Dear Bill:
I've had very good stable isotope results from using  double purified gelatin
extracted from collagen using a hot weak acid, then sampling the gel for stable
iso analysis. The practice allows me to first test for CN ratios indicative of
non-degraded bone protein (ratios should be between 2.9 and 3.6; modern, fresh
bone is about 3.2)  Ajie's is a useful technique, however, if there is
exceptional degradation of protein.

Cheers,
Nancy

Nancy Beavan Athfield
Rafter Radiocarbon Lab
Inst. Geological and Nuclear Sciences
NEW ZEALAND
http://www.gns.cri.nz/atom/rafter/rafter.htm