Effect of heating on the stable carbon and nitrogen isotope ratios of bone collagen

The effects of heat on the stable carbon and nitrogen isotopic ratios of collagen in bone were studied. Boiling or roasting did not change the δ¹³C and δ¹³N values by more than 1‰. More extreme heating, such as might occur if bones were burned or a body cremated, shifted δ¹³C and δ¹⁵N values by as much as 5 and 4‰ respectively. These large shifts were accompanied by changes in the atomic carbon-to-nitrogen ratios of the collagen. These results indicate that collagen samples extracted from prehistoric bones which display anomalous atomic carbon-to-nitrogen ratios may have been subjected to heating extreme enough to have altered their ${}^{13}\text{C}{}^{12}\text{C}$ and/or ${}^{15}\text{N}{}^{14}\text{N}$ ratios and therefore should not be used for dietary reconstruction.