Carbonate Assignment and Calibration in the Raman Spectrum of Apatite

A series of apatites with varying carbonate levels was prepared in order to assign the carbonate bands and calibrate for Raman analysis of natural materials. Overlap of carbonate bands with phosphate peaks was resolved by curve fitting. A peak at 1,071 cm⁻¹ was assigned to a combination of the carbonate ν₁ mode at 1,070 cm⁻¹ with a phosphate ν₃ mode at 1,076 cm⁻¹. In addition, the carbonate ν₄ mode was identified in apatite samples with >4% carbonate. The carbonate ν₄ bands at 715 and 689 cm⁻¹ identify the samples as B-type carbonated apatite. The carbonate content of apatite was calibrated to a carbonate Raman band, and the method was used to determine the carbonate content of a sample of bovine cortical bone, 7.7 ± 0.4%.