6 research outputs found
USGS44, a new high purity calcium carbonate reference material for δ13 C measurements
RATIONALE: The stable carbon isotopic (δ13 C) reference material (RM) LSVEC Li2 CO3 has been found to be unsuitable for δ13 C standardization work because its δ13 C value increases with exposure to atmospheric CO2 . A new CaCO3 RM, USGS44, has been prepared to alleviate this situation. METHODS: USGS44 was prepared from 8 kg of Merck high purity CaCO3 . Two sets of δ13 C values of USGS44 were determined. The first set of values was determined by on-line combustion, continuous-flow (CF) isotope-ratio mass spectrometry (IRMS) of NBS 19 CaCO3 (δ13 CVPDB = +1.95 milliurey (mUr) exactly, where mUr = 0.001 = 1 ‰), and LSVEC Li2 CO3 (δ13 CVPDB = -46.6 mUr exactly), and normalized to the two-anchor δ13 CVPDB-LSVEC isotope-delta scale. The second set of values was obtained by dual-inlet (DI) IRMS of CO2 evolved by reaction of H3 PO4 with carbonates, corrected for cross contamination, and normalized to the single anchor δ13 CVPDB scale. RESULTS: USGS44 is stable and isotopically homogeneous to within 0.02 mUr in 100-μg amounts. It has a δ13 CVPDB-LSVEC value of -42.21 ± 0.05 mUr. Single-anchor δ13 CVPDB values of -42.08 ± 0.01 and -41.99 ± 0.02 mUr were determined by DI-IRMS with corrections for cross contamination. CONCLUSIONS: The new high-purity, well homogenized calcium carbonate isotopic reference material USGS44 is stable and has a δ13 CVPDB-LSVEC value of -42.21 ± 0.05 mUr for both EA-IRMS and DI-IRMS measurements. As a carbonate relatively depleted in 13 C, it is intended for daily use as a secondary isotopic reference material to normalize stable carbon isotope-delta measurements to the δ13 CVPDB-LSVEC scale. It is useful in quantifying drift with time, determining mass-dependent isotopic fractionation (linearity correction), and adjusting isotope-ratio-scale contraction. Due to its fine grain size (smaller than 63 μm), it is not suitable as a δ18 O reference material. A δ13 CVPDB-LSVEC value of -29.99 ± 0.05 mUr was determined for NBS 22 oil
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
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^2H_(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) n-alkanes, 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 ^2H-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 δ2H 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 ^(13)C and carbon-bound organic ^2H-enrichments at different molecular sites to provide RMs for potential site-specific isotopic analysis in future studies
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
Final report on pilot study CCQM-P211:carbon isotope delta measurements of vanillin
This pilot study was conducted in parallel to the key comparison CCQM-K167. Vials containing 0.25 mg of vanillin were prepared at NRC and distributed to four participating institutes. Institutes could choose any suitable reference materials and methodology to perform carbon isotope delta measurements. Participants reported analysis details, and a carbon isotope delta value and associated uncertainty for the vanillin sample. Each of the carbon isotope delta results of vanillin were compared to the KCRV established from CCQM-K167, and metrological compatibility to the KCRV was determined. Three expert laboratories participated in this study, and their reported results serve as a benchmark to compare the performance of all other participants to these world-class institutes
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
Organic Reference Materials for Hydrogen, Carbon, and Nitrogen Stable Isotope-Ratio Measurements: Caffeines, <i>n</i>‑Alkanes, Fatty Acid Methyl Esters, Glycines, l‑Valines, Polyethylenes, and Oils
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