Establishing collagen quality criteria for sulphur isotope analysis of archaeological bone collagen

Sulphur isotope measurements of bone collagen from archaeological sites are beginning to be applied more often, yet there are no clear criteria to assess the quality of the collagen and therefore the validity of the sulphur isotope values. We provide elemental data from different methods (DNA sequences, amino acid sequences and mass spectrometric measurements) which are used to establish a reliable system of quality criteria for sulphur isotope analyses of bone collagen. The difference in the amount of sulphur from fish and mammalian collagen type I led to the suggestion to use different criteria to assess the in vivo character of the collagen between these two categories. For establishing quality ranges, the bone collagen of 140 modern animals were analysed. The amount of sulphur in fish and mammalian bone collagen is 0.63+/-0.08% and 0.28+/-0.07%, respectively. Based on these results we define for mammalian bone collagen an atomic C: S ratio of 600+/-300 and an atomic N:S ratio of 200+/-100, and for fish bone an atomic C: S ratio of 175+/-50 and an atomic N: S ratio of 60+/-20. These quality criteria were then applied to 305 specimens from different archaeological contexts.