Minor Phase Quantification in Octacalcium Phosphate Using Solid-State ³¹P Nuclear Magnetic Resonance Spectroscopy

Octacalcium phosphate (OCP) has recently attracted attention as a bone substitute material because of its excellent osteoconductivity. In most cases, the synthesis of OCP is accompanied by precipitation of a secondary phase such as hydroxyapatite (HAp). However, a method for quantifying a secondary phase in OCP has not yet been established, which is a long-standing issue. This study proposes a method for quantifying the HAp subphase in OCP using solid-state ³¹P nuclear magnetic resonance (NMR) spectroscopy. OCP + HAp powders prepared by the standard-addition method were used to construct a calibration curve in which the HAp subphase content obtained through peak deconvolution of ³¹P-NMR spectra was plotted. The HAp subphase content in OCP was determined to be 5.3 wt.% with a ±0.4 wt.% uncertainty at a 95% confidence level. The proposed method for quantifying a subphase in OCP using solid-state ³¹P-NMR would be effective not only for HAp but also for other coprecipitated subphases.