Carbonate Reference Materials Research Articles

Calcium Isotopes (δ44/40Ca) in MPI‐DING Reference Glasses, USGS Rock Powders and Various Rocks: Evidence for Ca Isotope Fractionation in Terrestrial Silicates

We report δ44/40Ca(SRM 915a) values for eight fused MPI‐DING glasses and the respective original powders, six USGS igneous rock reference materials, the U‐Th disequilibria reference material TML, IAEA‐CO1 (Carrara marble) and several igneous rocks (komatiites and carbonatites). Sample selection was guided by three considerations: (1) to address the need for information values on reference materials that are widely available in support of interlaboratory comparison studies; (2) support the development of in situ laser ablation and ion microprobe techniques, which require isotopically homogenous reference samples for ablation; and (3) provide Ca isotope values on a wider range of igneous and metamorphic rock types than is currently available in the scientific literature. Calcium isotope ratios were measured by thermal ionisation mass spectrometry in two laboratories (IFM‐GEOMAR and Saskatchewan Isotope Laboratory) using 43Ca/48Ca‐ and 42Ca/43Ca‐double spike techniques and reported relative to the calcium carbonate reference material NIST SRM 915a. The measurement uncertainty in both laboratories was better than 0.2‰ at the 95% confidence level. The impact of different preparation methods on the δ44/40Ca(SRM 915a) values was found to be negligible. Except for ML3‐B, the original powders and the respective MPI‐DING glasses showed identical δ44/40Ca(SRM 915a) values; therefore, possible variations in the Ca isotope compositions resulting from the fusion process are excluded. Individual analyses of different glass fragments indicated that the glasses are well homogenised on the mm scale with respect to Ca. The range of δ44/40Ca(SRM 915a) values in the igneous rocks studied was larger than previously observed, mostly owing to the inclusion of ultramafic rocks from ophiolite sections. In particular, the dunite DTS‐1 (1.49 ± 0.06‰) and the peridotite PCC‐1 (1.14 ± 0.07‰) are enriched in 44Ca relative to volcanic rocks (0.8 ± 0.1‰). The Carrara marble (1.32 ± 0.06‰) was also found to be enriched in 44Ca relative to the values of assumed precursor carbonates (< 0.8‰). These findings suggest that the isotopes of Ca are susceptible to fractionation at high temperatures by, as yet, unidentified igneous and metamorphic processes.

GSJ炭酸塩標準物質（JCp-1, JCt-1）の炭素および酸素安定同位体比

同位体比質量分析計を用いて炭酸塩試料の炭素・酸素安定同位体比（δ13C・δ18O）を測定する際には，国際標準試料によってPDBスケールに値付けされた作業標準試料を用いる場合が多い．本研究では，成分情報が公表されている炭酸塩標準試料JCp-1 およびJCt-1が作業標準試料として適切であるかを検討するために，同位体比を測定し，均一性を評価した．JCp-1がδ13CPDB ＝－1.63±0.03‰，δ18OPDB ＝－4.71±0.03‰，JCt-1がδ13CPDB ＝＋2.79±0.02‰，δ18OPDB ＝－0.496 ±0.03‰と均一であり，作業標準試料として適切であることを確認した．JCp-1 およびJCt-1を作業標準試料に使用する場合，－5.01‰＜δ13CPDB ＜1.95‰，－22.97‰＜δ18OPDB ＜－2.20‰の範囲において，1点検量法により未知試料のPDB値を求めることができる．

Interlaboratory comparison study of calibration standards for foraminiferal Mg/Ca thermometry

An interlaboratory study of Mg/Ca and Sr/Ca ratios in three commercially available carbonate reference materials (BAM RS3, CMSI 1767, and ECRM 752‐1) was performed with the participation of 25 laboratories that determine foraminiferal Mg/Ca ratios worldwide. These reference materials containing Mg/Ca in the range of foraminiferal calcite (0.8 mmol/mol to 6 mmol/mol) were circulated with a dissolution protocol for analysis. Participants were asked to make replicate dissolutions of the powdered samples and to analyze them using the instruments and calibration standards routinely used in their laboratories. Statistical analysis was performed in accordance with the International Standardization Organization standard 5725, which is based on the analysis of variance (ANOVA) technique. Repeatability (RSDr%), an indicator of intralaboratory precision, for Mg/Ca determinations in solutions after centrifuging increased with decreasing Mg/Ca, ranging from 0.78% at Mg/Ca = 5.56 mmol/mol to 1.15% at Mg/Ca = 0.79 mmol/mol. Reproducibility (RSDR%), an indicator of the interlaboratory method precision, for Mg/Ca determinations in centrifuged solutions was noticeably worse than repeatability, ranging from 4.5% at Mg/Ca = 5.56 mmol/mol to 8.7% at Mg/Ca = 0.79 mmol/mol. Results of this study show that interlaboratory variability is dominated by inconsistencies among instrument calibrations and highlight the need to improve interlaboratory compatibility. Additionally, the study confirmed the suitability of these solid standards as reference materials for foraminiferal Mg/Ca (and Sr/Ca) determinations, provided that appropriate procedures are adopted to minimize and to monitor possible contamination from silicate mineral phases.

Calcite‐CO2 mixed into CO2‐free air: a new CO2‐in‐air stable isotope reference material for the VPDB scale

AbstractIn order to generate a reliable and long‐lasting stable isotope ratio standard for CO2 in samples of clean air, CO2 is liberated from well‐characterized carbonate material and mixed with CO2‐free air. For this purpose a dedicated acid reaction and air mixing system (ARAMIS) was designed. In the system, CO2 is generated by a conventional acid digestion of powdered carbonate. Evolved CO2 gas is mixed and equilibrated with a prefabricated gas comprised of N2, O2, Ar, and N2O at close to ambient air concentrations. Distribution into glass flasks is made stepwise in a highly controlled fashion. The isotopic composition, established on automated extraction/measurement systems, varied within very small margins of error appropriate for high‐precision air‐CO2 work (about ±0.015‰ for δ13C and ±0.025‰ for δ18O). To establish a valid δ18O relation to the VPDB scale, the temperature dependence of the reaction between 25 and 47°C has been determined with a high level of precision. Using identical procedures, CO2‐in‐air mixtures were generated from a selection of reference materials; (1) the material defining the VPDB isotope scale (NBS 19, δ13C = +1.95‰ and δ18O = −2.2‰ exactly); (2) a local calcite similar in isotopic composition to NBS 19 (‘MAR‐J1’, δ13C = +1.97‰ and δ18O = −2.02‰), and (3) a natural calcite with isotopic compositions closer to atmospheric values (‘OMC‐J1’, δ13C = −4.24‰ and δ18O = −8.71‰). To quantitatively control the extent of isotope‐scale contraction in the system during mass spectrometric measurement other available international and local carbonate reference materials (L‐SVEC, IAEA‐CO‐1, IAEA‐CO‐8, CAL‐1 and CAL‐2) were also processed. As a further control pure CO2 reference gases (Narcis I and II, NIST‐RM 8563, GS19 and GS20) were mixed with CO2‐free synthetic air. Independently, the pure CO2 gases were measured on the dual inlet systems of the same mass spectrometers. The isotopic record of a large number of independent batches prepared over the course of several months is presented. In addition, the relationship with other implementations of the VPDB‐scale for CO2‐in‐air (e.g. CG‐99, based on calibration of pure CO2 gas) has been carefully established. The systematic high‐precision comparison of secondary carbonate and CO2 reference materials covering a wide range in isotopic composition revealed that assigned δ‐values may be (slightly) in error. Measurements in this work deviate systematically from assigned values, roughly scaling with isotopic distance from NBS 19. This finding indicates that a scale contraction effect could have biased the consensus results. The observation also underlines the importance of cross‐contamination errors for high‐precision isotope ratio measurements.As a result of the experiments, a new standard reference material (SRM), which consists of two 5‐L glass flasks containing air at 1.6 bar and the CO2 evolved from two different carbonate materials, is available for distribution. These ‘J‐RAS’ SRM flasks (‘Jena‐Reference Air Set’) are designed to serve as a high‐precision link to VPDB for improving inter‐laboratory comparability.a Copyright © 2005 John Wiley & Sons, Ltd.

Concentrations of Trace Elements in Carbonate Reference Materials Coral JCp‐1 and Giant Clam JCt‐1 by Inductively Coupled Plasma‐Mass Spectrometry

Trace elements in the Geological Survey of Japan carbonate reference materials Coral JCp‐1 and Giant Clam JCt‐1 were determined by inductively coupled plasma‐mass spectrometry after digestion with 2% v/v HNO3. A standard addition method was adopted in this determination in order to neutralise the Ca matrix effect. In addition, Sc, Y, In and Bi were used as internal standards to control the matrix effect and correct instrumental drift. Of the eighteen elements measured in JCp‐1, precisions for fourteen elements, including Cu, Cd and Ba, were better than 10% RSD and concentrations ranged from 0.002 μg g‐1 (Cs) to 8.02 μg g‐1 (Ba). The concentrations of measured trace elements in JCt‐1, except for Cu, were lower than those in JCp‐1. Precisions for all elements with concentrations higher than 0.04 μg g‐1 in JCt‐1 were also better than 10% RSD and concentrations were found to be between 0.001 μg g‐1 (Cs) and 4.84 μg g‐1 (Ba). The concentrations of more than fifteen trace elements in the aragonite reference materials are reported here for the first time. Both reference materials are suitable for use in geochemical studies of environmental reconstruction based upon biogenic carbonate materials.

Instrumental Neutron Activation Analysis of Fourteen Carbonate Reference Materials from the NBS and George Frederic Smith and Eleven Industrial Geological Samples from the Bureau of Analysed Samples

New data are presented for the analysis of the elements: REE, Na20, Fe2O3, Cr, Co, Rb, Cs, Ba, Hf, Ta, Th and Il in twenty‐five less well known carbonate and industrial geological reference materials by instrumental neutron activation analysis. The materials include NBS 1c, 15e, 88a and 120b from the National Bureau of Standards, Washington DC; GFS 400‐403, 405, 407, 411, 412, 415 and 417 carbonate materials from George Fredrick Smith, Columbus, Ohio and BCS 267, 269, 309, 315, 319, 367, 368, 375, 376, 381 and 382/1 from the Bureau of Analysed Samples, Middles‐borough, Cleveland, UK. Particular attention has been given to the correction of interferences due to the fission of uranium in the determination of the elements La, Ce, Nd and Zr.