Evaluating uncertainty in the calculation of non‐exchangeable hydrogen fractions within organic materials

We calculated the fraction of exchangeable hydrogen atoms in proteinaceous materials commonly analyzed for stable isotopic composition related to the region‐of‐origin of an animal. These included several types of α ‐ and β ‐keratin, and muscle tissue. We find that the fraction of H atoms in keratin available for exchange at a biologically relevant temperature (25°C) averaged 9% across a range of ground organic materials, but was as high as ∼17% in cut hair; muscle tissue has ∼12% exchangeable H atoms. Under most analysis conditions, the difference in exchangeable fractions due to physical sample processing has a minimal effect on the calculated δ 2 H values of the non‐exchangeable H atoms within a keratin‐containing tissue (<2‰). However, extreme mismatches between sample and reference material types could affect δ 2 H values. Copyright © 2009 John Wiley & Sons, Ltd.