Showing papers in "Journal of Analytical Atomic Spectrometry in 2018"

LIBS analyses for industrial applications – an overview of developments from 2014 to 2018

Abstract: Measuring distances in the range between a few centimetres and a few metres are of special interest for automated industrial LIBS applications. They allow for a reliable optical access to measuring objects in a process line under harsh industrial environments. In that range a compromise can be found between the conflicting requirements with respect to the protection of the optics facing the measuring object on one side, and sufficiently high laser irradiance and high receiving solid angle of the measuring radiation on the other side. A concise overview about LIBS studies published in the last four years focusing on industrial applications or perspectives therefore is given. Recent RD (b) sorting of refractories; (c) identification of steel blooms in a rolling mill; (d) inverse production scenario for the recovery of valuable materials from end-of-life electronic equipment. For measuring distances of only a few centimetres the size of a LIBS instrument can be downscaled significantly allowing to set up handheld LIBS analysers. Whereas the precursors of such concepts were studied already more than fifteen years ago, quite recently a competitive market arose where various models of handheld LIBS systems are offered. Industrial application fields are mainly positive material identification of metals and sorting of light metal scraps for recycling purposes. A comparative synopsis of features of these LIBS systems will be presented and arising research themes in this context are outlined.

ICP-MS for the analysis at the nanoscale – a tutorial review

Abstract: This tutorial review focuses on the use of ICP-MS based techniques for the analysis of metal-containing nanoparticles and colloids. Within the first part the capabilities of “stand alone” ICP-MS for the analysis of total metal contents and the suitability of stable isotopes for nanoparticle tracking (stable isotope labelling and naturally occurring variation in isotope ratios) are introduced (Chapter 3). Special focus was given on single particle ICP-MS (sp-ICP-MS) mode (Chapter 4). Upon a brief introduction into the theoretical concept, critical aspects such as calibration strategies, dwell time as well as ionic background were discussed and practical advice is given. References to current data assessment sheets are provided. Furthermore, a brief chapter on general sample preparation aspects is included within the first part (Chapter 2). The second part is dedicated to fractionation/separation systems, such as field-flow fractionation (FFF), hydrodynamic chromatography (HDC), high performance liquid chromatography (HPLC) and capillary electrophoresis (CE) coupled on-line with ICP-MS detection for metal-based nanoparticle and colloid analysis (Chapter 5). Each section starts with an introduction into the theoretical concept of the respective fractionation/separation system, followed by practical hints regarding method development (e.g. selection of appropriate carrier/mobile phase, membrane/stationary phase) as well as critical aspects and limitations. Particular attention is payed to laser ablation ICP-MS (LA-ICP-MS) for spatially resolved nanoparticle analysis. Each section concludes with selected application examples of the respective analytical technique from the most relevant fields of nanoparticle use or exposure (consumer products, food, medicine and environment), highlighting the performance of each technique in metal-based nanoparticle analysis. Chapter 6 is dedicated to aspects of quality assurance. Various critical points regarding method development and validation, mass balance, size calibration and quantification from the previous sections are revisited, discussed and practical advice is given. Finally, the authors provide some concluding remarks and future perspectives (Chapter 7). Furthermore, a flow-chart is included as a “hands-on” overview on all ICP-MS based techniques discussed within this tutorial review intended as a “method-decision tool” for users.

High-precision 41K/39K measurements by MC-ICP-MS indicate terrestrial variability of δ41K

Abstract: Potassium is a major component in continental crust, the fourth-most abundant cation in seawater, and a key element in biological processes. Until recently, difficulties with existing analytical techniques hindered our ability to identify natural isotopic variability of potassium isotopes in terrestrial materials. However, measurement precision has greatly improved, and a range of K isotopic compositions has now been demonstrated in natural samples. In this study, we present a new technique for high-precision measurement of K isotopic ratios using high-resolution, cold plasma multi-collector mass spectrometry. We apply this technique to demonstrate natural variability in the ratio of 41K to 39K in a diverse group of geological and biological samples, including silicate and evaporite minerals, seawater, and plant and animal tissues. The total range in 41K/39K ratios is ca. 2.6‰, with a long-term external reproducibility of 0.17‰ (2σ, N = 108). Seawater and seawater-derived evaporite minerals are systematically enriched in 41K compared to silicate minerals by ca. 0.6‰, a result consistent with recent findings. Although our average bulk-silicate Earth value (−0.54‰) is indistinguishable from previously published values, we find systematic δ41K variability in some high-temperature sample suites, particularly those with evidence for the presence of fluids. The δ41K values of biological samples span a range of ca. 1.2‰ between terrestrial mammals, plants, and marine organisms. Implications of terrestrial K isotope variability for the atomic weight of K and K-based geochronology are discussed. Our results indicate that high-precision measurements of stable K isotopes, made using commercially available mass spectrometers, can provide unique insights into the chemistry of potassium in geological and biological systems.

Multi-element analysis of single nanoparticles by ICP-MS using quadrupole and time-of-flight technologies

Abstract: Determining composition, shape, and size of nanoparticles dispersed in a complex matrix is necessary in the assessment of toxicity, for regulatory actions, and environmental monitoring. Many types of nanoparticles that are currently used in consumer products contain more than one metal which are often not uniformly distributed (e.g., core–shell nanoparticles). This compositional and structural complexity makes their characterization difficult. In this study, we investigate the capability of single particle inductively coupled plasma mass spectrometry (spICP-MS) using time-of-flight (TOF) and quadrupole (Q) mass analyzers to determine the composition, size distribution, and concentration of a series of nanoparticles that are used in a variety of industrial applications: BiVO4, (Bi0.5Na0.5)TiO3 and steel (which contains Fe, Cr, Ni, Mo) nanoparticles. In addition, we tested both types of mass analyzers with Au-core/Ag-shell nanoparticles, which are well-characterized and have already been used for assessment of multi-element capabilities of spICP-MS. The results confirm that both types of mass analyzers produce accurate estimations of the size of Au-core/Ag-shell particles. For other multi-element nanoparticles, spICP-MS provided the size of aggregates and/or agglomerates in the prepared suspensions. In general, particle size detection limits (dLOD) of spICP-TOFMS instruments with values of 29 nm for Ti, 14 nm for Mo, and 7 nm for Au, are smaller than those obtained for the quadrupole instruments. This study finds that only spICP-TOFMS can accurately assess the elemental composition of nano-steel particles. By contrast, spICP-QMS is limited to the detection of 2 elements in an individual particle and the elemental composition of nano-steel particles is less accurate. In general, spICP-TOFMS was able to quantify multiple elements with high precision and that currently makes it the first choice for multi-element detection of unknown nanoparticles.

A critical review on isotopic fractionation correction methods for accurate isotope amount ratio measurements by MC-ICP-MS

Abstract: Multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) is a powerful research tool for obtaining accurate and precise isotope amount ratios in a wide range of applications. Compared to thermal ionization mass spectrometry (TIMS), MC-ICP-MS suffers from much larger isotopic fractionation/mass bias. In addition to the commonly believed mass-dependent fractionation (MDF) phenomenon, recognition and reporting of mass-independent fractionation (MIF) within MC-ICP-MS itself has proliferated in the last decade. Traditional isotopic fractionation correction models, such as the widely used exponential and Russell laws, were designed to account for the mass-dependent fractionation as a function of nuclide mass. The latest findings of MIF within MC-ICP-MS itself have a significant impact on the choice of these isotopic fractionation correction models, as the use of mass-dependent models to correct for instrumental bias for isotopes which display mass-independent fractionation would result in biased isotope amount ratios. This review focuses on the latest developments related to isotopic fractionation and its correction models for MC-ICP-MS, and the implications of MIF within MC-ICP-MS on several popular mass bias correction models for obtaining accurate isotope amount ratios by MC-ICP-MS are discussed in detail.

Impact of air, laser pulse width and fluence on U-Pb dating of zircons by LA-ICPMS

Abstract: The accuracy of zircon U–Pb dating by LA-ICPMS is limited by matrix effects related to differences in U–Pb fractionation between an unknown and the calibration standard. Zircon radiation dose has a strong influence on the ablation rate, which in turn affects the amount of U–Pb fractionation and subsequent age calculations. Presented in this study is a previously unrecognized source of uncertainty in LA-ICPMS U–Pb ages due to variations of atmospheric air absorbed onto the surfaces of samples. Laser properties such as fluence (J cm−2) will change the laser ablation rate, and therefore the degree of U–Pb fractionation, and this can change the amount of zircon matrix effect. To improve the accuracy of U–Pb dating by LA-ICPMS, a systematic error component related to radiation dose needs to be included, or alternatively a correction to U–Pb dates can be applied as a function of radiation dose relative to the primary calibration standard. This study proposes a method to calculate a correction factor for the zircon matrix effect by measurement of several zircon reference materials with varying radiation dosages.

Exploration of megapixel hyperspectral LIBS images using principal component analysis

Abstract: Laser-Induced Breakdown Spectroscopy (LIBS) has achieved promising performance as an elemental imaging technology, and considerable progress has been achieved in the development of LIBS over the last several years, which has led to great interest in the use of LIBS in various fields of applications. LIBS is a highly attractive technology that is distinguished by its table top instrumentation, speed of operation, and operation in ambient atmosphere, able to produce megapixel multi-elemental images with micrometric resolution (10 μm) and ppm-scale sensitivity. However, the points that limit the development of LIBS are undeniably the expertise and the time required to extract a relevant signal from the LIBS dataset. The complexity of the emission spectra (e.g., elemental responses, structure of the baseline), the high dynamic range of measurement (i.e., possibility to image major to trace elements), and the large number of spectra to process require new data analysis strategies. Such new strategies are particularly critical for multi-phase materials. In this paper, we report a new methodology based on the well-known Principal Component Analysis (PCA) approach for the multivariate hyperspectral analysis of LIBS images. The proposed methodology is designed for large, raw, and potentially complex series of LIBS spectra, that allows various and exhaustive levels of information to be extracted (including the characterization of mineral phases, assessment of the measurement and identification of isolated elements) and facilitates the manipulation of such hyperspectral datasets.

Recent advances in LIBS and XRF for the analysis of plants

Abstract: The ability to provide a fast and multielemental analytical response directly from a solid sample makes both laser-induced breakdown spectroscopy (LIBS) and X-ray fluorescence spectrometry (XRF) very versatile tools for plant nutrition diagnosis. This review focuses on the main developments and advances in LIBS and XRF in the analysis of plant materials over the last ten years. Fundamental aspects and instrumentation are given for both techniques. The developments in the quantitative analysis of plant leaves are discussed, with special emphasis on the key aspects and challenges concerning field sampling protocols, sample preparation, and calibration strategies. Microchemical imaging applications by LIBS and XRF (including synchrotron radiation) are also presented in a broader selection of plant compartments (e.g., leaves, roots, stems, and seeds). Challenges, expectations and complementarities of LIBS and XRF towards plant nutrition diagnosis are thoroughly discussed.

Elemental imaging by laser-induced breakdown spectroscopy for the geological characterization of minerals

Abstract: Geological studies increasingly require highly sensitive elemental techniques able to image the distribution of elements in minerals with microscopic-scale resolution. In this paper, we present an evaluation of megapixel laser-induced breakdown spectroscopy (LIBS) imaging for the geological characterization of minerals. The study is conducted on a hydrothermal ore sample with a complex mineral structure involving five different mineral phases (galena, sphalerite, chalcopyrite, quartz and ankerite). A new methodology of data treatment adapted to a multi-phase material and megapixel LIBS imaging is also detailed. We demonstrate for the first time, to our knowledge, that LIBS-imaging technology is able to both detect and image rare earth elements (here La and Y) in carbonate as well as substituents present at the ppm-scale level in various mineral phases (i.e., cadmium in sphalerite; bismuth, silver and antimony in galena; beryllium and aluminum in quartz; and tin in chalcopyrite). These results appear extremely promising for the geological domain and should pave the way for innumerable applications.

Detection and characterization of biogenic selenium nanoparticles in selenium-rich yeast by single particle ICPMS

Abstract: A method based on single particle inductively coupled plasma mass spectrometry (SP-ICPMS) was developed for the analysis of commercial Se-rich yeasts, to confirm the occurrence of selenium nanoparticles in these food supplements. A considerable reduction of background levels was achieved by combining data acquisition at microsecond dwell times and the use of a H2 reaction cell, improving by a factor of 10 the current state-of-the-art methodology, and bringing size detection limits down to 18 nm for selenium nanoparticles. The presence of nanoparticulate selenium was revealed by size-exclusion chromatography ICPMS, with detection of a selenium peak at the exclusion volume of the column showing absorption at a wavelength corresponding to selenium nanoparticles. SP-ICPMS allowed us to confirm the presence of Se-nanoparticles, as well as to calculate the nanoparticle size distribution, from information about the shape and elemental composition of the nanoparticles obtained by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS), respectively. These results reveal the significance of nanoparticles in the speciation of metals and metalloids in biological samples and the capability of SP-ICPMS in combination with TEM-EDS to carry out these analyses.

Determination of Mn, Fe, Ni, Cu, Zn, Cd and Pb in seawater using offline extraction and triple quadrupole ICP-MS/MS

Abstract: Highly resolved temporal and spatial distributions of trace elements in ocean water can provide insight into ocean processes but carry a significant analytical demand which requires methods that combine accuracy and precision with high sample throughput. Here a multi-element method is presented which combines the commercially-available seaFAST preconcentration system with ICP-MS/MS for the analysis of Mn, Fe, Ni, Cu, Zn, Cd and Pb in seawater. Samples (20 mL or 40 mL) are loaded on to a chelation resin column and trace metals eluted into 2.5 mL of 1.6 N HNO3. Analysis of the eluate was carried out by ICP-MS/MS, which combines two mass-selecting quadrupoles separated by an octopole collision/reaction cell. The collision/reaction cell was pressurized with O2 gas for the analysis of Mn, Ni, Cu, Cd and Pb and H2 gas for the analysis of Fe and Zn, which removed common interferences (e.g. ArO+ on 56Fe and MoO+ on Cd) yet maintained the highest instrument sensitivity across the entire mass range. Measured blanks and detection limits were ≤0.050 nmol L−1 levels, except for the Fe (blank 0.14 nmol L−1) and were suitable for open-ocean seawater analysis. We report results for the certified reference material NASS-6, consensus reference standards SAFe S and SAFe D and depth profiles of trace metals from the Arctic Ocean, collected as part of the Canadian GEOTRACES program.

Accuracy improvement of boron by molecular emission with a genetic algorithm and partial least squares regression model in laser-induced breakdown spectroscopy

Abstract: Laser-induced breakdown spectroscopy (LIBS) is an atomic emission spectrometry technique for material component analysis. However, the spectral signal distortion and the low analytical accuracy remain as challenges due to the self-absorption effect of atomic lines in LIBS. Here, to overcome this flaw, we demonstrated a method to build calibration with molecular emission, which was measured from a mixture of H3BO3 and C6H12O6·H2O in powder form. We compared the calibration established by typical atomic emission and molecular emission of boron monoxide. The results showed that the self-absorption effect and R2 values were improved by using molecular spectra. Furthermore, to improve the accuracy of molecular emission content determination, a genetic algorithm and partial least squares regression (GA-PLSR) combination model was adopted. The achieved root mean square error of prediction (RMSEP) and the mean prediction error (MPE) for the GA-PLSR model were 0.8667 wt% and 10.9685%, respectively. The results demonstrated that it is a potential method to overcome the self-absorption effect with molecular emission and the accuracy of boron content determination of molecular emission can be improved with the GA-PLSR model.

U–Pb age determination of schorlomite garnet by laser ablation inductively coupled plasma mass spectrometry

Abstract: We report the first U–Pb geochronological investigation of schorlomite garnet from carbonatite and alkaline complexes and demonstrate its applicability for U–Pb age determination using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) due to its relatively high U and Th abundances and negligible common Pb content. The comparative matrix effects of laser ablation of zircon and schorlomite are investigated and demonstrate the necessity of a suitable matrix-matched reference material for schorlomite geochronology. Laser-induced elemental fractional and instrumental mass discrimination were externally-corrected using an in house schorlomite reference material (WS20) for U–Pb geochronology. In order to validate the effectiveness and robustness of our analytical protocol, we demonstrate the veracity of U–Pb age determination for five schorlomite samples from: the Magnet Cove complex, Arkansas (USA); the Fanshan ultrapotassic complex, Hebei (China); the Ozernaya alkaline ultramafic complex, Kola Peninsula (Russia); the Alno alkaline–rock carbonatite complex (Sweden); and the Prairie Lake carbonatite complex, Ontario (Canada). The schorlomite U–Pb ages range from 96 Ma to 1160 Ma, and are almost identical to ages determined from other accessory minerals in these complexes and support the reliability of our analytical protocol. Schorlomite garnet U–Pb geochronology is considered to be a promising new technique for understanding the genesis of carbonatites, alkaline rocks, and related rare-metal deposits.

A rapid and simple single-stage method for Ca separation from geological and biological samples for isotopic analysis by MC-ICP-MS

Abstract: A new simple and rapid method was developed for the purification of Ca from geological and biological samples. The proposed separation protocol is based on DGA resin and consists of only three elution steps and two types of eluents (6.8 mL 4 mol L−1 HNO3 and 3 mL DI-water), which afford a straightforward separation of Ca with a high yield (95–99%), good purity and low blank level. Moreover, a vacuum box was employed which enables Ca purification for a batch of twelve samples within two hours, with greatly improved efficiency compared to conventional gravity flow separation methods. Ca isotopic ratios were measured by multi-collector inductively coupled plasma mass-spectrometry (MC-ICP-MS) using a standard–sample bracketing method. Based on repeated measurements of NIST SRM 915a and Alfa Ca, the long-term reproducibility was evaluated at ±0.07‰ (2SD) for δ44/42Ca. The validity of the proposed method was demonstrated by the analysis of thirteen international geological and biological reference materials with satisfactory results which are in good agreement with published values. Therefore, the proposed method can be used for a rapid and efficient determination of stable Ca isotopic ratios in geological and biological samples.

Comparison of the suitability of alkaline or enzymatic sample pre-treatment for characterization of silver nanoparticles in human tissue by single particle ICP-MS

Abstract: To understand potential harmful effects of silver nanoparticles (AgNPs) for the growing fetus, studies dealing with the translocation and accumulation of NPs across the placental barrier are of great importance. Quantitative methods for determination of NP mass and number concentration and their size are required for studying NP accumulation in placental tissue. In the present study, we applied and compared two sample preparation techniques, alkaline and enzymatic treatment, followed by single particle ICP-MS (spICP-MS) analysis, for characterizing AgNPs spiked to human placental tissue. Both sample preparation approaches are currently used for AgNPs in biological tissues but have not been directly compared yet. We showed that the method using enzymatic tissue treatment followed by spICP-MS is efficient for determination of mass and number concentration and size distribution of AgNPs in human placental tissues. Properties of the AgNPs were preserved during enzymatic digestion and comparable with the primary particles. The matrix effect on the determination of Ag sensitivity and transport efficiency in spICP-MS analysis was systematically evaluated as well. The method was applied to human placenta, exposed to AgNPs with two different surface modifications: 27 nm polyethylene glycol (AgPEG NPs) or 34 nm sodium carboxylate groups (AgCOONa NPs) in an ex vivo human placental perfusion model. The Ag mass concentration obtained with spICP-MS following enzymatic sample pretreatment was not significantly different from the Ag concentration obtained by conventional ICP-MS analysis of acid digested tissue. With this we confirmed the ability of the procedure to quantitatively characterize AgNPs accumulated in human tissue under realistic exposure scenario.

Multi-energy calibration as a strategy for elemental analysis of fertilizers by microwave-induced plasma optical emission spectrometry

Abstract: Multi-energy calibration (MEC) was applied for the determination of As, Ba, Cd, Cr, and Pb in fertilizer samples by microwave-induced plasma optical emission spectrometry. Commercial fertilizer samples and a certified reference material of mineral fertilizer (CRM NIST 695) were digested using microwave-assisted acid. The MEC approach was carried out using only two calibration solutions: S1, composed of 50% v/v digested sample and 50% v/v standard reference solution containing the analytes, and S2, composed of 50% v/v sample and 50% v/v blank solution. The accuracy of the method was evaluated by analyzing CRM NIST 695, with recoveries in the 96–101% range. Addition and recovery experiments were also carried out for Cd determination, with recoveries between 92 and 105% for the evaluated samples. The MEC strategy was compared with traditional external standard calibration and standard additions methods and was the only one to provide accurate results for all evaluated analytes.

The role of mass spectrometry in radioactive contamination assessment after the Fukushima nuclear accident

Abstract: The Fukushima nuclear accident caused the release of large amounts of radionuclides into the environment. After the accident, radioactive contamination assessment in environmental samples is essential for radiation dose estimation and radioactive remediation. Mass spectrometry characterized by high sensitivity, low detection limit, short measuring time, high sample throughput, and the capability to obtain atomic ratios is a promising technique for the analysis of the accident released long-lived radionuclides. This review describes the developed analytical methods based on mass spectrometric techniques for the determination of radionuclides (Pu isotopes, U isotopes, radiocesium, radioiodine, radiostrontium, etc.) with regards to Fukushima samples. The real applications of mass spectrometric techniques for radioactive source identification, radiation protection and geochemical tracing are discussed to highlight the importance of mass spectrometric techniques in radioactive contamination assessment after the accident. Future research prospects of mass spectrometric techniques for the analysis of radionuclides with application to Fukushima samples are briefly outlined.

Influence of pH and low-molecular weight organic compounds in solution on selected spectroscopic and analytical parameters of flowing liquid anode atmospheric pressure glow discharge (FLA-APGD) for the optical emission spectrometric (OES) determination of Ag, Cd, and Pb

Abstract: Atmospheric pressure glow discharge operated in contact with a flowing liquid anode (FLA-APGD), with the solution pH adjusted to pH 6.0 or pH 1.0, was performed to elucidate plasma-chemical processes and reactions occurring in the discharge and the liquid phase. The morphologies in the emission spectra of both FLA-APGD systems in reference to molecular (NO, OH, N2, and N2+) and atomic (H and O) excited species in addition to selected spectroscopic parameters, including the rotational, vibrational, and excitation temperatures and electron number density, were assessed for both discharge systems and compared with those evaluated for APGD operated in contact with a flowing liquid cathode (FLC-APGD). The effect of low-molecular weight (LMW) alcohols (methanol and ethanol) and carboxylic acids (formic acid and acetic acid) added to the FLA solution on the morphology of the spectra and spectroscopic parameters of both discharge systems was studied as well. The analytical performance of both FLA-APGD systems, compliant with the intensities of the atomic lines of Ag, Cd, and Pb, the signal-to-background ratios of these lines, and the detection limits of Ag, Cd, and Pb, under conditions of the absence and presence of the aforementioned LMW organic compounds was determined and compared. It was established that APGD operated in contact with FLA solutions acidified to pH 1.0 or buffered to pH 6.0 conferred a unique set of advantages as compared to the case of the FLC-APGD system. Both FLA-APGD systems were characterized by a large population of high energy electrons and molecular and atomic excited states not quenched by H2O vapor, as in the case of FLC-APGD. Particularly, for the FLA-APGD (pH 1.0) system, the addition of LMW organic compounds resulted in an improvement in its analytical performance for the detection and determination of Ag, Cd, and Pb.

Online isotope analysis of 37Cl/35Cl universally applied for semi-volatile organic compounds using GC-MC-ICPMS

Abstract: Stable chlorine isotope analysis of organic compounds is potentially applicable in various fields in forensics and environmental analytics to investigate the fate of these substances in the environment, but a wider use of this technique is still hampered by the limited applicability of available offline and online techniques. In a previous study we presented a method for compound-specific chlorine isotope analysis of volatile organics including chlorinated methanes, ethanes and ethenes using gas chromatography interfaced with multiple-collector inductively coupled plasma mass spectrometry (GC-MC-ICPMS). In the current study we modified further the setup in order to extend the range of analytes towards semi-volatile organic substances with boiling points of up to 350 °C. The modified method was evaluated by using offline characterized in-house reference materials, such as chloroethenes, chloroacetic acid and hexachlorocyclohexenes. Additionally, analysis of various chlorinated benzenes, chlorinated phenols, chlordecone, dichlorodiphenyltrichloroethane (DDT) and related derivatives was demonstrated. The analytical precision (1σ) was usually better than ±0.2 mUr for single compound and ±0.3 mUr for compound-specific analysis of mixtures. Achieved accuracy was within ±0.2 mUr compared to available offline values. The isotopic detection limit could be significantly improved by one order of magnitude (250 pmol Cl on column, corresponding to ∼10 ng Cl) and is superior to other online state of the art approaches. The demonstrated method allows for the compound-specific stable chlorine isotope analysis of virtually all GC-compatible organics with versatility, high accuracy, and sensitivity.

UV photochemical vapor generation of noble metals (Au, Ir, Pd, Pt and Rh): a feasibility study using inductively coupled plasma mass spectrometry and seawater as a test matrix

Abstract: The results originated from the application of a simple and straightforward photochemical reactor to generate volatile species from noble metals (Au, Ir, Pd, Pt and Rh) are presented. Seawater samples were spiked with known amounts of the analytes and mixed with formic acid, followed by irradiation of the solution at 253.7 nm. The irradiated solution was driven to a gas–liquid separator and the volatile species were carried by an argon stream for detection using inductively coupled plasma mass spectrometry. Parameters such as formic acid concentration, carrier gas flow rate, UV irradiation period and RF power were evaluated. The optimum conditions were determined as 20% (v/v) formic acid, 1.0 L min−1 Ar, 45 s of UV exposure for Au, Pd, Pt and Rh or 120 s for Ir and 1300 W ICP RF power. Evaluation of potential interferences has shown that the addition of Cu2+ at ppm levels improved the overall efficiency of the photochemical process for Ir and Rh. Hence, Cu2+ was added as a modifier prior to the quantitation of Ir and Rh. Three seawater samples collected locally were used to evaluate the ability to carry out quantitative analysis of the investigated elements. The concentration of noble metals was, as expected, below the quantification limit, but recovery tests were successfully performed. Detection limits ranged from 0.02 to 0.1 μg L−1. Typical relative standard deviations were lower than 13% and the method was proven successful as an alternative to carry out the analysis of mildly diluted seawater samples.

A modified ZSM-5 zeolite/Fe2O3 composite as a sorbent for magnetic dispersive solid-phase microextraction of cadmium, mercury and lead from urine samples prior to inductively coupled plasma optical emission spectrometry

Abstract: The purpose of this work is to present a simple, fast, cost effective and environmentally friendly magnetic dispersive solid-phase microextraction (MDSPME) method, employing a composite based on ZSM-5 zeolite decorated with iron oxide magnetic nanoparticles (i.e., ZSM-5/Fe2O3) as a valuable sorbent, for the simultaneous separation and preconcentration of cadmium (Cd), mercury (Hg) and lead (Pb) from urine samples for subsequent measurement by inductively coupled plasma optical emission spectrometry. The composite was first saturated with zinc and then modified with a hexadecyltrimethylammonium bromide surfactant and sodium diethyldithiocarbamate trihydrate chelating agent. A two-step multivariate strategy, using Plackett–Burman and circumscribed central composite designs, has been employed to optimize experimental parameters affecting MDSPME. The method has been evaluated under optimized extraction conditions (i.e., amount of sorbent, 50 mg; sample pH, 4.0; extraction time, 3 min; eluent solvent, nitric acid; eluent solvent volume, 432 μL; eluent solvent concentration, 11.8 M and elution time, 2 min) using standard addition calibration. Calibration curves using standards between 0 and 100 μg L−1 gave a good linearity with correlation coefficient values ranging from 0.998 to 0.9997 for Cd, from 0.998 to 0.9998 for Hg and from 0.9996 to 0.9999 for Pb (N = 8). The repeatability of the method has been evaluated at 3 and 50 μg L−1 obtaining coefficients of variation between 2 and 5% (n = 6). The limit of detection values ranged from 0.15 to 0.20 μg L−1 for Cd, from 0.42 to 0.73 μg L−1 for Hg and from 0.23 to 0.39 μg L−1 for Pb. These values satisfy the threshold limit (3.4 μg L−1 for Cd, 10.0 μg L−1 for Hg and 85.0 μg L−1 for Pb) established by the Ministry of Labour and Social Affairs (Spain) for normal content of these metals in human urine and by the World Health Organization for normal mercury content in urine (i.e., 10 μg L−1). Finally, three urine samples were used to assess the applicability of the developed procedure. Recovery values ranged between 87 and 107% showing negligible matrix effects.

An improved method of Cr purification for high precision measurement of Cr isotopes by double spike MC-ICP-MS

Abstract: Chromium (Cr) isotopes have been used to trace pollution processes and reconstruct paleo-redox conditions. However, the precise determination of Cr isotopes is still challenged by difficulties in purifying Cr from samples with low Cr and high matrix content. Here, we developed an improved, flexible and easily operated three-step chromatographic procedure to separate Cr from high-matrix samples. A continuous, two-stage column (Step I) filled with 2 mL cation resin AG50W-X8 (200–400 m) and 2 mL anion resin AG1-X8 resin (100–200 m), followed by Step II, with 1 mL of AG1-X8 resin (200–400 m), was used to remove at least 99% of Ca, Fe, and Ti, and >90% of V and most other matrix elements, even for samples with Fe/Cr ≈ 6000 and Ti/Cr ≈ 1000. The recovery of Cr in both Step I and Step II can reach nearly 100%. Step III utilizes 2 mL AG1-X8 (100–200 m) combined with an (NH4)2S2O8 oxidant to remove residual matrix elements and achieve high-purity Cr. The total yield of Cr through our three-step procedure is greater than 80% even for low-Cr (2.6 μg kg−1) samples. A relatively small sample amount (300–600 ng Cr) is enough to achieve high precision Cr isotope measurement due to a low procedural blank (<1 ng). Chromium isotopes in geological reference materials (BHVO-2, JDo-1, JP-1, etc.) were measured on a Neptune Plus MC-ICP-MS. The long-term external precision is 0.06‰ (2SD), and the δ53Cr values are in great agreement with previously reported values. The δ53Cr of the upper continental crust is estimated to be −0.10 ± 0.10‰ using a suite of granite, diamictite, sediment and loess samples. Both plants and human hair are ∼0.1‰ heavier than the upper continental crust. Tests show that our improved purification procedure is applicable to various geological and environmental samples.

Compact diode-pumped Nd:YAG laser for remote analysis of low-alloy steels by laser-induced breakdown spectroscopy

Abstract: A low weight diode-pumped Nd:YAG laser (400 g, 1064 nm, 5 ns, 130 mJ per pulse) was developed for a compact laser-induced breakdown spectroscopy (LIBS) system to be installed on a robotized arm. Fiber optics delivery vs. conventional LIBS were compared for C, Si, Mn and Cr analysis in low-alloy steels. Fiber optics transformed the multimode laser beam to a flat-top beam with an improved fluence profile stability, resulting in shallow and more reproducible craters. A fast imaging study revealed that plasma generated by fiber optic pulses was plane-shaped, more uniform and dissipated two-fold faster compared with the plasma induced by direct laser beam focusing. Greater peak fluence for conventional LIBS provided plasma with 20–100 times more intensive emission due to the greater ablated mass, higher temperature and electron density. Improved reproducibility of shot-to-shot measurements was observed for plasma induced by fiber optic pulses, due to more stable ablation. The analytical capabilities of LIBS were compared for fiber optics vs. conventional LIBS in terms of calibration curve linearity, limits of detection and the root mean square error of the cross-validation procedure. Limits of detection for Si, Cr and Mn were always better for direct laser beam focusing; however, more importantly, the conventional LIBS system provided quantitative analysis for carbon in low-alloy steels (0.025–0.5% wt) with acceptable detection limits (55 ppm) while fiber optic pulses produced too-low intensity plasma.

Single nanoparticle analysis by ICPMS: a potential tool for bioassay

Abstract: Inductively coupled plasma mass spectrometry (ICPMS) has already been demonstrated as a promising technique for metallic nanoparticle tagged bioassays due to its high sensitivity, wide dynamic linear range, and more importantly multiplex and absolute quantification ability. Besides, single nanoparticle analysis by ICPMS has also recently been applied for many metal nanoparticles. Moreover, its short data acquisition dwell times (serval hundred microseconds) lead to an extremely high signal to noise ratio for metal nanoparticles (i.e., low detection limits). This perspective focuses on single nanoparticle analysis-based ICPMS bioassays, which provide high sensitivity without any sophisticated signal amplification procedures. Herein, the recent development of single nanoparticle analysis, ICPMS instrument design, and single molecule analysis is discussed. Considering the vast types of metallic nanoparticles currently available and simultaneous multiplex detection capability of TOF-ICPMS, single nanoparticle analysis-based bioassays may open a new avenue for multiplex single molecule analysis.

Multi-energy calibration (MEC) applied to laser-induced breakdown spectroscopy (LIBS)

Abstract: In this study, the multi-energy calibration (MEC) method is applied to solid sample analysis by laser-induced breakdown spectroscopy (LIBS). The MEC method uses only two calibration standards and several atomic emission wavelengths with different sensitivities to determine the analyte concentration in the sample. Both calibration mixtures are prepared using the same amount of sample, which contributes to minimizing matrix effects. The MEC-LIBS method was used to determine Ca, Cu, Fe, Mn and Zn in complex-matrix samples of cattle mineral supplements with an adequate sample throughput (15 samples per h). The limits of detection (LODs) calculated for these elements in the solid sample were 11 g kg−1, 45, 188, 53 and 44 mg kg−1, respectively. For Cu, Mn and Zn, these LODs were approximately 10, 10, and 20 times lower than the minimum level required in a commercial product by the Brazilian legislation. The method's accuracy was evaluated by analyzing five reference materials (RM) of cattle mineral supplements, and by comparing values determined in six commercial samples with results from ICP-OES determinations. No statistically significant difference was observed between MEC-LIBS and RM or ICP-OES-determined values at the 95% confidence level (Student’s t-test, n = 3). LIBS is an inherently atomic-emission-rich technique, which suffers from severe matrix effects. MEC is an efficient matrix-matching method, for which the larger the number of analytical signal sources for an analyte the more precise the results. Therefore, MEC is a highly compatible, complementary approach to LIBS calibration.

High-precision Ca isotopic measurement using a large geometry high resolution MC-ICP-MS with a dummy bucket

Abstract: Wide application of stable Ca isotopes requires reliable production of high-precision data and in recent years multiple collector inductively coupled plasma mass spectrometers (MC-ICP-MS) have been used as an alternative to traditional thermal ionization mass spectrometers. The main challenges in using MC-ICP-MS to measure stable Ca isotopes are scattered ions and peak tailing of high level 40Ar+ and 40Ca+ ion beams, along with variable interferences. In this study we optimize Ca isotopic measurements on a large geometry high resolution MC-ICP-MS (Nu Plasma 1700) operating in conventional hot Ar-plasma mode. 40Ar+ and 40Ca+ were trapped by a specially designed dummy bucket, to prevent scattering of ions that might affect the Ca isotopic measurement. Strontium and matrix elements in samples were eliminated to blank levels by chemical separation. Instrumental mass bias of Ca isotopes was corrected by a sample-standard bracketing method using a purified sea water Ca isotope standard. Potential effects of Ar-related interferences, Ca-hydride, acid molarity, concentration mismatch and matrix elements were evaluated. The results from both measurements and modeling suggest that 40Ar+ peak tailing and Ca-hydride cause negligible Ca isotopic offset under normal MC-ICP-MS operating conditions. The precision and accuracy were validated using the measurement of twelve well-characterized international reference materials and a pure Ca standard solution. The long-term external precisions are better than ±0.07‰ (2SD) for δ44/42Ca and ±0.10‰ (2SD) for δ43/42Ca. Calcium isotopic compositions of all reference materials measured in this study agree with previously published data within uncertainties.

Online solid phase extraction-HPLC-ICP-MS system for mercury and methylmercury preconcentration using functionalised carbon nanotubes for their determination in dietary supplements

Abstract: A hyphenated system was developed for Hg(II) and methylmercury (MeHg) preconcentration and speciation analysis by the online coupling of solid phase extraction (SPE), high performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP-MS). Both analytes, Hg(II) and MeHg, were preconcentrated on a microcolumn filled with multiwalled carbon nanotubes (MWCNTs) functionalised with poly-L-methionine (polymet-MWCNTs). During the method development the sorbent material was carefully studied and the solid phase extraction conditions were optimised. An enrichment factor of 190 for Hg(II) and MeHg was obtained when 20 mL of sample was passed through the microcolumn. For the chromatographic separation, a mobile phase composed of a ternary mixture of 0.5% formic acid + 0.2% 2-mercaptoethanol + 20% methanol was used. Separation of both mercurial species was accomplished in ∼10 min on a 250 mm C18 column. The detection limits of the SPE-HPLC-ICP-MS method were 15 ng L−1 for Hg(II) and 17 ng L−1 for MeHg. The relative standard deviations of peak area for 5 ng L−1 of each Hg species were below 5%. Recoveries of Hg(II) and MeHg were never less than 93%. For checking the accuracy, BCR 643-tuna fish and TORT-3 lobster hepatopancreas certificate reference materials were analysed. Mercury species were determined in spiked fish oil-based dietary supplements and Antarctic water.

Determination of coal properties using laser-induced breakdown spectroscopy combined with kernel extreme learning machine and variable selection

Abstract: Rapid and online analysis of coal properties is extremely important for reasonable and clean utilization of coal. In this study, laser-induced breakdown spectroscopy (LIBS) was applied for analysis of coal properties. The kernel extreme learning machine (K-ELM) method was used to establish a nonlinear model, and particle swarm optimization (PSO) was used as the variable selection method to eliminate useless information and improve prediction ability of the model. The influence of different pretreatment methods was also investigated by 10-fold cross validation (CV); moreover, based on the optimal pretreatment method, three K-ELM models with full spectra, characteristic lines and PSO were developed and compared for predicting ash content, volatile matter content and calorific value of coal. The root mean squared error of cross-validation (RMSECV), correlation coefficient of cross-validation (RCV), root mean square error of prediction (RMSEP) and correlation coefficient of prediction (RP) were used to evaluate model performance; the corresponding RMSEP and RP values were 1.8957% and 0.9936 for ash content based on the K-ELM model with characteristic lines, 1.0874% and 0.9945 for volatile matter, and 0.6999 MJ kg−1 and 0.9872 for calorific value based on the K-ELM model with PSO. The results demonstrate that LIBS coupled with K-ELM and variable selection is a promising technique for rapid analysis of coal properties, and it will also be helpful for effective, clean utilization of traditional energy sources.

Assessment of matrix effects associated with Fe isotope analysis using 266 nm femtosecond and 193 nm nanosecond laser ablation multi-collector inductively coupled plasma mass spectrometry

Abstract: This study evaluated matrix effects during Fe isotope analysis using a 266 nm femtosecond (fs) laser and a 193 nm nanosecond (ns) laser coupled to a multi-collector ICP-MS. During 150 second spot analysis on pyrite, Fe isotope fractionation was not observed for fs-laser ablation (fs-LA), but was evident for ns-LA. The observed downhole Fe isotope fractionation during ns-LA is caused by multiple processes comprising ablation, transport, and ionization in the ICP. Contrary to the common perception of “matrix-free” analysis, matrix effects clearly exist during fs-LA analysis; small deviations of up to ∼0.2‰ in the measured 56Fe/54Fe ratios from the true value of magnetite grains with ≥∼8 wt% impurities were resolved using a nearly pure magnetite as the bracketing standard. Moreover, inaccurate and imprecise 56Fe/54Fe results were obtained when magnetite and pyrrhotite was measured against a non-matrix-matched standard (pyrite or Fe metal). The observed matrix effects during fs-LA cannot be explained by formation of a large heat-affected zone during ablation, but result from the influence of different chemical compositions of samples and standards on space-charge effects in the ICP-MS. Such matrix effects can be largely suppressed by water addition during analysis at a price of reduced sensitivity, so that precise and accurate Fe isotope analysis to a ∼0.1‰ level can be routinely achieved under “wet” conditions without matrix-matching between sample and standard. These results may reconcile dramatically different precisions previously reported for Fe isotope analysis by fs-lasers, and also highlight fs-LA-MC-ICP-MS as an appealing option for in situ Fe isotope analysis on samples with complex matrices and high-symmetry minerals, both of which encounter significant analytical difficulties using secondary ion mass spectrometry (SIMS). For ns-LA, in addition to similar composition-related matrix effects experienced by fs-LA in the ICP, matrix effects also originate from ablation-related processes that produce sample particles with matrix-dependent size distributions and, often, larger aerodynamic sizes, resulting in highly inaccurate 56Fe/54Fe results during non-matrix-matched analysis under “dry” conditions. The collective matrix effects during Fe isotope analysis by ns-LA cannot be fully suppressed by water addition, therefore, matrix matching is required for accurate Fe isotope analysis by ns-LA.

Estimation of the mechanical properties of steel via LIBS combined with canonical correlation analysis (CCA) and support vector regression (SVR)

Abstract: Degradation of steel is a significant issue in the field of material aging, with the mechanical properties of steel degrading during service, affecting the safety of equipment. In this work, laser-induced breakdown spectroscopy (LIBS) was applied to investigate the mechanical properties of steel. T91 steel specimens with different degrees of microstructure aging were selected as model samples. Surface hardness was chosen as the key indicator of mechanical properties. The correlation between emission line intensity and hardness was analyzed in order to establish a calibration model of hardness. Multivariate analysis methods (principal component analysis [PCA] and canonical correlation analysis [CCA]) were introduced to identify the important variables from the whole spectrum. Then, two regression algorithms (partial least-squares regression [PLSR] and support vector regression [SVR]) were used to establish the calibration models with the selected variables. The results showed that it is feasible to couple CCA and SVR to estimate hardness, which can effectively identify the correlated variables and establish the correlation between emission lines and hardness, with maximum values for mean relative error (MRE), relative standard deviation (RSD) and root mean square error of prediction (RMSEP) of 2.47%, 2.94% and 6.14, respectively. In addition, the influence of collinearity variables on the established model was investigated in order to show that there is little multicollinearity issue in the calibration models constructed with CCA and SVR according to the values of RMSEP, RSD and MRE. This demonstrates that LIBS technology coupled with chemometrics (CCA and SVR) is an appropriate method to estimate the mechanical properties of steel.