Precise Isotope Ratio Measurements Research Articles

Tracing Mercury Contamination from the Idrija Mining Region (Slovenia) to the Gulf of Trieste Using Hg Isotope Ratio Measurements

To demonstrate the power of precise isotope ratio measurements of Hg in environmental samples and, more particularly, to test the use of stable isotopes as distinct tracers of the contamination source, we investigated a well-documented system, the Hg mining region near Idrija, Slovenia. Sediments alongside the Idrijca River, the Soca/Isonzo River, and in the Gulf of Trieste were analyzed to determine the variation in Hg isotopic composition versus distance from the source. Similar Hg isotopic signatures were observed among samples collected from the rivers Idrijca, Soca/Isonzo, and around the river mouth in the Gulf of Trieste, suggesting that sediments throughout the watershed of the Soca/Isonzo River to the Gulf of Trieste are dominated by Hg exported from the headwaters of the Idrijca River. Only locations on the southern part of the gulf, outside the river plume, showed lower values of the isotopic composition comparable to the Hg isotopic signature of Adriatic Sea sediments. Using a simple binary mixing-model, we could demonstrate that all samples investigated in this study were a result of variable proportions of Hg originating from the Idrija region (progressively decreasing from >90% in the northern partto <50% in the southern gulf) and from the Adriatic Sea. These results are, so far, the first evidence that tracking of mercury sources in natural systems using mercury stable isotope ratios is feasible.

Accurate and Precise Zinc Isotope Ratio Measurements in Urban Aerosols

We developed an analytical method and constrained procedural boundary conditions that enable accurate and precise Zn isotope ratio measurements in urban aerosols. We also demonstrate the potential of this new isotope system for air pollutant source tracing. The procedural blank is around 5 ng and significantly lower than published methods due to a tailored ion chromatographic separation. Accurate mass bias correction using external correction with Cu is limited to Zn sample content of approximately 50 ng due to the combined effect of blank contribution of Cu and Zn from the ion exchange procedure and the need to maintain a Cu/Zn ratio of approximately 1. Mass bias is corrected for by applying the common analyte internal standardization method approach. Comparison with other mass bias correction methods demonstrates the accuracy of the method. The average precision of delta(66)Zn determinations in aerosols is around 0.05 per thousand per atomic mass unit. The method was tested on aerosols collected in Sao Paulo City, Brazil. The measurements reveal significant variations in delta(66)Zn(Imperial) ranging between -0.96 and -0.37 per thousand in coarse and between -1.04 and 0.02 per thousand in fine particular matter. This variability suggests that Zn isotopic compositions distinguish atmospheric sources. The isotopic light signature suggests traffic as the main source. We present further delta(66)Zn(Imperial) data for the standard reference material NIST SRM 2783 (delta(66)Zn(Imperial) = 0.26 +/- 0.10 per thousand).

Precise isotope ratio measurements by MC-ICP-MS and application of the isotope dilution technique for the determination of germanium in the Gallium Neutrino Observatory

Summary In the Gallium Neutrino Observatory (GNO) experiment solar neutrinos are studied. Low energy neutrinos interact with 71Ga producing radioactive 71Ge, which decays with a half-life of 11.43 days back to 71Ga. This β+-decay is used for quantifying the number of solar neutrinos observed. Stable Ge isotopes are used as carriers when 71Ge atoms are extracted from the GaCl3 target for measuring their decay. The carrier serves at the same time for quantification of the chemical yield of the extraction process. Ge-removal from the GaCl3 detector solution proceeds exponentially and a small amount of Ge carrier remains in the Ga-tank, which is removed only during the following extraction(s). The use of different stable enriched Ge isotopes (70Ge, 72Ge, 74Ge and 76Ge) in alternating sequence allows one to determine the extraction yield of the carrier by high precision isotope ratio measurements. The measurements are carried out using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The exact quantification of any residual Ge carrier from the preceding run is achieved through isotope dilution calculations and isotope mixture calculations. In this paper we describe the evaluation of the results using the two-isotopes and two-components approach, as well as the multi-isotope and three-components approaches. We could demonstrate that the measured isotopic composition of the carrier after extraction can be fully modelled by a mixture of the initially used Ge carrier, of the Ge carrier from the previous run and of a small, but non-negligible contribution of a natural Ge contamination.

High precision and continuous field measurements of δ 13C and δ 18O in carbon dioxide with a cryogen-free QCLAS

The present paper describes a compact and cryogen-free, quantum cascade laser based absorption spectrometer (QCLAS) designed for in situ, continuous and high precision isotope ratio measurements of atmospheric CO2. The mobile instrument incorporates several new features including a novel astigmatic multi-pass cell assembly, a quasi-room temperature quantum cascade laser, thermoelectrically cooled detectors as well as a new retrieval approach. The combination of these features now makes it possible to measure isotope ratios of ambient CO2 with a precision of 0.03 and 0.05‰ for δ13C and δ18O, respectively, using a 100 s integration time. A robust and optimized calibration procedure was developed to bring the retrieved isotope ratios on an absolute scale. This assures an accuracy better than 0.1‰ under laboratory conditions. The instrument performance was also assessed in a field campaign in which the spectrometer operated autonomously and provided mixing ratio values for the main three CO2 isotopologues at one second time resolution. An accuracy of 0.2‰ was routinely obtained for both isotope ratios during the entire period. The results were in excellent agreement with the standard laboratory-based isotope ratio mass spectrometer measurements made on field-collected flask samples. A few illustrative examples are used to depict the potential of this optical method in atmosphere–biosphere research.

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-. A solution of 0.15% l-cysteine in 0.06 M HCl was found to be the most convenient eluent for subsequent MC-ICPMS measurements. The optimized procedure provides separation of Hg from virtually all concomitant matrix elements while maintaining quantitative (>95%) recovery. In addition, band displacement chromatographic experiments were conducted to assess whether the anion-exchange purification can produce Hg isotope fractionation artifacts. No isotope fractionation between the Hg(II)-l-cysteine complex in aqueous solution and Hg ions in the anion-exchange resin was observed. Hg isotope ratio measurements were performed using the bracketing standards approach and on-line correction for instrumental mass discrimination using Tl spiking and normalization to the 205Tl/203Tl ratio. The absence of spectral interference during Hg isotope ratio measurements was verified using a three-isotope plot. Uncertainties of Hg isotope ratio measurements for replication of the entire procedure, expressed as two standard deviations, are better than +/-0.08 per thousand/amu. The described procedure facilitates study of variations in the isotopic composition of Hg in nature.

Laser ablation coupled with ICP-MS applied to U–Pb zircon geochronology: A review of recent advances

Improvements in the technology of laser ablation and ICP-MS instruments make LA-MC-ICPMS a rapid, precise and accurate method for U–Pb zircon geochronology. In this review we describe the main stages of the evolution of this in situ approach from the early 1990s to the present time. Some key points have been progressively improved. The crater size has been reduced to achieve real in situ measurements. The laser wavelength has been reduced as well as the duration of each pulse in order to lower inter-element fractionation. The blank from the gas has to be lowered as far as possible. Double focusing instruments and magnetic field sectors allow flat-topped peaks required for precise isotope ratio measurement to be obtained. The use of a multi-ion counting system significantly improves the sensitivity of the method and the static mode of integration favours the precision of measurement of the transient signal originating from a noisy laser ablated particle beam. Combining the use of a 213 nm UV laser and a MC-ICPMS equipped with a multi-ion counting system operating in static mode, the common precisions achieved for the key ratios 207Pb/ 206Pb and 206Pb/ 238U are better than 1% and 3% (2 σ) respectively, including error propagation associated with standard normalization. Until now, the use of a zircon standard has remained necessary to ensure the accuracy of the calculated age. A strategy for common-Pb correction is proposed according to the age of the zircon and according to the Th/U ratio of the grains. After recording sixteen to twenty spot analyses the precision usually achieved on the age is about 1% and even significantly better for Proterozoic samples. In order to show the performance achieved by modern LA-MC-ICPMS geochronology, we tested four zircon samples covering a wide age range from 290 to 2440 Ma. These new age determinations can be compared in term of precision and accuracy since they have already been dated by reference methods (ID-TIMS and SHRIMP). Further developments in the technology of ion counters equipping modern MC-ICPMS and in laser systems will certainly be applied to a large field of geochronology studies in the near future as an alternative to SIMS for in situ age determination.

Solid-spiking isotope dilution laser ablation ICP-MS for the direct and simultaneous determination of trace elements in soils and sediments

The direct and simultaneous determination of Cu, Zn, Sn and Pb in soil and sediment samples by femtosecond laser ablation inductively coupled plasma isotope dilution mass spectrometry (fs-LA-ICP-IDMS) has been accomplished in this work with the development of a solid-spiking sample preparation procedure. The total analysis time, in comparison with previous approaches, has been significantly reduced by developing a solid-spiking procedure based on the synthesis of a unique isotopically-enriched solid spike and the preparation of isotope-diluted blend pellets for each sample. The laser repetition rate and the ablation mode were carefully selected (10 kHz and the 2D scanning sampling mode, respectively) in order to reduce the effect of possible local inhomogeneities of the powdered samples on the precision of isotope ratio measurements. Special attention was focused on the heterogeneous distribution of trace elements in the isotopically-enriched solid spike and the isotope-diluted blend samples in order to assure that the measured isotope ratios remained constant (precisions lower than 10% RSD; n = 8). The proposed methodology was tested for the analysis of two soil (CRM 142R, GBW-07405) and two sediment (PACS-2, IAEA-405) reference materials. The concentrations obtained by solid-spiking fs-LA-ICP-IDMS were in agreement not only with the certified values but also with those obtained by ICP-IDMS after the microwave-assisted digestion of the solid samples, demonstrating therefore the validity of the proposed solid-spiking procedure for a rapid and accurate analysis of solid samples.

Selected isotope ratio measurements of light metallic elements (Li, Mg, Ca, and Cu) by multiple collector ICP-MS.

The unique capabilities of multiple collector inductively coupled mass spectrometry (MC-ICP-MS) for high precision isotope ratio measurements in light elements as Li, Mg, Ca, and Cu are reviewed in this paper. These elements have been intensively studied at the Geological Survey of Israel (GSI) and other laboratories over the past few years, and the methods used to obtain high precision isotope analyses are discussed in detail. The scientific study of isotopic fractionation of these elements is significant for achieving a better understanding of geochemical and biochemical processes in nature and the environment.

Environmental applications of single collector high resolution ICP-MS

The number of environmental applications of single collector high resolution ICP-MS (HR-ICP-MS) has increased rapidly in recent years. There are many factors that contribute to make HR-ICP-MS a very powerful tool in environmental analysis. They include the extremely low detection limits achievable, tremendously high sensitivity, the ability to separate ICP-MS signals of the analyte from spectral interferences, enabling the reliable determination of many trace elements, and the reasonable precision of isotope ratio measurements. These assets are improved even further using high efficiency sample introduction systems. Therefore, external factors such as the stability of laboratory blanks are frequently the limiting factor in HR-ICP-MS analysis rather than the detection power. This review aims to highlight the most recent applications of HR-ICP-MS in this sector, focusing on matrices and applications where the superior capabilities of the instrumental technique are most useful and often ultimately required.

239 + 240Pu concentration and isotope ratio (240Pu/239Pu) in aerosols during high dust (Yellow Sand) period, Korea

Concentration and isotope ratio of Pu were analyzed for aerosols collected at Anmyeondo located in the western coast of Korea using multiple collector inductively coupled plasma mass spectrometer equipped with desolvated micro-concentric nebulizer. Aerosols were collected from June 2001 to April 2002 using high volume air sampler. The samples consist of high dust samples (Yellow Sand), and also low dust samples; maximum Al concentration was 74.2 μg/m3 and minimum was 0.17 μg/m3.Pu was concentrated using 0.1 ml TEVA resin columns after conc. HNO3 extraction. Isotope dilution using 242Pu spike and mass bias correction using 233U and 236U mixed solution enabled the quantification of Pu and measurement of isotope ratio simultaneously. The contribution of 238U from both spikes and samples was minimized by careful chemical separation and optimization of spike concentration. The 238U1H and tail contribution on 239Pu peak were about 0.75×10−5 and 1×10−5 of 238U intensity, respectively, and they were corrected from 239Pu using externally determined (238U1H+tailing)/238U ratio and 238U measurement during acquisition. The detection limits of this analytical procedure were 0.61 fg/ml and 0.56 fg/ml for 239Pu and 240Pu, respectively (4 nBq/m3 and 12 nBq/m3 for 239Pu and 240Pu, respectively). The precision of isotope ratio measurement was better than 2% for larger quantity than 20 fg of 239Pu.In spring, maximum concentration of 0.580 μBq/m3 for 239Pu and 0.404 μBq/m3 for 240Pu was observed when Al concentration was maximum, so called as Yellow Sand event. Pu concentrations in aerosols are well correlated with Al, a tracer of soil dust. The ratios of Pu/Al were 0.0082 (μBq/μg) and 0.0055 (μBq/μg) for 239Pu/Al and 240Pu/Al, respectively. Isotope ratios of Pu (240Pu/239Pu) in Yellow Sand samples show 0.191±0.014 close to those of global fallout. These facts indicate that Yellow Sand plays an important role in the behavior of Pu in the environment like other concomitant metals such as Al, Fe etc.

Precise ruthenium fission product isotopic analysis using dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS)

99 Tc is a contaminant of interest at numerous nuclear facilities because it is quite mobile in sub-surface environments and is a key contributor to long-term risk. However, as a mono-isotopic fission product, 99Tc is limited in its use as a signature to differentiate between different waste disposal pathways that could have contributed to sub-surface contamination at these facilities. Ruthenium fission-product isotopes are attractive analogues for the characterization of 99Tc sources because of their direct similarity to technetium with regard to subsurface mobility, their large fission yields, and low natural background concentrations. We developed an inductively coupled plasma mass spectrometry (ICP-MS) method capable of measuring ruthenium isotopes in groundwater samples and water extracts of vadose zone sediments. Samples were analyzed directly on a PerkinElmer ELAN DRC II ICP-MS after a single pass through a 1-ml bed volume of Dowex AG 50W-X8 100–200 mesh hydronium-based cation exchange resin. Precise ruthenium isotopic ratio measurements were achieved using a low-flow Meinhard-type nebulizer and long sample acquisition times (150000 ms). Relative standard deviations of triplicate replicates were maintained at less than 0.5% when the total ruthenium solution concentration was 0.1 ng ml−1 or higher. Further work was performed to minimize the impact caused by mass interferences using the dynamic reaction cell (DRC) with O2 as the reaction gas. Aqueous concentrations of 96Mo and 96Zr, two potential interferents to the analysis of total ruthenium concentration, were reduced by more than 99.7% in the reaction cell prior to injection of the sample into the mass analyzer quadrupole. The DRC was used in combination with mass correction to quantitatively analyze samples containing up to two orders of magnitude more zirconium and molybdenum than ruthenium. The analytical approach documented herein provides an efficient and cost-effective way to precisely measure ruthenium isotopes and quantitate total ruthenium (natural versus fission-product) in aqueous matrixes.

Atomic spectrometry update. Environmental analysis

This is the twenty-first annual review published in JAAS of the application of atomic spectrometry to the chemical analysis of environmental samples. In the analysis of air, there is ongoing development of instrumentation for the interrogation of particles at the nanometre scale. It would seem that there is continuing interest in the measurement of trace levels of mercury species in the atmosphere, particularly those emissions from point sources such as coal-fired power stations. In the analysis of water, elemental speciation protocols have again received considerable attention and there is a renewed trend for using methods based on vapour generation for the determination of selected elements. Dominant themes in the analysis of soils include the application of sequential extraction techniques and the continuing development of speciation protocols for elements such as As, Hg and Se. Laser ablation is readily being adopted as a solid sampling tool in many geochemical laboratories. In a similar vein, multi-collector ICP-MS is increasingly being used to perform high precision isotope ratio measurements. Not only is the focus on developing robust measurement procedures for routine use but also on carrying out more fundamental work, designed to increase our understanding of these techniques.

Precise Zn Isotopic Ratio Measurements of Human Red Blood Cell and Hair Samples by Multiple Collector-ICP-Mass Spectrometry

Precise 66Zn/64Zn and 68Zn/64Zn isotopic ratios of biochemical samples have been measured using multiple collector-ICP-mass spectrometry (MC-ICPMS). In order to eliminate the mass spectrometric interferences on Zn isotopes (e.g., 64Ni+ and 136Ba2+), we chemically purified the analyte using an ion chromatographic technique. The resulting precisions of the 66Zn/64Zn and 68Zn/64Zn ratio measurements were 0.05/1000 and 0.10/1000 (2SD), respectively, which were enough to detect the isotopic variation of Zn in nature. Red blood cell (RBC) samples were collected from five volunteers (four males and one female), including a series of 12 RBC samples from one person through monthly-based sampling over a year. These were analyzed to test possible seasonal changes and variations in 66Zn/64Zn and 68Zn/64Zn ratios among the individuals. The 66Zn/64Zn and 68Zn/64Zn ratios for a series of 12 RBC samples collected over a year were 0.43/1000 and 0.83/1000 higher than the values of highly purified Zn metal (JMC Zn), and no seasonal change could be found. The 66Zn/64Zn and 68Zn/64Zn ratios for RBC samples collected from five volunteers did not vary significantly. In order to investigate Zn isotopic heterogeneity in a human body, Zn isotopic ratios of a hair sample collected from one of the volunteers was also analyzed. The 66Zn/64Zn and 68Zn/64Zn ratios for the hair sample were 0.59/1000 and 1.14/1000 lower than the mean value of RBC samples. This result demonstrates that detectable isotopic fractionation occurs in the human body. The data obtained here suggest that the isotopic ratios of trace metals could provide new information about transportation of metal elements in vivo.

Isotope ratios on transient signals with GC–MC–ICP-MS

ICP-MS instruments with multiple ion collectors (MC–ICP-MS) provide highly precise and accurate isotope ratio measurements. These instruments are easily coupled to chromatography, laser ablation or flow injection devices because of the ICP source, and thus attract general analytical interest for measurement of highly precise element isotope ratios on transient signals. Some few papers have been published today where MC–ICP-MS was employed for isotope ratios on transient signals, and in general, results are encouraging. Isotope ratio precision obtained is usually at least 10-fold superior compared to measurements with ICP-QMS. Nevertheless, most authors describe a drift of isotope ratios during the transient peak. This behaviour was either interpreted as a problem in the sample introduction system, or was related to instrumental mass bias drift, but has to date not been completely evaluated or explained. In this paper, we systematically investigate the drift observed on lead and mercury isotopes during short transient signals obtained from GC coupled to different MC–ICP-MS systems. We can clearly show that neither changes in instrumental mass bias, nor chromatographic fractionation effects are the source of the observed isotope ratio drift. An influence of analyte concentration on the observed drift was as well excluded as a source for this drift, because the slope on isotope ratios show the same values for different concentrations evaluated. In contrast, the peak width was found to influence the extent to which the isotope ratio drifts during peak elution. Thus, the relative intensity change per time seems to be an important factor for the measurements of transient signals with MC–ICP-MS.

Isotope ratio precision with transient sample introduction using ICP orthogonal acceleration time-of-flight mass spectrometry

An assessment of inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry (ICP-oa-TOF-MS) for measurement of isotope ratios arising from steady-state and transient signal detection is presented. An HPLC pump and autosampler were used to introduce microliter volumes of analyte solution into a carrier flow to generate precise and repeatable transient signals having a FWHM of approximately 1 s. Analog and pseudo pulse data processing modes were evaluated and found to obey Poisson statistics for prediction of isotope ratio performance. Use of pseudo pulse counting is restricted by the limited linear range of response and cannot exceed approximately 0.2 counts per pushout. This limitation does not impede analog detection, which thus permits precise isotope ratio measurements to be achieved at higher analyte concentrations using shorter integration times. For transient signals, area measurements are superior to averaging point-to-point measurements across the peak for optimum ratio precision. Although the TOF system provides for simultaneous sampling of the extracted pulse, thereby permitting elimination of correlated noise through ratioing techniques, detection remains sequential and noise components present in the detection system limit isotope ratio precision in this study to 0.04% RSD.

Feasibility study of solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of particulate uranium in swipe samples from nuclear facilities

The feasibility of a solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for “the particle analysis of safeguards environmental swipe samples” was studied with polycarbonate (PC) film samples containing thallium (Tl), lead (Pb) and uranium (U) particles in single element and with their solution sample. The influences of instrumental operating conditions on analytical results, especially accuracy and precision in isotope ratio measurements, were investigated. Isotope ratios obtained for Tl and Pb solution samples containing a few picogram amounts of particles were in good agreement with the reference values obtained using pneumatic nebulizer ICP-MS. It is revealed that when vaporization temperature was set to be optimal, the pyrolysis temperatures in the temperature range of this study did not affect the magnitude of integrated signals. Isotope ratios obtained for PC film samples including a few picogram amounts of particles were comparable to those of solution samples, and good values of isotope ratio were obtained in the wide range of measurement parameters even though analyte losses occurred in inappropriate temperature conditions. The pyrolysis and vaporization temperature dependence of the integrated signal was different from those of the solution sample, which is ascribed to the difference of transport efficiency of the vaporized analyte in both samples. Absolute limit of detection for PC film sample was found to be about 2 fg, which corresponds to 2 pg/g for a typical sample mass of 1 mg.

Accurate and precise Pb isotope ratio measurements in environmental samples by MC-ICP-MS

Analytical protocols for accurate and precise Pb isotope ratio determinations in peat, lichen, vegetable, chimney dust, and ore-bearing granites using MC-ICP-MS and their application to environmental studies are presented. Acid dissolution of various matrix types was achieved using high temperature/high pressure microwave and hot plate digestion procedures. The digests were passed through a column packed with EiChrom Sr-resin employing only hydrochloric acid and one column passage. This simplified column chemistry allowed high sample throughput. Typically, internal precisions for approximately 30 ng Pb were below 100 ppm (±2 σ) on all Pb ratios in all matrices. Thallium was employed to correct for mass discrimination effects and the achieved accuracy was below 80 ppm for all ratios. This involved an optimization procedure for the 205 Tl/ 203 Tl ratio using least square fits relative to certified NIST-SRM 981 Pb values. The long-term reproducibility (±2 σ) for the NIST-SRM 981 Pb standard over a 5-month period (35 measurements) was better than 350 ppm for all ratios. Selected ore-bearing granites were measured with TIMS and MC-ICP-MS and showed good correlation (e.g., r=0.999 for 206 Pb/ 207 Pb ratios, slope=0.996, n=13). Mass bias and signal intensities of Tl spiked into natural (after matrix separation) and in synthetic samples did not differ significantly, indicating that any residual components of the complex peat and lichen matrix did not influence mass bias correction. Environmental samples with very different matrices were analyzed during two different studies: (i) lichens, vegetables, and chimney dust around a Cu smelter in the Urals, and (ii) peat samples from an ombrotrophic bog in the Faroe Islands. The presented procedure for sample preparation, mass spectrometry, and data processing tools resulted in accurate and precise Pb isotope data that allowed the reliable differentiation and identification of Pb sources with variations as small as 0.7% for 206 Pb/ 207 Pb .

Determination of trace elements in serum samples by isotope dilution inductively coupled plasma mass spectrometry using on-line dialysis

An on-line dialysis flow system coupled to inductively coupled plasma mass spectrometry to determine trace elements in serum samples by isotope dilution is presented. Isotope dilution was performed on samples incubated with enriched 65Cu, 66Zn, 77Se and 206Pb for 24 h at 36 °C prior to dialysis to quantified total element concentrations. The sample and acceptor solutions flowed through the dialysis unit with cellophane membrane placed in between the compartments. The serum sample (1 mL) was left to recycle in a closed path while the acceptor solution was continuously pumped along the dialyzer channel and through a cationic AG50W X-8 resin column. After 10 min, around 70% of Na, K and Cl migrate from the sample. Three replicate injections of 0.1 mL were performed for the clean sample after each separation step. The on-line coupling of the dialyzer to ICP-MS allowed isotope dilution for total element determination either in the cleaned sample or by eluting the cations retained in the resin to be carried out. Results demonstrated no matrix effects from alkaline elements or spectral interference from ArNa+ on 63Cu, ArCl+ on 77Se and 34SO2+ on 66Zn. The precision of isotope ratio measurements for Cu and Zn was around 1% and for Se and Pb was around 2.5%. The values found for the reference serum sample IMEP-17 were in good agreement with the certified values for Cu, Zn and Se.

Analytical Methods for Non-Traditional Isotopes

This chapter is devoted to the analytical methods employed for making high precision isotope ratio measurements that preserve naturally occurring mass-dependent isotopic variations. The biggest challenge in making these types of measurements is deconvolving mass-dependent isotopic fractionation produced in the laboratory and mass spectrometer, from naturally occurring mass-dependent isotopic fractionation, because the patterns of isotope variation produced by these processes are identical. Therefore, the main theme of this chapter is the description and mathematical treatment of mass-dependent isotopic variations and the possible pitfalls in deconvolving instrumental mass bias from naturally occurring mass-dependent isotopic variations. This chapter will not attempt to catalog methods for isotopic analysis of different elements. These details are better discussed in later chapters where ‘element specific’ analytical issues are covered. Rather, the effort in the chapter will be to focus on those specific items that make mass analysis of non-traditional isotopes challenging and unique, and the methods that can be employed to make precise and accurate isotope ratios. Isotopic analysis of non-traditional isotopes is made using three main types of mass spectrometers. Elements that can easily be introduced as gases, such as Cl or Br, are typically analyzed using a gas source mass spectrometer. In contrast, metal elements are analyzed using either a thermalionization mass spectrometer (TIMS) or a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). The main difference between these three types of instruments is how the sample is introduced into the instrument, and how the sample is ionized. In contrast, the analyzer part of each instrument is similar. All three types of instruments use a stack of lenses with variable potential to focus the ion beam, a magnet to resolve the ion beam into different masses, and a series of collectors to measure ion currents of different isotopes simultaneously. The core of the mass analyzer …

Determination of rhenium and osmium concentrations in molybdenite using laser ablation double focusing sector field ICP-MS

A technique for the in situ determination of Re and Os in molybdenite samples using direct solid sampling by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is described. The sample preparation is limited to molybdenite separation followed by grinding and pressing to pellets. For Re determination, the best results were obtained using external calibration in conjunction with internal standardization. Isotopes of both molybdenum and sulphur could be used as internal standards. This quantification approach provides precision levels generally better than 10% the relative standard deviation (RSD) with similar levels of accuracy. Os concentrations were derived from Re concentrations and measured isotopic ratios of intensities measured at masses 187 and 185, using W isotopes for on-line mass bias correction. As a rule, LA-ICP-MS results for Os agree with corresponding isotope dilution ICP-MS data to within 30%. Reproducibility is strongly dependent on the age of the molybdenite as well as on the precision of isotope ratio measurements, which in turn depend on Re and W concentrations. The proposed technique provides a rapid estimation of Re and Os concentrations for subsequent precise analysis by isotope dilution ICP-MS.