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<sup>2</sup>H<sub>VSMOW‑SLAP</sub> values from −210.8
to +397.0 mUr or ‰, for δ<sup>13</sup>C<sub>VPDB‑LSVEC</sub> from −40.81 to +0.49 mUr and for δ<sup>15</sup>N<sub>Air</sub> 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<sub>16</sub> <i>n</i>-alkanes, <i>n</i>-C<sub>20</sub>-fatty acid methyl esters
(FAMEs), glycines, and l-valines, together with polyethylene
powder and string, one <i>n</i>-C<sub>17</sub>-FAME, a vacuum
oil (NBS 22a) to replace NBS 22 oil, and a <sup>2</sup>H-enriched
vacuum oil. A total of 11 laboratories from 7 countries used multiple
analytical approaches and instrumentation for 2-point isotopic normalization
against international primary measurement standards. The use of reference
waters in silver tubes allowed direct normalization of δ<sup>2</sup>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. Because of exchangeable
hydrogen, amino acid RMs currently are recommended only for carbon-
and nitrogen-isotope measurements. Some amino acids contain <sup>13</sup>C and carbon-bound organic <sup>2</sup>H-enrichments at different
molecular sites to provide RMs for potential site-specific isotopic
analysis in future studies