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

Abstract

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 alpha- and beta-keratin, and muscle tissue. We find that the fraction of H atoms in keratin available for exchange at a biologically relevant temperature (25 degrees C) averaged 9% across a range of ground organic materials, but was as high as approximately 17% in cut hair; muscle tissue has approximately 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 delta2H values of the non-exchangeable H atoms within a keratin-containing tissue (<2 per thousand). However, extreme mismatches between sample and reference material types could affect delta2H values.

Stable isotope and trace metal compositions of Australian prawns as a guide to authenticity and wholesomeness

“…As a simplified approach we applied a correction for exchangeable hydrogen based on published literature (Chesson, Podlesak, Cerling, & Ehleringer, 2009), discussed below.…”

“…The fraction of exchangeable H atoms (f ex ) for muscle was taken as 0.2 and for chitin as 0.15 (Chesson et al, 2009). For both materials the fractionation factor (a) between H atoms in the equilibration water and sample was taken as 1 (Chesson et al, 2009). This estimation of non-exchangeable hydrogen was considered appropriate for a comparative study.…”

Foraging segregation and genetic divergence between geographically proximate colonies of a highly mobile seabird

“…We also analyzed the dD composition of muscle from a variety of species from the Pacific Ocean. Whereas hydrogen exchangeability in muscle has received little study compared to keratin, the magnitude of exchange appears to be similar (Wassenaar and Hobson 2000;Chesson et al 2009). To this end, we analyzed lipidextracted muscle tissue in the same fashion as feather samples, including normalization to keratin standards (Doucett et al 2007;Finlay et al 2010).…”

A test of comparative equilibration for determining non‐exchangeable stable hydrogen isotope values in complex organic materials

“…[7][8][9] A challenge for the future of H isotope applications in migratory ecology is to better understand the source and meaning of variance in dD isotope data obtained from various species. [10][11][12] One of the first challenges encountered is that complex organic substrates like most biological tissues contain exchangeable H. 13 Left untreated, tissues dynamically exchange a proportion of their H atoms with ambient moisture, which leads to dD results that cannot be compared among laboratories. Some biological substrates (e.g.…”