Tree ring microanalysis by LA–ICP–MS for environmental monitoring: validation or refutation? Two case histories

An empirical approach is presented for validating trace metal profiles in tree rings for use as environmental archives. Concentration profiles of Zn, Cd, Cu, Pb and U in tree rings and lake sediments are compared for assessing the reliability of the former as an environmental proxy. Laser ablation sampling in conjunction with inductively coupled plasma mass spectrometry (LA–ICP–MS) is used for the direct analysis of tree rings. An optimised analytical protocol is devised with particular emphasis on sample preparation and quantification strategy. Significant correlations in the two environmental archives were found for zinc, copper and uranium, while cadmium and lead temporal trends, although showing enrichment in recent years, do not agree with the concentration profiles in lacustrine sediment cores. A chemical model based on metal affinity for hard type ligands present in wood is proposed to explain these results. Moreover, spring and winter wood are analysed separately thanks to the high spatial resolution of laser ablation sampling. As a result, enhanced metal loadings are shown to lead to intraring differences in trace metal concentrations.     

Direct Determination of Aluminum in Archaeological Clays by Laser‐Induced Breakdown Spectroscopy

Abstract

Instrumental techniques that allow the direct analysis of solids with little or no sample preparation are particularly important for the evaluation of samples that are difficult to analyze such as refractory or geological materials. Laser‐induced breakdown spectroscopy (LIBS) is a promising technique for the direct, rapid analysis of elements in solid materials with minimal sample preparation. The main advantages over wet techniques are virtual nondestructiveness and analysis speed. The goal of this work is the direct determination of aluminum of archaeological pieces using laser‐induced breakdown spectroscopy. The corresponding signals of metals were interpolated from calibration graphs of different salts of the metals. The matrix effects from the direct determination of these elements were thoroughly investigated. The potential of this technique for direct quantitative analysis of real archaeological materials (from Department of Ancient Science, University of Zaragoza) was evaluated, and the reproducibility of LIBS spectra from different archaeological samples was measured as a function of the number of laser shots. Finally, the results from LIBS are compared with those obtained by laser ablation inductively coupled plasma mass spectrometry.     

Scanning vs. single spot laser ablation (λ=213 nm) inductively coupled plasma mass spectrometry

Sampling strategy is defined in this work as the interaction of a repetitively pulsed laser beam with a fixed position on a sample (single spot) or with a moving sample (scan). Analytical performance of these sampling strategies was compared by using 213 nm laser ablation ICP-MS. A geological rock (Tuff) was quantitatively analyzed based on NIST series 610-616 glass standard reference materials. Laser ablation data were compared to ICP-MS analysis of the dissolved samples. The scan strategy (50 μm/s) produced a flat, steady temporal ICP-MS response whereas the single spot strategy produced a signal that decayed with time (after 60 s). Single-spot sampling provided better accuracy and precision than the scan strategy when the first 15 s of the sampling time was eliminated from the data analysis. In addition, the single spot strategy showed less matrix dependence among the four NIST glasses.     

Development and fundamental investigation of Laser Ablation Glow Discharge Time-Of-Flight Mass Spectrometry (LA-GD-TOFMS)

Glow Discharge (GD) spectroscopy is a well known and accepted technique for the bulk and surface composition analysis, while laser ablation (LA) provides analysis with high spatial-resolution analysis in LIBS (laser-induced breakdown spectroscopy) or when coupled to inductively coupled plasma spectrometry (ICP-OES or ICP-MS). This work concerns the construction of a Laser Ablation Glow Discharge Time-Of-Flight Mass Spectrometry (LA-GD-TOFMS) instrument to study the analytical capabilities resulting from the interaction of a laser-generated sample plume with a pulsed glow discharge. Two ablation configurations were studied in detail. In a first approach, the laser-generated plume was introduced directly into the GD, while the second approach generated the plume inside the GD. The ablated material was introduced at different times with respect to the discharge pulse in order to exploit the efficient ionization in the GD plasma. For both LA-GD configurations, direct ablation into the afterglow of the pulsed glow discharge leads to an ion signal enhancement of up to a factor of 7, as compared to the ablation process alone under the same experimental conditions. The LA-GD enhancement was found to occur exclusively in the GD afterglow, with a maximum ablation S/N occurring in a few hundred microseconds after the termination of the glow discharge. The duration of the enhanced signal is about two milliseconds. Both the laser pulse energy and the position of the ablation plume (with respect to the sampling orifice) were found to affect the amount of mass entering the afterglow region and consequently, the enhancement factor of ionization.     

Laser ablation sample transfer for localized LC‐MS/MS proteomic analysis of tissue

We have developed a mid‐infrared laser ablation sampling technique for nano‐flow liquid chromatography coupled with tandem mass spectrometry proteomic profiling of discrete regions from biological samples. Laser ablation performed in transmission geometry was used to transfer material from 50‐µm thick tissue sections mounted on a glass microscope slide to a capturing solvent. Captured samples were processed using filter‐aided sample preparation and enzymatically digested to produce tryptic peptides for data‐dependent analysis with an ion trap mass spectrometer. Comparison with ultraviolet laser capture microdissection from neighboring regions on the same tissue section revealed that infrared laser ablation transfer has higher reproducibility between samples from different consecutive sections. Both techniques allowed for proteomics investigation of different organelles without the addition of surfactants. Copyright © 2016 John Wiley & Sons, Ltd.     

Analysis of solid samples by ICP-mass spectrometry

Summary ICP-Mass spectrometry is typically used as a technique for very rapid multielement analysis at trace and ultra-trace levels of solutions by continuous sample aspiration and nebulization. However, ICP-MS is well suited to be used as a detector for other sample introduction devices. For the analysis of solid samples laser sampling and electrothermal vaporization accessories may be used as sample introduction devices for ICP-MS. Laser sampling permits the analysis of many different types of solid materials. For solid sampling ETV-ICP-MS analysis it is of advantage to reduce the sample to a fine powder prior to analysis. For automated analysis powders may be introduced as slurries into the graphite furnace by means of a slurry sampling device. Since appropriate certified solid reference materials are not always available for calibration, or since they are not certified for all analyte elements of interest, the analyses discussed in this contribution were performed semiquantitatively. The instrument response function was established using reference materials which were similar in their composition to the samples. The results of semiquantitative bulk analyses of glass (NIST 612) and geological material (USGS GXR-3) by laser sampling ICP-MS are in good agreement with the certified values. The concentrations of the analytes determined in the glass sample were in the range of 10 g/g to 80 g/g. The lowest analyte concentration in the geological sample was 0.4 g/g (Eu) and the highest was approximately 186 mg/g (Fe). The precision achieved was in the order of 5% to 15%. Laser sampling ICP-MS is not only suitable to bulk analysis but also to analyses where spatial information is required. As an example for such an application the determination of Pb in a wine bottle cork stopper is dicussed. The slurry sampling technique was used for the semiquantitative analysis of NIST coal reference samples by electrothermal vaporization ICP-MS. The accuracy achieved with this approach was within a factor of ±2 of the reference values.     

电感耦合等离子体质谱激光烧蚀固体进样技术新进展

本文简单地介绍了电感耦合等离子体质谱(LA-ICP-MS)的基本原理及装置。分别对LA-ICP-MS在飞秒激光器、紫外激光器、固液气溶胶混合进样、集合式小样品标样、原位统计分布技术上的技术新进展进行了详细的评述。     

Evaluation of different sample introduction approaches for the determination of boron in unalloyed steels by inductively coupled plasma mass spectrometry

An extended study of different sampling introduction approaches using inductively coupled plasma mass spectrometry (ICP-MS) is presented for the determination of boron in steel samples. The following systems for sample introduction were applied: direct sample solution nebulization by continuous nebulization (CN) using a cross-flow nebulizer and with flow injection (FI), applied to 0.1% (m/v) and 0.5% (m/v) sample solutions, respectively; FI after iron matrix extraction, using acetylacetone–chloroform, and isotopic dilution (ID) analysis as the calibration method; FI with on-line electrolytic matrix separation; and spark ablation (SA) and laser ablation (LA) as solid sampling techniques. External calibration with matrix-matching samples was used with CN, SA, and LA, and only acid solutions (without matrix matching) with FI methods. When FI was directly applied to a sample solution, the detection limit was of 0.15 μg g⁻¹, improving by a factor of 4 that was obtained from the CN measurements. Isotopic dilution analysis, after matrix removal by solvent extraction, made it possible to analyse boron with a detection limit of 0.02 μg g⁻¹ and, with the on-line electrolytic process, the detection limit was of 0.05 μg g⁻¹. The precision for concentrations above 10 times the detection limit was better than 2% for CN, as well as for FI methods. Spark and laser ablation sampling systems, avoiding digestion and sample preparation procedures, provided detection limits at the μg g⁻¹ levels, with RSD values better than 6% in both cases. Certified Reference Materials with B contents in the range 0.5–118 μg g⁻¹ were used for validation, finding a good agreement between certified and calculated values.     

Laser ablation isotope ratio mass spectrometry for enhanced sensitivity and spatial resolution in stable isotope analysis

Stable isotope analysis permits the tracking of physical, chemical, and biological reactions and source materials at a wide variety of spatial scales. We present a laser ablation isotope ratio mass spectrometry (LA‐IRMS) method that enables δ¹³C measurement of solid samples at 50 µm spatial resolution. The method does not require sample pre‐treatment to physically separate spatial zones. We use laser ablation of solid samples followed by quantitative combustion of the ablated particulates to convert sample carbon into CO₂. Cryofocusing of the resulting CO₂ coupled with modulation in the carrier flow rate permits coherent peak introduction into an isotope ratio mass spectrometer, with only 65 ng carbon required per measurement. We conclusively demonstrate that the measured CO₂ is produced by combustion of laser‐ablated aerosols from the sample surface. We measured δ¹³C for a series of solid compounds using laser ablation and traditional solid sample analysis techniques. Both techniques produced consistent isotopic results but the laser ablation method required over two orders of magnitude less sample. We demonstrated that LA‐IRMS sensitivity coupled with its 50 µm spatial resolution could be used to measure δ¹³C values along a length of hair, making multiple sample measurements over distances corresponding to a single day's growth. This method will be highly valuable in cases where the δ¹³C analysis of small samples over prescribed spatial distances is required. Suitable applications include forensic analysis of hair samples, investigations of tightly woven microbial systems, and cases of surface analysis where there is a sharp delineation between different components of a sample. Copyright © 2011 John Wiley & Sons, Ltd.     

固体进样元素分析技术在农业领域的应用

重金属是农产品、农田土壤、肥料、饲料等农业样品中的重要污染物,传统的实验室分析方法需繁琐的前处理,耗时费力,无法满足重金属的快速检测需求。固体进样元素分析技术具有简化样品前处理、便捷、绿色、高效等优势,在农业领域中元素的快速检测分析中具有良好的应用前景。通过对固体进样元素分析技术,包括样品导入技术和电热蒸发、电感加热、激光烧蚀、X射线荧光光谱、激光诱导击穿光谱等固体进样分析系统进行综述,并对这些技术在农业领域中的应用做了进一步的梳理。固体进样分析技术已在农业样品中元素的快速检测、现场监测、风险评估等工作中发挥着举足轻重的作用,相信随着仪器研发、材料科学、机器学习等新兴技术的快速发展,其结构小巧、使用简单、分析迅速等优势将会充分发挥,为农业领域中质量安全监管提供一种更为有效、可靠的快速检测手段。     

Methodologies for laboratory Laser Induced Breakdown Spectroscopy semi-quantitative and quantitative analysis—A review

Since its early applications, Laser Induced Breakdown Spectroscopy has been recognized as a useful tool for solid state chemical analysis. However the quantitative accuracy of the technique depends on the complex processes involved in laser induced plasma formation, ablation, atomization, excitation and ion recombination. Problems arising from laser target coupling, matrix effect, fractionation in target vaporization, local thermodynamic equilibrium assumption and interferences from additional air ionization should be properly addressed in order to obtain reliable quantitative results in laboratory to be used as starting point during field campaigns.     

Application of laser ablation inductively coupled mass spectrometry (LA-ICP-MS) for the determination of major, minor, and trace elements in bark samples

The large surface area of barks from many tree species enables the effective accumulation of pollutants. Therefore, the analysis of bark material will provide useful information about the degree of pollution of a certain region. The determination of main, minor, and trace elements (Al, Ca, Cd, Ce, Cr, Cu, Fe, Mn, P, Pb, S, Ti and Zn) in bark was performed with an Nd:YAG laser coupled to an ICP-MS system. Bark standards for the calibration by laser ablation ICP-MS were prepared from different bark layers which differ for some relevant elements in concentrations. Four digestion procedures for the decomposition of the standard pellets, the numbers of laser shots per sample and of samples per region necessary have been investigated. Representative results were obtained for 5 or more samples taken from different individuals of one species of a sampling area and the averaged element concentrations of 10 separately placed laser shots for each sample. Laser ablation ICP-MS was applied for the characterization of real bark samples from different regions with high and low pollution burden. It was shown that the method is well suited to characterize different degrees of environmental impact. Anthropogenic sources were responsible for the higher concentrations of most of the elements under investigation.     

Direct determination of polycyclic aromatic hydrocarbons in solid matrices using laser desorption/laser photoionization ion trap mass spectrometry

The development and characterization of a new instrument for solid sampling which couples IR laser desorption followed by UV laser photo-ionization and analysis using an ion trap mass spectrometer has been investigated. For calibration, a new type of solid sample preparation involving activated charcoal as the solid substrate was used. This solid sample provided a steady signal for several thousand laser shots, which allowed optimization of the experimental procedure. It was found that both the IR and UV intensity and the delay between them play an important role in both the magnitude and type of signals observed. A method of gas phase accumulation with multiple laser shots was examined. Finally, this technique was demonstrated to be effective in providing direct qualitative information for N.I.S.T. SRM 1944 river sediment sample with no sample pre-treatment.     

Combining transmission geometry laser ablation and a non‐contact continuous flow surface sampling probe/electrospray emitter for mass spectrometry based chemical imaging

This paper describes the coupling of ambient pressure transmission geometry laser ablation with a liquid‐phase sample collection into a continuous flow surface sampling probe/electrospray emitter for mass spectrometry based chemical imaging. The flow probe/emitter device was placed in close proximity to the surface to collect the sample plume produced by laser ablation. The sample collected was immediately aspirated into the probe and onto the electrospray emitter, ionized and detected with the mass spectrometer. Freehand drawn ink lines and letters and an inked fingerprint on microscope slides were analyzed. The circular laser ablation area was about 210 µm in diameter and under the conditions used in these experiments the spatial resolution, as determined by the size of the surface features distinguished in the chemical images, was about 100 µm. Published in 2011 by John Wiley & Sons, Ltd.     

Application of laser ablation inductively coupled mass spectrometry (LA-ICP-MS) for the determination of major, minor, and trace elements in bark samples

The large surface area of barks from many tree species enables the effective accumulation of pollutants. Therefore, the analysis of bark material will provide useful information about the degree of pollution of a certain region. The determination of main, minor, and trace elements (Al, Ca, Cd, Ce, Cr, Cu, Fe, Mn, P, Pb, S, Ti and Zn) in bark was performed with an Nd:YAG laser coupled to an ICP-MS system. Bark standards for the calibration by laser ablation ICP-MS were prepared from different bark layers which differ for some relevant elements in concentrations. Four digestion procedures for the decomposition of the standard pellets, the numbers of laser shots per sample and of samples per region necessary have been investigated. Representative results were obtained for 5 or more samples taken from different individuals of one species of a sampling area and the averaged element concentrations of 10 separately placed laser shots for each sample. Laser ablation ICP-MS was applied for the characterization of real bark samples from different regions with high and low pollution burden. It was shown that the method is well suited to characterize different degrees of environmental impact. Anthropogenic sources were responsible for the higher concentrations of most of the elements under investigation. Received: 26 April 1999 / Revised: 24 August 1999 / /Accepted: 28 August 1999     

Quantitative analysis by resonant laser ablation with optical emission detection: Resonant laser-induced breakdown spectroscopy

Resonant laser ablation (RLA) is a solid sampling technique that makes use of radiation trapping, and desorption induced by electronic transitions (DIET), to produce enhanced numbers of analyte atoms in the laser-induced plasma (LIP). This is achieved by tuning the laser ablation wavelength to a gas-phase resonant transition of the analyte. In this paper, RLA was coupled with detection of optical emission in the LIP to perform resonant laser-induced breakdown spectroscopic (RLIBS) experiments with a miniature, portable spectrometer. The experiments were designed to continue an examination of the proposed mechanism of RLA, and to perform an initial assessment of the applicability of RLIBS for quantitative analysis. The study indicated that for a multi-component sample, such as steel, the signal of the wavelength-targeted atom was enhanced the most compared to other constituents, and this supported the hypothesis that the DIET phenomenon is involved. Also, RLIBS experiments indicated that ablation yields of other components were enhanced by resonant ablation of the major component, which supported the contribution of radiation trapping to the RLA phenomenon. A linear, positive slope of the RLA induced atom yield as a function of concentration suggested that the RLA mechanism allows for quantitative analysis of solid samples. Calibration graphs were created for tungsten in spectrographic steels using RLIBS. A limit of detection of 4% was calculated for tungsten in steel.     

Multiplicity and contiguity of ablation mechanisms in laser-assisted analytical micro-sampling

Laser ablation is implemented in several scientific and technological fields, as well as a rapid sample introduction technique in elemental and trace analysis. At high laser fluence, the ejection of micro-sized droplets causes the enhancement of the surface recession speed and depth resolution degradation as well as the alteration of the sampling stoichiometry. The origin of such large particles seems to be due to at least two different processes, phase explosion and melt splashing. Experimental evidence for both was found in metallic matrices, whereas non-metallic samples showed more complex phenomena like cracking. The spatial distribution of the beam energy profile is responsible for significant differences in the ablation mechanism across the irradiated region and for heterogeneous sampling. Under Gaussian irradiance distribution, the center of the crater, where the irradiance is the highest, experienced a fast heating with rapid ejection of a mixture of particles and vapor (spinodal breakdown). The crater periphery was subjected to more modest irradiation, with melt mobilization and walls formation. The overall resulting particle size distribution was composed of an abundant nano-sized fraction, produced by vapor condensation, and a micro-sized fraction during melt expulsion.     

双电离源(辉光放电/激光溅射电离)四极杆质谱仪的研制

本研究将辉光电离源与激光溅射电离源巧妙地结合在同一台仪器中,使固体样品在离子源腔体中既能辉光电离,也能激光电离;并且使用同一质量分析器,两种离子源的结果可以相互比对,进而得到更为准确的分析结果.此仪器主要由真空系统、离子源、离子传输系统、四极杆质量分析器及检测与数据采集系统等组成.实验中分别用两种离子源测试了标准样品SRM 1262b,并获得了半定量结果.结果表明,仪器具有定性能力强,分析速度快,检测灵敏度高等优点,对固体样品元素分析的检出限可达μg/g量级.实验表明,激光溅射电离质谱的性能优于辉光放电质谱.     

Laser ablation inductively coupled plasma atomic emission spectrometry of a uranium-zirconium alloy: ablation properties and analytical behavior

The ablation properties and analytical behavior of a uranium-zirconium alloy have been examined using tandem laser ablation/pneumatic nebulization sample introduction in conjunction with inductively coupled atomic emission spectrometry (LA-ICP-AES). An apparent change in composition of the laser ablation aerosol (1–15 GW cm⁻² Zr deficient, 40–250 GW cm⁻² Zr rich) is observed. This phenomenon is independent of laser wavelength. After collection and bulk chemical analysis of the ablation product, this phenomenon is attributed to an atomization interference in the ICP.

Two distinct modes of laser ablation have been observed which depend upon the wavelength of the ablating laser (visible or near infrared). These two modes result in characteristic ablation crater types and analyte emission behavior. Ablation yields at 1064 nm are dependent upon laser power density only, whilst yields at 532 nm are dependent upon both laser power density and illumination area. The latter is considered to be symptomatic of direct interaction of the laser light with the surface, and the former, of indirect coupling of laser energy, via a micro-plasma, into the surface.