Hydroxyl content of solution-precipitated calcium phosphates

Abstract

A method is described for determination of the titratable hydroxide ion in calcium phosphate precipitates. The procedure requires accurate analysis of the other titratable species in the crystal lattice but is unaffected by the presence of other lattice constituents or impurities. The method was applied to precipitates that had been previously analyzed by solution thermodynamic techniques, and the results were consistent with the earlier observations. The hydroxide content of the precipitates increased with crystal maturity and with increasing pH of the precipitation medium. The hydroxide content of the amorphous phase and the immediate postamorphous-crystalline transformation phase was shown to be nearly zero. After 3 to 4 days' maturation, the hydroxide content of precipitates prepared at pH values of 7, 8, and 9 was shown to increase to approximately 23, 40, 56% of that required for pure hydroxyapatite.

Formation and structure of Ca-deficient hydroxyapatite

“…The amounts of P2074-formed in our work and Berry's are in good agreement with the amounts predicted from the formula Cal0 xHx(PO4)6(OH)2-x [1], supporting the idea that Ca-deficient apatites are also hydroxyl deficient as has been suggested by others [1,7]. Indeed, recent titration experiments [19] showed that precipitated Ca-deficient HA does contain OH deficiencies. A alp nuclear magnetic resonance study of Ca-deficient apatites, using magic-angle sample spinning, was recently carried out [20].…”

A comparative study of the metastable equilibrium solubility behavior of high-crystallinity and low-crystallinity carbonated apatites using pH and solution strontium as independent variables

“…An example is the established correlation [4,13] between the mean pIAP of CAP and CAP crystallinity (crystallite microstrain) where crystallinity is a (mean) bulk property. Another example is that based on the outcomes of the present research: the MES of CAPs of low crystallinity may be governed by a surface complex with the calcium/hydroxide deficient hydroxyapatite stoichiometry-which is consistent with literature that poorly crystallized hydroxyapatite has a propensity toward having a bulk stoichiometry of Ca 9 (HPO 4 )(PO 4 ) 5 OH [29][30][31][32][33][34][35][36][37][38].…”

Preparation of amorphous calcium-magnesium phosphates at pH 7 and characterization by x-ray absorption and fourier transform infrared spectroscopy

“…At pH 7.4, scribe the maturation of these ACPs to form about 10% of the phosphate was HPO~ions as brushite. The usefulness of Fourier transform injudged from the form of the solubility product frared spectroscopy to distinguish between the controlling precipitation [2], and at higher pH the acidic and basic ACPs is demonstrated and we composition became more complex as OH-ions show that the short range structure around the may have been incorporated [3]. Likewise, in precalcium ions in these acidic ACPs is similar to that cipitations from solutions containing magnesium in the basic ACP.…”

“…The specare in agreement in demonstrating that an appretrometer used was a Nicolet 20 SX B model ciable fraction of the phosphate groups are prooperating at a resolution of 2 cm' over the range tonated. Titration methods such as the oxalate 4000-250 cm method or the acid/base titration of Meyer [3] or To erthance features of the infrared spectra, the charge balance calculation do not determine Fourier self-deconvolution was employed [26], as the separate H + and OH -components but only implemented in the FSD software package from their difference. The infrared spectroscopic evithe instrument manufacturer.…”