Accurate Isotope Ratio Measurements Research Articles

Evaluation of iGDGT carbon isotope fractionation in high performance liquid chromatography

Careful assessment of fractionation associated with High Performance Liquid Chromatography (HPLC) is essential for ensuring accurate carbon isotope ratio (δ13C) measurements. Here we report these effects for orthogonal dimensions of HPLC separation of iGDGTs. We observe 13C fractionation during normal phase separations using an amino-bonded stationary phase, finding that the heavy isotope preferentially elutes relative to its lighter counterpart, while negligible fractionation occurs during reverse phase HPLC. We argue that the fractionation during normal phase is caused by diminished Van der Waals attraction between 13C-enriched iGDGTs and the stationary phase and appears to depend on the structure of the analyte. Ultimately, these results emphasize the necessity of complete peak collection to preserve the isotopic character of iGDGTs.

Gd matrix effects on Eu isotope fractionation using MC-ICP-MS: Optimizing europium isotope ratio measurements in geological rock samples

Europium (Eu) has only two isotopes (151Eu and 153Eu). As sequential rare earth elements, Eu and Gd do not easily separate from each other during column chromatography, making it difficult to measure accurate and precise Eu isotope ratio during mass spectral analysis. Eu isotope ratios can be determined by MC-ICP-MS using internal Sm or Gd spikes to correct for mass discrimination. In this report, we discuss and propose optimal conditions for precise and accurate Eu isotope ratio measurements in geological materials (igneous rock samples) using MC-ICP-MS. The NIST3117a ultrapure chemical reagent showed almost no Eu isotope fractionation regardless of the kind of isotope pair used in normalization. A pure Eu fraction with almost no Gd matrix extracted from rock samples also showed nearly the same degree of Eu isotope fractionation regardless of the isotope pair used in normalization. In the case of Eu fraction extracted from highly fractionated granite and high silica volcanic rocks, when 154Gd interference relative to the internal 154Sm standard exceeded ca. 0.1% (due to incomplete Eu separation), this Gd matrix effect created artifactual variation in Eu isotope ratios during MC-ICP-MS analysis. In order to obtain the best estimates of Eu isotope fractionation in geological samples, especially high silica rocks, our analytical methods require complete Eu separation without Gd matrix during sample preparation.

Direct Uranium Isotopic Analysis of Swipe Surfaces by Microextraction-ICP-MS.

The ability to directly measure uranium isotope ratios on environmental swipes has been achieved through a solution-based microextraction process and represents a significant advancement toward the development of a rapid method to analyze international nuclear safeguard samples. Here, a microextraction probe is lowered and sealed onto the swipe surface, and analytes within the sampling site (∼8 mm2) are dissolved and extracted into a flowing solvent of 2% nitric acid (HNO3). The mobilized species are subsequently directed into an inductively coupled plasma-mass spectrometer (ICP-MS) for accurate and precise isotope ratio determination. This work highlights the novelty of the sampling mechanism, particularly with the direct coupling of the microextraction probe to the ICP-MS and measurement of uranium isotope ratios. The preliminary method detection limit for the microextraction-ICP-MS method, utilizing a quadrupole-based MS, was determined to be ∼50 pg of 238U. Additionally, precise and accurate isotope ratio measurements were achieved on uranium reference materials for both the major (235U/238U) and minor (234U/238U and 236U/238U) ratios. While the present work is focused on directly measuring uranium isotopic systems on swipe surfaces for nuclear safeguards and verification applications, the benefits would extend across many applications in which direct solid sampling is sought for elemental and isotopic analysis.

Vanadium Stable Isotopes in Biota of Terrestrial and Aquatic Food Chains.

Vanadium, a potentially toxic metal, is enriched in the environment from anthropogenic releases, particularly during fossil fuel production and use and steel manufacturing. Metal stable isotopes are sophisticated tools to trace pollution; however, only recent analytical advances have allowed for the accurate and precise measurement of vanadium isotope ratios (δ51V). To examine its potential as a tracer in terrestrial and aquatic ecosystems, δ51V was measured in soil, plant, lichen, marten, and lake sediment from sites near vanadium emissions at oil sands mines (Alberta, Canada) and in the sediment and biota (algae, zooplankton, fish) from a remote subarctic lake (Northwest Territories, Canada). Samples from Alberta had distinct δ51V values with marten liver the lowest (-1.7 ± 0.3‰), followed by lichen (-0.9 ± 0.1‰), soil (-0.7 ± 0.1‰), sediment (-0.5 ± 0.2‰), and plant root (-0.3 ± 0.2‰). Average values were lower than Alberta bitumen and petroleum coke (-0.1 ± 0.1‰). Plant roots had systematically higher δ51V than the soil from which they grew (Δ51Vplant-soil = 0.4 ± 0.1‰), while δ51V of lichen and aquatic biota were lower (0.1-0.3‰) than likely crustal sources. These δ51V measurements in terrestrial and aquatic biota demonstrate promise for tracer applications, although further study of its biological fractionation is needed.

Precise measurement of 234U/238U, 235U/238U and 236U/238U isotope ratios in Fukushima soils using thermal ionization mass spectrometry

Precise and accurate isotope ratio measurements of 234U/238U, 235U/238U and 236U/238U were performed simultaneously in Fukushima contaminated soil samples using thermal ionization mass spectrometry (TIMS). 234U, 235U and 236U isotopes were measured by Daly ion counting system whereas 238U was measured by Faraday collector using mass peak jumping method. Fukushima radio‑cesium contaminated soil samples were digested using microwave oven for complete decomposition. A combined AER-UTEVA separation scheme was applied for purification of U and its accurate isotope ratios measurement in Fukushima soils rich with Fe. Analytical validation of the modified U separation method was tested with certified reference material (CRM) JSd-2. The analytical precision (RSD%) of 234U/238U, 235U/238U and 236U/238U isotope ratios obtained by long-term repeatability for CRM NBL U010 was 0.288% (2σ), 0.017% (2σ) and 0.235% (2σ), respectively. Validation of accurate U isotope ratios measurement was checked with a CRM IRMM-184. This procedure was applied successfully to CRM JSd-2, SRM NIST 4354 and Fukushima soil samples. The concentration of 236U in Fukushima contaminated soils varied from 21.7–194.7 fg/g which showed the mixing effect of global fallout and Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident fallout.

Isotope abundance ratio measurements using femtosecond laser ablation ionization mass spectrometry.

Accurate isotope ratio measurements are of high importance in various scientific fields, ranging from radio isotope geochronology of solids to studies of element isotopes fractionated by living organisms. Instrument limitations, such as unresolved isobaric inferences in the mass spectra, or cosampling of the material of interest together with the matrix material may reduce the quality of isotope measurements. Here, we describe a method for accurate isotope ratio measurements using our laser ablation ionization time-of-flight mass spectrometer (LIMS) that is designed for in situ planetary research. The method is based on chemical depth profiling that allows for identifying micrometer scale inclusions embedded in surrounding rocks with different composition inside the bulk of the sample. The data used for precise isotope measurements are improved using a spectrum cleaning procedure that ensures removal of low quality spectra. Furthermore, correlation of isotopes of an element is used to identify and reject the data points that, for example, do not belong to the species of interest. The measurements were conducted using IR femtosecond laser irradiation focused on the sample surface to a spot size of ~12 μm. Material removal was conducted for a predefined number of laser shots, and time-of-flight mass spectra were recorded for each of the ablated layers. Measurements were conducted on NIST SRM 986 Ni isotope standard, trevorite mineral, and micrometer-sized inclusions embedded in aragonite. Our measurements demonstrate that element isotope ratios can be measured with accuracies and precision at the permille level, exemplified by the analysis of B, Mg, and Ni element isotopes. The method applied will be used for in situ investigation of samples on planetary surfaces, for accurate quantification of element fractionation induced by, for example, past or present life or by geochemical processes.

Isotope fractionation of micropollutants during large-volume extraction: heads-up from a critical method evaluation for atrazine, desethylatrazine and 2,6-dichlorobenzamide at low ng/L concentrations in groundwater

ABSTRACT Micropollutants are frequently detected in groundwater. Thus, the question arises whether they are eliminated by natural attenuation so that pesticide degradation would be observed with increasing residence time in groundwater. Conventional analytical approaches rely on parent compound/metabolite ratios. These are difficult to interpret if metabolites are sorbed or further transformed. Compound-specific stable isotope analysis (CSIA) presents an alternative for identifying degradation based on the analysis of natural isotope abundances in pesticides and their changes during degradation. However, CSIA by gas chromatography–isotope ratio mass spectrometry is challenged by the low concentrations (ng/L) of micropollutants in groundwater. Consequently, large amounts of water need to be sampled requiring enrichment and clean-up steps from interfering matrix effects that must not introduce artefacts in measured isotope values. The aim of this study was to evaluate the accuracy of isotope ratio measurements of the frequently detected micropollutants atrazine, desethylatrazine and 2,6-dichlorobenzamide after enrichment from large water volumes (up to 100 L) by solid-phase extraction with consecutive clean-up by HPLC. Associated artefacts of isotope discrimination were found to depend on numerous factors including organic matter content and extraction volume. This emphasizes the necessity to perform a careful method evaluation of sample preparation and sample pre-treatment prior reliable CSIA.

Characterization of the new isotopic reference materials IRMM-524A and ERM-AE143 for Fe and Mg isotopic analysis of geological and biological samples

Isotopic reference materials (IRMs) are crucial for securing accurate and precise isotope ratio measurements of non-traditional stable isotopic systems and for enabling comparison of isotope ratio data obtained at different labs.

High-Sensitivity Measurement of Cr Isotopes by Double Spike MC-ICP-MS at the 10 ng Level.

High-sensitivity and high-precision (2 SD ≤ 0.06‰) measurement of chromium (Cr) isotopes at the 10 ng level was successfully carried out using double spike multiple-collector inductively couple plasma mass spectrometry (MC-ICP-MS). To enhance the signal sensitivity and stability, the Aridus II desolvating nebulizer system was improved by placing its waste gas trap bottle in an ice chamber (5 °C cold trap). This setup, beyond Cr isotope analysis, can be applied to most heavy metal isotope measurements. The sensitivity of the 52Cr signal is ≥300 V mg-1 L (with a 1011Ω amplifier and a 110 μL min-1 uptake rate), an enhancement of ≥1.5 times compared to the Aridus II without the cold trap. In addition, the relative standard deviation of the 52Cr signal varied ≤4% over 8 h, demonstrating high stability. The δ53Cr values of common geological reference materials determined using 10 ng of Cr are in excellent agreement with results measured at 25 ng and 50 ng and are consistent with previous determinations, validating the accurate and precise Cr isotope ratio measurements. An empirical method is proposed to correct for the residual (after subtraction) effect of Fe interference on δ53Cr determination. This method relies on a linear relationship between the [Fe]/[Cr] and δ53Cr shift within one analytical session. Finally, we report the δ53Cr values of 19 new reference materials, ranging from -0.44‰ to 0.49‰. Among them, GSS-7 (-0.44 ± 0.02‰, 2 SD, n = 5), GSS-4 (0.48 ± 0.02‰, 2 SD, n = 5), and GSD-10 (0.49 ± 0.05‰, 2 SD, n = 5) can be used as candidate reference materials for interlaboratory comparisons to complement existing ones that are mostly isotopically unfractionated from the bulk silicate earth.

Investigation of the crucial factors affecting accurate measurement of strontium isotope ratios by total evaporation thermal ionization mass spectrometry.

An absolute method that does not require calibration is very important in several areas of isotope analysis due to the shortage of suitable certified reference materials (CRMs). As total evaporation thermal ionization mass spectrometry (TE-TIMS) theoretically overcomes mass fractionation through integrating the ion currents till the sample on the filament is completely exhausted, it could be an absolute method that does not require the use of CRMs for calibration. However, the lack of reliable method verification and reasonable uncertainty evaluation restricts its extensive application, and these effects need to be quantitatively evaluated. A series of different amounts of strontium reference material SRM987 was deposited on both single and triple tantalum filament sources, and analyzed by TE-TIMS. The work function of the tantalum filament loaded with the sample was measured by ultraviolet photoelectron spectroscopy. In order to evaluate the change in ion transmission efficiency, we terminated the total evaporation process manually after running for a certain period of time, and recorded the ion beam intensity before and after this operation. The TE results obtained with the triple filament source agreed well with the reference values of SRM987, while the TE results obtained with the single filament source changed significantly with the amount of sample loading. The crucial effect factors on TE-TIMS, including ionization temperature fluctuation, variation of ion transmission efficiency and ion loss before data acquisition, were quantitatively assessed. These factors were used to correct the single filament TE results and the measurement uncertainty was quantitatively evaluated. The reliability of strontium isotopic ratio measurement with triple filament TE-TIMS was verified. The mathematical model for correction of each crucial effect factor was successfully established, thus providing a feasible way for the correction of single filament TE-TIMS results.

Correction of Mass Spectrometric Interferences for Rapid and Precise Isotope Ratio Measurements of Calcium from Biological Samples Using ICP-Mass Spectrometry.

Stable isotope compositions of calcium (Ca) provide useful information concerning metabolic alterations of Ca in human and animal bodies. For the measurements of Ca isotope ratio, great care must be taken for the mass spectrometric interferences on Ca isotopes (42Ca+, 43Ca+, and 44Ca+) from doubly charged strontium (Sr) ions (84Sr2+, 86Sr2+, and 88Sr2+). To obtain reliable stable isotope data of Ca, we developed a new correction technique for the mass spectrometric interferences by mSr2+ ions based on standard addition method. Addition of a small fraction of Sr onto a Ca solution shifts the measured Ca isotope ratios on a three-isotope diagram (i.e., δ44Ca and δ43Ca) along a mixing line defined by both the true Ca isotope ratio and the Sr isotope ratio. Therefore, the true Ca isotope ratio of a sample can be obtained as the crossover point of mass dependent fractionation line and the mixing line. With the present correction technique, precise and accurate isotope ratio measurements can be made on analyte solutions having a CSr/CCa ratio (concentration ratio) of 0.03, which is 6 times higher than the CSr/CCa ratio applicable to the conventional correction technique.

Considerations for uranium isotope ratio analysis by atmospheric pressure ionization mass spectrometry.

The accurate measurement of uranium isotope ratios from trace samples lies at the foundation of achieving nuclear nonproliferation. These challenging measurements necessitate both the continued characterization and evaluation of evolving mass spectrometric technologies as well as the propagation of sound measurement approaches. For the first time in this work, we present the analysis of uranium isotope ratio measurements from discrete liquid injections with an ultra-high-resolution hybrid quadrupole time-of-flight mass spectrometer. Also presented are important measurement considerations for evaluating the performance of this type and other atmospheric pressure and ambient ionization mass spectrometers for uranium isotope analysis. Specifically, as the goal of achieving isotope ratios from as little as a single picogram of solid material is approached, factors such as mass spectral sampling rate, collision induced dissociation (CID) potentials, and mass resolution can dramatically alter the measured isotope ratio as a function of mass loading. We present the ability to accurately measure 235UO2+/238UO2+ down to 10s of picograms of solubilized uranium oxide through a proper consideration of mass spectral parameters while identifying limitations and opportunities for pushing this limit further.

Ultra-trace Cu isotope ratio measurements via multi-collector ICP-mass spectrometry using Ga as internal standard: an approach applicable to micro-samples

The capabilities of Cu isotope ratio measurements are often restricted by the small volumes of sample available and/or their low Cu concentration. In this work, an analytical approach was developed for performing Cu isotopic analysis via multi-collector ICP-mass spectrometry (MC-ICP-MS) at ultra-trace level using Ga as an internal standard for mass bias correction. The minimum concentration of Cu required for accurate and precise isotope ratio measurements was established to be 20 μg L−1 with wet plasma conditions and 5 μg L−1 with dry plasma conditions. The use of Ga as an internal standard for mass bias correction provided several advantages compared to Ni, i.e. improved internal precision on δ65Cu values and lower blank levels. Ga can also be used at a 4-fold lower concentration level than Ni. However, in wet plasma conditions, the signals of 36Ar16O21H+ and 40Ar15N16O+ interfered with the signals of 69Ga+ and 71Ga+, respectively, while in dry plasma conditions, realized by the use of a desolvation unit, 69Ga+ suffered from spectral interference from 40Ar14N21H+. These interferences were resolved by using medium mass resolution. For validation purposes, the approach was applied to commercially available blood and serum samples. The δ65Cu values for the samples measured at a concentration level of 5 μg L−1 Cu and 5 μg L−1 Ga using dry plasma conditions were in good agreement with those obtained for isotope ratio measurements at the “standard” concentration level of 200 μg L−1 Cu and 200 μg L−1 Ni using wet plasma conditions. In addition, the δ65Cu values obtained for micro-samples of serum/blood (volume of 100 µL) were in good agreement with the corresponding ones obtained using the “standard” volume for isotopic analysis (500 μL).

Accurate measurement of uranium isotope ratios in solid samples by laser ablation multi-collector inductively coupled plasma mass spectrometry

A multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) coupled to a 213 nm ns-laser was used to measure uranium isotope ratios (234U/238U, 235U/238U, and 236U/238U) in six solid nuclear certified reference materials (CRMs).

Accurate and precise measurement of Ce isotope ratios by thermal ionization mass spectrometry (TIMS)

The La-Ce isotope system has been rarely applied, mostly due to analytical difficulties. Recent technical refinements of mass spectrometers have overcome some of these technical limitations, but Ce isotope analyses still face considerable analytical challenges. These are mainly related to the low abundance of the minor isotopes 136Ce and 138Ce relative to the main isotopes 140Ce and 142Ce (136Ce=0.19%, 138Ce=0.25%, 140Ce=88.45%, 142Ce=11.11%). Hence simultaneous measurement of ion beams over a large dynamic range is required, resulting in large differences in count statistical uncertainty on the individual ion beams. In addition, the large abundance of 140Ce introduces a tailing effect of the large 140CeO ion beam onto the 136CeO and 138CeO ion beams, which requires adequate correction. Here, we present a chemical purification scheme and high-precision thermal ionization mass spectrometric (TIMS) method for analyzing CeO isotope ratios in silicate samples. The advantages and disadvantages of different mass spectrometric strategies for data acquisition by TIMS were evaluated, including the use of 1010, 1011, and 1012Ω amplifiers and different strategies for the 140CeO tail correction. An optimization scheme was developed for different on-peak and off-peak collection schemes, in combination with different tail and baseline correction methods. It is shown that, as long as the integration times for the on-peak, off-peak (half-mass), and baseline signals are adequately optimized for the employed collection scheme and tail correction method, different strategies yield Ce isotope ratios with similar precision of 20–40ppm (2 S.D.). In contrast to previous studies, we have acquired 140CeO by using a 1010Ω amplifier, and have determined a long-term average 140Ce/142Ce of=7.94319±2. Using a common 136Ce/142Ce=0.01688 for mass fractionation correction, the 136Ce/138Ce of the international rock reference materials BCR-1, BCR-2, and BHVO-2 of this study agree well with those recently reported, when all Ce isotope ratios are reported relative to a common 138Ce/136Ce=1.337366 for the average Ames Ce metal. In addition, Ce isotope ratios for several other widely available international rock reference materials (AGV-2, BE-N, BIR-1, DNC-1, W2A) are presented, and facilitate easy inter-laboratory comparison.

Contrasting particle size distributions and Fe isotope fractionations during nanosecond and femtosecond laser ablation of Fe minerals: Implications for LA-MC-ICP-MS analysis of stable isotopes

Laser ablation coupled to a multi-collector inductively coupled mass spectrometer (LA-MC-ICP-MS) is a promising tool for in situ analysis of metal and metalloid stable isotope ratios. Potential isotopic fractionation associated with laser ablation may, however, cause biased sampling of the substrate, posing a major challenge for precise and accurate isotope ratio measurements. To better characterize the nature of laser ablation induced isotopic fractionation, this study compared particle morphologies, sizes, and size-dependent Fe isotope fractionations produced by ablation of a suite of semi-conductive samples, including natural Fe oxide, sulfide, and carbonate minerals, under various conditions using a 193nm ArF nanosecond (ns) laser and a 266nm Ti:sapphire femtosecond (fs) laser. Ablation-produced particles were sorted based on aerodynamic size using a cascade impactor, and Fe isotope compositions of size-sorted particles were then measured offline using conventional solution nebulization ICP-MS to quantify isotopic fractionation produced by the laser ablation. Particle morphology and size distributions produced by ns-laser ablation are more substrate and fluence dependent as compared to fs-laser ablation, resulting from the thermal nature of ns-laser ablation. Often, a higher proportion of the ablated Fe mass resides in particles with large aerodynamic sizes during ns-laser ablation as compared to fs-laser ablation, posing a potential difficulty for LA-ICP-MS analysis due to the increased possibility of incomplete ionization of large particles. Significant size-dependent Fe isotope fractionations of up to several per mil can occur during both ns- and fs-laser ablation, highlighting the importance of quantitative transport of particles to the ICP-MS for accurate Fe isotope analysis. Size-dependent Fe isotope fractionation observed for fs-laser ablation of all Fe minerals can be explained by particle formation through a condensation model, but multiple processes need to be considered to explain the observed Fe isotope fractionation during ns-laser ablation. Mass-balance calculations suggest that ns-laser ablation does not sample magnetite stoichiometrically for Fe isotope compositions at low fluence (1J/cm2), but does at higher fluences for all minerals. In contrast, fs-laser ablation always provides stoichiometric sampling for Fe isotopes regardless of fluence. Results of this study demonstrate that ns-laser ablation is substrate- and fluence-dependent, resulting in variable particle size distributions and Fe isotope fractionations, and possible non-stoichiometric sampling of semi-conductive samples for Fe isotope analysis. Instead, fs-laser ablation largely minimizes the substrate and fluence dependence, providing more consistent ablation.

Ion Exchange Chromatography and Mass Bias Correction for Accurate and Precise Zn Isotope Ratio Measurements in Environmental Reference Materials by MC-ICP-MS

Precise and accurate d66/64Zn data for environmental reference materials (RMs) including rocks, sediments, soils and plants are presented in order to improve the metrological traceability and analytical control of Zn isotope ratio determinations in future environmental studies. Previously developed ion exchange chromatography protocols were adjusted to enable faster sample throughput and instrumental mass bias processes were investigated. The improved chromatographic protocol yielded precise and quantitative recoveries (99 ± 7%, σ, n = 16), while the mass bias correction using Cu as external dopant provided precisions better than 0.02‰, 2σ, n = 7. Investigations into spectral and non-spectral interferences identified significant formation of Cr and Ti oxides and hydroxide ionic species. Analysis of six RMs (BHVO-2 basalt (USGS), BCR-2 basalt (USGS), AGV-2 andesite (USGS), 2709 San Joaquin soil (NIST), 1646a estuarine sediment (NIST) and 1573a tomato leaves (NIST)) showed good reproducibility (< 0.01‰, 2s, 5 ≤ n ≥ 1).

Errors in Isotope Dilution Caused by Matrix-induced Mass Bias Effect in Quadrupole Inductively Coupled Plasma-Mass Spectrometry

Yong-Nam PakDepartment of Chemistry Education, Korea National University of Education, Chung Buk 363-791, KoreaE-mail: pakyn@knue.ac.krReceived July 2, 2014, Accepted August 8, 2014Matrix-induced mass bias and its effect on the accuracy of isotope ratio measurements have been examined fora quadrupole-based inductively coupled plasma-mass spectrometer (Q ICP-MS). Matrix-induced mass biaseffect was dire ctly proportional to % mass d ifference, and its magnitude varied for element and nebulizer flowrate. For a given element and conditions in a day, the effect was consistent. The isotope ratio of Cd106/Cd114under 200 µg g

CAMAM: A Miniature Laser Ablation Ionisation Mass Spectrometer and Microscope‐Camera System for In Situ Investigation of the Composition and Morphology of Extraterrestrial Materials

Performance studies of a microscope‐camera system (MCS) and a laser ablation/ionisation mass spectrometer (LIMS) instrument (referred to here as a laser mass spectrometer or LMS) are presented. These two instruments were designed independently for in situ analysis of solids on planetary surfaces and will be combined to a single miniature instrument suite for in situ chemical and morphological analysis of surface materials on planetary bodies. LMS can perform sensitive chemical (elemental, isotope and molecular) analyses with spatial resolution close to micrometre‐sized grains. It allows for studies with mass resolution (M/ΔM) up to 800 in ablation mode (elemental composition) and up to 1500 in desorption mode (molecular analysis). With an effective dynamic range of at least eight orders of magnitude, sensitive and quantitative measurements can be conducted of almost all elements and isotopes with a concentration larger than a few ppb atoms. Hence, in addition to the major element composition, which is important for the determination of mineralogical constituents of surface materials, trace elements can also be measured to provide information on mineral formation processes. Highly accurate isotope ratio measurements can be used to determine in situ geochronology of sample material and for investigations of various isotope fractionation processes. MCS can conduct optical imagery of mm‐sized objects at several wavelengths with micrometre spatial resolution for the characterisation of morphological surface details and to provide insight into surface mineralogy. Furthermore, MCS can help in the selection of sample surface areas for further mass spectrometric analysis of the chemical composition. Surface auto‐fluorescence measurements and images in polarised light are additional capabilities of the MCS, to identify either fluorescing minerals or organic materials, if present on the analysed surface, for further investigation by LMS. The results obtained by investigations of NIST reference materials, amino acid films and a natural graphite sample embedded in silicate rock are presented to illustrate the performance of the instruments and their potential to deliver chemical information for mineral and organic phases in their geological context.

Rapid, precise and accurate Os isotope ratio measurements of nanogram to sub-nanogram amounts using multiple Faraday collectors and amplifiers equipped with 1012 Ω resistors by N-TIMS

We present a new approach to obtain rapid and precise (0.1 % or better) Os isotopic compositions for small (nanogram to sub-nanogram) amounts of Os extracted from geological samples using static collection with Faraday cups and amplifiers equipped with 1012 Ω resistors, by negative thermal ionization mass spectrometry (N-TIMS/Triton Plus). The results show that the measurement repeatability of Os isotopic ratios (190Os/188Os, 187Os/188Os and 186Os/188Os) changes as a function of signal intensity that varied from 0.005 to 0.05V for 192OsO3− (here and throughout the text, given intensities are equivalent signals that would be obtained using a 1011 Ω standard amplifier; 0.001V (1mV) is equivalent to ~62500 cps). At 192OsO3− ion beams greater than 0.02V with 50 ratios measured over a 10min acquisition time, the repeatability on 187Os/188Os, as well as 186Os/188Os and 190Os/188Os, is better than that obtained by the conventional peak-hopping electron multiplier (SEM) at 192OsO3−=~200,000 cps with 500–100 ratios measured over a 30–60min acquisition time. At 192OsO3− ion beams of ~0.04V or above, the 187Os/188Os and 186Os/188Os data for loads of 1 and 0.1ng Os reference materials can be measured with a repeatability of <0.1% (2σ) and deviate by <0.1% from the accepted values. Similar results can be achieved for Os load sizes in geological samples as low as~0.025ng. In addition, duplicate Faraday measurements of six spiked peridotitic samples (total Os loaded=0.3–1.2ng) yield results within uncertainty of data obtained by peak-hopping SEM, including both 187Os/188Os and Os concentration. At much higher 192OsO3− ion beams (~0.5–1V) with 300 ratios taken (total acquisition time circa one hour), the Faraday measurements of 1 to 3ng Os loads of reference material solutions can generate high-precision 186Os/188Os data with a repeatability of 30–50ppm and a mean intermediate precision of 10–30ppm. Collectively, our tests demonstrate that the use of Faraday cups equipped with 1012 Ω amplifiers in a static collection mode by N-TIMS can rapidly produce precise and accurate (within 0.1 %) Os isotopic data (both 187Os/188Os and 186Os/188Os) for small amounts of Os (as low as 0.025ng) extracted from geological samples. The optimum 192OsO3− signal is 0.04V or above to achieve the best results. While the smaller signal intensities used in concert with 1012 Ω amplifiers necessarily yield lower precision measurements than the best achievable with larger signals on 1011 Ω amplifiers, the repeatability we have achieved on reference materials can expand the application of the 190Pt–186Os decay system to geological samples containing significantly less Os than those normally measured on 1011 Ω amplifiers, if isotopic variations in excess of 50ppm are present.