19F and 31P NMR spectroscopy of calcium apatites

Abstract

Glass ceramics that include apatite crystals are used as implant materials. Because most of these glass ceramics are comprised of fluoride-containing glass compositions, the included apatites could be hydroxyapatite, fluorapatite or fluoride-substituted hydroxyapatite. However, these apatites differ in regard to their solubility and thermal stability. The purpose of the current study was to determine the possibilities of distinguishing between these apatities. High resolution solid-state 19F and 31p magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of two fluorapatites, a hydroxyapatite and a fluoridated hydroxyapatite have been obtained. Using 31 p NMR investigations it is possible to distinguish between calcium apatites and other calcium phosphates, but the distinction between fluoride-containing apatite and hydroxyapatite is not possible. However, 19F high-resolution solid-state NMR investigations permit the distinction between these various apatites. The results of the NMR investigations could be used for the characterization of glass ceramics. The application of those results was demonstrated using a newly developed apatite-containing glass ceramic.

Real time neutron diffraction and solid state NMR of high strength apatite–mullite glass ceramic

“…This second site corresponds to a F-Ca(n) species. After heat treatment the resonance narrows and shifts to −103 ppm, consistent with FAP [28] and in agreement with the neutron diffraction results.…”

“…The large FWHM of this peak (≈20 ppm) indicates underlying features with centre of gravity at the pyrophosphate environments with presumably Al-O-P linkages [32]. The heat treated sample showed a sharply resolved resonance at 3.1 ppm (FAP [28]) as a major and a more broad signal between −25 and −28 ppm (AlPO 4 [33]). Presence of several polymorphs of AlPO 4 is confirmed from the spectrum, though the cristobalite form (at −27.1 ppm [34]) gives the closest match with corresponding value for the 31 P peak position.…”

Sintering Behavior of Magnesium-Substituted Fluorapatite Powders Prepared by Hydrothermal Method

“…For FA, the chemical shift is of 2.75 ppm. This value is in agreement with the values reported in the literature for FA [34]. However, for the substituted samples, a slight chemical shift towards lower values occurred as the Mg concentration increased, and concomitantly the peaks became broader.…”

The Molecular Environment of Phosphorus in Sewage Sludge Ash: Implications for Bioavailability

“…Nevertheless, we can discuss the differences in isotropic chemical shifts of the Ca phosphate species by dividing the Ca phosphate species into chemical Ca‐P environments. The isotropic chemical shift of PO 4 3− in a variety of apatites ranges from 2.3 to 3.3 ppm (Braun et al, 1995; Miquel et al, 1990; Rothwell et al, 1980). On the other hand, β‐tricalcium phosphate contains three different Ca‐P environments with resonances of 2.3 to 4.5 ppm [P(1)], 1.2 to 1.6 ppm [P(2)], and 0 to 0.1 ppm [P(3)] (Marchandise et al, 1992; Miquel et al, 1990; Quillard et al, 2011).…”