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Showing papers in "Journal of Analytical Atomic Spectrometry in 2020"


Journal ArticleDOI
TL;DR: In this paper, the authors made a comprehensive investigation on allanite U-Th-Pb chronology using secondary ion mass spectrometry (SIMS) and five allanites with variable elemental compositions and common lead concentrations have been used.
Abstract: Allanite, an epidote group mineral, occurs as a common accessory mineral in igneous, metamorphic rocks and hydrothermal deposits. It contains radioactive elements Th and U, making it a valuable U–Th–Pb geochronometer for various geological processes. Due to the structural and compositional complexity of allanite, in situ dating method is a better choice when the allanite is heterogeneous or has crystallized in multi-stage events. The wide variation of chemical compositions, however, raises the potential for matrix effects and complicates the use of in situ methods for allanite U–Th–Pb chronology. To address this issue, we made a comprehensive investigation on allanite U–Th–Pb chronology using Secondary Ion Mass Spectrometry (SIMS). Five allanite samples (CAP, Daibosatsu, SQ-51, Toba OTT, TARA allanite) with variable elemental compositions and common lead concentrations have been used. Allanites with variations in FeO (from 12.8 to 16.1 wt%) and similar ThO2 contents (around 1–2%) do not show significant matrix effects, as suggested by a previous study. While, obvious changes in calibration parameters (UO2+/U+, ThO2+/Th+) were noticed for allanites with a large range of Th contents (from 300 ppm to 2.0 wt%). By employing power law relationships between Pb+/U+versus UO2+/U+, Pb+/Th+versus ThO2+/Th+ with suitable exponentials, we do not observe obvious matrix effects with ThO2 concentrations variations. This study demonstrates that allanite can be a good geochronometer for multi-stage mineralization of hydrothermal deposits, providing valuable complementary information to zircon and monazite.

551 citations


Journal ArticleDOI
TL;DR: In this article, a review of single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is presented, where the authors identify necessary improvements and suggest directions for further developments which have the potential to bring the method closer to the ideal method for atomic spectroscopy.
Abstract: Single particle inductively coupled plasma mass spectrometry (spICP-MS or SP-ICP-MS depending on the author) is becoming an important tool for the characterization of nanoparticles (NPs). The method allows determining the size, size distribution, and particle number concentrations of NPs in suspensions after a mere few minutes of measurement. This review is modeled after the concept of “an ideal method for atomic spectroscopy” introduced by Gary M. Hieftje in his publication dedicated to Howard Malmstadt. This review discusses the instrumental developments in spICP-MS of recent years step-by-step, from the sample introduction system to the detector. The authors identify necessary improvements and suggest directions for further developments which have the potential to bring the method closer to “an ideal method for atomic spectroscopy”. The review also discusses the literature on coupling spICP-MS to separation and fractionation techniques including capillary electrophoresis (CE), field flow fractionation (FFF), and differential mobility analysis (DMA). The second part of the review is dedicated to the applications of spICP-MS. Key steps in sample preparation and selected instrumental conditions that were used in the published literature are summarized in a tabular form. Most frequently, spICP-MS is used for silver (Ag), gold (Au), and titanium dioxide (TiO2) nanomaterial analysis. Data acquisition was typically performed with millisecond dwell times in the past while a time resolution of hundreds of microseconds has been used more often in the last five years. The table may serve as a guide to choose an experimental procedure depending on the matrix that is present in the sample under investigation.

113 citations


Journal ArticleDOI
TL;DR: New freeware software, Iso-Compass, is presented, offering the potential to become a universal isotope data reduction platform for the geochemical community and two examples (radiogenic Sr isotope analysis and stable Zr isotopic analysis) are presented to demonstrate the effectiveness of this software.
Abstract: Currently, laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is a prominent and powerful method for in situ isotopic analysis. It provides high precision and spatially resolved isotopic information in solid samples. Data reduction of LA-MC-ICP-MS is inherently challenging owing to the severe mass spectral interferences and complex mass bias behaviors that occur during the analytical process. In this study, we present new freeware software, Iso-Compass, for isotope data reduction in LA-MC-ICP-MS. This software provides highly practical functions, including a simple data input interface, manually defined selection of laser and background signals, background correction, internal or external mass bias correction, interference correction, visual data presentation, and formatted data output. These functions can achieve easier and efficient reduction of LA-MC-ICP-MS data. The flexible formula editing mode enables Iso-Compass to be used in different isotope systems, thereby offering the potential to become a universal isotope data reduction platform for the geochemical community. Moreover, we present two examples (radiogenic Sr isotope analysis and stable Zr isotope analysis) to demonstrate the effectiveness of Iso-Compass.

92 citations


Journal ArticleDOI
TL;DR: In this article, an improved separation method (single column) permits the complete purification of K from the matrix elements, which is efficient and convenient and achieves a high yield (99.5 ± 0.6%) and low blank (<10 ng K) under complex matrix extraction conditions.
Abstract: Previous studies have shown that significant K isotope fractionation is found in continental weathering, oceanic crust subduction, and plant growth, suggesting that K isotopes could be a potentially important tracer. However, the complicated separation method and analytical conditions limit the precise analysis of potassium isotopes via MC-ICP-MS under “cold” plasma conditions. Here, an improved separation method (single column) permits the complete purification of K from the matrix elements. This method is efficient and convenient and achieves a high yield (99.5 ± 0.6%) and low blank (<10 ng K) under complex matrix extraction conditions. The high-resolution mode with a desolvating nebulizer system was used to increase the signal intensity of 41K+ and 39K+ and reduce 38ArH+, 40ArH+, and some oxide/nitride interference. To eliminate scattered ions or secondary electrons, we used a new dummy bucket to collect high intensity 40Ar+ beams. Besides, potassium isotopes for the standard SRM 3141a and new geological, environmental and biological reference materials such as DNC-1a, JMS-2, and GSB-14 were determined on a Nu Plasma 3 MC-ICP-MS instrument. Overall, the reproducibility of K isotope analysis was better than ±0.06‰ (2SD) that reported in most laboratories around the world. The measured δ41K values of the rock samples are homogeneous, consistent with the previous published data. However, the K isotope composition in soils, sediments, and plants is inhomogeneous and varies greatly from −0.85‰ to −0.25‰. These results show that potassium isotopes have great application potential in the geological, environmental, and biological fields.

70 citations


Journal ArticleDOI
TL;DR: In this article, the authors used inductively coupled plasma-mass spectrometry (ICP-MS) operated in single-particle mode for the characterization of metallic nanoparticles and their quantitative determination (particle number density).
Abstract: The occurrence of microplastics in many, if not all environmental compartments is a matter of increasing concern and deserves proper attention. However, there is still a lack of analytical tools for straightforward monitoring of these tiny plastic particles at environmentally relevant levels in water. Inductively coupled plasma-mass spectrometry (ICP-MS) operated in single-particle mode (SP-ICP-MS) was demonstrated to be a powerful technique for the characterization of metallic nanoparticles, but to the best of the authors' knowledge, SP-ICP-MS has not yet been evaluated for the purpose of detection of microplastics and their quantitative determination (particle number density). In this work, spherical polystyrene microspheres of 1 and 2.5 μm – to mimic microplastics coming from plastic waste – have been detected using ICP-MS. The approach developed relies on the ultra-fast monitoring of transient signals (with a dwell time of 100 μs) when using a quadrupole-based ICP-MS unit in the so-called single-event mode and registering the signal spikes produced by individual microparticles by monitoring the signal intensity at a mass-to-charge ratio (m/z) of 13 (13C+). The accuracy of the number-based concentration results (particle number densities) has been assessed by comparing the number of events detected when monitoring 13C+ to those detected when monitoring 165Ho+ for 2.5 μm lanthanide-doped polystyrene beads. Additionally, the results obtained for both polystyrene microspheres in terms of size (most frequently occurring intensity of the signal distribution) compare well with the size as determined using electron microscopy. ICP-MS operated in single-event mode thus allows information on both the size distribution and mass concentration of microplastics to be obtained. As this approach makes use of instrumentation already available in many routine labs analyzing environmental samples, it can enable these labs to analyze microplastics by using their instrument in single-event mode.

67 citations


Journal ArticleDOI
TL;DR: In this article, a review of the most commonly used techniques for solid sample analysis is presented, relating the main instrumental advances to the expansion of the methods developed in this subject, pointing out the potential ability to overcome spectral interference and matrix effects through the development of calibration strategies to achieve the success of solid sampling in several application areas.
Abstract: In recent decades, direct solid sample analysis has been reported in the literature as an alternative to traditional methods of sample preparation, becoming well established in the atomic spectrometry field. Therefore, this review discusses recent advances in different techniques such as flame atomic absorption spectrometry, graphite furnace atomic absorption spectrometry, high-resolution continuum source graphite furnace atomic absorption spectrometry, electrothermal vaporization, laser ablation, laser-induced breakdown spectroscopy, X-ray fluorescence spectrometry, glow discharge optical emission and mass spectrometry and arc/spark optical emission spectrometry, which are the most commonly used techniques for solid sample analysis. New possibilities such as nonmetal detection through molecular emission or absorption signals, speciation analysis, portable instrumentation for in situ analysis, and surface elemental mapping for obtaining chemical imaging will be discussed. Aspects associated with advantages and limitations are presented, relating the main instrumental advances to the expansion of the methods developed in this subject, pointing out the potential ability to overcome spectral interference and matrix effects through the development of calibration strategies to achieve the success of solid sampling in several application areas.

51 citations


Journal ArticleDOI
TL;DR: In this article, the authors highlight the fundamentals, instrumentation, and most recent trends of single-cell analysis by use of inductively coupled plasma-mass spectrometry (ICP-MS).
Abstract: This tutorial review article is highlighting the fundamentals, instrumentation, and most recent trends of single-cell analysis by use of inductively coupled plasma-mass spectrometry (ICP-MS). It is shown that metals and hetero-elements being intrinsically present in cells, taken up by cells (for instance engineered metallic nanoparticles) or binding to a cell can be detected qualitatively by existing ICP-MS technologies on a single cell level. Adding a quantitative dimension to single-cell analysis by (laser ablation-) ICP-MS requires dedicated calibration and validation strategies, which are currently being established and are being critically discussed. In a tutorial part, the ICP-MS instruments, the measurement conditions, and the sample introduction and preparation techniques are introduced. The application section focuses on the state-of-the-art of single-cell analysis in suspension, using laser ablation or (imaging) mass cytometry. Finally, future trends are critically assessed.

40 citations


Journal ArticleDOI
TL;DR: In this paper, an improved Cd purification and cleaning resin scheme for low-Cd samples using AGMP-1M resin with >90% Cd recovery, the ratios of trace elements Sn, Mo, Zr, etc. to Cd in the samples, which could potentially jeopardize the accuracy and precision of Cd isotope analysis under a high-sensitivity setup, were less than 0.001 after purification.
Abstract: With new advancements in MC-ICP-MS technology, small Cd isotope fractionations in geological processes have attracted more interest in recent years. However, challenges remain in obtaining high-precision Cd isotope data for geological samples with low Cd concentrations and complex matrices. By an improved Cd purification and cleaning resin scheme for low-Cd samples using AGMP-1M resin with >90% Cd recovery, the ratios of trace elements Sn, Mo, Zr, etc. to Cd in the samples, which could potentially jeopardize the accuracy and precision of Cd isotope analysis under a high-sensitivity setup, were less than 0.001 after purification, and the total procedure blank is ≤0.1 ng. Hence, a sample containing 20–30 ng Cd can be employed for purification and subsequent isotope measurement. Cadmium isotope fractionation (expressed in δ114/110Cd relative to NIST 3108) during column separation and instrument mass bias was corrected for by a 111Cd–113Cd double spike. NIST 3108 was determined at a concentration of 5–25 ng mL−1 on a Neptune Plus (112Cd signal intensity: ∼640 V ppm−1) and 25–50 ng mL−1 on a Nu plasma III (112Cd signal intensity:∼280 V ppm−1) MC-ICP-MS equipped with an Aridus II/III desolvator for more than one year, with a total external analytical precision of 0.034‰ (2SD, n = 181). NIST SRM 2711a, NOD-P-1 and GSS-1 were measured at 5, 10, 20, 25 and 50 ng mL−1 levels to be 0.532 ± 0.038‰, 0.133 ± 0.038‰ and 0.098 ± 0.027‰, respectively, indicating that good accuracy and precision of Cd isotope analysis can be achieved with an injecting sample size as low as 5 ng Cd. Our method can be reliably applied to various geological reference materials (GRMs). The δ114/110Cd values of GRMs with relatively high and low Cd concentrations are consistent with previous studies: NOD-A-1 (0.124 ± 0.067‰), GSD-11 (−0.274 ± 0.037‰) and BCR-2 (−0.030 ± 0.063‰). SGR-1b (0.069 ± 0.049‰), GSH-1 (−0.337 ± 0.077‰) and others are reported for the first time in this paper. The δ114/110Cd in basalt and stream sediments is relatively homogeneous and overlaps with that of the bulk silicate earth (BSE). The δ114/110Cd in shale and soils varies greatly from −0.694 to 0.532‰. Human hair and other animal organs are enriched in light isotopes relative to BSE, whereas terrestrial plants are enriched in heavy isotopes.

36 citations


Journal ArticleDOI
TL;DR: A review of the literature in the field of arsenic speciation analysis of environment samples published between 2004 and 2018 can be found in this article, with the focus on the analytical procedures according to the matrix investigated and the species researched.
Abstract: Relevant papers in the field of arsenic speciation analysis of environment samples published between 2004 and 2018 have been reviewed, with the focus on the analytical procedures according to the matrix investigated and the species researched. It emerged that suitable analytical methods have been developed for the identification and quantification of about fifty arsenic compounds in the main environmental matrices, including soil, sediments, terrestrial and marine organisms, atmospheric particulate and various types of natural waters. Various extraction/partitioning schemes have been applied, depending on the arsenic species (water- or lipid-soluble) and the matrix (biotic or abiotic), whereas water samples were generally analyzed directly. Liquid chromatography (LC) combined with inductively coupled plasma mass spectrometry was by far the analytical technique of choice, but a significant number of works also applied other couplings (LC to further atomic and mass spectrometry techniques) or X-ray methods. By the application of these procedures, a great amount of information on the occurrence of arsenic in the environment has been obtained, as well as the elucidation of the main processes involved and the discovery of new compounds, like arsenolipids and thio-arsenicals. However, remaining gaps and challenges still exist, both in the fundamental research on the origin and transformation of arsenic compounds in various environmental compartments and in the routine monitoring of toxic arsenic species. It is hence likely that the attempt to address these issues will drive the future research in the field.

34 citations


Journal ArticleDOI
Qingyang Li1, Ye Tian1, Boyang Xue1, Nan Li1, Wangquan Ye1, Yuan Lu1, Ronger Zheng1 
TL;DR: In this article, the authors developed an effective normalization method by using the plasma image information for underwater LIBS analysis, showing a good linear relationship between the spectral line intensity and plasma image intensity.
Abstract: Laser-induced plasma in water always suffers from strong pulse-to-pulse fluctuations due to the multiple breakdown phenomenon, leading to a poor stability of underwater LIBS signals. The traditional normalization method by using the internal standard element is often limited in some practical cases due to the lack of a suitable element as a reference. In this work, we developed an effective normalization method by using the plasma image information for underwater LIBS analysis. Correlations between the plasma images and LIBS spectra were firstly studied, showing a good linear relationship between the spectral line intensity and plasma image intensity. Subsequently, the spectral line intensities were standardized by using the corresponding image intensities and then used for quantitative analysis. A good normalization model was established by using partial least squares regression (PLSR). With the proposed method, the average relative standard deviations (RSDs) of validation samples were significantly reduced from 10.71% to 5.76%, and the average relative errors (AREs) of the validation samples were also reduced from 7.80% to 7.55%. Moreover, by combining the proposed method with the internal standard method, the average RSD and ARE can be further reduced to 4.07% and 4.86%, respectively, both of which are better than those obtained using the internal standard method only.

30 citations


Journal ArticleDOI
TL;DR: In this article, microdroplets composed of elemental solutions are used for the transport of discrete amounts of elemental species into the ICP, and signals produced from micro-droplets closely match those produced by NPs.
Abstract: In single-particle inductively coupled plasma mass spectrometry (sp-ICP-MS), individual nanoparticles are detected by measuring ICP-MS signals with high temporal resolution. At high time resolution, particle-based signals—which are around 200–500 μs in duration—make up a larger fraction of the signal measured. If the dissolved background is low enough and the mass of element(s) of interest in the particles is high enough, then nanoparticle (NP) signals are recognized as signal spikes on the time trace. With modern instrumentation, sp-ICP-MS can be used to quantify NPs with element mass down to single-digit attogram levels. Monodisperse microdroplets composed of elemental solutions are vehicles for the transport of discrete amounts of elemental species into the ICP, and signals produced from microdroplets closely match those produced by NPs. Temporal durations and element sensitivities obtained from microdroplets and NPs are so similar that microdroplets may be used as NP proxies. Unlike NPs, microdroplets offer a flexible platform for user-designed sp-ICP-MS measurements because—with microdroplets—we can precisely control the absolute mass of elements injected into the plasma in each droplet. Controlled introduction of analyte mass into the ICP enables us to use microdroplets to generate sensitivity calibration factors and also to use microdroplets as NP proxies to study sp-ICP-MS measurement accuracy. Here, were report several instances of how measuring microdroplet-based element signals with ICP-TOFMS has allowed us to expand the versatility, as well as the general understanding, of sp-ICP-TOFMS measurements. First, we summarize how microdroplets can be used for online calibration of analyte NP element mass and particle-number concentration. Second, we describe how the measurement of microdroplets with tailored analyte masses helps us to refine, test, and validate sp-ICP-TOFMS data analysis strategies. Specifically, we use microdroplets to study the accuracy and robustness of split-event correction and signal-thresholding approaches for NP detection. Together, these experiments describe how the use of monodisperse microdroplets allows us to design better sp-ICP-MS experiments.

Journal ArticleDOI
TL;DR: In this article, an analytical protocol for in situ U-Pb isotope dating of wolframite series minerals (Fe,Mn)WO4, the main ore mineral for tungsten, by LA-SF-ICP-MS is presented.
Abstract: We present an analytical protocol for in situ U–Pb isotope dating of wolframite series minerals [(Fe,Mn)WO4], the main ore mineral for tungsten, by LA-SF-ICP-MS. Precision and accuracy of the protocol was intensively assessed using our newly developed well-characterized U–Pb wolframite reference material. The tungsten oxide interference on Hg and Pb was investigated in detail. The matrix effect between ferberite and hubnerite during laser ablation was thoroughly examined for wolframite series minerals with a different Mn/(Mn + Fe) ratio. The closure temperature of wolframite, with respect to the U–Pb system, was evaluated. The application of eleven wolframite samples, with ages from ∼1780 Ma to ∼26 Ma, robustly demonstrated the feasibility of our approach. Most studied wolframite series minerals yielded U–Pb concordant or subconcordant ages. Samples with a relatively high U content and negligible common Pb content typically had a 206Pb/238U age precision of ca. 1%. The new in situ data agree well with published cassiterite or wolframite ages from the same locations. LA-SF-ICP-MS, with the advantages of high sensitivity, rapidity, and relatively low cost, as well as moderate spatial resolution (i.e., 32 or 44 μm) that is sufficiently high to avoid sulfide inclusions, is the method of choice for in situ wolframite U–Pb microanalysis.

Journal ArticleDOI
TL;DR: In this article, a method for the accurate determination of number concentration of inorganic nanoparticles (NP) by single particle inductively coupled plasma mass spectrometry (spICP-MS) using the novel dynamic mass flow (DMF) approach is systematically described.
Abstract: Methodology for the accurate determination of number concentration of inorganic nanoparticles (NP) by single particle inductively coupled plasma mass spectrometry (spICP-MS) using the novel dynamic mass flow (DMF) approach is systematically described. Using this method the determination of transport efficiency (TE) is achieved without the need for a reference nanomaterial. The impact of key parameters on the accuracy and uncertainty of the number concentration data obtained with this approach was evaluated. In particular the number of detected NP in the time scan is the major contributing factor to the overall measurement uncertainty. For Au NP of spherical shape with number based concentration in the range of 4.0 × 1012 to 2.0 × 1014 kg−1 (depending on the particle size) a relative expanded uncertainty (k = 2) of less than 10% was achieved. This reference methodology was also evaluated for the accurate determination of number concentration of more complex NP namely triethanolamine (TEA)-stabilised TiO2 NP, for which like-for-like NP reference materials are not available. Using a sample mass flow of 0.3578 g min−1 (with an associated uncertainty of 0.0002 g min−1, k = 1) the average transport efficiencies for Au NP (in trisodium citrate) and TiO2 NP (in TEA/NaOH) were very similar (7.57 ± 0.13% and 7.77 ± 0.22%, k = 1, respectively). Finally the number concentration values for both NP types agreed well with those obtained using particle tracking analysis (PTA), providing evidence for the good agreement between mass-based TE of the sample and NP-based TE with the newly proposed method.

Journal ArticleDOI
TL;DR: In this paper, the application of laser-induced breakdown spectroscopy (LIBS) for classification of rocks with the total alkali-silica (TAS) diagram is considered.
Abstract: The application of laser-induced breakdown spectroscopy (LIBS) for classification of rocks with the total alkali-silica (TAS) diagram is considered in this work. The attractive feature of LIBS compared to other spectrochemical techniques used for TAS classification in geological studies and especially for Mars exploration, such as X-ray fluorescence (XRF) and alpha particle X-ray spectrometry (APXS), consists in its ability for in situ stand-off analysis of samples in their natural state. The analysis accuracy of LIBS for geological samples, rocks, crusts, and soils, is however, seriously affected by the matrix effects due to the various chemical compositions and the different surface physical states of the samples. In this work with an originally designed experiment, a collection of 20 rocks were analyzed in the three different states: natural rock, with a polished surface and pressed pellets. This allowed the simulation of a real application scenario where a prediction model built with calibration standards prepared in a laboratory in the form of pressed pellets, is used to predict chemical compositions with the LIBS spectra acquired from geological samples in their natural state. In the framework of the TAS classification, the concentration of the major compounds in the rocks, SiO2, Na2O, and K2O, was thus determined first with univariate calibration models which were clearly affected by both the chemical and physical matrix effects. Multivariate calibration models were then developed based on machine learning to predict the concentrations of the above 3 compounds and perform the TAS classification. An efficient reduction of the chemical matrix effect has been demonstrated, and the influence of the physical matrix effect has been investigated in the cases of both univariate and multivariate calibration models.

Journal ArticleDOI
TL;DR: In this paper, a thermal ionization mass spectrometer (TIMS) was used for the determination of stable zirconium isotope ratios in geological materials by using a single DGA resin column with a small usage of acids.
Abstract: A new analytical method for the accurate and precise determination of stable zirconium isotope ratios in geological materials by thermal ionization mass spectrometry (TIMS) is presented. Isobaric interference from Mo was largely eliminated during filament heating and further reduced by off-line Mo interference correction. This methodology allows the complete elimination of Mo interference even with a Mo/Zr ratio up to 1. Separation of Zr from natural sample matrices was achieved by using a single DGA resin column with a small usage of acids (15 mL of 7 mol L−1 HNO3 and 3 mL of 1 mol L−1 HF). A 91Zr–96Zr double spike was admixed with samples before digestion, which enabled the correction of isotope fractionation that could occur during column separation and mass spectrometry measurement. The long-term measurement reproducibility of δ94Zr is generally better than ±0.06‰ (uncertainty represented by two standard deviations, hereinafter referred to as 2 SD), assessed by repeated analyses of Zr standard reference NIST SRM 3169 and eleven geological reference materials. The Zr isotope ratios of geological reference materials BHVO-2 and AGV-2 obtained in this study are consistent with the reported values measured by MC-ICP-MS, confirming the accuracy of the proposed method. This new method greatly simplifies the chemical separation process and is particularly suitable for Zr isotope analysis of complex matrix (especially for high Mo) samples.

Journal ArticleDOI
TL;DR: In this paper, a support vector machine (SVM) classification method was used to classify coal samples into three categories and then, the partial least squares regression (PLSR) was employed to establish different models for each type of coal.
Abstract: Determination of the ash content, volatile matter and calorific value in coal with laser-induced breakdown spectroscopy (LIBS) is significantly affected by the matrix effect, due to the physical and chemical properties of different types of coals. This work aimed to achieve more accurate determination of the ash content, volatile matter and calorific value via the classification of coal samples by their ash contents. The support vector machine (SVM) classification method, which was optimized by using a genetic algorithm (GA), was used to classify the coal samples into three categories. And then, the partial least squares regression (PLSR) was employed to establish different models for each type of coal. With this detailed classification scheme, the coefficient of determination (R2) of the training set and test set of volatile matter was improved from 0.9269 and 0.9310 to 0.9959 and 0.9888, respectively. The root-mean-square error of cross-validation (RMSECV) and the root-mean-square error of prediction (RMSEP) of volatile matter were also reduced from 1.9940% and 1.8320% to 0.4989% and 0.7719%, respectively. The results of the ash content and calorific value are also improved. This work demonstrated that this LIBS-based quantitative analysis method can be widely used in the coal industry to improve current coal property analysis.

Journal ArticleDOI
TL;DR: In this paper, a random forest (RF) model fusing variable importance and wavelet transform was proposed to determine the K content in a potassic salt ore, and the effect of different variable importance thresholds on the quantitative results was explored.
Abstract: Potash is the main raw material for the production of agricultural fertilizers. Herein, random forest (RF) models fusing variable importance and wavelet transform were proposed to determine the K content in a potassic salt ore. Specifically, 53 potassic salts samples were analyzed, of which 37 were treated as the calibration set. An original RF model was developed for regression with the optimized parameters ntree and mtry. However, RP2 (0.7399) and the modeling time (251.8 s) of the RF model were not satisfactory. Thus, we initially explored the effect of different variable importance (VI) thresholds on the quantitative results. When the VI threshold was set to 0.090, the variable number of the VIRF model was reduced from 27 620 to 3355. There were no significant improvements for VIRF in the other model performance parameters such as RMSEP and RP2. Then, wavelet transform was adopted to screen the input variables of the RF model (defined as WTRF). Their promotion ratios were 16% (RP2 from 0.7399 to 0.8555), 38% (RMSEP from 0.1798 to 0.1106), 62% (MRE from 0.2740 to 0.1032), and 11% (MRSD from 0.0686 to 0.0613). In the case of modeling time, it was promoted by about three orders of magnitude. Upon further using the variable importance for the WTRF model (defined as WT-VIRF), because all the selected input variables filtered by wavelet transform contributed significantly to the quantitative results, no more variables were removed and then, the WT-VIRF model achieved the exact result with the WTRF model. Thus, all the results demonstrate that the RF model combined with WT is a promising methodology for the quantitative analysis of the K content in potassic salt ores.

Journal ArticleDOI
TL;DR: In this paper, an automated two-stage chromatographic procedure, combining a pre-purification stage to remove the majority of matrix elements (AG® 50W-X12), with an adaptation of an existing method using anion exchange resin AG®MP-1 has been used to overcome these problems.
Abstract: Measurements of Cu isotopes from low concentration and high salinity matrices require high recovery and purity, prior to measurement. An automated two-stage chromatographic procedure, combining a pre-purification stage to remove the majority of matrix elements (AG® 50W-X12), with an adaptation of an existing method using anion exchange resin AG®MP-1 has been used to overcome these problems. A series of matrices were tested, from low (river water) to high salinity (synthetic seawater, human serum), using several standards and reference materials such as Trace Metals 1 (−0.21‰ ± 0.08 2SD), SLRS-5 (+0.30‰ ± 0.05 2SD), Seronorm™ (−0.25‰ ± 0.04 2SD), and NASS-7 seawater, doped with ERM®-AE633 (0.00‰ ± 0.14 2SD). Results demonstrated highly pure (>98%) Cu separations, low procedure blanks (<1% of loaded Cu), and much improved measurement reproducibility of <0.14‰ (2SD) for high salinity samples. This is an important development for δ65Cu measurement from low Cu concentrations commonly encounted in research of medical isotope metallomics, mineral exploration, and environmental geochemistry. As with other studies, combining standard-sample bracketing with Ga for internal normalisation to correct instrumental mass bias (C-SSBIN) resulted in a significant improvement in the precision of measurements (versus standard sample bracketing alone), typically improving the external reproducibility of measurements from 0.10 down to 0.03‰ (2SD).

Journal ArticleDOI
TL;DR: In this article, the role of ambient air pressure during the interaction of an ultrafast laser beam with two metallic targets (brass and uranium) with significantly different oxygen gas-phase reactivity was explored.
Abstract: Ultrafast laser ablation coupled with optical emission spectroscopy is currently under development for standoff detection of elements and their isotopes for a wide range of application areas. In this work, we explore the role of ambient air pressure during the interaction of an ultrafast laser beam with two metallic targets (brass and uranium) with significantly different oxygen gas-phase reactivity. Plasma plumes were generated by focusing ∼800 nm, ∼35 fs pulses from an ultrafast laser system using a long focal length lens (f = 1 m). Two-dimensional spectral imaging was performed over the pressure range of 30 mTorr to 700 Torr air to evaluate emission dynamics, plasma chemistry, signal-to-background ratio, and characteristic parameters (i.e. excitation temperature, electron density). An increase in ambient air pressure during ultrafast laser ablation leads to plume confinement and subsequent changes in the emission dynamics due to plasma chemistry as well as changes in plasma generation conditions (i.e. focused fs laser ablation versus filament ablation). Ablation crater morphologies were also investigated via scanning electron microscopy. Results indicate atomic emission intensity and signal-to-background ratios peak at moderate pressure levels (∼50–100 Torr air) for both targets studied, although plasma chemistry influences uranium emission signatures. The emission features of the uranium plasma at pressures ≥10 Torr showed the presence of oxide molecules. We also find filament ablation leads to wider, more shallow craters compared to focused laser ablation. Our study provides unique insight into the interplay between plume dynamics, confinement, and plasma chemistry of fs laser-produced plasmas and how these phenomena evolve with changing ambient air pressure.

Journal ArticleDOI
TL;DR: In this article, the double-spike method was applied to test whether zircon crystallization in carbonatite magmatic systems is a driver of Zr isotope fractionation.
Abstract: Zirconium (Zr) plays a key role in the development of phases like zircon (ZrSiO4) and baddeleyite (ZrO2) in magmatic systems. These minerals are crucial for the study of geologic time and crustal evolution, and their high resistivity to weathering and erosion results in their preservation on timescales of billions of years. Although zircon and baddeleyite may also preserve a robust record of Zr isotope behavior in high-temperature terrestrial environments, little is known about the factors that control Zr isotope partitioning in magmatic systems, the petrogenetic significance of fractionated compositions, or how these variations are recorded in Zr-rich accessory phases. Here, we describe a new analytical protocol for accurately determining the Zr stable isotope composition of zircon by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS), using the double-spike method to correct for procedural and instrumental mass bias. We apply this technique to test whether zircon crystallization in carbonatite magmatic systems is a driver of Zr isotope fractionation by interrogating the internal zonation of a zircon megacryst from the Mud Tank carbonatite (MTUR1). We find the MTUR1 megacryst to lack internal zoning within analytical uncertainties with a mean μ94/90ZrNIST = −55 ± 28 ppm (2 SD, n = 151), which suggests that zircon crystallization is not a driver of Zr isotope fractionation in carbonatite magmas. This observation is in stark contrast with those made in silicate magmatic systems, raising the possibility that the bonding environment of Zr4+ ions may be fundamentally different in carbonatite vs. silicate melts. Because of its remarkable homogeneity, the MTUR1 megacryst is an ideal natural reference material for Zr isotopic analysis of zircon using both solution and spatially resolved methods. The reproducibility of a pure Zr solution and our chemically purified zircon fractions indicate that the external reproducibility of our method is on the order of ±28 ppm for μ94/90Zr, or ±7 ppm per amu, at 95% confidence.

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TL;DR: In this article, the matrix effect in two-element Zr-containing alloys using TOF-SIMS was investigated and it was observed that Zr ionization efficiency is over four times higher in the Si matrix than in the Cu matrix and over two times higher when compared to the results obtained in the Al matrix.
Abstract: The matrix effect, i.e. the dependence of element ion yield on the surrounding chemical state, is very often considered as a negative and limiting factor in elemental characterization. In fact, it is the main reason making Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) a non-quantitative technique as element ionization efficiency can span over several orders of magnitude depending on the matrix. Despite that, even small chemical variations of an experimental setup can cause interpretation of TOF-SIMS depth profiles a challenging task. However, the sensitivity of element ionization to the neighboring atoms can also be very beneficial as ion yields can be enhanced in the presence of particular species such as oxygen, cesium, water and fluorine. In this work, we make an attempt to estimate the matrix effect in two-element Zr-containing alloys using TOF-SIMS. The Zr ionization efficiency as well as its response to the surface and interface contaminants was investigated depending on Al, Si and Cu matrices. It was observed that Zr ionization efficiency is over four times higher in the Si matrix than in the Cu matrix and over two times higher when compared to the results obtained in the Al matrix.

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TL;DR: In this paper, the effects of laser wavelength (213 nm and 193 nm), laser frequency (5 Hz and 10 Hz), laser carrier gas (He, H2, and N2), dwell time, and external standard calibration on the accuracy and precision of 87Rb/86Sr and 87Sr/86 Sr ratios and ages are investigated.
Abstract: The Rb–Sr isotopic system is widely used in geochronology. Conventionally burdened by the isobaric overlap of 87Rb and 87Sr, Rb/Sr dating in situ has only recently become achievable with the newly developed LA-ICP-MS/MS system. Simultaneous use of reactive gas (e.g. O2, N2O, or CH3F) during LA-ICP-MS/MS analysis has been shown to resolve the Rb and Sr overlap, thus now making available key spatial and temporal information that can only be accessed via in situ analytical techniques. The accuracy and precision of Rb/Sr ratios and ages are largely dependent on the laser and ICP-MS/MS parameters used. Rb/Sr isotopic analysis by LA-ICP-MS/MS is a recently developed technique and these parameters are yet to be fully explored. We investigate the effects of laser wavelength (213 nm and 193 nm), laser frequency (5 Hz and 10 Hz), laser carrier gas (He, H2, and N2), dwell time, and external standard calibration on the accuracy and precision of 87Rb/86Sr and 87Sr/86Sr ratios and ages. These analytical conditions have been tested on the commercially available reference materials: NIST SRM 610, USGS BHVO-2G, and pressed nano-particulate powder tablet CRPG Mica-mg, as well as a Monastery phlogopite megacryst. Our results show that accuracy and precision for 87Rb/86Sr and 87Sr/86Sr ratios are significantly affected by laser wavelength and frequency. Variation in these parameters can strongly magnify any matrix effects which directly influences the ability to apply effective external corrections. We obtain the best accuracy and precision when using a 193 nm laser wavelength, ablating at a frequency of 5 Hz (0.30 2s% and 0.15 2s% for 87Rb/86Sr and 87Sr/86Sr ratios, respectively). Meanwhile we find that age accuracy is highly dependant on external reference materials. When these analytical settings are put to test on the Monastery phlogopite, we obtain an age of 90.0 ± 3.6 (0.24% accuracy) when using mica-mg (87Rb/86Sr) and NIST 610 (87Sr/86Sr) as external standards.

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TL;DR: In this article, a 6 W low pressure Hg lamp, with a coiled quartz reactor and atomic fluorescence spectrometric detection, was used to produce cadmium ultraviolet photochemical vapor.
Abstract: Cadmium ultraviolet photochemical vapor generation was investigated using a 6 W low pressure Hg lamp, with a coiled quartz reactor and atomic fluorescence spectrometric detection. Volatile species of cadmium can be reproducibly generated from a formic acid based medium with the addition of ferrous ions, which enhances the generation efficiency some 2.6-fold. Further improvement can be achieved by increasing the pH of the medium to 2.7 and through the addition of Triton X-100 downstream of the reactor. The overall generation efficiency was estimated by two approaches; from the remaining waste, to be 17.3% (SD 2.2%) and from a comparison of the response to direct solution nebulization coupled to an inductively coupled plasma mass spectrometer, to be 5.5% (SD = 0.2%). A limit of detection of 1.8 ng mL−1 and repeatability (RSD) of 2.1% at 250 ng mL−1 were achieved with atomic fluorescence spectrometric detection. Severe interferences were observed from nitric acid and nitrates as well as from the –SH group containing compounds and selected chalcogens, which makes the routine application of this methodology difficult.

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TL;DR: In this article, the laser-induced breakdown spectroscopy (LIBS) technique coupled with random forest (RF) and least squares support vector machine (LSSVM) methods was proposed to perform the quantitative and classification analyses of atmospheric sedimentation.
Abstract: The laser-induced breakdown spectroscopy (LIBS) technique coupled with random forest (RF) and least squares support vector machine (LSSVM) methods was proposed to perform the quantitative and classification analyses of atmospheric sedimentation. The LIBS spectra of 16 atmospheric sedimentation samples with different locations were obtained via the LIBS measurement system, and the major elements of the atmospheric sedimentation samples were identified by the National Institute of Standards and Technology (NIST) database. For quantitative analysis, first, the best pretreatment method needs to be selected to process the LIBS spectra of the four metal elements (Pb, Cu, Zn and Al) of atmospheric sedimentation samples obtained from 16 locations. Then, RF, LSSVM and PLS calibration models were constructed with the optimal pretreatment spectra as input variables. The performances of the three calibration models were compared by the correlation coefficient of cross-validation (RCV2) and root mean square error of cross-validation (RMSECV) to obtain an optimal model. Finally, the optimal model was verified by the correlation coefficient of prediction (RP2) and root mean square error of prediction (RMSEP). The satisfactory quantitative results of Pb, Cu and Al are the RF calibration model, and Zn is the LSSVM calibration model. For classification analysis, first, the best pretreatment method needs to be selected to process the LIBS spectra of the atmospheric sedimentation samples. Then, RF, LSSVM and PLS-DA were constructed with the best pretreatment spectra as input variables. Finally, the five factors, i.e., accuracy, sensitivity, precision, specificity and area under curve (AUC) were used to evaluate the predictive performance of the three classification models, and the LSSVM classification model exhibited better prediction in pollution source discrimination. It was confirmed that the LIBS technique coupled with the RF and LSSVM methods is a promising approach to achieve the analysis of atmospheric sedimentation.

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Wen Zeng1, Jing Hu1, Hanjiao Chen1, Zhirong Zou1, Xiandeng Hou1, Xiaoming Jiang1 
TL;DR: In this paper, a method of cobalt ion assisted enhancement of photochemical vapor generation-atomic fluorescence spectrometry (PVG-AFS) was proposed for sensitive determination of ultratrace tellurium(IV).
Abstract: A method of cobalt ion assisted enhancement of photochemical vapor generation-atomic fluorescence spectrometry (PVG-AFS) was proposed for sensitive determination of ultratrace tellurium(IV). With a mixture of 5% (v/v) formic acid and 20% (v/v) acetic acid as the reaction medium, more than 13-fold improvement in AFS intensity for Te(IV) was achieved simply by adding 1 mg L−1 Co2+ as a homogeneous catalyst. A possible reaction mechanism was proposed with the characterization results of GC-MS and electron paramagnetic resonance (EPR). Under optimal conditions, the limit of detection (LOD) for Te(IV) was 0.06 μg L−1, with a relative standard deviation (RSD) of 1.3% (10 μg L−1 Te, 7 times). The accuracy and utility of this methodology were validated by analysis of real water samples, with satisfactory recoveries of 91–108%.

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TL;DR: In this article, the effect of a third additional laser pulse on orthogonal double-pulse laser-induced breakdown spectroscopy (DP LIBS) was examined and the 3P LIBS results showed up to 5fold improvement of the signal to background ratio compared with both DP LIBS arrangements and up to 228fold improvement in comparison to conventional SP LIBS.
Abstract: The goal of this work is to examine the effect of a third additional laser pulse on orthogonal double-pulse laser-induced breakdown spectroscopy (DP LIBS). Namely, a pre-ablation laser pulse and re-heating laser pulse were combined into triple-pulse LIBS (3P LIBS) to achieve plasma emission enhancement. The experiment was designed with emphasis on causing minimal sample damage by utilizing nanosecond laser pulses. It means that the energy of ablation laser pulses was set to the minimal value for which the intensities of selected spectral lines were above the limits of detection. This energy as well as the energies of the pre-ablation and the re-heating laser pulses were kept constant for all experimental arrangements. The interpulse delays for both DP LIBS and for 3P LIBS configurations were optimized for signal enhancements. The 3P LIBS results showed up to 5-fold improvement of the signal to background ratio compared with both DP LIBS arrangements and up to 228-fold improvement in comparison to conventional SP LIBS. In addition, it has been shown that the spectral lines with a higher value of excitation energy prove higher enhancement in both DP LIBS and 3P LIBS configurations. To explain this effect, the dimensions of ablation craters were measured for each configuration using a 3D optical microscope and the temperature was determined from the slope of the Boltzmann plot. It was shown that the pre-ablation causes an increase of ablation crater dimensions and the re-heating increases the plasma temperature.

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TL;DR: In this article, the pH effect on the detection of toxic metals in wastewater by laser-induced breakdown spectroscopy coupled with a phase transformation method (LIBS-PT) was investigated.
Abstract: Heavy metal particles in water are mainly derived from acidic industrial wastewater and seriously endanger the environment and public health. In this work, the pH effect on the detection of toxic metals in wastewater by laser-induced breakdown spectroscopy coupled with a phase transformation method (LIBS-PT) was investigated. Heavy metals of cadmium (Cd) and chromium (Cr) were selected as examples. The results showed that the presence of acids in wastewater inhibited the spectral enhancement of LIBS-PT on a metal substrate. This was mainly due to the presence of the salt floccule formed by the reaction of an acid with a metal substrate on the substrate surface. The floccule content increased as pH decreased, and the corresponding substrate ablation threshold increased. Therefore, more laser energy was used for ablation, resulting in reduced laser energy for ionization and reduced electron density. Eventually, spectral intensity decreased as electron density decreased. However, there was no significant change in plasma temperature. Meanwhile, the determination coefficients (R2) of Cd and Cr were all above 0.99 under the optimal pH 6.5 and on the optimal zinc (Zn) substrate. Limits of detection (LoDs) of 0.0089 mg L−1 and 0.0006 mg L−1 for Cd and Cr were obtained, respectively. The LoDs of Cd and Cr elements met the sewage discharge standard of China. The results indicated that the detection sensitivity of heavy metal elements in acidic wastewater can be significantly improved by optimizing the pH value of the solution using LIBS-PT.

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TL;DR: In this article, different approaches relying on either chemical or physical (mass) resolution, to avoid this spectral interference otherwise jeopardizing accurate results, were assessed, and the performance of on-mass and mass-shift approaches was evaluated using different types of quadrupole-based ICP-MS instrumentation, including single-quadrupole (SQ) and tandem ICPMS (ICP-MS/MS) units.
Abstract: As a result of their unique physical, chemical and/or biological properties, the use of engineered nanoparticles (ENPs) is growing very rapidly. Iron oxide nanoparticles (IONPs) are of particular interest owing to their magnetic properties, and thus the development of suitable methods for their characterization is essential. Inductively coupled plasma-mass spectrometry (ICP-MS) operated in single-particle (SP) mode provides different types of relevant information, such as size distribution and particle number and mass concentrations. However, the use of SP-ICP-MS becomes less straightforward when the analyte signal is subject to spectral overlap. In the case of IONPs, characterization by means of SP-ICP-MS is hindered by the occurrence of ArO+ polyatomic ions with the same nominal mass-to-charge (m/z) ratio as the most abundant Fe isotope. In this work, different approaches relying on either chemical or physical (mass) resolution, to avoid this spectral interference otherwise jeopardizing accurate results, were assessed. In the case of chemical resolution, the performance of on-mass and mass-shift approaches was evaluated using different types of quadrupole-based ICP-MS instrumentation, including single-quadrupole (SQ) and tandem ICP-MS (ICP-MS/MS) units. Physical resolution was accomplished using a new generation of sector field (SF) ICP-MS instrumentation, capable of dealing with transient signals of extremely short duration (10–100 μs dwell time), even when operated at higher mass resolution (pseudo-resolution mode). Based on the figures-of-merit obtained for the different approaches evaluated, an on-mass approach using NH3 as the reaction gas in SQ-ICP-MS, an on-mass approach using H2 as the collision/reaction gas in ICP-MS/MS and pseudo-medium resolution in SF-ICP-MS were found to be the best-suited approaches for fast interference-free monitoring of the ion signals generated by IONPs in SP mode. While the use of chemical (H2/on-mass) and physical (pseudo-medium) resolutions also provided accurate and precise results for custom-made Fe3O4 (magnetite) NPs of ≈50 nm, the use of NH3 was less successful, as it leads to an extension of the SP pulse profile and a lower signal-to-background ratio. Finally, SF-ICP-MS operated in pseudo-medium resolution mode was used for the characterization of Fe3O4 NPs synthesized electrochemically (batch and continuous operation mode).

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Zongyu Hou1, Muhammad Sher Afgan1, Sahar Sheta1, Jiacen Liu1, Zhe Wang1 
TL;DR: In this article, the authors modulated the evolution of the laser-induced plasma by shaping the laser beam from a commonly used Gaussian profile to a flat-top profile with a more homogeneous distribution of laser power density.
Abstract: Uncertainty reduction is of great importance for laser-induced breakdown spectroscopy (LIBS) In this work, we modulated the evolution of the laser-induced plasma by shaping the laser beam from a commonly used Gaussian profile to a flat-top profile With a more homogeneous distribution of laser power density, the flat-top beam was expected to achieve a more stable plasma morphology by more uniform ablation, which would lead to higher repeatability of LIBS signals, and to reduce plasma shielding effects by avoiding excessively high laser power at the center of the laser beam, which would lead to stronger signals The results showed that by using a flat-top beam, the aluminum–magnesium alloy plasma morphology was meliorated with a larger and more stable plasma core, the relative standard deviation (RSD) of the Mg(I) 28521 nm line was reduced from 33% to 18% for a laser energy of 30 mJ, and the signal intensity was enhanced 15 to 35 times for different laser energies Overall, plasma modulation using beam shaping was proved to be very effective in improving LIBS signal quality

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TL;DR: In this article, laser-induced breakdown spectroscopy (LIBS) using a handheld instrument was evaluated as a fast and easy method to analyse the silver content in natural gold.
Abstract: Gold is traded in virtually every country around the world. Consequently, tracing gold provenance is a difficult but necessary task to ensure a responsible supply chain from deposit to consumer. Measuring the silver content is often the first step in characterizing gold to retrace its origin. In this study, laser-induced breakdown spectroscopy (LIBS) using a handheld instrument was evaluated as a fast and easy method to analyse the silver content in natural gold. Six commercial gold alloys and natural gold from French Guiana were used. Our results demonstrate that handheld LIBS is relevant to gold traceability and is simple to use in the field. The micron-scale focused laser beam allows in situ analyses of small gold grains with acceptable reproducibility. Univariate and multivariate regression modelling was performed to assess the best calibration model for quantification of the Ag content. The quadratic univariate model was selected for its good predictive ability, with a coefficient of determination R2 of 0.99 and a mean average error of 0.36 wt% Ag for prediction. The LIBS analyses of natural gold were compared to the EPMA data using a statistical test that allow distinct gold populations to be discriminated (or matched) and the results indicate it would be suitable for identifying unknown samples. We were able to successfully trace the origin of our “unknown” samples, a promising first step in the goal of delivering a low-cost field-based tool for responsible supply chain management.