Portable Laser-induced Breakdown Spectroscopy Research Articles

Reassociation of Skeletal Remains Using Laser-Induced Breakdown Spectroscopy.

A major challenge in forensic anthropology and bioarcheology is the development of fast and effective methods for sorting commingled remains. This study assesses how portable laser-induced breakdown spectroscopy (LIBS) can be used to group skeletal remains based on their elemental profiles. LIBS spectra were acquired from the remains of 45 modern skeletons, with a total data set of 8388 profiles from 1284 bones. Spectral feature selection was conducted to reduce the spectral profiles to the peaks exhibiting the highest variation among individuals. Emission lines corresponding to 9 elements (Ca, P, C, K, Mg, Na, Al, Ba, and Sr) were found important for classification. Linear discriminant analysis (LDA) was concurrently used to classify each spectral profile. From the 45 individuals, each LIBS spectrum was successfully sorted to its corresponding skeleton with an average accuracy of 87%. These findings indicate that variation exists among the LIBS profiles of individuals' skeletal remains, highlighting the potential for portable LIBS technology to aid in the sorting of commingled remains.

Detection of Cadmium and Lead Heavy Metals in Soil Samples by Portable Laser-Induced Breakdown Spectroscopy

Heavy metal pollution in soil is becoming more and more serious. LIBS is one of the most promising technologies for rapid detection of heavy metal contamination in soil. However, due to the wide variety of soils and complex matrices, accurate quantification remains a challenge. In total, 451 soil samples were prepared and detected by the portable detector of LIBS, which were divided into six categories based on the compactness of the soil pellets, and a separate quantitative model for each type of soil sample was used for quantitative analysis by external standard method. It did not need a lot of data to train the model, and only a small number of calibration samples could be used for quantitative analysis of a large number of samples. The results showed that 78 standard samples and 334 collected samples were quantitatively analyzed by 39 standard samples. Compared with the standard value, the correlation coefficients were all above 0.95. A comparative experiment indicated that the portable LIBS system combined with soil classification and calibration methods can achieve fast and accurate quantitative detection.

Evaluation of T91 Steel Aging Grade Based on Portable Laser-Induced Breakdown Spectroscopy Device

Evaluation of T91 Steel Aging Grade Based on Portable Laser-Induced Breakdown Spectroscopy Device

Assessment of gunshot residue detection on a large variety of surfaces by portable LIBS system for crime scene application

The application of Laser-Induced Breakdown Spectroscopy (LIBS) in forensic science has garnered increasing attention. The ability to perform real-time, on-site analysis of Gunshot Residue (GSR) particles and potential elements originating from bullets or projectile cores on various surfaces holds the potential to assist in resolving firearms-related cases. This includes facilitating trajectory determination by locating distinct impact points and identifying the types of ammunition used. This study evaluates the utilization of a portable LIBS device for ballistic forensic purposes. Additionally, it focuses on the assessment of potential false positives and false negatives arising from the different materials where the shots have been fired. Since the system performs laser ablation of both surface particles and the substrate, it emphasizes the importance of conducting preliminary screening in an area with the same composition as the impact zone to minimize potential false positives during direct surface analysis. Furthermore, the results demonstrate the capability to detect the constituent elements of characteristic gunshot residue particles (GSR particles): lead (Pb), antimony (Sb), and barium (Ba) adhering to bullets, as well as the principal elements composing the jacket or core of the projectile: lead (Pb), copper (Cu), and zinc (Zn) through direct analysis, without the need for a sampling kit, on different surfaces such as walls, furniture, or fabrics. Analyses conducted a month after the shots were fired indicate the potential for finding residues in the vicinity of the bullet hole. Analyses conducted a month after the shots were fired indicate the possibility of finding residues in the area around the bullet hole.

Development of a portable laser-induced breakdown spectroscopy device for in situ and rapid characterization of wall composition on the first wall of EAST tokamak

During the long-pulse operation of nuclear fusion devices, plasma-material interaction processes such as material erosion, transportation of eroded materials, and impurity redeposition can deteriorate the performance of plasma-facing components (PFCs). Accurately identifying impurities and their spatial distributions on the first wall is crucial to comprehensively and deep understanding these processes. Laser-induced breakdown spectroscopy (LIBS) is a powerful spectral analytical technique that offers rapid, in situ, multi-elemental, and portable instrumentation advantages over the other techniques. Due to its unique and distinctive features, LIBS is a practical technique for composition and profilometry analysis in nuclear fusion devices. In this study, we report the development of a novel, compact, and portable LIBS device for in situ, real-time measurement of impurity distributions in nuclear fusion devices. This device is equipped with a mini-sized laser that can deliver 10 mJ per pulse, a main unit enclosing a power supply module, spectrometer modules, and customized software. The system was employed to characterize impurities on the first wall of the EAST tokamak under atmospheric conditions after the 2021 EAST spring-summer campaign. The successful in situ measurement demonstrates the feasibility of using the portable LIBS system integrated into a robotic arm in nuclear fusion device. The implement of this portable device can facilitate the operation of the nuclear fusion device by enabling real-time and continuous monitoring of impurities as well as the fuel retention.

Quantitative Analysis of Coal Quality by a Portable Laser Induced Breakdown Spectroscopy and Three Chemometrics Methods

Laser-induced breakdown spectroscopy (LIBS) technology has the characteristics of small sample demand, simple sample preparation, simultaneous measurement of multiple elements and safety, which has great potential application in the rapid detection of coal quality. In this paper, 59 kinds of coal commonly used in Chinese power plants were tested by a lab-designed field-portable laser-induced breakdown spectrometer. The data set division methods and the quantitative analysis algorithm of ash content, volatile matter and calorific value of coal samples were carried out. The accuracy and prediction accuracy of three kinds of dataset partitioning methods, random selection (RS), Kennard–Stone (KS) and sample partitioning based on joint X-Y distances (SPXY), coupled with three quantitative algorithms, partial least squares regression (PLS), support vector machine regression (SVR) and random forest (RF), were compared and analyzed in this paper. The results show that the model featuring SPXY combined with RF has the best prediction performance. The R2 of ash content by the RF and SPXY method is 0.9843, the RMSEP of ash content is 1.3303 and the mean relative error (MRE) is 7.47%. The R2 of volatile matter is 0.9801, RMSEP is 0.7843 and MRE is 2.19%. The R2 of calorific value is 0.9844, RMSEP is 0.7324 and MRE is 2.27%. This study demonstrates that the field-portable LIBS device combining appropriate chemometrics algorithms has a wide application prospect in the rapid analysis of coal quality.

Utilising Portable Laser-Induced Breakdown Spectroscopy for Quantitative Inorganic Water Testing

At present, the majority of water testing is carried out in the laboratory, and portable field methods for the quantification of elements in natural waters remain to be established. In contrast, portable instruments like portable X-ray fluorescence (pXRF) analysis and portable laser-induced breakdown spectroscopy (pLIBS) have become routine analytical methods for the quantification of elements in solids. This study aims to show that pLIBS can also be used for chemical compositional measurements of natural waters. Bottled mineral waters were selected as sample materials. A surface-enhanced liquid-to-solid conversion technique was used to improve the detection limits and circumvent the physical limitations in liquid analysis. The results show that low to medium mineralised waters can be analysed quantitatively for their ions using the documented method. For more highly concentrated samples, typically above an electrical conductivity (EC) of 1000 µS/cm, further adjustment is required in the form of self-absorption correction. However, water with a conductivity up to this limit can be analysed for the main cations (Li+, Na+, Mg2+, K+, Ca2+, and Sr2+) as well as the main anions (SO42− and Cl−) using the documented method. This study demonstrates that there is significant potential for developing field-based pLIBS as a tool for quantitative water analysis.

Combined in situ XRF–LIBS analyses as a novel method to determine the provenance of central Mediterranean obsidians

This work presents a new calibration method for determining the provenance of obsidian artefacts based on the combined use of XRF and laser-induced breakdown spectroscopy (LIBS). At first, obsidian samples collected from the main Mediterranean sources were characterized using portable XRF and LIBS systems. After data treatment, elemental information was used to carry out principal component analysis (PCA) for each technique. Rb, Sr, Zr, Y and Fe elements, detected by using XRF, were found to be the key parameters enabling obsidians discrimination. Likewise, LIBS data helped differentiating the analysed patterns by the intensity of their main elemental components (Ca, Al, Mg and K). After selecting the key parameters detected by each technique, a new data matrix combining XRF and LIBS data was finally built. According to PCA results, the discrimination of Mediterranean sources based on combined XRF–LIBS data ensured a higher reliability over mono-analytical models, by increasing the Euclidean distance between sources projections over three-dimensional principal components plots. Knowing that the representativeness of elemental data could be compromised by the presence of superficial degradation products or deposition patinas, a shot-to-shot comparison of in-depth LIBS analyses is finally proposed as a method to disclose whether the spot under analysis was superficially contaminated or altered. Thus, the proposed strategy based on the combined use of portable XRF and LIBS spectrometers could be particularly useful for the in situ analysis of obsidian artefacts that underwent superficial alteration or could be covered by patina products.Graphical abstract

Quantitative analysis of Li, Na and K in single-element standard solutions using portable laser-induced breakdown spectroscopy

Laboratory-based laser-induced breakdown spectroscopy (LIBS) instruments have proven themselves for trace element analysis of an extensive range of elements. As portable devices have evolved greatly in recent years, new areas of field application are opening up. However, no portable LIBS (pLIBS) has yet been used for quantitative inorganic water analysis. The aim of this study was to explore whether pLIBS combined with a surface-enhanced liquid-to-solid conversion method can quantify light alkali element concentrations in standard solutions. Multivariate calibrations were performed with single-element standard solutions at detection limits of 0.006, 0.011 and 0.007 mg l −1 for Li, Na and K, respectively. Coefficients of determination ( R 2 ) for the calibration lines from 0.1 to 100 mg l −1 for Li and Na, and 0.1 to160 mg l −1 for K were between 0.96 and 0.99. It has been shown that the surface preparation technique used improves the homogeneity of the spread and shape of the evaporation residue and thus the accuracy and precision of the analysis. Hence, this study demonstrates that it is possible to quantify light alkali metals in single-element standard solutions in the range of 0.1 to 160 mg l −1 using handheld LIBS.

Analytical approaches for food authentication using LIBS fingerprinting

Laser-induced breakdown spectroscopy (LIBS) is a widely acknowledged elemental analysis approach used in various study domains due to its rapid measurement capability and minimal sample-preparation requirements. Recently, there has been an increase in interest in the applications of LIBS in the realm of food safety and quality. Given that the majority of commonly consumed foods exhibit only modest trace-element variations, discovering predictive spectral patterns through multivariate analysis is crucial for the data-analysis pipeline. The efficacy of multivariate analysis and machine-learning algorithms to identify the most predictive spectral features, conduct class recognition and classification was evaluated in this paper, utilizing both a custom-developed benchtop LIBS system and a commercially available portable one. Specifically, this study's objective was to evaluate the performance of spectral variable selection using elastic-net multinomial logistic regression. The data processing pipeline and the LIBS hardware were evaluated in the context of food authentication and identification, a rising field of research addressing the issue of food fraud. Our findings indicated that classifying food samples with carefully selected fewer variables reduces model overfitting and improves the accuracy of LIBS pattern classification. In a broader sense, the results support the continued development of field-deployable, portable LIBS equipment designed for food authentication and fingerprinting activities.

Calibrating a Handheld LIBS for Li Exploration in the Barroso–Alvão Aplite-Pegmatite Field, Northern Portugal: Textural Precautions and Procedures When Analyzing Spodumene and Petalite

In pegmatites containing abundant petalite and spodumene, such as those from the Barroso–Alvão (BA) aplite-pegmatite field, calibrating a portable laser-induced breakdown spectroscopy (pLIBS) equipment to identify and analyze these minerals may be challenging. Forty-nine samples of spodumene, petalite and spodumene + quartz were collected from 22 aplite-pegmatites from the BA field and sent for inductively coupled plasma-mass spectroscopy analysis. One calibration for both spodumene and petalite has been proven to be impossible since almost all the LIBS intensity ratios, including for Li, overlapped on both minerals. Thus, three calibrations were developed: one qualitative to distinguish both minerals and two more quantitative, specifically made for each mineral. The first LIBS calibration only has Fe since it is the sole element with intensity ratios different enough to distinguish both minerals. Eleven calibration lines were created: Li, Al, Si, Be, Na, P, K, Mn, Fe, Rb and Cs; however, only the Li, Al, and Si have consistent errors below 20%. Thin sections were produced and observed with optical microscopy and cathodoluminescence (CL) to control the purity and mineral paragenesis of the samples. The petalite pellets were also controlled with cold CL since petalite crystals often present fine spodumene and quartz inclusions.

Rapid Food Authentication Using a Portable Laser-Induced Breakdown Spectroscopy System.

Laser-induced breakdown spectroscopy (LIBS) is an atomic-emission spectroscopy technique that employs a focused laser beam to produce microplasma. Although LIBS was designed for applications in the field of materials science, it has lately been proposed as a method for the compositional analysis of agricultural goods. We deployed commercial handheld LIBS equipment to illustrate the performance of this promising optical technology in the context of food authentication, as the growing incidence of food fraud necessitates the development of novel portable methods for detection. We focused on regional agricultural commodities such as European Alpine-style cheeses, coffee, spices, balsamic vinegar, and vanilla extracts. Liquid examples, including seven balsamic vinegar products and six representatives of vanilla extract, were measured on a nitrocellulose membrane. No sample preparation was required for solid foods, which consisted of seven brands of coffee beans, sixteen varieties of Alpine-style cheeses, and eight different spices. The pre-processed and standardized LIBS spectra were used to train and test the elastic net-regularized multinomial classifier. The performance of the portable and benchtop LIBS systems was compared and described. The results indicate that field-deployable, portable LIBS devices provide a robust, accurate, and simple-to-use platform for agricultural product verification that requires minimal sample preparation, if any.

Rapid classification of copper concentrate by portable laser-induced breakdown spectroscopy combined with transfer learning and deep convolutional neural network

This paper investigates the combination of laser-induced breakdown spectroscopy (LIBS) and deep convolutional neural networks (CNNs) to classify copper concentrate samples using pretrained CNN models through transfer learning. Four pretrained CNN models were compared. The LIBS profiles were augmented into 2D matrices. Three transfer learning methods were tried. All the models got a high classification accuracy of >92%, with the highest at 96.2% for VGG16. These results suggested that the knowledge learned from machine vision by the CNN models can accelerate the training process and reduce the risk of overfitting. The results showed that deep CNN and transfer learning have great potential for the classification of copper concentrates by portable LIBS.

Accurate Quantitative Analysis of LIBS With Image Form Spectra by Using a Hybrid Deep Learning Model of a Convolutional Block Attention Module-Convolutional Neural Network-Long Short-Term Memory

With the development of miniaturized Laser-induced breakdown spectroscopy (LIBS) instruments, the desire for accuracy and stability of quantitative analysis of portable LIBS systems is growing. In this research, a hybrid deep learning model of a convolutional block attention module combined with a convolutional neural network and a long short-term memory (CBAM-CNN-LSTM) was for the first time used for quantitative analysis in a LIBS system with a portable spectrometer. Among them, the spectra collected by LIBS were in the form of the image, the CNN module was responsible for feature extraction of image spectra, mining deep features through the CBAM, and the simultaneous accurate quantitative analysis of Ca, Mg, Na and Ba was realized by the LSTM module. Meanwhile, a linear regression (LR), a CNN and a CNN-LSTM model were compared to the CBAM-CNN-LSTM model. The results showed that the performance of this model was much better than the LR model. More importantly, compared to CNN and CNN-LSTM, the average relative error of CBAM-CNN-LSTM was reduced by 80.5% and 68.1%, the average root mean square error was reduced by 56.7% and 53.4%, and the average stability was increased by 62.3% and 58.8%, respectively. In addition, the feature visualization results of CNN-LSTM and CBAM-CNN-LSTM displayed that CBAM can more effectively extract the features of characteristic peaks of corresponding elements and suppress the irrelative features. It indicated that the model can achieve an accurate and stable quantitative analysis of LIBS, which has the potential to be applied in the in-site analysis.

An Archaeometric Investigation into the Former Cataract House Hotel via Elemental Analysis

Over the course of the 19th century, the former Cataract House Hotel of Niagara Falls, New York, became one of the largest hotels in the region while also serving as an important “station” on the Underground Railroad. A park now occupies the area covering its demolished ruins. Since 2017, archaeological excavations of the site have taken place, led by the Anthropology Department at SUNY Buffalo. Although much is known about the overall design of the Cataract House Hotel, a clearer understanding of its construction phases, as well as its role in the Underground Railroad, could be determined from spectroscopic analysis in tandem with ongoing archaeological investigations. In 2022, in situ data collection was performed on plaster walls at the excavation site using a portable X-ray fluorescence (pXRF) instrument. These elemental data were used in conjunction with archaeological information to form conclusions regarding different construction phases of the hotel. Samples of plaster walls were also collected for further ex situ analyses with pXRF and portable laser-induced breakdown spectroscopy (pLIBS) in a laboratory setting. Future work will include data collection and analysis by additional spectroscopic methods of other artifacts collected at the site, such as pigment samples removed from an unearthed stone step.

Model transfer method based on piecewise direct standardization in laser-induced-breakdown spectroscopy.

A large number of certified samples are usually required to build models in the quantitative analysis of complicated matrices in laser-induced-breakdown spectroscopy (LIBS). Because of differences among instruments, including excitation and collection efficiencies, a quantitative model made on one instrument is difficult to apply directly to other instruments. Each instrument requires a large number of samples to model, which is very labor intensive and will hinder the rapid application of the LIBS technique. To eliminate the differences in spectral data from different instruments and reduce the cost of building new models, a piecewise direct standardization method combined with partial least squares (PLS_PDS) is studied in this work. Two portable LIBS instruments with the same configuration are used to obtain spectral data, one of which is called a master instrument because its calibration model is directly built on a large number of labeled samples, and the other of which is called a slave instrument because its model is obtained from the master instrument. The PLS_PDS method is used to build a transfer function of spectra between the master instrument and slave instrument to reduce the spectral difference between two instruments, and thus one calibration model can adapt to different instruments. Results show that for multiple elemental analyses of aluminium alloy samples, the number of samples required for slave modeling was reduced from 51 to 14 after model transferring by PLS_PDS, and the quantitative performance of the slave instrument was close to that of the master instrument. Therefore, the model transfer method can obviously reduce the sample number of building models for slave instruments, and it will be beneficial to advance the application of LIBS.

Design and construction of a low-cost 3D-printed portable LIBS system

Laser-Induced Breakdown Spectroscopy (LIBS) is a widely used non-destructive analysis technique, which is however costly. In this paper we present the development of a low-cost 3D-printed portable LIBS system designed and built with a Technology Readiness Level 5 (TRL 5), i.e., technology validated in a relevant environment. The proposed LIBS system is compact and includes a passive Q-switch Nd3+:YAG pulsed laser, a handheld measuring device, a power supply, an optical spectrometer and a processing software. The electronic control system guarantees a stable laser triggering, thanks to the use of optical connections (optocouplers) avoiding wired electrical connections of the circuits. In addition, we found the correct energy characteristics of the passive Q-switch regime, to generate a single laser pulse, thus making the system operate more efficiently. Our low-cost 3D-printed portable LIBS system was validated with several tests with real samples of atomic elements (i.e., lithium, copper, silver, gold and lead).

Access to quantitative analysis of carbonates using a portable LIBS instrument: First applications to single minerals and mineral mixtures

Natural carbonate standards of calcite structure were analysed using a handheld Laser-Induced Breakdown Spectroscopy (LIBS) device to investigate the spectral applicability for quantitative analysis in the Ca-Mg-Fe-Mn carbonate system. To obtain an initial understanding of the relationship between the elemental concentrations and LIBS signals, the determination coefficient (R2), root mean square error (RMSE) and mean arctangent absolute percentage error (MAAPE) for cross-validation and forecast accuracy were used, respectively. To relate the changes in spectral characteristics to the mineral content of carbonate mixtures, different spectral ratios were compared with mixture ratios between the two carbonate minerals. We found that spectral information from LIBS emission lines showed high correlations to their elemental concentration (Ca, Mg, Fe, and Mn), and their spectral ratios in carbonate mixtures showed a linear correlation with mineral content. Principal component analysis (PCA) was investigated the chemometric capability of the discrimination for carbonate minerals. This study demonstrates that handheld LIBS can be effectively applied in the field for the discrimination and identification of carbonate endmembers and their quantification for the case of mixtures.

In Situ Study of Cave 98 Murals on Dunhuang Grottoes Using Portable Laser-Induced Breakdown Spectroscopy

The investigation of painted layers on murals at Cave 98 from Dunhuang Grottoes was carried out in situ using portable laser-induced breakdown spectroscopy (LIBS) for the first time. The ablation effect of laser pulses on a mural surface was evaluated under fixed experimental parameters, and the results showed that the influence of laser ablation on ancient murals was acceptable. Then the pigments used in the red, green, and blue layers were indicated with the LIBS spectral data of the corresponding color coupled with a classifiable model of pigments based on the principal component analysis (PCA) method. Finally, the depth profiling of the multilayer structure composed with overlapped painted layers was determined based on the pigment size information of the superficial green layer and the relationship of laser shots and ablation depth, and the thickness of the superficial green layer was analyzed quantitatively, which fits well with the result of the cross-sectional analysis. Therefore, this work can shed light on the great potential for ancient mural applications in LIBS.

Handheld LIBS analysis for in situ quantification of Li and detection of the trace elements (Be, Rb and Cs)

The world's lithium demand is currently increasing due to its use in batteries and in green energy technologies. As a consequence, Li has recently been added to the list of critical materials in Europe. Finding new deposits is necessary in order to guarantee a mid- to long-term stable supply. Granites and associated pegmatites are the primary ‘hard-rock’ source for Li, where it is present in a variety of aluminosilicate minerals. Li is a light element that typically occurs at low concentrations in rocks and minerals, which presents challenges for some analytical techniques (e.g., portable X-ray fluorescence) for exploration. Laser induced breakdown spectroscopy (LIBS) is a powerful analytical technique for the acquisition of simultaneous almost all elements of the periodic table. LIBS has particular sensitivity to the light elements (Z < 13) and, therefore, handheld LIBS has significant potential for the exploration of pegmatite- or granite-related Li mineralization. For this study, a suite of 16 pegmatite-hosted Li ore minerals comprising the three main aluminosilicate species (spodumene, lepidolite and petalite) that contained between 1.36 and 3.54 wt% Li was analyzed using a handheld LIBS instrument. A univariate calibration curve was developed for LIBS quantification of Li in these minerals using the strong Li emission lines at 610.36 nm and 670.79 nm (R2 > 0.9, RMSD = 0.2 wt% Li). Simultaneous quantification of Li contents and measurement of major element ratios (e.g., Si/Al) using portable LIBS permits rapid discrimination between different Li-bearing silicates, such as spodumene and petalite, that can be difficult to identify in the field on the basis of macroscopic criteria. Moreover, the detection of minor/trace elements such as Be, Rb and Cs is possible by handheld LIBS, which can provide useful information for rare metal pegmatite and granite exploration. Thus, qualitative and quantitative analysis by handheld LIBS represents a very promising approach for Li exploration.