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In this work, we report the results on the application of Laser-Induced Breakdown Spectroscopy (LIBS) to the analysis of coal, for the determination of its Ash Content. This parameter is critical for an efficient use of coal to produce electrical energy in power plants. The results obtained are compared with the ones obtained through conventional chemical laboratory analysis. The study here presented, although performed in the Laboratory, was set up trying to reproduce the real industrial conditions, with the purpose of easing the transfer of the results obtained to the on-line monitoring of coal quality at the power plant. Unlabelled Image • Ash Content of Coal is determined by LIBS. • Real Industrial conditions are reproduced. • Selection of spectra is applied to improve the quality of the results. • An average absolute error of 0.5 w% is achieved. • 4 w% maximum absolute error is obtained. [ABSTRACT FROM AUTHOR]

In this paper, we will discuss a new method for obtaining information about the plasma temporal evolution in Laser-Induced Breakdown Spectroscopy (LIBS) experiments using a time-integrated spectrometer. The method, inspired to the Bredice 3D-Boltzmann plot formalism, allows a precise determination of the temporal evolution of the emission line intensity in a LIBS plasma, starting from a series of time-integrated measurements obtained at different delay times after the laser pulse. In this way the application of a calibration-free algorithm using a time-integrated spectrometer is made possible. Examples of the application of the method are given in the analysis of two Zamac (a zinc alloy containing aluminum, magnesium, and copper) certified samples. A good agreement is obtained between the calculated and nominal concentrations of the two samples. A further validation of the method was performed on a third Zamac sample, of unknown composition. The sample was first characterized using a conventional CF-LIBS approach on a time-resolved spectrum; the obtained composition was then compared with the one determined using the series of time-integrated spectra. [Display omitted] • A new analytical method based on the Bredice 3D-Boltzmann plot technique is proposed. • The application of the method is demonstrated for the analysis of three Zamac samples. • The composition of the samples is measured with a time-integrated spectrometer. • A good agreement with the certified composition of the samples is obtained. [ABSTRACT FROM AUTHOR]

In this paper we face the problem of assessing similarities in the composition of different metallic alloys, using the laser-induced breakdown spectroscopy technique. The possibility of determining the degree of similarity through the use of artificial neural networks and self-organizing maps is discussed. As an example, we present a case study involving the comparison of two historical brass samples, very similar in their composition. The results of the paper can be extended to many other situations, not necessarily associated with cultural heritage and archeological studies, where objects with similar composition have to be compared. [ABSTRACT FROM AUTHOR]

Abstract: In this work we compare the analytical results obtained by traditional calibration curves (CC) and multivariate Partial Least Squares (PLS) algorithm when applied to the LIBS spectra obtained from ten brass samples (nine standards of known composition and one ‘unknown’). Both major (Cu and Zn) and trace (Sn, Pb, Fe) elements in the sample matrix were analyzed. After the analysis, the composition of the ‘unknown’ sample, measured by X-ray Fluorescence (XRF) technique, was revealed. The predicted concentrations of major elements obtained by rapid PLS algorithms are in very good agreement with the nominal concentrations, as well as with those obtained by the more time-consuming CC approach. A discussion about the possible effects leading to discrepancies of the results is reported. The results of this study open encouraging perspectives towards the development of cheap LIBS instrumentation which would be capable, despite the limitations of the experimental apparatus, to perform fast and precise quantitative analysis on complex samples. [ABSTRACT FROM AUTHOR]

Many of the current analytical application of LIBS are based on the build of a 'simple' univariate and linear calibration curve, where the signal is plotted as a function of the concentration of the analyte in the calibration standards. Recently, it has been proposed to consider also in LIBS, as was done in other spectroanalytical techniques, the use an inverted calibration curve, obtained by plotting the standard concentration as a function of the corresponding LIBS signals. The purpose of this communication is evidencing that some peculiar characteristics of the LIBS signal, including the non-homoscedasticity of the data used for building the calibration curve, in most of the cases make the application of inverse methods less convenient than the classical direct approach. An example is given using real spectral signals acquired on brass samples for the measure of the composition of the alloy, showing that, in that specific case, the use of inverse calibration leads to analytical results less precise than the direct one, at the same time giving a severe underestimation of the limits of confidence of the corresponding calibration curve. Based on these findings, a general method for obtaining a symmetrical calibration curve, which takes correctly into account the indetermination on both the standards' concentration and the LIBS signal, is proposed. Unlabelled Image • The problem of inverse and direct calibration in LIBS analysis is discussed. • The two methods are tested on experimental data (calibration curve for Sn in Brass). • Direct calibration is found to be more precise, and the reasons are discussed. • Inverse calibration in LIBS is found to be useful only in few particular cases. • In general, symmetric best fit methods are suggested instead of inverse calibration. [ABSTRACT FROM AUTHOR]

The present work aims to evaluate the alteration conditions of historical limestone rocks exposed to urban environment using the Laser-Induced Breakdown Spectroscopy (LIBS) technique. The approach proposed is based on the microscale three dimensional (3D) compositional imaging of the sample through double-pulse micro-Laser-Induced Breakdown Spectroscopy (DP-μLIBS) in conjunction with optical microscopy. DP-μLIBS allows to perform a quick and detailed in-depth analysis of the composition of the weathered artifact by creating a ‘virtual thin section’ (VTS) of the sample which can estimate the extent of the alteration processes occurred at the limestone surface. The DP-μLIBS analysis of these thin sections showed a reduction with depth of the elements (mainly Fe, Si and Na) originating from atmospheric dust, particulate deposition and the surrounding environment (due to the proximity of the sea), whereas, the LIBS signal of Ca increased in intensity from the black crust to the limestone underneath. [ABSTRACT FROM AUTHOR]

Laser-Induced Breakdown Spectroscopy (LIBS) micro-mapping is an important analytical tool for the study of geomaterials. In this work, this technique was applied, for the first time, to the analysis of alkali-activated materials and geopolymers, as well as rocks, mortars and bricks. The results obtained were compared with the ones obtained using Energy-Dispersive X-Ray Fluorescence (ED-XRF) macro-mapping and the advantages of the LIBS approach (speed, lateral and in-depth resolution, capability of light elements analysis) were highlighted. The issues associated with the quantitative determination of the samples' composition from the analysis of the LIBS spectra were also briefly discussed. [Display omitted] • XRF and LIBS mapping systems are compared for geomaterials analyses. • Micro-mapping LIBS was applied, for the first time, to the analysis of alkali-activated materials and geopolymers. • Combined XRF-LIBS data strongly increased the samples characterization. [ABSTRACT FROM AUTHOR]

The usual approach to laser-induced breakdown spectroscopy (LIBS) quantitative analysis is based on the use of calibration curves, suitably built using appropriate reference standards. More recently, statistical methods relying on the principles of artificial neural networks (ANN) are increasingly used. However, ANN analysis is often used as a ‘black box’ system and the peculiarities of the LIBS spectra are not exploited fully. An a priori exploration of the raw data contained in the LIBS spectra, carried out by a neural network to learn what are the significant areas of the spectrum to be used for a subsequent neural network delegated to the calibration, is able to throw light upon important information initially unknown, although already contained within the spectrum. This communication will demonstrate that an approach based on neural networks specially taylored for dealing with LIBS spectra would provide a viable, fast and robust method for LIBS quantitative analysis. This would allow the use of a relatively limited number of reference samples for the training of the network, with respect to the current approaches, and provide a fully automatizable approach for the analysis of a large number of samples. [ABSTRACT FROM AUTHOR]

The elemental analysis of human bones can give information about the dietary habits of the deceased, especially in the last years of their lives, which can be useful for forensic studies. The most important requirement that must be satisfied for this kind of analysis is that the concentrations of analyzed elements are the same as ante mortem . In this work, a set of bones was analyzed using Laser-Induced Breakdown Spectroscopy (LIBS) and validated using Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP-OES), in order to compare those two techniques and to investigate the effect of possible alterations in the elemental concentrations' proportion resulting from the treatment usually applied for preparing the bones for traditional forensic analysis. The possibility that elemental concentrations' changes would occur after accidental or intentional burning of the bones was also studied. [ABSTRACT FROM AUTHOR]

Archeological mortars are often composed of highly inhomogeneous materials and detailed analysis in most cases can be quite difficult. In this work, a Laser-Induced Breakdown Spectroscopy (LIBS) equipment with microscopic-scale spatial resolution was used to image the distribution of elements on real archeological samples of mortars and construction material used in the foundations of the Smederevo Fortress (Republic of Serbia). A double-pulse Nd:YAG at the fundamental wavelength (λ = 1064 nm) and a CCD spectrometer coupled with a commercial microscope were used to generate the plasma and acquire the LIBS spectra. Thanks to the combined use of an unsupervised clustering algorithm and the calibration-free procedure, the results obtained show that it is possible to obtain a good discrimination between materials of different composition, allowing a quick classification for further mineral-petrographic investigations. [Display omitted] • Elementary imaging on highly inhomogeneous samples. • LIBS mapping application on historical mortar samples. • Performed CF-LIBS analysis on average spectrum, to estimate the elemental composition of the different zones of the sample. [ABSTRACT FROM AUTHOR]

The composition of atmospheric aerosols (particulate matter - PM) has been studied through the quantification of major elements in filter samples by laser induced breakdown spectroscopy (LIBS). After the collection of PM on over quartz filters, the samples were directly analyzed without the need of wet chemistry. The spectral analysis was performed by calibration free method (CF-LIBS), which also avoids using calibration standards. The major mineral elements found in PM 10 and PM 2.5 samples were Al, Ca, Fe, Mg, K, Na and Si. Furthermore, elements such as C, O and H, which form part of the organic matter and/or water, were also identified and quantified. In addition to CF-LIBS fastness and feasibility, it has been demonstrated that CF-LIBS is a complementary technique for the characterization of PM. Unlabelled Image • Characterization of atmospheric PM is essential for monitoring of air pollution. • Filters used for air monitoring in Barcelona, Spain were analyzed by LIBS. • CF-LIBS method allowed the analysis without the need of calibration standards. [ABSTRACT FROM AUTHOR]

In this paper a review of different approaches for handling the self-absorption effect in Laser-Induced Breakdown Spectroscopy (LIBS) applications is presented. From an analytical point of view, self-absorption is a major issue affecting the accuracy of LIBS quantitative analysis. Self-absorption impacts emission line profiles and intensities, resulting in non-linear calibration curves and influencing the estimation of the sample composition. The main purpose of this work is presenting a summary of the experimental parameters giving raise to self-absorption and a thorough study of the different strategies for its estimation, compensation and exploitation in order to improve the analytical accuracy of the LIBS technique. Unlabelled Image • some approaches to estimate the self-absorption degree of spectral lines are reviewed, • the effects of the experimental parameters in LIBS plasmas are discussed, • we review exploitation of self-absorbed lines for diagnostics or quantitative analysis. [ABSTRACT FROM AUTHOR]

In this paper we introduce a new time-independent Extended C-sigma approach for the analysis of Laser Induced Breakdown Spectroscopy (LIBS) spectra and apply it to the determination of the Stark broadening coefficient of several neutral and ionic emission lines of tantalum. The method proposed is based on the recently introduced Extended C-sigma procedure and exploits the spectral information extracted from LIBS spectra acquired at different delay times after the laser pulse for building a time-independent Extended C-sigma curve. The method intrinsically includes in the calculation the effects of self-absorption, which is one of the main sources of indetermination in LIBS applications to the determination of spectroscopic fundamental parameters, such as transition probabilities and Stark broadening coefficients. Unlabelled Image • The Stark broadening coefficients of tantalum have been determined. • A new Time-Independent Extended C-sigma method is presented. • Self-absorption effects are taken into account. • The method can be used to determine Stark broadening coefficients of transition probabilities. [ABSTRACT FROM AUTHOR]

In this paper a new approach to quantitative Laser-Induced Breakdown Spectroscopy (LIBS) analysis of silicate rocks is presented. The method is adapted from the Franzini and Leoni algorithm, a method widely used in X-Ray Fluorescence analysis for correcting the matrix effects in the determination of the composition of geological materials. To illustrate the features of the new method proposed, nine elements were quantified in 19 geological standards by building linear univariate calibration curves, linear multivariate calibration surfaces (PLS) and using Artificial Neural Networks. The results were then compared with the predictions derived from the application of the algorithm here proposed. It was found that the Franzini and Leoni approach gives results much more precise than linear uni- and multivariate approaches, and comparable with the ones derived from the application of Artificial Neural Networks. A definite advantage of the proposed approach is the possibility of building multivariate non-linear calibration surfaces using linear optimization algorithms, a feature which makes the application of the Franzini and Leoni method in LIBS analysis much simpler (and controllable) with respect to the algorithms based on Artificial Neural Networks. Unlabelled Image • The Franzini-Leoni method, used in XRF analysis, is adapted to LIBS. • 19 geological samples are analyzed with this method. • The method is compared with linear/non-linear univariate and multivariate approaches. • The non-linear model can be obtained using linear optimization algorithms. [ABSTRACT FROM AUTHOR]