Predict Water Solubility of Quinclorac by Henderson-Hasselbalch Equation under Different pH Solutions

摘要

Solubility is one of the most important molecular physico-chemical parameters in herbicide research. However, the reported water solubility values of quinclorac were inconsistent. Since quinclorac is an ionizable pesticide, the water solubility of quinclorac was determined by saturation shake-flask method and the effect of pH on the solubility was observed. The results indicated that equilibrium solubility value of quinclorac in deionized water (20 °C) in the present study was 63.28 + 1.57 mg/L, the reported solubility 62 to 72 mg/L of quinclorac in deionized water were reliable due to the error from different laboratory system, the solubility 0.065 mg/L might be in error. The equilibrium solubility increased from 3.61 to 10457.65 mg/L when the solution pH increased from 1.0 to 8.95. The Henderson-Hasselbalch equation was used to calculate the solubility in different pH buffer systems and found the Henderson-Hasselbalch equation can predict the pH-dependent solubility of quinclorac.