Measurement of fluoride substitution in precipitated fluorhydroxyapatite nanoparticles

Fluoride substitution can improve the chemical stability and biocompatibility of precipitated hydroxyapatite nanoparticles, leading to advantages such as improved cell adhesion in osteo applications and reduction of tooth enamel erosion in dental applications. To achieve the desired improvement and minimise the risk of excess fluoride release, the concentration of fluoride and the mechanism of incorporation must be known. This is difficult due to the small effect fluoride substitution has on the hydroxyapatite structure, the low concentration of fluoride in fluorhydroxyapatite (0–3.77 wt%), and the interference of impurities as a result of the precipitation process. Several techniques for measuring fluoride substitution in precipitated fluorhydroxyapatite nanoparticles have therefore been investigated. Fluorhydroxyapatite nanoparticles with fluoride substitution levels ranging from 0 to ∼92% have been synthesised by wet precipitation and characterised using XRD, FTIRS, XPS, TEM, and chemical analysis. XRD and FTIRS measured fluoride substitution more accurately than bulk concentration methods, as they detected apatite fluoride separately from other fluoride in the sample.