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Online normalisation to isotope ratio of admixed internal standards is an important technique in isotopic analysis by multicollector ICP-MS (MC-ICP-MS). It is widely used for minimising drift in measurements of δ-values and calibrating isotope amount ratios for medium and heavy mass elements. However, its potential has been underexplored for light elements, largely due to the greater magnitude of instrumental isotope fractionation (IIF) observed in the low mass region and the need to conduct measurements in dynamic mode. This work reports for the first time a comprehensive assessment of the performance of Li, C, and Mg as internal standards for both relative and absolute 11B/10B isotope ratio measurements by MC-ICP-MS. The data show that normalisation to any of the tested elements allowed correcting for drift in IIF and obtaining more reproducible results. The regression model has been used to determine n(11B)/n(10B) isotope ratios in the NIST SRM 951a boric acid isotopic material with a certified boron isotope amount ratio. The n(11B)/n(10B) values and expanded uncertainties (k = 2) determined for this material by using isotopically certified Li, C, and Mg internal standards were 4.0688(569), 4.0439(264) and 4.0294(706), respectively, and agree well with the NIST SRM 951a certified value of 4.0437(033). Carbon has shown the best internal standard performance in the measurement of both δ11B and n(11B)/n(10B) values. Calibration of n(11B)/n(10B) isotope ratios using internal standards with SI-traceable isotope ratios offers a low-cost alternative method for establishing traceability of results to the SI. The ease of implementation of the method makes it a useful tool for fostering quality control procedures in laboratories seeking the ISO/IEC 17025:2017 accreditation.

Variations in the stable isotopic composition of carbon are commonly expressed as δ(13C) values, and are used in diverse fields, including biology, environmental sciences, food and drug authentication and forensic applications. Progress in these fields requires accurate and comparable stable carbon isotope ratio measurements between laboratories and over time. Yet concerns about comparability of measurement results for stable carbon isotopes have been raised due to both replacement of one primary reference material by another and, more recently, due to the increase of δ(13C) values of the second primary reference material (LSVEC) when exposed to the atmosphere. Establishing traceability to the SI as a stable metrological reference system can be a sustainable solution in ensuring accuracy and metrological traceability of measurement results. To address the shortage of reference materials certified for carbon isotope ratios traceable to the SI, a new reference material LGC171-KT has been produced in this study. This consists of three glycine solutions with certified n(13C)/n(12C) isotope amount ratios of 0.010642, 0.010821 and 0.011227 with expanded uncertainties (k = 2) of 0.000030, 0.000030 and 0.000032, respectively, and indicative δ(13C)VPDB values of −42.22‰, −24.66‰ and +12.55‰ with expanded uncertainties (95% confidence) of 0.34‰, 0.24‰ and 0.22‰, respectively. A strategy for the development and characterisation steps has been described in detail and includes an improved approach for evaluating results of homogeneity testing. The n(13C)/n(12C) isotope amount ratio for the zero point of the VPDB scale was also re-determined and the current best estimate, based on all available results, was determined to be 0.011117 with expanded uncertainty of 0.000039 (k = 2.6).

Species-specific Hg isotope ratio data has increasingly become an important tool in understanding biogeochemistry of mercury. Among the plethora of analytical techniques capable of separating Hg species to date only gas chromatography has been used to study natural variations in their isotopic composition. Here, we report new methodology for precise and accurate Hg isotope ratio measurements of methylmercury in fish tissues at environmentally relevant levels using high performance liquid chromatography (HPLC) and cold vapour generation multi-collector inductively coupled plasma mass spectrometry (CVG MC-ICPMS). The chromatographic baseline separation of Hg species such as methylmercury (CH3Hg) and inorganic Hg (iHg) was achieved in isocratic mode using reverse phase HPLC with a mobile phase containing L-cysteine as a complexing agent and without the need for species derivatisation. The signal-to-noise ratio of Hg detection by MC-ICP-MS was improved using a cold vapour generation interface with SnCl2 as reducing agent. Challenges driven by the non-reactivity of CH3Hg with SnCl2 and, interferences caused by the presence of L-cysteine in the mobile phase were efficiently overcome through complete oxidation of isolated Hg species prior to cold vapour generation and species-specific Hg isotope ratio measurements. Combined standard uncertainties of δ199/198Hg, δ200/198Hg, δ201/198Hg and δ202/198Hg values determined from replicated measurements of CH3Hg in fish tissue reference materials BCR 463 and NIST SRM 1947 ranged from 0.10‰ to 0.22‰. The obtained δ-values for the Hg isotope ratios are in very good agreement with indicative values of NIST SRM 1947 and those previously reported for BCR 463 material. The developed technique offers a complimentary measurement method to gas chromatography MC-ICPMS in producing isotopically certified species-specific reference materials for Hg. Furthermore, evidence for Hg isotope fractionation induced by dissociation of CH3Hg and interactions with sulphur compounds in solution is provided here as well.

Improved methodology for high accuracy Mo isotope amount ratio measurements by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) using normalisation to an internal standard is presented. It is based on the use of the regression model to correct for instrumental mass discrimination with NIST Standard Reference Material 987, certified for Sr isotope ratios, as the internal standard. Calibration factors for measured Mo isotope ratios were calculated from calibration factors for Sr isotope ratios by using an experimentally established relationship between variations in simultaneously measured Mo and Sr isotope ratios. The novelty of the developed methodology lies in the use of controlled changes in the magnitude of instrumental mass discrimination, achieved by small incremental changes in RF power of the plasma in the measurements, in order to better define a relationship between isotope ratios of the analyte and internal standard. The Mo isotope amount ratios with associated expanded uncertainties (k = 2), as determined for an in-house standard, a high-purity Mo metal rod from Johnson Matthey, were as follows: 92Mo/95Mo = 0.9223(15), 94Mo/95Mo = 0.5790(3), 96Mo/95Mo = 1.0500(6), 97Mo/95Mo = 0.06028(9), 98Mo/95Mo = 1.5278(30), 100Mo/95Mo = 0.6124(25). These values are in excellent agreement with those obtained previously for the same standard using calibration with synthetic isotope mixtures. Overall, the measurement uncertainties obtained by the two calibration approaches are fairly comparable. Performance of the regression model with the improved measurement strategy, in terms of accuracy and precision of Mo isotope amount ratios, was shown to be superior to that of other available models to correct for instrumental mass bias, including the linear, exponential and power models. For the first time in MC-ICPMS, a test of ruggedness of Mo isotope ratio measurements with normalisation to internal standard was performed using a Plackett–Burman factorial design. Full uncertainty budgets for the measurements are presented and identification of the major sources of uncertainty is provided. The developed methodology has been demonstrated to be a promising tool for certification of reference materials for isotopic measurements by offering an independent and less expensive calibration method to the one based on the use of synthetic isotope mixtures.

This paper demonstrates that the combination of simultaneous measurements of 12C+ and 13C+ ion currents by MC-ICPMS and calibration based on the use of gravimetrically prepared synthetic isotope mixtures provides a unique possibility for accurate determination of absolute 13C/12C isotope amount ratios which are metrologically traceable to the SI units. We have applied this approach to the determination of 13C/12C isotope amount ratios in glycine – an amino acid of importance in a variety of applications, including paleoecological studies and food security analysis. Eleven synthetic isotope mixtures with different n(13C)/n(12C) isotope amount ratios were prepared by gravimetric weighing and mixing of two well-characterized parent glycines, each highly enriched in either 12C or 13C isotopes. The parent materials were dissolved in dilute nitric acid and mixed as solutions. In measurements of the 13C/12C isotope ratio in aqueous solutions it was found essential to account for the relatively high procedural blank and for spectral interference of 12C1H+ ions in 13C+ ion current. The former is due to dissolution of atmospheric CO2 gas and presence of non-ionic organic contaminants even in high purity water. An improved measurement protocol was used in this study to address the above features. It involved performing 13C/12C isotope ratio measurements in high resolution mode of MC-ICPMS to completely resolve the spectral interference in 13C+ ion current and keeping elevated concentrations of carbon (∼0.5%) in the measured samples to minimize contribution of the blank. A value of the 13C/12C isotope amount ratio of 0.010648 ± 0.000042 (expanded uncertainty, k = 2) was obtained for the glycine candidate reference material in 12 measurement sessions with independently prepared calibration mixtures. This work shows excellent agreement between the iteration procedure and analytical solution which were used for the calculation of the calibration factor K. It also demonstrates that possible non-linearity between measured ion currents and isotope amount fractions has an insignificant effect on the accuracy of 13C/12C isotope amount ratio measurements of natural glycine.

Compounds of the types M(CO)4L2 and Mo(CO)3L2Y have been prepared where M = Cr, Mo, and W, L2=Z-pyridine-2-aldehyde 2′-pyridylhydrazone and Y = PPh3, AsPh3, SbPh3, Ph3PSe and SO2. The E-isomer of the hydrazone can be stabilised in the compounds Mo(CO)4L2, Mo(CO)3L2(PPh3) and Mo(CO)2L2I2. Some results of the halogen oxidations of Mo(CO)4L2 where L2= either E- or Z-hydrazone are presented, compounds such as Mo(CO)3(L2)X2, where L2=Z-hydrazone and X = Br, I, and [L2H2]MoOX5, where X = Cl, Br, having been isolated.

Spectroscopic evidence indicates that aliphatic dinitriles σ-bond in M(CO)3(dinitrile)X complexes (M = Mn and Re; X = Cl, Br, and I) using one donor nitrogen atom only, and do not act as π-bonding chelates as previously suggested.