Showing papers in "Journal of Analytical Atomic Spectrometry in 2014"

What happens when n= 1000? Creating large-n geochronological datasets with LA-ICP-MS for geologic investigations

Abstract: The direct age dating of individual mineral components in sedimentary rocks through the analysis of radiogenic parent and daughter isotopes has been routinely applied to better understand sediment provenance and dispersal patterns for several decades. Time, labor, and financial cost—sadly, not scientific inquiry—are typically the determining factors in the number of analyses run for a sedimentary rock sample during provenance investigations. The number of observations reported for detrital zircon provenance investigations using secondary ion mass spectrometers SIMS and laser-ablation inductively-coupled-plasma mass-spectrometers LA-ICP-MS typically range from n = 60–120. In this range, minor, but commonly geological relevant, age components are commonly not identified from the sample aliquot. In addition, the relative proportions of zircon ages from within an age component are typically unreliable for intersample comparisons because the relative proportions of ages from aliquots of n = 60–120 may poorly reflect the ‘true’ proportions of ages from a sample. This study investigates the practicality and usefulness of generating large-n (n = 300–1000) datasets. A LA-MC-ICP-MS and LA-SC-ICP-MS were used to generate four n ≈ 1000 datasets. We show that precision large-n U–Pb detrital zircon datasets can be created using LA-ICP-MS with total sample-run analysis times that are on par with more traditional studies. At best, most provenance investigations based on n = 60–100 have been statistically limited to identifying principle age components. The statistical robustness on n = 1000 datasets not only significantly increase the probability that exotic or low abundance age components (i.e., f < 0.05) are identified in detrital samples, but it allows for the quantitative comparisons between relatively high abundance age components in samples. This potentially transformative outcome of large-n has the potential to stimulate new avenues of research in sedimentology and tectonics.

High-precision copper and iron isotope analysis of igneous rock standards by MC-ICP-MS

Abstract: Stable isotopic systematics of Cu and Fe are two important tracers for geological and biological processes. Generally, separation of Cu and Fe from a matrix was achieved by two independent, completely different methods. In this study, we report a method for one-step anion-exchange separation of Cu and Fe from a matrix for igneous rocks using strong anion resin AG-MP-1M. Cu and Fe isotopic ratios were measured by multi-collector inductively coupled plasma mass-spectrometry (Neptune plus) using a sample–standard bracketing method. External normalization using Zn to correct for instrumental bias was also adopted for Cu isotopic measurement of some samples. In addition, all parameters that could affect the accuracy and precision of isotopic measurements were examined. Long-term external reproducibility better than ±0.05‰ (2SD) for δ65Cu and ±0.049‰ (2SD) for δ56Fe was routinely obtained. Cu and Fe isotopic compositions of commercially accessible igneous rock standards including basalt, diabase, amphibolite, andesite and granodiorite were measured using this method. δ65Cu values of igneous rock standards vary from −0.01 to +0.39‰ (n = 11) with an overall range (0.40‰) that exceeds about 8 times that of the current analytical precision. The improved precisions of stable Cu isotopic analysis thus demonstrate that igneous rocks are not homogeneous in Cu isotopic composition. The procedure for one-step separation of Cu and Fe and high-precision analysis of Cu and Fe isotopic ratios have an important advantage for economical and efficient study of stable Cu and Fe isotopic systematics in geological and biological fields.

Review of the applications of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to the analysis of biological samples

Abstract: Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has received significant attention over the last 10 years and has been widely used for the analysis of biological samples. The technique allows the determination of elements and isotopes in biological tissues and related materials with a spatial resolution typically ranging from 10 to 100 μm. When compared to other techniques usually employed to obtain bioimages, the greater advantage of LA-ICP-MS is its higher sensitivity. The literature survey over the last 10 years concerning the use of LA-ICP-MS for biological tissue analysis is reviewed in this article. Instrumentation, strategies of calibration for quantitative analysis, challenges and recent advances in this field are discussed. Applications of the isotope ratio (IR), including tracer experiments, and isotope dilution (ID), are reviewed for biological samples (briefly for proteins, in order to show the utility of LA-ICP-MS). Bioimaging methods, studies and applications for animal and plants tissues are emphasized, demonstrating the importance of bioimaging of metals and metalloids in biomedical research, bioaccumulation and bioavailability studies for ecological and toxicological risk assessment in humans, animals and plants. The usefulness of the IR associated with bioimaging for predicting geographical origin, habitat, movement of subjects, diet and lifestyle are also demonstrated.

Rapid, simultaneous separation of Sr, Pb, and Nd by extraction chromatography prior to isotope ratios determination by TIMS and MC-ICP-MS

Abstract: A straightforward separation scheme is described for the separation of Sr, Pb, and Nd from silicate rocks. It allows the concomitant isolation, without any intervening evaporation, of these three elements of great interest in radiogenic isotope geology and cosmochemistry. Following digestion with HF–HNO3, the sample residue is dissolved in 1 M HNO3. After addition of ascorbic acid to reduce Fe(III) to Fe(II), this solution is passed through two tandem columns containing 250 μL of Sr Spec and TRU Spec extraction chromatography resins, respectively. The upper Sr Spec column extracts Sr and Pb, while the lower TRU Spec column extracts the LREE. Sr and Pb are back-extracted with 0.05 M HNO3 and 6 M HCl, respectively. The LREE are eluted directly onto a longer column containing 300 mg of the HDEHP-based EXC material Ln Spec, to obtain, through sequential elution with 0.25 M HCl, a Nd fraction free of any Sm contribution. The whole procedure is achieved within a single working day. The Sr and Nd fractions separated in this way are ready for isotope ratio measurements by TIMS (Sr, Nd) or MC-ICP-MS (Nd). The Pb fraction is converted to the nitrate form before isotopic analysis by MC-ICP-MS. The potential of this method is exemplified by analysis of different powder aliquots of several iron-rich, international standard rocks of basaltic composition.

Atomic spectrometry update – a review of advances in environmental analysis

Abstract: This is the 30th annual review of the application of atomic spectrometry to the chemical analysis of environmental samples. This Update refers to papers published approximately between August 2013 and July 2014 and continues the series of Atomic Spectrometry Updates (ASUs) in environmental analysis that should be read in conjunction with other related ASUs in the series, namely: clinical and biological materials, foods and beverages, advances in atomic spectrometry and related techniques, elemental speciation,X-ray fluorescence spectrometry, and the analysis of metals, chemicals and functional materials. In the field of air analysis, highlights within this review period included: the use of 3D printing technology for the rapid prototyping of new air sampler components; single particle ICP-MS studies; use of a new triple-quadrupole ICP-MS for the analysis of radioactive species and the use of FEG-SEM and IBA for the analysis of gun-shot residues. In the field of water analysis, methods continue to be developed: for the extraction and preconcentration of elements; speciation of As, Cr, Hg and Sb forms and determination of elemental constituents in colloidal and NP fractions. Instrumental developments reported include the use of MC-ICP-MS for isotopic tracer studies and a review of XRF techniques and associated preconcentration procedures for trace element analysis. Many articles featuring the analysis of plants and soils appeared but, as usual, most focused on environmental applications rather than the advancement of atomic spectrometry. There have, however, been interesting developments, such as the almost bewildering increase in types of micro-extraction for analyte preconcentration and the resurgence of CS-AAS. Clearly LIBS is maturing rapidly, with soil analysis becoming more routine in nature. Also notable was the way the accident at the Fukishima-Daiichi nuclear power plant triggered development of analytical methods for the assessment of contamination in the surrounding area. Recent research indicates that geological applications still drives many of the instrumental and methodological advances in LA-ICP-MS. Fundamental studies continue to shed light on the processes involved and hence ways of improving the analysis of laser-produced aerosols. The preparation of NP powders for the production of matrix-matched RMs for microanalytical techniques such as LA-ICP-MS and SIMS showed great promise for addressing one of the major issues when analysing geological materials by these techniques. Steady advances in MC-ICP-MS methodology is feeding through to applications in isotope geochemistry, while new SIMS instrumentation is being directed towards probing fine growth structures in biogenic carbonates and inferring past climate conditions from their geochemistry. Feedback on this review is most welcome and the review coordinator can be contacted using the email address provided.

An XPS/AES comparative study of the surface behaviour of nano-silicon anodes for Li-ion batteries

Abstract: In this paper, the surface of composite electrodes made of nano-silicon is studied by using two surface characterization techniques: X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). Several electrodes were analyzed at different States Of Charge (SOC) during the first electrochemical cycle. Firstly, the Solid Electrolyte Interphase (SEI) as well as the Si oxides present at the particle surface were thoroughly investigated. The behaviour of the SEI is close to that which forms on graphite: (i) its composition is similar and (ii) its thickness is greater at the lithiated state. Besides, our AES analyses carried out at the end of the first electrochemical cycle demonstrate that this behaviour strongly depends on the material it forms on: silicon or carbon fibers. Concerning SiO2, which is initially present at the Si particles' surface, it is reduced irreversibly during the first lithiation. Simultaneously, our results clearly show the formation of Li2O and LixSiOy; these species are still observed during the aging of the electrode and systematically react at each cycle. Secondly, by using AES combined with a sputtering technique, the first lithium insertion and the associated LixSi alloys were studied: several Si particles were investigated individually with respect to their electrode environment. After a capacity of 360 mA h g−1, the estimated Li concentration is different from one Si particle to another indicating that the first lithiation is a strongly heterogeneous process.

Nano-particulate pressed powder tablets for LA-ICP-MS

Abstract: We developed an advanced method for producing undiluted nano-particulate pressed powder tablets without addition of any binder applying wet-milling protocols in aqueous suspension using a high power planetary ball mill and agate tools. The method was tested and optimized for the milling time, ball size, ball-to-powder ratio and water-to-powder ratio using pulverized diorite DR-N containing abundant zircon crystals that are especially difficult to break down by both milling and acid-digestion methods. The new method produces nano-particulate powders with typical grain size d50 < 1.5 μm allowing us to form pressed powder tablets with excellent cohesion and homogeneity suitable for laser ablation micro-analysis. The optimized milling protocol was applied to a selection of other natural rock CRMs (BHVO-2, JGb-1, UB-N, AC-E, GA) covering a wide range of rock types, and formed powder tablets were analyzed by LA-ICPMS. Precision was found to be in the same range of <2–5%RSD as it is obtained from laser ablation analysis of glasses (e.g., volcanic glasses, vitrified rock powders), and preferred values could be reproduced within uncertainty for most of the 38 trace and ultra-trace elements analyzed. Our new method accomplishes the preparation of refractory sample materials or materials containing refractory mineral phases (e.g., plutonic rocks and sediments, ultramafic rocks, oxides as in banded iron formation, ceramics) for subsequent analysis by LA-ICPMS. Even more importantly, this method opens up new prospects for the manufacturing (and possibly isotopic spiking) of homogenized reference materials from natural minerals that are urgently needed for true matrix-matched calibration and validation of LA-ICP-MS geochemical and isotope data.

Effect of dwell time on single particle inductively coupled plasma mass spectrometry data acquisition quality

Abstract: The characterization, sizing, and quantification of metal-based nanoparticles (NP) in a variety of matrices using single particle-inductively coupled plasma-mass spectrometry (SP-ICP-MS) is becoming increasingly popular due to the sensitive nature of the technique. Nanoparticle events in the plasma are less than 0.5 ms in duration; however current quadrupole-based ICP-MS instruments are limited to instrument dwell times in the millisecond range and have data acquisition overhead that adversely affects data quality. Novel instrument settings and data processing techniques can be used to explore the benefits of continuous data acquisition rates as fast as 105 Hz (or 10 μs dwell times). This paper provides data on the different effects data acquisition rate has on the quality of data that can be obtained by SP-ICP-MS. The effect of varying the dwell time and its influence on particle integration, particle counting, particle sizing, and background signal is discussed. This paper provides data on identifying the significant instrument settings and their implications on nanoparticle characterization.

LA-ICP-MS Pb–U dating of young zircons from the Kos–Nisyros volcanic centre, SE Aegean arc

Abstract: Zircon Pb–U dating has become a key technique for answering many important questions in geosciences. This paper describes a new LA-ICP-MS approach. We show, using previously dated samples of a large quaternary rhyolitic eruption in the Kos–Nisyros volcanic centre (the 161 ka Kos Plateau Tuff), that the precision of our LA-ICP-MS method is as good as via SHRIMP, while ID-TIMS measurements confirm the accuracy. Gradational age distribution over >140 ka of the Kos zircons and the near-absence of inherited cores indicate near-continuous crystallisation in a growing magma reservoir with little input from wall rocks. Previously undated silicic eruptions from Nisyros volcano (Lower Pumice, Nikia Flow, Upper Pumice), which are stratigraphically constrained to have happened after the Kos Plateau Tuff, are dated to be younger than respectively 124 ± 35 ka, 111 ± 42 ka and 70 ± 24 ka. Samples younger than 1 Ma were corrected for initial thorium disequilibrium using a new formula that also accounts for disequilibrium in 230Th decay.

A novel approach for the quantitative analysis of multiple elements in steel based on laser-induced breakdown spectroscopy (LIBS) and random forest regression (RFR)

Abstract: A novel method based on laser induced breakdown spectroscopy (LIBS) and random forest regression (RFR) was proposed for the quantitative analysis of multiple elements in fourteen steel samples. Normalized LIBS spectra of steel with characteristic lines (Si, Mn, Cr, Ni and Cu) identified by the NIST database were used as analysis spectra. Then, two parameters of RFR were optimized by out-of-bag (OOB) error estimation. The performance of the calibration model was investigated by different input variables (the whole spectral bands (220–800 nm) and spectra feature bands (220–400 nm)). In order to validate the predictive ability of the multiple element calibration RFR model in steel, we compared RFR with partial least-squares (PLS) and support vector machines (SVM) by means of prediction accuracy and root mean square error (RMSE). Thus, the RFR model can eliminate the influence of nonlinear factors due to self-absorption in the plasma and provide a better predictive result. This confirms that the LIBS technique coupled with RFR has good potential for use in the in situ rapid determination of multiple elements in steel and even in the field of metallurgy.

Lead isotope analysis of melt inclusions by LA-MC-ICP-MS

Abstract: Pb isotope compositions of melt inclusions provide unique information about the composition of primary magmas and their source In this study, we have developed a method for measuring Pb isotopes in small olivine-hosted melt inclusions (>40 μm) from young and old volcanoes by LA-MC-ICP-MS We used a new interface cone assemblage consisting of a Jet sample cone and X skimmer cone A small flow of N2 gas was added to the carrier gas and passed through the assemblage to enhance the signal intensity In addition the energy and repetition rate of the laser conditions were reduced and the signal integration time was shortened in order to lengthen the laser ablation time and to collect enough data Mass bias and instrument drift were corrected using a standard–sample–standard bracketing method The analysis routine employed eight ion counters to receive 238U, 235U, 232Th, 208Pb, 207Pb, 206Pb, 204Pb and 202Hg signals simultaneously, which allowed Hg interference to be corrected on 204Pb, and in old samples U–Th decay to be age-corrected Using the Jet and X cones, under the same laser ablation conditions, the precisions for almost all the measured standard glasses are improved by at least a factor of two compared to using standard cones At 208Pb signal intensity >200 000 cps, external precisions of ratios involving 204Pb are better than 13% (2RSD) and precisions of 208Pb/206Pb and 207Pb/206Pb are better than 023% (2RSD) The results of Pb isotopes in olivine-hosted melt inclusions, using 45 μm laser spots, show that the internal precisions of 208Pb/206Pb and 207Pb/206Pb for most analyzed melt inclusions are better than 02% (2RSE) and for ratios involving 204Pb are better than 08% (2RSE) We are able to present the first ever Pb isotope data from ∼260 Ma Emeishan flood basalt olivine-hosted melt inclusions They show the importance to do age correction which results in the reduction of the spread of data in old samples The mean values of age-corrected 208Pb/206Pb and 207Pb/206Pb have 12% and 28% deviations from the uncorrected mean values, respectively The method developed here provides a fast, precise and accurate in situ Pb isotopic composition analysis, applicable not only to melt inclusions from young basalts, but also from old samples that require correction for U–Th decay

A signal deconvolution method to discriminate smaller nanoparticles in single particle ICP-MS

Abstract: Single particle ICP-MS (spICP-MS) analysis of inorganic nanoparticles (NPs) cannot accurately distinguish dissolved ion signals and signals from relatively small NPs, although these particles are often more reactive than their larger counterparts. A signal deconvolution method was developed for spICP-MS analysis using gold (Au) NPs of nominally 10, 15 or 30 nm diameter. The signal distributions of dissolved Au standards were parameterised as a function of concentration using a mixed Polyagaussian probability mass function. Dissolved curves were fitted using this parameterisation to the low-intensity signals of samples containing NPs to subtract and deconvolute the dissolved signals from the particle signals. The dissolved signals were quantified in this process. The accuracy of the deconvolution method was confirmed for all NP suspensions studied when comparing the size and number concentration obtained with the deconvolution method with values based on transmission electron microscopy. This method thus allows analysis of NP suspensions with spICP-MS where it was hitherto not possible. The applicability domain lies predominantly with relatively small NPs and/or when a relatively high concentration of dissolved ions of the element of interest is present, where overlapping between dissolved and particulate signals occurs.

Optimisation of laser parameters for the analysis of sulphur isotopes in sulphide minerals by laser ablation ICP-MS

Abstract: The effects of laser type (Nd:YAG and excimer lasers) and their analytical parameters on 34S/32S isotopic fractionation during LA-ICP-MS analysis were investigated. Laser fluence has a larger fractionation effect when ablating pyrite with the New Wave Nd:YAG 193 nm laser, compared to the Resonetics 193 nm excimer laser which did not produce significant fractionation over the same range of fluence (1.3–3.7 J cm−2). Matrix effects occurred between pyrite and bornite on both laser systems, especially at low fluence. However, matrix effects can be reduced with increasing fluence lessening the need for matrix matched reference materials. The effects of interface tubing configuration were also investigated and the addition of a ‘squid’ mixing device, a coil of small diameter Tygon tubing and a small volume glass bulb, was found to improve signal precision and reproducibility and decrease the washout time of the S signal between analyses. The degassing of air from the inner surfaces of the interface tubing can produce significant isotopic drift (8‰ h−1), hence flushing the tubing prior to analyses is crucial for reproducible analyses. The isotopic composition and homogeneity of a range of sulphide minerals were characterised for use as potential reference materials. We present preliminary data for a large, isotopically homogeneous pyrite crystal (PPP-1) which could be considered as a new isotopic reference material (δ34SV-CDT = 5.3 ± 0.2‰).

High-resolution continuum source graphite furnace atomic absorption spectrometry for direct analysis of solid samples and complex materials: a tutorial review

Abstract: The purpose of this review is to examine the literature devoted to direct sample analysis using high-resolution continuum source atomic absorption spectrometry in a tutorial way, in an attempt to provide guidelines on the most critical issues to consider when developing a new method. This review discusses in detail the advantages and limitations of this technique, highlighting its benefits in comparison with classic line source atomic absorption spectrometry instrumentation in the context of direct analysis of solid samples, slurries and complex liquid samples, trying to establish in which situations the use of this technique can be particularly beneficial. Some of the aspects that are addressed comprise: (i) the improved potential to detect and correct for spectral interferences; (ii) the different options to adjust the sensitivity to the analyte content; (iii) strategies to minimize matrix effects and calibrate with aqueous standard solutions; (iv) possibilities to carry out multi-element analysis.

Collection of atmospheric gaseous mercury for stable isotope analysis using iodine- and chlorine-impregnated activated carbon traps

Abstract: The trace levels of Hg in the atmosphere pose an analytical challenge for Hg stable isotope research. Here we propose a new method using iodine- and chlorine-impregnated activated carbon (IC and CLC) traps for collection of atmospheric total gaseous mercury (TGM). Decontamination of IC and CLC yielded low blank levels of 0.3 ng Hg per g of carbon, corresponding to 92%) at flow rates of 2, 10, and 20 LPM respectively. These flow rates enabled high-resolution (12–24 h) and low-resolution (bi-weekly) sampling of TGM. We also tested bi-weekly TGM sampling using commercial gold traps at a low flow rate of 0.3 LPM. TGM collected on IC and CLC traps at the Pic du Midi Observatory was desorbed and pre-concentrated into aqueous solution using an off-line combustion and trapping technique. Hg isotopic compositions were determined using cold vapor multicollector-inductively coupled plasma-mass spectrometry (CV-MC-ICPMS). The field measurements showed mean recoveries of 88 ± 5% (1σ, n = 11) for 12 h and 24 h and 90 ± 6% (1σ, n = 25) for the bi-weekly field samples. Laboratory additions of Hg vapor of known isotopic composition to CLC and gold traps indicated that recoveries >81% did not induce isotopic artifacts. Samples with recoveries <81% showed a positive mass dependent fractionation bias. Typical expanded uncertainties (2σ) on δ202Hg (mass dependent fractionation of 202Hg) and Δ199Hg (mass independent fractionation of 199Hg) for the bi-weekly sampling, processing and CV-MC-ICPMS analysis are 0.13‰ and 0.09‰, respectively. Our study suggests that the proposed method meets the criteria for accurate and precise measurements of atmospheric TGM isotopic compositions.

Basic mechanisms of signal enhancement in ns double-pulse laser-induced breakdown spectroscopy in a gas environment

Abstract: Understanding the mechanisms of the signal enhancement in double-pulse laser-induced breakdown spectroscopy is highly desirable. It is evident, however, that it is not possible to fit a unique general model to the observations obtained in collinear or in orthogonal geometries, in pre-spark or in re-heating schemes, using ns or fs pulses, in a gas or liquid environment. We believe, instead, that by considering separately the specific experimental cases (for example: a given irradiation geometry, a given pulse timing, etc.) the comprehension of the processes occurring during double-pulse experiments might become easier. We focus on one specific experimental case, namely ns double-pulse irradiation of solid targets in a gaseous environment, and classify the experiments according to the irradiation mode (orthogonal pre-spark, collinear and orthogonal re-heating). Then, we propose a description of the processes occurring in the different cases, on the basis of data and interpretations that are available in the literature.

The zircon ‘matrix effect’: Evidence for an ablation rate control on the accuracy of U–Pb age determinations by LA-ICP-MS

Abstract: Many studies now acknowledge the occurrence of systematic discrepancies between U–Pb ages determined in zircons in situ by LA-ICP-MS and the benchmark analytical method ID-TIMS. In this study, we present detailed investigations into the ablation characteristics of zircons that suggest an underlying mechanism responsible for these age biases relative to ID-TIMS. Confocal laser scanning microscopy of laser ablation pits reveals that there are small but significant differences in the amount of material removed by the laser between different zircons. Based on numerous pit depth and LA-ICP-MS 206Pb/238U ratio measurements of a suite of natural zircon reference materials and samples, we demonstrate that a systematic age bias is strongly correlated with the offset in ablation rates between the primary reference material and sample zircons. We offer further insights concerning the effects of thermal annealing on the ablation behaviour of zircons and demonstrate that, although there is a change in laser ablation rates for annealed zircons, the variations between different zircons are not eliminated. Finally, we show that slight variations in laser focus also influence the ablation behaviour of zircons and may further degrade the accuracy of U–Pb age determinations.

A critical overview of Cr speciation analysis based on high performance liquid chromatography and spectrometric techniques

Abstract: The role and impact of chromium (Cr) on the environment and living organisms depends primarily on its chemical form. High toxicity of hexavalent Cr is well documented, while trivalent Cr is an essential micronutrient. In the last decades numerous analytical procedures have been developed for the determination of Cr(VI) in different sample matrices. To obtain reliable speciation data it is important to preserve species integrity during the sample storage, pre-treatment, extraction and the determination of Cr species. Among different speciation methods combination of high performance liquid chromatography (HPLC) with atomic spectrometry techniques provides comprehensive information on the presence of Cr species in a variety of sample matrices, while hyphenation of HPLC to inductively coupled plasma mass spectrometry (ICP-MS) represents the most powerful and the most sensitive analytical tool for Cr speciation. Precise isotope ratio measurement enables the application of isotope dilution techniques for the quantification of trace amounts of individual Cr species in various environmental and biological samples. Furthermore, enriched stable isotopes can be introduced as tracers to investigations on the fate and role of Cr in the environment and living organisms or to monitor the species transformation during the analytical procedure. Despite general understanding of Cr chemistry, which is closely related to its trivalent and hexavalent oxidation states and knowledge on conditions that may influence species transformation, there are still open questions that should be addressed to obtain reliable speciation analysis data. So, this article is focused mostly to overview recent developments in methodological approaches for Cr speciation in different sample matrices by applying HPLC and spectrometric techniques. Different procedures for preparation of isotopically enriched Cr spike solutions are critically evaluated. The advantages of their use as tracers to follow and account for species transformation during sample preparation and for the quantification of Cr species by HPLC-ID-ICP-MS are discussed. The importance of the use of adequate analytical methodologies and speciation analysis in the determination of Cr(VI) is highlighted in order to avoid inadequate conclusions to be made based on wrongly applied analytical methodologies. An increasing need to develop speciation procedures for selective determination of Cr(III) species is also emphasized.

Evaluation of a digestion procedure based on the use of diluted nitric acid solutions and H2O2 for the multielement determination of whole milk powder and bovine liver by ICP-based techniques

Abstract: Many efforts have been made in order to reduce the amount of reagents and waste produced in analytical laboratories. However, suitable digestion efficiency must be considered, and depending on the sample preparation procedure, incomplete digestion can result in severe matrix effects during analysis by spectrometric techniques such as ICP OES and ICP-MS. In the present work a procedure based on the use of H2O2 was developed in order to minimize the consumption of HNO3 without decreasing the efficiency of digestion. Although H2O2 has been used combined with HNO3 for sample digestion, its role is still not completely elucidated even as its action combined with O2 in pressurized systems. The performance obtained using H2O2 was similar to that observed when adding O2 to the reaction vessel, driving the better understanding of the role of H2O2 in closed digestion procedures. Digestion using H2O2 allowed the use of HNO3 solutions as diluted as 1 mol L−1 to digest sample masses of biological materials as high as 500 mg. The proposed procedure allowed a reduction of up to 14 and 9.3-fold in the HNO3 amount normally used in whole milk powder and bovine liver digestions, respectively, without decreasing the digestion efficiency. Calcium, Cu, Fe, K, Mg, Mn, Mo, Na, and Zn were determined by ICP OES, while Cd, Co, and Pb were determined by ICP-MS. Using diluted HNO3 solution low blank values were obtained resulting in relatively lower limits of detection and relative standard deviations. The accuracy was evaluated by using certified reference materials of milk powder and bovine liver (agreement was better than 95% to certified values for all evaluated analytes).

Ultra-precise titanium stable isotope measurements by double-spike high resolution MC-ICP-MS

Abstract: In this contribution, we present a new technique for the ultra-precise determination of titanium stable isotope composition (expressed as δ49Ti or deviation of the 49Ti/47Ti ratio to the reference standard) of geological samples by multi-collection plasma source mass spectrometry (MC-ICPMS) using the double spike method to correct for instrumental mass bias. Tails of polyatomic spectral interferences on 46Ti are accounted for by using sample-standard bracketing in high-resolution mode. Choice of ideal double and triple spike composition is investigated and results show that analytical error for a single measurement is optimised for a 47Ti–49Ti double spike composed of ca. 50% of each spike and mixed with ca. 52% of sample. Measurements of pure Ti solution show that internal error on single measurements of ca. 0.010‰ (95% c.i.) is attainable on δ49Ti, in agreement with the error model. Due to the lack of a widely available reference isotopic standard for titanium, all results are expressed as deviations relative to newly created reference material (OL-Ti standing for Origins Laboratory – titanium) prepared from an ultra-pure titanium metal rod. A range of analytical tests demonstrates the robustness of our method. An external reproducibility of ca. 0.020‰ (2sd) is routinely achievable for Ti stable isotopes. Data for a range of basaltic rock standards as well as a subduction zone basalt reference suite is presented and show that the Ti stable isotope compositions of terrestrial basalt show resolvable variations but are overall very close to the OL-Ti reference standard. The average Ti isotopic composition of the basalts studied here is the present best estimate of the upper mantle composition; δ49Ti = +0.004 ± 0.062‰ (2sd).

Sensitivity improvement in the detection of V and Mn elements in steel using laser-induced breakdown spectroscopy with ring-magnet confinement

Abstract: To improve the detection sensitivity of vanadium (V) and manganese (Mn) elements in steel using laser-induced breakdown spectroscopy (LIBS), a ring magnet was employed to spatially and magnetically confine plasmas produced from steel samples using an Nd:YAG laser. The results showed that the optical emission and signal-to-noise ratios (SNRs) for both V I 437.92 nm and Mn I 403.08 nm lines were enhanced by the ring-magnet confinement. The enhancements were found to be due to an increase in the plasma temperature and electron density as a result of both spatial and magnetic confinement. The calibration curves of V I 437.92 nm and Mn I 403.08 nm with/without confinement were established. The 3σ-limits of detection (LoDs) for V and Mn in steels were 11 and 30 ppm with the ring magnet, lower than the 18 and 41 ppm with a degaussed magnet and the 41 and 56 ppm in open air, respectively.

Simultaneous 3-dimensional elemental imaging with LIBS and LA-ICP-MS

Abstract: Laser Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) are used simultaneously for spatially resolved mapping of major and trace elements and isotopes within a Bastnasite rare earth ore sample. The combination of the two techniques provides complementary measurements for elements that are separately unattainable due to low sensitivity and/or strong interferences. Two dimensional (2D) layer-by-layer mapping, 2D cross-sectional imaging and three-dimensional (3D) volume rendering of elements and isotopes in the Bastnasite matrix are presented. These results pave the way for improved 3D elemental imaging through simultaneously acquired LIBS and LA-ICP-MS measurements.

Determination of radioactive cesium isotope ratios by triple quadrupole ICP-MS and its application to rainwater following the Fukushima Daiichi Nuclear Power Plant accident

Abstract: A method was developed for the determination of 134Cs/137Cs and 135Cs/137Cs in rainwater samples using a triple quadrupole ICP-MS, with the objective of investigating radioactive cesium isotope ratios released by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The high background caused by Ba ions and Xe impurities in argon plasma gas has made it difficult to carry out determination of the 134Cs/137Cs and 135Cs/137Cs ratios on conventional ICP-MS instruments without prior chemical separation. In this study, nitrous oxide was used as the reaction gas for reducing the isobaric interference by 134Ba, 135Ba, 137Ba and 134Xe, and an additional quadrupole in front of the reaction cell was shown to effectively remove Sn and Sb that could have produced possible interference such as SbO and SnO by the N2O reaction. The detection limit for 134Cs, 135Cs and 137Cs in solution containing Ba was successfully improved. In order to confirm the applicability of this method to the measurement of 134Cs/137Cs and 135Cs/137Cs ratios of rainwater, four samples were collected for analysis from 40–200 km away from the FDNPP. The measured 134Cs/137Cs ratios in the samples are consistent with the values determined by Ge semiconductor analysis to within the analytical error, suggesting that the developed method can provide reliable isotopic data without any correction of the mass-discrimination effect. No variation was found in the 135Cs/137Cs ratios of the four samples, suggesting either the same contamination source or a uniformly consistent mixing ratio between contamination sources. The measured 135Cs/137Cs ratios in the samples are different from global fall-out values and from that of Chernobyl. This result indicates that the value of the rainwater samples can be used as a radiocesium tracer in the environment.

Study of pressure effects on laser induced plasma in bulk seawater

Abstract: It is a big challenge to apply laser induced breakdown spectroscopy (LIBS) to ocean in situ detection, but there are ample opportunities for LIBS development too. In the present work, laboratory investigations of LIBS on natural seawater at different pressures from 0.1 to 40 MPa were carried out. Pressure and laser pulse energy effects on LIBS emission were investigated. The result showed that enhanced LIBS emission can be obtained under elevated ambient pressure conditions. The line broadening of lines increases as a function of pressure. The time resolved LIBS emission results demonstrated that plasma emission is weakly dependent on the ambient pressure during the early stage of plasma and the pressure has a significant influence on the plasma form during plasma evaluation at a later stage of plasma. The obtained results suggested that the LIBS technique has the potential to be developed as an in situ chemical sensing technique for ocean applications.

Improving the accuracy of single particle ICPMS for measurement of size distributions and number concentrations of nanoparticles by determining analyte partitioning during nebulisation

Abstract: Application of single particle ICP-MS (spICPMS) for measurement of the size and number concentration, c(p), of nanoparticles is currently hampered by insufficient accuracy. The relative contributions of different types of noise to the overall uncertainty during spICPMS measurements of Ag and Au nanoparticle dispersions were quantified showing that the accuracy of spICPMS is mainly limited by the uncertainty in nebulization efficiency (f(neb)). This uncertainty was improved by correcting f(neb) for analyte partitioning effects during nebulization, and the calculated Ag and Au nanoparticle sizes were in close agreement with sizes determined by scanning electron microscopy. The duration of the particle events was measured, which allowed correction for incomplete particle events and detector dead time, and determination of the effective dwell time for particle counting. The c(p) measured with spICPMS agreed with that measured by counting particles deposited on filters, and calculated from the mass concentration of the analyte.

Precise measurement of chromium isotopes by MC-ICPMS.

Abstract: We report novel analytical procedures allowing for the concurrent determination of the stable and mass-independent Cr isotopic composition of silicate materials by multiple collector inductively coupled mass spectrometry (MC-ICPMS). In particular, we focus on improved precision of the measurement of the neutron-rich isotope 54Cr. Because nitride and oxide interferences are a major obstacle to precise and accurate 54Cr measurements by MC-ICPMS, our approach is designed to minimize these interferences. Based on repeat measurements of standards, we show that the mass-independent 53Cr and 54Cr compositions can be routinely determined with an external reproducibility better than 2.5 and 5.8 ppm (2 sd), respectively. This represents at least a two-fold improvement compared to previous studies. Although this approach uses significantly more Cr (30–60 μg) than analysis by thermal ionization mass spectrometry (TIMS), our result indicate that it is possible to obtain an external reproducibility of 19 ppm for the μ54Cr when consuming amounts similar to that typically analyzed by TIMS (1 μg). In addition, the amount of time required for analysis by MC-ICPMS is much shorter thereby enabling a higher sample throughput. As a result of the improved analytical precision, we identified small apparent mass-independent differences between different synthetic Cr standards and bulk silicate Earth (BSE) when using the kinetic law for the mass bias correction. These differences are attributed to the Cr loss by equilibrium processes during production of the synthetic standards. The stable isotope data concurrently obtained have a precision of 0.05‰ Da−1, which is comparable to earlier studies. Comparison of the measured isotopic composition of four meteorites with published data indicates that Cr isotope data measured by the technique described here are accurate to stated uncertainties. The stable Cr composition of the Bilanga and NWA 2999 achondrites suggests that the differences in the stable Cr isotope composition of Earth and chondrites may reflect heterogeneity of their precursor material rather than Cr isotope fractionation during metal–silicate segregation of Earth. Lastly, a step wise dissolution experiment of the CI chondrite Ivuna reveals previously unknown carriers of large mass-dependent Cr stable isotope variations that co-vary with the known presence of carriers of large nucleosynthetic anomalies, demonstrating one advantage of this technique.

A simplified protocol for measurement of Ca isotopes in biological samples

Abstract: We describe a chemical separation protocol of calcium from biological materials for isotopic measurement by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS). The method was tested using elution profiles along with HCl and HNO3 acids only, on human urine, sheep serum and red blood cells (RBC), seawater and herbaceous plants. It allows the elimination of all interfering species (including K, Sr, Mg) and the remaining matrix (including Fe, P, Na and S) beyond required levels. In order to further test this protocol and better understand the Ca isotopic signatures of mammalian fluids and organs, we purified and analyzed a wide range of materials from sheep, i.e. serum, RBC, muscle, liver, kidneys, enamel, bone, urine and feces. The data show a wide range of variations, expressed as δ, over 1‰ per amu, with a precision of 0.1‰ or better, spanning most of the variability reported so far. Red blood cells appeared to be heavier than serum by 0.3‰ per amu. This isotopic difference between serum and red blood cells was not taken into account in previous studies and it provides further information on Ca isotopic cycling in organisms. The Ca isotopic compositions of organs are correlated with concentrations, bone and RBC representing the two end-members, bone being Ca rich and 44Ca-depleted and RBC Ca poor and 44Ca-enriched. The trend is compatible with a distillation process by which Ca is extruded from cells along with a kinetic fractionation process favoring lighter Ca isotopes.

Precise determination of δ88Sr in rocks, minerals, and waters by double-spike TIMS: a powerful tool in the study of geological, hydrological and biological processes

Abstract: We present strontium isotopic (88Sr/86Sr and 87Sr/86Sr) results obtained by 87Sr–84Sr double spike thermal ionization mass-spectrometry (DS-TIMS) for several standards as well as natural water samples and mineral samples of abiogenic and biogenic origin. The detailed data reduction algorithm and a user-friendly Sr-specific stand-alone computer program used for the spike calibration and the data reduction are also presented. Accuracy and precision of our δ88Sr measurements, calculated as permil (‰) deviations from the NIST SRM-987 standard, were evaluated by analyzing the NASS-6 seawater standard, which yielded δ88Sr = 0.378 ± 0.009‰. The first DS-TIMS data for the NIST SRM-607 potassium feldspar standard and for several US Geological Survey carbonate, phosphate, and silicate standards (EN-1, MAPS-4, MAPS-5, G-3, BCR-2, and BHVO-2) are also reported. Data obtained during this work for Sr-bearing solids and natural waters show a range of δ88Sr values of about 2.4‰, the widest observed so far in terrestrial materials. This range is easily resolvable analytically because the demonstrated external error (±SD, standard deviation) for measured δ88Sr values is typically ≤0.02‰. It is shown that the “true” 87Sr/86Sr value obtained by the DS-TIMS or any other external normalization method combines radiogenic and mass-dependent mass-fractionation effects, which cannot be separated. Therefore, the “true” 87Sr/86Sr and the δ87Sr parameter derived from it are not useful isotope tracers. Data presented in this paper for a wide range of naturally occurring sample types demonstrate the potential of the δ88Sr isotope tracer in combination with the traditional radiogenic 87Sr/86Sr tracer for studying a variety of biological, hydrological, and geological processes.

DOTA based metal labels for protein quantification: a review

Abstract: Today, quantitative data play a pivotal role in the understanding of biological processes. This is particularly true for the proteome: protein quantification always follows protein identification. To obtain useful and reliable quantitative data, rather sophisticated strategies using electrospray and MALDI mass spectrometry have been developed, which allow relative and sometimes even absolute quantification. All of those strategies have merits and limitations. In order to overcome some of these limits, methods based on the reliable and sensitive detection and quantification of heavy metals present in proteins using inductively coupled plasma (ICP)-MS have been reported. With specific labels carrying heavy metals, the applicability of ICP-MS has been extended to almost every protein. One of such covalently bound metal tags, allowing the quantification of low abundant proteins, uses 1,4,7,10-tetraazacyclododecane N,N′,N′′,N′′-tetraacetic acid (DOTA) chelate complexes carrying lanthanides as the metal core. In this review the scope and limitations of peptide and protein quantification will be addressed. The metal tags do not only provide low detection limits, but also due to the large number of different lanthanides and lanthanide isotopes, multiplexing capabilities and previously unknown accuracy based on inherently possible isotope dilution methods came into reach. The developed workflows, including electrophoretic and chromatographic separation and preconcentration techniques, will be addressed to allow a comparison with already established procedures.

Improved precision and spatial resolution of sulfur isotope analysis using NanoSIMS

Abstract: High precision analyses of all four sulfur isotopes in four pyrite and three sphalerite standards and in working reference samples were carried out using a CAMECA NanoSIMS 50L instrument. The measurements were made using three different settings of the Faraday cup (FC) and/or electron multiplier (EM) detectors, which meet different requirements for spatial resolution. The effects of EM aging and quasi-simultaneous arrival were corrected before the calibration of instrumental mass fractionation by a standard–sample–standard bracket method using the standards measured together with the samples. High analytical precision was achieved by counting 32S, 33S and 34S with the FCs and 36S with the EM (i.e. the FC–FC–FC–EM mode) using a 0.7 μm diameter ∼350 pA Cs+ primary beam and scanning over areas of 5 × 5 μm2. The standard deviations of spot-to-spot and grain-to-grain (external reproducibility 1 SD) measurements were less than 0.3, 0.3 and 0.7‰ for δ33S, δ34S and δ36S, respectively. To achieve a higher lateral resolution of ≤2 × 2 μm2, the Cs+ beam was reduced to 7–10 pA with a diameter of ∼200 nm; 32S was measured with the FC and the other signals were measured with the EMs. The external reproducibility (1 SD) was better than 0.5‰ for both δ33S and δ34S and was 3‰ for δ36S. To achieve the highest lateral resolution for the analysis of submicron-sized sulfides, a ∼0.7 pA Cs+ beam of ∼100 nm diameter was used, scanning over areas of 0.5 × 0.5 μm2, and all 32S, 33S and 34S were counted with the EMs. The external reproducibility (1 SD) was better than 1.5‰ for both δ33S and δ34S. These three modes have important applications in the isotope analysis of micron-sized sulfur samples, such as pyrite framboids and areas of complex zoning in sulfide minerals.