| Abstract: |
The purpose of this study was to compare three different collagen extraction methods commonly used in isotope laboratories conducting dietary studies. The authors evaluated their resultant differences in δ13C and δ15N, collagen quality and collagen yield. . The study was based on well-preserved skeletal material from the medieval period in Denmark; it shows that there is a systematic significant difference in the yield and the δ13C values between the three methods. Using the method of DeNiro and Epstein (M J DeNiro and S Epstein, `Influence of diet on the distribution of nitrogen isotopes in animals' in Geochimica et Cosmochimica Acta 45 (1981), pages 341--51) with NaOH as cleaning agent, would, according to the study, give δ13C values that are on average ±0.32o/oo more positive than using the ultra-filtration method (T A Brown, D E Nelson, J S Vogel and J R Southon, 1988. `Improved collagen extraction by modified Longin method' in Radiocarbon 30:2 (1988), pages 171--7, modified in M P Richards and R E M Hedges, `Stable isotope evidence for similarities in the types of marine foods used by late Mesolithic humans at sites along the Atlantic coast of Europe' in Journal of Archaeological Science 26 (1999), pages 717--22). The third method, which is a modified version of the second method, excluded the ultra-filtration step. This method seems to give δ13C values that lie in between the other methods. The study did not show any significant difference in δ15N values. Although the differences between the methods are very small, the authors conclude that the use of stable isotope analysis in food determination studies requires adherence to routine methods for preparing and measuring samples. |
