3 research outputs found
An international intercomparison of stable carbon isotope composition measurements of dissolved inorganic carbon in seawater
We report results of an intercomparison of stable carbon isotope ratio measurements in seawater dissolved inorganic carbon (δ 13CâDIC) which involved 16 participating laboratories from various parts of the world. The intercomparison involved distribution of samples of a Certified Reference Material for seawater DIC concentration and alkalinity and a preserved sample of deep seawater collected at 4000âm in the northeastern Atlantic Ocean. The betweenâlab standard deviation of reported uncorrected values measured with diverse analytical, detection, and calibration methods was 0.11â° (1Ď ). The multiâlab average δ 13CâDIC value reported for the deep seawater sample was consistent within 0.1â° with historical measured values for the same water mass. Application of a correction procedure based on a consensus value for the distributed reference material, improved the betweenâlab standard deviation to 0.06â°. The magnitude of the corrections were similar to those used to correct independent data sets using crossover comparisons, where deep water analyses from different cruises are compared at nearby locations. Our results demonstrate that the accuracy/uncertainty target proposed by the Global Ocean Observing System (Âą0.05â°) is attainable, but only if an aqueous phase reference material for δ 13CâDIC is made available and used by the measurement community. Our results imply that existing Certified Reference Materials used for seawater DIC and alkalinity quality control are suitable for this purpose, if a âCertifiedâ or internally consistent âconsensusâ value for δ 13CâDIC can be assigned to various batches.publishedVersio
On estimating the precision of stable isotope ratios in processed tree-rings
This is the accepted manuscript of an article published by Elsevier.Stable isotope dendrochronology is a well-developed field of research, but improvements to methodologies are on-going. We propose an improved method for estimating the precision of stable isotope ratios (δ) of tree-ring samples that are processed from whole wood to various end products such as cellulose-nitrate, Îą-cellulose, or cellulose intermediates. The status quo method for estimating the δ precision of organic solids is to characterize the long-term 2-sigma range of δ values for a ready-made Quality Assurance (QA) standard that is included in each analysis run of samples. While the status quo method is appropriate for characterizing analytical uncertainties associated with the mass spectrometer, combustion or pyrolysis system, and analyte specifics, it does not reflect uncertainties associated with sample processing from inadvertent and unrealised operator error (e.g., contamination by airborne particles, incomplete chemical processing, sample storage issues, and other unforeseen errors), although such errors would probably be rare with an experienced operator. The proposed method improves upon the status quo method as it respects the Identical Treatment principle by subjecting QA standards to the same processing steps that samples undergo. As such, analytical uncertainties associated with sample processing would be integrated into the QA standardâs δ value and precision estimate. In effect, the proposed method is a system to monitor inter-batch reproducibility and, by the same token, can be used to identify batches that were potentially compromised during processing. A pilot study example is used to demonstrate the proposed method for δ18O analysis of Îą-cellulose samples.This work benefited from an NSERC postgraduate scholarship to T. Porter