Preparation and characterization of bone and tooth collagen for isotopic analysis

Criteria are presented for the identification of diagenetic alteration of carbon and nitrogen isotope ratios of bone and tooth collagen prepared by a widely used method. Measurements of collagen concentrations in tooth and bone, atomic C:N ratios, and carbon and nitrogen concentrations in collagen of 359 historic and prehistoric African humans, and modern and prehistoric East African non-human mammals are described. Carbon isotope ratios of collagen lipids from four bones are also presented. Compared to bone, whole teeth have significantly lower collagen concentrations, lower carbon and nitrogen concentrations in collagen, and similar C:N ratios. Carbon and nitrogen concentrations and C:N ratios are relatively constant over a wide range of collagen concentrations. However, prehistoric specimens with very low collagen concentrations have highly variable C:N ratios, very low carbon and nitrogen concentrations in collagen, and stable carbon and nitrogen isotope ratios unlike collagen. At the transition from well-preserved to poorly preserved collagen the most reliable indicator of collagen preservation is the concentration of carbon and nitrogen in collagen. Concentrations of C and N drop abruptly by an order of magnitude at this transition point. These attributes provide simple criteria for assessing sample quality. Since collagen preservation can vary greatly within prehistoric sites, these attributes should be reported for each specimen. Use of purification procedures that remove acid- and base-soluble contaminants and particulate matter (carbonates, fulvic acids, lipids, humic acids, sediments and rootlets) are recommended. Wider adoption of these procedures would insure comparability of results between laboratories, and permit independent and objective evaluation of sample preservation, and more precise dietary, climatic, and habitat interpretations of collagen isotopic analyses.