Organic Reference Materials for Hydrogen, Carbon, and Nitrogen Stable Isotope-Ratio Measurements: Caffeines, n-Alkanes, Fatty Acid Methyl Esters, Glycines, l-Valines, Polyethylenes, and Oils

Abstract

An international project developed, quality-tested, and determined isotope-δ values of 19 new organic reference materials (RMs) for hydrogen, carbon, and nitrogen stable isotope-ratio measurements, in addition to analyzing pre-existing RMs NBS 22 (oil), IAEA-CH-7 (polyethylene foil), and IAEA-600 (caffeine). These new RMs enable users to normalize measurements of samples to isotope-δ scales. The RMs span a range of δ 2 H VSMOW-SLAP values from-210.8 to +397.0 mUr or ‰, for δ 13 C VPDB-LSVEC from-40.81 to +0.49 mUr, and for δ 15 N Air from-5.21 to +61.53 mUr. Many of the new RMs are amenable to gas and liquid chromatography. The RMs include triads of isotopically contrasting caffeines, C 16 nalkanes, n-C 20-fatty acid methyl esters (FAMEs), glycines, and L-valines, together with polyethylene powder and string, one n-C 17-FAME, a vacuum oil (NBS 22a) to replace NBS 22 oil, and a 2 H-enriched vacuum oil. Eleven laboratories from 7 countries used multiple analytical approaches and instrumentation for 2-point isotopic calibrations against international primary measurement standards. The use of reference waters in silver tubes allowed direct calibration of δ 2 H values of organic materials against isotopic reference waters following the principle of identical treatment. Bayesian statistical analysis yielded the mean values reported here. New RMs are numbered from USGS61 through USGS78, in addition to NBS 22a. Due to exchangeable hydrogen, amino acid RMs currently are recommended only for carbon-and nitrogen-isotope measurements. Some amino acids contain 13 C and carbon-bound organic 2 Henrichments at different molecular sites to provide RMs for potential site-specific isotopic analysis in future studies.

Re‐evaluation of the hydrogen stable isotopic composition of keratin calibration standards for wildlife and forensic science applications

“…This finding supports the concept and potential of seeking ‘matrix equivalence’ in developing new complex organic reference materials, for example, using only keratin calibration standards for keratin samples, etc. This will be a key challenge for the scientific community in the future development of new complex organic isotopic reference materials for δ 2 H values, along with the subsequent appropriate use of new calibration materials by isotope practitioners across disciplines …”

Position‐specific 13C/12C analysis of amino acid carboxyl groups – automated flow‐injection analysis based on reaction with ninhydrin

“…Calculated from information supplied by Qi or Schimmelmann assuming either 99 or 96% purity of the α‐carboxyl labelled materials used.…”

“…The CSIA uncertainty was included to represent possible physical inhomogeneity in the RMs and resulting variability in isotope ratios . The δ 13 C CARBOXYL value assigned to USGS41a will probably be subject to larger uncertainty than the 0.9 ‰ given in Table because the value has an associated extrapolation uncertainty as it fell far outside the calibration range of the underlying LSVEC and LSUB RMs.…”

“…Samples of L‐glutamic acid, glycine and L‐valine RMs were purchased from the US Geological Survey Stable Isotope Laboratory (Reston, VA, USA). These materials (Table ) are internationally available and have well‐characterised CSIA δ 13 C VPDB values …”

“…A sample of natural abundance L‐valine (D01) that was used to prepare L‐valine RMs USGS74 and 75 was kindly supplied by colleagues from Indiana University (Bloomington, IN, USA) …”