Treatment methods for the determination of δ²H and δ¹⁸O of hair keratin by continuous‐flow isotope‐ratio mass spectrometry

Abstract

The structural proteins that comprise approximately 90% of animal hair have the potential to record environmentally and physiologically determined variation in delta2H and delta18O values of body water. Broad, systematic, geospatial variation in stable hydrogen and oxygen isotopes of environmental water and the capacity for rapid, precise measurement via methods such as high-temperature conversion elemental analyzer/isotope ratio mass spectrometry (TC/EA-IRMS) make these isotope systems particularly well suited for applications requiring the geolocation of hair samples. In order for such applications to be successful, however, methods must exist for the accurate determination of hair delta2H and delta18O values reflecting the primary products of biosynthesis. Here, we present the results of experiments designed to examine two potential inaccuracies affecting delta2H and delta18O measurements of hair: the contribution of non-biologic hydrogen and oxygen to samples in the form of sorbed molecular water, and the exchange of hydroxyl-bound hydrogen between hair keratin and ambient water vapor. We show that rapid sorption of molecular water from the atmosphere can have a substantial effect on measured delta2H and delta18O values of hair (comprising approximately 7.7% of the measured isotopic signal for H and up to approximately 10.6% for O), but that this contribution can be effectively removed through vacuum-drying of samples for 6 days. Hydrogen exchange between hair keratin and ambient vapor is also rapid (reaching equilibrium within 3-4 days), with 9-16% of the total hydrogen available for exchange at room temperature. Based on the results of these experiments, we outline a recommended sample treatment procedure for routine measurement of delta2H and delta18O in mammal hair.

Tracking human travel using stable oxygen and hydrogen isotope analyses of hair and urine

“…The helium was dried prior to use in the autosampler by passing it through an Alltech All-pure column (Grace, Deerfield, IL USA). By freeze drying our solid samples for !10 days our approach was consistent with that described by Bowen et al, 42 to increase analytical …”

“…O and dD values of the complex suite of items that composes modern human diets warrants further investigation. 42 Despite the isotopic overlap and variability in diets, hair d 18 O and dD values differed significantly between residents of Fairbanks and East Greenbush and showed little variation within each population. These differences were consistent with differences in tap water d 18 O and dD in the two regions.…”

Hydrogen and oxygen isotope ratios in human hair are related to geography

“…Even after synthesis, a fraction of the 2 H in hair is subject to continuous isotopic exchange with the environment and our discussion is therefore limited to only that proportion of the H atoms not subject to postsynthesis isotopic exchange (17). In advance of any synthesis reaction, the amino acids interact with their aqueous medium.…”

“…Keratin is synthesized from amino acids in the hair follicle, and these keratin sheets form the basis of hair tissue. With the exception of a fraction of the H atoms that freely exchange with environmental water (17), H atoms in keratin are no longer subject to isotopic exchange and are recorders of isotopic inputs to and cycling within a person's body, as has been shown for carbon isotopes (2,4,6,7). We develop a steady-state model that considers new inputs of amino acids to an individual's body, and assume that recycling of other body tissues is in equilibrium with dietary inputs.…”

“…Although the H atoms in carboxyl, amide, and sulfhydryl groups exchange with the H in water, this is not the case with H atoms in C-H bonds. Some fraction of the exchangeable H atoms (Ϸ10% of total H) remain exchangeable after hair production (17). These H atoms were effectively excluded from our measurements of keratin hair H through postanalysis correction (see Materials and Methods) and are not considered here.…”