Octacalcium Phosphate Solubility Product from 4 to 37-Degree-C

Octacalcium phosphate (OCP) is proving to be an important intermediary in the formation of tooth and bone mineral and various pathological calcifications. Before this mineral can form, its solubility product must be exceeded. Thus, a knowledge of its precise values under various conditions is required for a basic understanding of calcification processes. The methodology suitable for measuring the solubility of metastable phases was developed and used to determine the negative logarithms of the solubility products of OCP, pK,p(OCP), at 4, 4.8, 6, 18, 23.5, and 37 .c. This methodology includes (1) the use of high solid-to-liquid ratio, 10 mglmL, to minimize the effects of hydrolysis, (2) frequent sampling during equilibration to detect possible effects of hydrolysis, (3) equilibration from supersaturation and from undersaturation, and (4) equilibration in the absence and presence of a CO2-containing atmosphere. September-October 1988