Comparison of two methods of extracting bone collagen for stable carbon and nitrogen isotope analysis: comparing whole bone demineralization with gelatinization and ultrafiltration

We compare two methods of isolating bone collagen for stable carbon and nitrogen isotope analysis. The older method (as practised at the University of Cape Town) demineralizes bone 'chunks', while the newer method (as practised at the Max Planck Institute for Evolutionary Anthropology in Leipzig) involves demineralization, gelatinization and ultra-filtration to select only higher molecular weight protein fragments for isotopic analysis. The latter method was developed for problematic (i.e. poorly-preserved) samples and while it is more rigorous, it is also significantly more expensive and more labor-intensive. Our aim is to find out whether there is any difference between the δ13C and δ15N of bone collagen isolated from relatively well-preserved bones using the two methods. Our sample set consists of 5 modern and 47 archaeological animal and human bones from the southern and western parts of South Africa. Archaeological specimens range in age from a few hundred to approximately six thousand years old. Collagen was extracted, its quality assessed using %C, %N and C:N, and δ13C and δ15N values measured independently in both laboratories. There are no statistically significant differences between the sets of δ13C and δ15N values from the two laboratories. For relatively well-preserved bones, the 'chunk' method of collagen preparation continues to be an acceptable alternative to more sophisticated collagen extraction protocols for C and N isotope analysis.