Fourier Transform Infrared Microspectroscopy (FTIRM) has been used to study the changes in mineral and matrix content and composition in replicate biopsies of nonosteoporotic human osteonal bone. Spectral maps in four orthogonal directions (in 10 μm steps) from the centers towards the peripheries of individual osteons were obtained from iliac crest biopsies of two necropsy cases. Mineral to matrix ratios, calculated from the ratio of integrated areas of the phosphate ν₂ band at 900–1200 cm⁻¹ to the amide I band at 1585–1725 cm⁻¹, increased from the center to the periphery of the osteon. The total carbonate (based on the ν₂ band at =850-900 cm⁻¹) to phosphate ν₁,ν₃ ratio decreased as the mineral to matrix ratio increased. Analysis of the ν₂ CO₃²⁻ band with a combination of second-derivative spectroscopy and curve fitting revealed a decrease in "labile" carbonate, a slight decrease in Type A and a slight increase in Type B carbonate from the center to the periphery of the osteon. Similar analysis of the components of the ν₂ phosphate band with a combination of second-derivative spectroscopy and curve fitting revealed the presence of 11 major underlying moieties. These components were assigned by comparison with published frequencies for apatite and acid-phosphate containing calcium phosphates. The most consistent variations were alterations in the relative percent areas of bands at ≈1020 and ≈1030 cm⁻¹, which had previously been assigned to nonstoichiometric and stoichiometric apatites, respectively. This ratio was used as an index of variation in crystal perfection throughout the osteon. This ratio decreased as the mineral to matrix ratio increased. The reproducibility of these parameters at multiple sites in multiple biopsies suggests their applicability for the analysis of mineral changes in disease.
Keywords: FTIR microspectroscopy; Calcium phosphates; Osteon; Bone apatites; Bone mineral