In response to Michael Jacoby's request about collagen purity in extinct
bears:

  A number of different criteria have been used to evaluate the purity of
collagen (or the reliability of isotope ratios obtained from them).  These
include C:N ratio - empirically between 2.9 - 3.6 (DeNiro 1985), the yield
of collagen extracted from bone and combustion yields of carbon and
nitrogen gas (Ambrose 1990), and amino acid analysis (Schwarcz 1985 is a
typical archaeological example, I am sure there are many others).  You
could also add amino acid racemization, for which I do not have a handy
citation.

  From what I have been able to gather, amino acid analysis is not all that
helpful, unless you fear contamination by proteins other than collagen.  If
anyone is aware of an example where a collagen sample was rejected solely
on the basis of its amino acid profile, I would enjoy hearing about it.  In
my personal opinion, amino acid analysis is not worth the trouble and
expenses of being a routine test, unless of course one happens to already
be doing them routinely anyway.

  Extraction yields and C:N ratio are very useful.  In general, samples
producing less than about 2% yields of collagen are probably going to give
poor isotope ratios.  Samples with C:N ratios far outside the empirical
range of 2.9 - 3.6 are also likely to be poor.  The nice thing about these
tests are that if you are extracting and running isotope ratios on your
samples, you can get this kind of information with just a little extra
effort, and there is not need to turn to an outside lab.  And if someone
else is doing your isotope ratios, they should be able to provide this info
with the delta values

Regards,
  -Mark Schurr

Ambrose, S. H.
1990  Preparation and Characterization of Bone and Tooth Collagen for
Isotopic Analysis. Journal of Archaeological Science 17:431-451.

DeNiro, M. J.
1985  Postmortem Preservation and Alteration of Invivo Bone Collagen
Isotope Ratios in Relation to Paleodietary Reconstruction. Nature 317:806-809.

Schwarcz, H. P., J. Melbye, M. A. Katzenberg, and M. Knyf
1985  Stable Isotopes in Human Skeletons of Southern Ontario:
Reconstructing Paleodiet.  Journal of Archaeological Science 12:187-206.


**************************************************************
Mark R. Schurr                                  Phone:  (219) 631-7638
Assistant Professor                             FAX:     (219) 631-8209
Department of Anthropology
University of Notre Dame
Notre Dame, IN  46556 USA