Elemental Analysis of Cement by Calibration-Free Laser Induced Breakdown Spectroscopy (CF-LIBS) and Comparison with Laser Ablation – Time-of-Flight – Mass Spectrometry (LA-TOF-MS), Energy Dispersive X-Ray Spectrometry (EDX), X-Ray Fluorescence Spectroscopy (XRF), and Proton Induced X-Ray Emission Spectrometry (PIXE)

The purpose of the present study is to determine the elemental composition of Pakistani cement brands using calibration-free laser induced breakdown spectroscopy (CF-LIBS) and to compare the obtained results with the other analytical techniques such as, laser ablation – time-of-flight – mass spectrometry (LA-TOF-MS), energy dispersive X-ray spectrometry (EDX), X-ray fluorescence spectroscopy (XRF) and proton induced X-ray emission spectrometry (PIXE). Compositional results reveal that all the cement brands are mainly composed of calcium, silicon, iron, aluminum, magnesium, potassium, sodium, titanium, lithium and strontium with varying concentrations. The compositions obtained by LIBS and LA-TOF-MS are in good agreement with results obtained by the other standard techniques and demonstrate the potential use of LIBS for the online monitoring of industrial cement production.     

Analysis of Soil by Magnetic Field Assisted Calibration-Free Laser Induced Breakdown Spectroscopy (CF-LIBS) and Laser Ablation – Time-of-Flight Mass Spectrometry (LA-TOF-MS)

The qualitative and quantitative analysis of soil samples collected from Sialkot, Pakistan (which contains leather industrial plants), has been performed using laser-induced breakdown spectroscopy (LIBS) and laser ablation time of flight mass spectrometry (LA-TOF-MS). The focused beam of a Q-switched Nd: YAG laser (532?nm) was used to ablate the soil samples in air at atmospheric pressure. The optical emission spectra demonstrate the presence of the spectral lines of Si, Fe, Al, Ca, Ti, K, Cr, Mg, Na, Ba, and Li in all of the samples. The emission lines intensities, electron number densities, and excitation temperatures were significantly enhanced in the presence of an external 0.3 T magnetic field applied perpendicular to the plasma plume. A maximum enhancement factor of approximately 8 was observed in the emission intensity. The emergence of several additional lines has also been detected using the magnetic field-assisted LIBS approach. The elemental composition determined using calibration-free laser-induced breakdown spectroscopy (CF-LIBS), with and without magnetic field, reveals that the external magnetic field only adjusts the laser-generated plasma dynamics without affecting the quantitative analysis of the samples. Importantly, the toxic and heavy elements such as chromium and barium were detected and quantified in all of the soil samples by both of these techniques. The variations in the compositional analysis using CF-LIBS with and without the applied magnetic field and LA-TOF-MS were less than 10%.     

Quantification of Aluminum Gallium Arsenide (AlGaAs) Wafer Plasma Using Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS)

In this work, we report the results of the compositional analysis of an aluminum gallium arsenide (AlGaAs) sample using the calibration-free laser-induced breakdown spectroscopy (CF-LIBS) technique. The AlGaAs sample was doped with three various concentrations of gallium (Ga), arsenic (As), and aluminum (Al), as reported by the manufacturer, and the CF-LIBS technique was employed to identify the doping concentration. A pulsed Q-switched Nd: YAG laser capable of delivering 200 and 400 mJ energy at 532 and 1064 nm, respectively, was focused on the target sample for ablation, and the resulting emission spectra were captured using a LIBS 2000+ spectrometer covering the spectral range from 200 to 720 nm. The emission spectra of the AlGaAs sample yielded spectral lines of Ga, As, and Al. These lines were further used to calculate the plasma parameters, including electron temperature and electron number density. The Boltzmann plot method was used to calculate the electron temperature, and the average electron temperature was found to be 5744 ± 500 K. Furthermore, the electron number density was calculated from the Stark-broadened line profile method, and the average number density was calculated to be 6.5 × 10¹⁷ cm⁻³. It is further observed that the plasma parameters including electron temperature and electron number density have an increasing trend with laser irradiance and a decreasing trend along the plume length up to 2 mm. Finally, the elemental concentrations in terms of weight percentage using the CF-LIBS method were calculated to be Ga: 94%, Al: 4.77% and As: 1.23% for sample-1; Ga: 95.63%, Al: 1.15% and As: 3.22% for sample-2; and Ga: 97.32%, Al: 0.69% and As: 1.99% for sample-3. The certified concentrations were Ga: 95%, Al: 3% and As: 2% for sample-1; Ga: 96.05%, Al: 1% and As: 2.95% for sample-2; and Ga: 97.32%, Al: 0.69% and As: 1.99% for sample-3. The concentrations measured by CF-LIBS showed good agreement with the certified values reported by the manufacturer. These findings suggest that the CF-LIBS technique opens up an avenue for the industrial application of LIBS, where quantitative/qualitative analysis of the material is highly desirable.     

A Comparative Study of Calibration Free Methods for the Elemental Analysis by Laser Induced Breakdown Spectroscopy

We have used two calibration free laser induced breakdown spectroscopy (CF-LIBS) methods for the quantitative analysis of Pb–Sn alloys with different compositions. The first method is based on Boltzmann plots where the elemental concentration is determined from the intercept along the y-axis whereas the second method is the electron density conservation method, in which elemental compositions are determined by comparing the experimentally measured number density with the theoretical results obtained by CF-LIBS. The neutral spectral lines of lead and tin have been used for the estimation of plasma temperature by the Boltzmann plot method whereas the Saha–Boltzmann equation has been used to calculate the electron number density. By comparing the results of both CF-LIBS methods, it is concluded that the CF-LIBS (electron number density conservation) method is more appropriate than the CF-LIBS (Boltzmann plot method) for the quantitative elemental analysis.     

Comparative measurements of mineral elements in milk powders with laser-induced breakdown spectroscopy and inductively coupled plasma atomic emission spectroscopy

Mineral elements contained in commercially available milk powders, including seven infant formulae and one adult milk, were analyzed with inductively coupled plasma atomic emission spectrometry (ICP-AES) and laser-induced breakdown spectroscopy (LIBS). The purpose of this work was, through a direct comparison of the analytical results, to provide an assessment of the performance of LIBS, and especially of the procedure of calibration-free LIBS (CF-LIBS), to deal with organic compounds such as milk powders. In our experiments, the matrix effect was clearly observed affecting the analytical results each time laser ablation was employed for sampling. Such effect was in addition directly observed by determining the physical parameters of the plasmas induced on the different samples. The CF-LIBS procedure was implemented to deduce the concentrations of Mg and K with Ca as the internal reference element. Quantitative analytical results with CF-LIBS were validated with ICP-AES measurements and nominal concentrations specified for commercial milks. The obtained good results with the CF-LIBS procedure demonstrate its capacity to take into account the difference in physical parameters of the plasma in the calculation of the concentrations of mineral elements, which allows a significant reduction of the matrix effect related to laser ablation. We finally discuss the way to optimize the implementation of the CF-LIBS procedure for the analysis of mineral elements in organic materials.     

Calibration-Free Laser-Induced Breakdown Spectroscopy: State of the art

The aim of this paper is offering a critical review of Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS), the approach of multi-elemental quantitative analysis of LIBS spectra, based on the measurement of line intensities and plasma properties (plasma electron density and temperature) and on the assumption of a Boltzmann population of excited levels, which does not require the use of calibration curves or matrix-matched standards. The first part of this review focuses on the applications of the CF-LIBS method. Quantitative results reported in the literature, obtained in the analysis of various materials and in a wide range of experimental conditions, are summarized, with a special emphasis on the departure from nominal composition values. The second part is a discussion of the simplifying assumptions which lie at the basis of the CF-LIBS algorithm (stoichiometric ablation and complete atomization, thermal equilibrium, homogeneous plasma, thin radiation, detection of all elements). The inspection of the literature suggests that the CF-LIBS method is more accurate in analyzing metallic alloys rather than dielectrics. However, the full exploitation of the method seems to be still far to come, especially for the lack of a complete characterization of the effects of experimental constraints. However, some general directions can be suggested to help the analyst in designing LIBS measurements in a way which is more suited for CF-LIBS analysis.     

Laser Spectroscopic Characterization for the Rapid Detection of Nutrients along with CN Molecular Emission Band in Plant-Biochar

We report a quantitative analysis of various plant-biochar samples (S1, S2 and S3) by utilizing a laser-induced breakdown spectroscopy (LIBS) technique. For LIBS analysis, laser-induced microplasma was generated on the target surface by using a focused beam through a high-power Nd: YAG laser and optical emission spectra were recorded using a charged coupled device (CCD) array spectrometer, with wavelength ranges from 200 nm to 720 nm. The spectroscopical analysis showed the existence of various ingredients, including H, Li, Ca, Na, Al, Zn, Mg, Sr, Si, and Fe, along with a CN molecular emission band due to B²Σ⁺ − X²Σ⁺ electronic transition. By assuming conditions of the plasma is optically thin and in LTE, calibration-free laser-induced breakdown spectroscopy (CF-LIBS) was utilized for the compositional analysis of the ingredients present in the three plant-biochar samples. To lower the uncertainties, we used an average composition (%) of the three plant-biochar samples. The quantitative study of the plant-biochar samples was also achieved using the energy dispersive X-ray (EDX) technique, showing good agreement with the CF-LIBS technique. In addition, statistical analysis, such as principal component analysis (PCA), was performed for the clustering and classification of the three plant-biochar samples. The first three PCs explained an overall ~91% of the variation in LIBS spectral data, including PC1 (58.71%), PC2 (20.9%), and PC3 (11.4%). These findings suggest that LIBS is a robust tool for rapid measurement of heavy as well as light elements, such as H, Li, and nutritional metals in plant-biochar samples.     

Laser Induced Breakdown Spectroscopy methodology for the analysis of copper-based-alloys used in ancient artworks

In this paper Laser Induced Breakdown Spectroscopy has been applied for determining the elemental composition of a set of ancient bronze artworks coming from archaeological site of Minervino Murge — Southern of Italy (dated around VII b.C.). Before carrying on the analysis of the archaeological samples, the characterization of the analytical technique has been accomplished by investigating the trueness of the typical assumptions adopted in LIBS, such as Local Thermodynamic Equilibrium, congruent ablation and plasma homogeneity. With this purpose, two different laser pulse durations, 7 ns and 350 fs, have been used. We have focused our attention on LIBS analysis of bronze standards by considering and discussing the bases of both methodology and analytical approach to be followed for the analysis of ancient copper-based-alloy samples. Unexpectedly, regardless from the laser pulse duration, the LIBS technique has shown, by considering an adequate approach on the emitting plasma features, that its peculiarities are anyway preserved so that a fast analysis of ancient copper-based-alloys can be achieved. After verifying the suitability of the methodology, it has been possible to fulfill the typical assumptions considered for the LIBS calibration curves method and use it for ancient bronze artworks analysis.     

Evaluation of laser induced breakdown spectroscopy for the determination of macronutrients in plant materials

Laser induced breakdown spectroscopy (LIBS) has become an analytical tool for the direct analysis of a large variety of materials in order to provide qualitative and/or quantitative information. However, there is a lack of information for LIBS analysis of agricultural and environmental samples. In this work a LIBS system has been evaluated for the determination of macronutrients (P, K, Ca, Mg) in pellets of vegetal reference materials. An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm and an Echelle spectrometer with ICCD detector. The plasma temperature was estimated by Boltzmann plots and instrumental parameters such as delay time, lens-to-sample distance and pulse energy were evaluated. Certified reference materials as well as reference materials were used for analytical calibrations of P, K, Ca, and Mg. Most results of the direct analysis of plant samples by LIBS were in reasonable agreement with those obtained by ICP OES after wet acid decomposition.     

Detection of heavy metals in Arabian crude oil residue using laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) was applied for the elemental analysis of Arabian crude oil residue samples. The spectra due to trace elements such as Ca, Fe, Mg, Cu, Zn, Na, Ni, K and Mo were recorded using this technique. The dependence of time delay and laser beam energy on the elemental spectra was also investigated. Prior to quantitative analysis, the LIBS system was calibrated using standard samples containing these trace elements. The results achieved through this method were compared with conventional technique like inductively coupled plasma.     

激光诱导击穿光谱(LIBS)法微损快速检测党参中Pb

中药材重金属元素快速检测对污染监控及人们健康具有重要意义。激光诱导击穿光谱技术(Laser Induced Breakdown Spectroscopy, LIBS)属于一种快速检测方法,研磨压片等预处理方法相对样品消解已有所简化,但破坏了样品的物理性质,且不能满足中药材大宗品种、大批量检测需求。若进一步简化样品预处理,将更加凸显LIBS快速检测的优势。本文建立了激光诱导击穿光谱技术(LIBS)快速微损检测中药材样品重金属元素定标方法。线性相关系数R2为0.7764,建立的微损定标曲线线性可用于切片党参LIBS快速检测,对待测党参切片样品检测平均相对误差为3.74%,与电感耦合等离子体质谱法(ICP-MS)对比,相关系数R2为0.7957,验证了LIBS技术微损检测的可行性。制备的党参参考定标样品可多次重复用于待测样定标和仪器标定等。实验对待测党参样品仅进行切片处理,避免了研磨、压片等预处理,更加充分地体现LIBS快速检测的优势,为LIBS技术应用于中药材重金属元素快检等领域提供了一种新方法。     

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.     

Laser ionization mass spectrometry in inorganic trace analysis

Summary Among the different spectrometric techniques for trace analysis Laser Ionization Mass Spectrometry (LIMS) is well established as a trace analytical method. With the LIMS technique the sample material is evaporated and ionized by means of a focused pulsed laser in a laser microplasma, which is formed in the spot area of the irradiated sample. All chemical elements in the sample materials are evaporated and ionized in the laser plasma. The ions formed are separated according to their mass and energy by a time-of-flight, quadrupole or double focusing mass spectrometer. In this review the characteristics and analytical features, some recent developments and applications of laser ionization mass spectrometry in inorganic trace analysis are described.     

Laser induced breakdown spectroscopy on meteorites

The classification of meteorites when geological analysis is unfeasible is generally made by the spectral line emission ratio of some characteristic elements. Indeed when a meteorite impacts Earth's atmosphere, hot plasma is generated, as a consequence of the braking effect of air, with the consequent ablation of the falling body. Usually, by the plasma emission spectrum, the meteorite composition is determined, assuming the Boltzmann equilibrium. The plasma generated during Laser Induced Breakdown Spectroscopy (LIBS) experiment shows similar characteristics and allows one to verify the mentioned method with higher accuracy. On the other hand the study of Laser Induced Breakdown Spectroscopy on meteorite can be useful for both improving meteorite classification methods and developing on-flight techniques for asteroid investigation.

In this paper certified meteorites belonging to different typologies have been investigated by LIBS: Dofhar 461 (lunar meteorite), Chondrite L6 (stony meteorite), Dofhar 019 (Mars meteorite) and Sikhote Alin (irony meteorite).     

Artificial neural network for Cu quantitative determination in soil using a portable Laser Induced Breakdown Spectroscopy system

Laser Induced Breakdown Spectroscopy (LIBS) is an advanced analytical technique for elemental determination based on direct measurement of optical emission of excited species on a laser induced plasma. In the realm of elemental analysis, LIBS has great potential to accomplish direct analysis independently of physical sample state (solid, liquid or gas). Presently, LIBS has been easily employed for qualitative analysis, nevertheless, in order to perform quantitative analysis, some effort is still required since calibration represents a difficult issue. Artificial neural network (ANN) is a machine learning paradigm inspired on biological nervous systems. Recently, ANNs have been used in many applications and its classification and prediction capabilities are especially useful for spectral analysis. In this paper an ANN was used as calibration strategy for LIBS, aiming Cu determination in soil samples. Spectra of 59 samples from a heterogenic set of reference soil samples and their respective Cu concentration were used for calibration and validation. Simple linear regression (SLR) and wrapper approach were the two strategies employed to select a set of wavelengths for ANN learning. Cross validation was applied, following ANN training, for verification of prediction accuracy. The ANN showed good efficiency for Cu predictions although the features of portable instrumentation employed. The proposed method presented a limit of detection (LOD) of 2.3 mg dm^− 3 of Cu and a mean squared error (MSE) of 0.5 for the predictions.     

Inductively coupled plasma mass spectrometric study of non-linear calibration behavior during laser ablation of binary Cu–Zn Alloys

Laser ablation behavior of a suite of 10 Cu–Zn binary alloys was studied using inductively coupled plasma mass spectrometry. Three laser systems (20 ns KrF excimer, 6 ns and 35 ps Nd:YAG) were used for ablation. Non-linear calibration plots for both Cu and Zn were observed using all three lasers, despite significant differences in laser ablation mechanisms and good stoichiometry of ablated mass. Crater volume measurements were used to determine the amount of mass removed during repetitive laser ablation from each sample. A change in mass ablation rate for samples with different composition explains observed phenomena. Despite the differences in ablation behavior of these alloys, linear calibration curves were obtained when Zn signal intensity was normalized to signal intensity of Cu or to crater volume.     

Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys

In the present work we are studying the influence of pulse duration (nanosecond (ns) and femtosecond (fs)) at λ = 248 nm on the laser-induced plasma parameters and the quantitative analysis results for elements such as Sn, Zn and Pb, in different types of bronze alloys adopting LIBS in ambient atmosphere. Binary (Sn–Cu), ternary (Sn–Zn–Cu or Sn–Pb–Cu) and quaternary (Sn–Zn–Pb–Cu) reference alloys characterized by a chemical composition and metallurgical features similar to those used in Roman times, were employed in the study. Calibration curves, featuring linear regression coefficients over 98%, were obtained for tin, lead and zinc, the minor elements in the bronze alloys (using the internal standardization method) as well as for copper, the major element. The effects of laser pulse duration and energy on laser-induced plasma parameters, namely the excitation temperature and the electron density have been studied in our effort to optimize the analysis. Finally, LIBS analysis was carried on three real metal objects and the spectra obtained have been used to estimate the type and elemental composition of the alloys based on the calibration curves produced with the reference alloys. The results obtained are very useful in the future use of portable LIBS systems for in situ qualitative and quantitative elemental analysis of bronze artifacts in museums and archaeological sites.     

Comments on the paper: “Accurate quantitative analysis of gold alloys using multi-pulse laser-induced breakdown spectroscopy and a correlation-based calibration method”

The problem of finding new methods for the analysis of precious alloys has stimulated, in recent years, a number of different proposals for improving the analytical procedures introducing more robust calibration (or calibration-free) methods. In the paper “Accurate quantitative analysis of gold alloys using multi-pulse laser-induced breakdown spectroscopy and a correlation-based calibration method” by G. Galbács, N.Jedinski, G.Cseh, Z. Galbács and L. Túri [Spectrochimica Acta Part B, Volume 63, Issue 5, 591–597 (May 2008)] the authors proposed the use of multiple-pulse LIBS and a correlation-based method for building calibration curves for quantitative analysis of gold alloys. The method is proposed for gold alloys prepared using a fixed proportion of the alloying element. The general case where the relative concentration of the elements of the matrix is not a priori known is not discussed in the paper. In this communication, we will demonstrate that the method proposed is extremely fragile against matrix effects, and therefore cannot be usefully applied for the purpose of actual analytical measurements on gold alloys without a previous knowledge of the matrix composition.     

Influence of pulse-to-pulse delay for 532 nm double-pulse laser-induced breakdown spectroscopy of technical polymers

Laser induced breakdown spectroscopy (LIBS) is an emerging technique for fast and accurate compositional analysis of many different materials. We present a systematic study of collinear double-pulse LIBS on different technical polymers such as polyamide, polyvinyl chloride, polyethylene etc. Polymer samples were ablated in air by single-pulse and double-pulse Nd:YAG laser radiation (8 ns pulse duration) and spectra were recorded with an Echelle spectrometer equipped with an ICCD camera. We investigated the evolution of atomic and ionic line emission intensities for different delay times between the laser pulses (from 20 ns to 500 μs) at a laser wavelength of 532 nm. We observed double-pulse LIBS signals that were enhanced as compared to single-pulse measurements depending on the delay time and the type of polymer material investigated. LIBS signals of polymer materials that are enhanced by double-pulse excitation may be useful for monitoring the concentration of heavy metals in polymer materials.     

Quantitative analysis of alloys and glasses by a calibration-free method using laser-induced breakdown spectroscopy

Space-, time- and spectrally resolved optical diagnostics of laser ablation plasma has provided the opportunity to realize calibration-free analyses of solid materials. In general, this variant of optical emission spectroscopy of pulsed plasma allows the plasma matrix effects to be overcome, yielding satisfactorily precise and accurate quantitative results on elemental composition of materials without using calibration curves, certified reference materials, and internal standards. Such analysis is very close to be nondestructive due to the minimum possible ablated mass, a feature which is very important in many applications, especially for unique museum exhibits and jeweler samples. In this paper, the use of the method for the analysis of elements in bronze, brass and gold alloys, glass samples, and archaeological findings is demonstrated. The results presented confirm the suitability of the approach for routine applications of our instrumentation, while at the same time simplifying the overall analytical procedure.