DETERMINATION OF THE CA/P RATIO IN CALCIUM-DEFICIENT HYDROXYAPATITE USING X-RAY-DIFFRACTION ANALYSIS

The determination of the calcium to phosphate ratio (Ca/P) in Ca-deficient hydroxyapatite [d-HAP; Ca10-x(HPO4)x(PO4)6-x(OH)2] using X-ray diffraction analysis (XRD) is reported. At temperatures above 700-degrees-C HPO42- groups are transformed to PO43- groups, thereby producing beta-tricalcium phosphate [beta-TCP; Ca3(PO4)2]. Thus, the deviation from stoichiometry, x, can be calculated from the mass fraction of beta-TCP, which in turn can be determined from quantitative XRD analyses. In this study d-HAP powders with various Ca/P ratios were prepared following several procedures. It is shown that the Ca/P ratio determined by quantitative XRD correlates well with that measured by chemical analyses.