Solubility of calcium oxalate monohydrate and hydroxyapatite in EDTA solutions

The effect of the addition of a buffer to an ethylenediaminetetracetic acid (EDTA) litholytic solution on the solubility of calcium oxalate monohydrate and hydroxyapatite is investigated. The experiments show that the addition of triethanolamine as a buffer to EDTA solutions at pH 8 and 8.5 enhances the solubility of these salts, confirming theoretical predictions. The solubility of calcium oxalate monohydrate at 25C in solutions with varying ratios of buffer to EDTA concentrations and an osmolality of 0.9 was determined. The solutions resulting in the highest solubility were finally tested for their litholytic ability at 37C. At pH 8 solubilities of 22.5 g X l-1 for calcium oxalate monohydrate and 20.2 g X l-1 for hydroxyapatite were obtained. The corresponding solubilities at pH 8.5 were respectively 24.5 g X l-1 and 19.2 g X l-1.