Case Study in Environmental Chemistry....

Author: Sarunya Hengpraprom and Cindy M.Lee, Environmental Engineering and Science, Clemson University.

Experimental Approach and Methods

The rates of hydrolysis of carbaryl were measured in deionized-distilled water at 4 pH values (6, 7, 9, 10). Each piece of glassware used in the experiment was sterilized by an autoclave. During the experiment, 500-mL of solution were adjusted to the desirable pH values by addition of buffer solutions. Appropriate amounts of carbaryl stock solution were then transferred to individual tubes, and the pH of the solution was measured again. The pH of the solution was measured before and after each round of sampling to ensure that the pH remained constant during the experiment. The vials were capped with Teflon-faced septum and incubated in a water bath at 25oC, which was kept in the dark to minimize photolysis. Ten mL aliquots were taken from each vial at time zero (approximately 1 hour after incubation) and subsequent time intervals, then transferred to 12 mL vial. Subsequently, the pH was immediately dropped to approximately 3 by adding phosphoric acid to minimize the hydrolysis reaction. Three-mL aliquots of the adjusted sample were removed and transferred into a 4 mL HPLC autosampler vial. The further addition of 1.0-mL of an internal standard (carbofuran) was spiked into each vial. The samples were analyzed by high performance liquid chromatography (HPLC) with detection by UV-visible spectrometry. The spectrometer was set to monitor effluent at a wavelength of 280 nm. HPLC is used rather than gas chromatography because carbaryl is sensitive to high temperatures.