Solubility of triazine pesticides in pure and modified subcritical water.

Solubility measurements in pure and modified water serve as a basis for optimizing the subcritical water extraction of target analytes such as food contaminants. The solvent strength of the water is affected by both the system's temperature and the amount and type of cosolvent modifier that is added to the water, which causes a reduction in the dielectric constant of water. In the present work, the solubilities of the triazine pesticides atrazine, cyanazine, and simazine were measured in pure and modified water at temperatures ranging from 50 to 125 degrees C and at a pressure of 50 atm. The solubility data were obtained using a static solubility apparatus with on-line liquid chromatographic (LC) detection. By increasing the temperature of the water, the solubilities of the triazine pesticides increased approximately 3-fold in pure water for each 25 degrees C temperature increment. Cyanazine was 5 times more soluble than atrazine and an order of magnitude more soluble than simazine at 100 degrees C. The solubility of atrazine was also measured in ambient and hot water modified with ethanol and urea. At 100 degrees C, the solubility of atrazine is doubled when the water is modified with urea, and is increased over an order of magnitude when ethanol is used as modifier. The data, therefore, indicate that adding a cosolvent to water in addition to increasing the system temperature increases the solubilities of triazine pesticides in subcritical water. It was further determined that the solutes do not thermally degrade or hydrolyze at the temperatures reported in this study.