FT-Raman spectroscopy as a method for screening collagen diagenesis in bone

This study examines Fourier transform (FT) Raman spectroscopy as a non-destructive screening method to determine collagen quality in archaeological and paleontological bones. Bone samples were characterized for collagen quality using well-established elemental abundance analyses (i.e., percentage nitrogen and C:N) as the primary criteria for classification. FT-Raman spectra were collected from outer surfaces and freshly cut cross-sections of both well-preserved and poorly-preserved historic mammal bones. Peak heights and peak areas were studied visually and with bivariate and multivariate statistics. Raman spectra from cross-sections provided the most accurate determination of collagen quality. A ratio of the 960 cm−1 and 1636 cm−1 peak heights provided the most unambiguous distinction between bones with well-preserved and poorly-preserved collagen. The 960 cm−1 and 1636 cm−1 peaks represent phosphate anion stretching in the bone mineral and amide carbonyl stretching in the collagen, respectively. FT-Raman spectra from bones with well-preserved collagen produced a 960 cm−1:1636 cm−1 ratio of 19.4 or less (after peaks were baseline corrected). This mineral to collagen ratio was typically greater in poorly-preserved samples as organic material tends to be more susceptible to early stages of diagenesis. These criteria now can be used to accurately determine collagen quality in bones before sacrificing samples to the lengthy and destructive chemical extractions necessary for carbon-14 dating, stable isotope analyses, proteomic analyses, and other techniques of archaeological or paleontological interest.