradation pathways of the thifensulfuron-methyl in aqueous solution are proposed.