Re-determination of R(C/C) for Vienna Peedee belemnite (VPDB).

Rationale: The isotope ratio for the internationally agreed but virtual zero-point of the carbon isotope-delta scale, Vienna Peedee belemnite (VPDB), plays a critical role in linking carbon isotope delta values to the SI. It is also a quantity used for various data processing procedures including 'O correction', clumped isotope analysis and conversion of carbon isotope delta values into other expressions of isotopic composition. A value for R(C/C) with small uncertainty is therefore desirable to facilitate these procedures.

Systematic comparison of post-column isotope dilution using LC-CO-IRMS with qNMR for amino acid purity determination.

Determination of the purity of a substance traceable to the International System of Units (SI) is important for the production of reference materials affording traceability in quantitative measurements. Post-column isotope dilution using liquid chromatography-chemical oxidation-isotope ratio mass spectrometry (ID-LC-CO-IRMS) has previously been suggested as a means to determine the purity of organic compounds; however, the lack of an uncertainty budget has prevented assessment of the utility this approach until now. In this work, the previously published ID-LC-CO-IRMS methods have not only been improved by direct gravimetric determination of the mass flow of C-labelled spike but also a comprehensive uncertainty budget has been established.

Investigation of mass dependence effects for the accurate determination of molybdenum isotope amount ratios by MC-ICP-MS using synthetic isotope mixtures.

Methodology for absolute Mo isotope amount ratio measurements by multicollector inductively coupled plasma-mass spectrometry (MC-ICP-MS) using calibration with synthetic isotope mixtures (SIMs) is presented. For the first time, synthetic isotope mixtures prepared from seven commercially available isotopically enriched molybdenum metal powders ((92)Mo, (94)Mo, (95)Mo, (96)Mo, (97)Mo, (98)Mo, and (100)Mo) are used to investigate whether instrumental mass discrimination of Mo isotopes in MC-ICP-MS is consistent with mass-dependent isotope distribution. The parent materials were dissolved and mixed as solutions to obtain mixtures with accurately known isotope amount ratios.

Calibration strategies for the determination of stable carbon absolute isotope ratios in a glycine candidate reference material by elemental analyser-isotope ratio mass spectrometry.

We report a methodology for the determination of the stable carbon absolute isotope ratio of a glycine candidate reference material with natural carbon isotopic composition using EA-IRMS. For the first time, stable carbon absolute isotope ratios have been reported using continuous flow rather than dual inlet isotope ratio mass spectrometry. Also for the first time, a calibration strategy based on the use of synthetic mixtures gravimetrically prepared from well characterised, highly (13)C-enriched and (13)C-depleted glycines was developed for EA-IRMS calibration and generation of absolute carbon isotope ratio values traceable to the SI through calibration standards of known purity.

Anion-exchange chromatographic separation of Hg for isotope ratio measurements by multicollector ICPMS.

A procedure is described for precise Hg isotope ratio measurements by solution nebulization multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Hg was released from geological samples using aqua regia extraction and then separated from other matrix elements with the aid of anion-exchange chromatography using strongly basic Dowex 1-X8 anion-exchange resin. Performance of the chromatographic procedure was evaluated using various types of replacement anions for elution of mercury, including l-cysteine, thiourea, NO3-, and SO42-.

Ion-specific isotopic fractionation of molybdenum during diffusion in aqueous solutions.

Experiments modeling diffusion of Mo in aqueous solutions have been performed and, using multicollector ICP-MS, the ratios of the diffusivities of Mo isotopes, D97Mo/ D95Mo, in aqueous solutions have been determined. Diffusion of MoO42- ions in solution was concomitant with Mo isotopic fractionation with D97Md/D95Mo = 0.99988+/-0.

Measurement of iron and zinc isotopes in human whole blood: preliminary application to the study of HFE genotypes.

Multi-collector inductively coupled plasma--sector field mass spectrometry was applied to the measurement of Fe and Zn isotopes in human whole blood samples. For the Fe present in the blood of healthy adults, enrichment of the lighter isotopes relative to a standard material was observed, in agreement with earlier studies. The level of fractionation was found to be lower in hemochromatosis patients exhibiting homozygous (C282Y/C282Y) mutation of the HFE gene.

Isotopic variations of Zn in biological materials.

Variations in the isotopic composition of Zn present in various biological materials were determined using high-resolution multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), following digestion and purification by anion exchange chromatography. To correct for differences in instrumental mass discrimination effects between samples and standards, Cu was employed as an elemental spike. Complementary analyses of Zn separates by sector field ICPMS instruments revealed that the concentrations of the majority of potentially interfering elements were reduced to negligible levels.

Isotopic fractionation during diffusion of transition metal ions in solution.

Isotope ratios and elemental concentrations were measured in aqueous solutions sampled at varying distances from sources of Fe or Zn ions. The measurements reveal fractionation of isotopes resulting from pure diffusion in solution. Our data demonstrate that diffusion alone can cause changes in (56)Fe/(54)Fe and (66)Zn/(64)Zn isotope ratios in excess of -0.