Study of calcium phosphate precipitation at 37 °C

The nature of the calcium phosphate formed when equal volumes of 20 mM CaCl2 and 15 mM or 12 mM K2HPO4 with pH 7.4 are rapidly mixed at 37 °C has been investigated by following the pH of the suspension as a function of time, by calorimetric and light scattering methods, chemical analysis and TEM. It is found that in the early stages of this process, there appears a spherular amorphous form of calcium phosphate, called ACP1, which transforms into a floccular amorphous form, called ACP2. We suggest that this transformation is solution‐mediated. ACP2 has not previously been clearly described as a separate phase and has not before been shown to be amorphous.