Mobile spectroscopic instrumentation in archaeometry research

Mobile instrumentation is of growing importance to archaeometry research. Equipment is utilized in the field or at museums, thus avoiding transportation or risk of damage to valuable artifacts. Many spectroscopic techniques are nondestructive and micro-destructive in nature, which preserves the cultural heritage objects themselves. This review includes over 160 references pertaining to the use of mobile spectroscopy for archaeometry. Following a discussion of terminology related to mobile instrumental methods, results of a literature survey on their applications for cultural heritage objects is presented. Sections devoted to specific techniques are then provided: Raman spectroscopy, X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy, laser-induced breakdown spectroscopy, and less frequently used techniques. The review closes with a discussion of combined instrumental approaches

Identifying and Minimizing Sources of Variability Within Modern Spectroscopic Techniques for the Forensic Analysis of Glass

Broken glass is a trace material frequently found at crime scenes such as hit-and-runs, burglaries, assaults, and homicides. Existing research encompassing the forensic analysis of glass evidence is vast. Published studies cover the analysis and interpretation of various types of glass. However, organizations such as the National Institute of Justice (NIJ), National Institute of Standards and Technology Organization of Scientific Area Committees (NIST-OSAC), and American Society of Trace Evidence Examiners (ASTEE) continue to identify glass-specific research needs to strengthen the scientific foundations of the field. Current gaps within the forensic glass community involve understanding modern glass formulations, re-evaluating the performance of technologically advanced instrumentation, assessing the effect of small glass fragments applied to standard practices, and developing new methods to advance data analysis and interpretation. This thesis aims to address these knowledge gaps by identifying, understanding, and proposing ways to minimize sources of variability within the elemental analysis of glass using laser-induced breakdown spectroscopy (LIBS) and micro X-ray fluorescence spectrometry (m-XRF). In the first objective of this thesis, LIBS and m-XRF were used to analyze small and irregular glass fragments between 0.4 mm and 1.0 mm in length from same-source and different-source sets. The analysis of the smaller glass resulted in poorer precision than full-thickness glass using both techniques. Using an increased number of known glass fragments resulted in better sample characterization and reduced the false exclusion rates for both small and full-thickness glass fragments analyzed with both instrumental techniques. When analyzing small and irregular samples, new protocols are recommended for sampling, analysis, and interpretation compared to current practice. The second objective of this thesis examined the elemental composition of modern glass from 30 portable electronic devices (PED), 15 tempered glass screen protectors (SP), and three liquid glass (LG) formulations using m-XRF and LIBS. Using spectral overlay of the m-XRF spectra resulted in five major PED groups and four SP groups based on their elemental composition. LIBS analysis corroborated the PED classes but severe cracking occurred during LIBS analysis. m-XRF comparisons of glass within PED and SP subgroupings achieved high discrimination powers and low false exclusion rates. The application of a newly proposed method based on spectral contrast angle ratios to m-XRF spectra of PED and SP glass provided an additional metric that complemented the spectral overlay results. The application of liquid glass to the surface of a PED screen did not significantly affect the m-XRF analysis of the PED glass. These findings provide the community with a preliminary assessment of the elemental composition of PED glass, SP glass, and LG and the forensic capabilities of m-XRF and LIBS applied to this glass type. The third objective of this thesis explores the multivariate quantitative analysis of glass using LIBS. Eight commonly used glass standards and characterized reference materials were used to construct calibration models to predict the concentrations of eight major and minor elements within soda-lime glass. Multivariate and univariate methods were compared using the coefficient of determination (R2) and bias to determine the best performing method. Multivariate methods outperformed univariate linear regression. An MLR calibration model using the entire LIBS spectrum provided bias values less than 10-20% while maintaining R2 values greater than 0.9 for all quantified elements. Inputting selected regions of the LIBS spectrum improved the performance of the MLR model. This thesis provides the recommended standards to quantify each of the eight target elements, demonstrating the feasibility of quantitative examinations of glass by LIBS. The culmination of this thesis addresses several current research gaps in the forensic glass community. The proposed methods involving the analysis of small glass fragments simulating casework-size items, the forensic comparisons of modern PED-related glass, and the quantification of elements within glass standards are anticipated to offer newer knowledge on sources of variability within forensic glass comparisons and approaches to minimize error rates. This research provides glass examiners with additional support when testifying about glass evidence within a court of law

Analytical methodology to elemental quantification of weathered terrestrial analogues to meteorites using a portable Laser-Induced Breakdown Spectroscopy (LIBS) instrument and Partial Least Squares (PLS) as multivariate calibration technique

The present work is focused on the in situ quantitative analysis of Si, Al,Mg, Ca, Ba, Na, and Fe, present in weathered terrestrial analogues to meteorites (black steel slag and impact glasses), using a portable Laser Induced Breakdown Spectroscopy (LIBS) instrument. For that purpose, several standards pellets of known elemental concentrations were manufactured. The elemental and molecular homogeneity of the pellets was studied by means of Scanning Electron Microscopy coupled to Energy Dispersive X-ray spectroscopy (SEM-EDS) and Raman spectroscopy. This checkwas always made before the LIBS analysis. Univariate andmultivariate (Partial Least Squares (PLS) regression) calibration approaches on LIBS spectra were selected as initial calibration models. After a comparison between both approaches, the former was discarded due to the poor linearity of the calibration curves, and PLS regressionwas chosen to treat the LIBS spectra as themultivariate calibration approach (in the ultraviolet (UV) and infrared (IR) spectral ranges). Predictive capabilities of each calibration model were evaluated by calculating regression coefficient (r), number of PLS factors (rank), relative errors of cross validation (RMSECV), residual predictive deviation (RPD) and the Bias value. At the end, the simultaneous use of both ranges of wavelengths was demonstrated to be more fruitful rather than using the individual ones, probably due to the higher number of emission lines, number of spectral variables and the PLS latent variables for each element. Moreover, a Reference Material was used as external validation, obtaining satisfactory results in the determination of elements. The predictive ability of the PLSmodelswas evaluated on samples of Darwin Glasses (Australia), Libyan Desert Glasses (Western Desert of Egypt) and black steel slag residues (steelworks of Basque Country). The obtained results were in concordance with the range of composition measured also by X-ray Fluorescence Spectrometer (ED-XRF). Our methodology is a good, rapid, simple and cost-effective alternative for in situ analysis of these terrestrial analogues over other techniques.Proyecto MINECO Retos de la Sociedad. Ref. ESP2014-56138-C3-2-

Calibration Methods of Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has gained great attention over the past two decades due to its many advantages, such as needless sample preparation, capability of remote measurement and fast multielement simultaneous analysis. However, because of its inherent uncertainty features of plasma, it is still a big challenge for LIBS community worldwide to realize high sensitivity and accurate quantitative analysis. Currently, many chemometric analytical methods have been applied to LIBS calibration analysis, including univariate regression, multivariate regression, principal component regression (PCR), partial least squares regression (PLSR) and so on. In addition, appropriate sample and spectral pretreatment can effectively improve the analytical performance (i.e., limit of detection (LOD), accuracy and repeatability) of LIBS. In this chapter, we briefly summarize the progress of these calibration methods and their applications on LIBS and provide our recommendations

Quantitative elemental mapping of biological tissues by laser-induced breakdown spectroscopy using matrix recognition

The present study demonstrates the importance of converting signal intensity maps of organic tissues collected by laser-induced breakdown spectroscopy (LIBS) to elemental concentration maps and also proposes a methodology based on machine learning for its execution. The proposed methodology employs matrix-matched external calibration supported by a pixel-by-pixel automatic matrix (tissue type) recognition performed by linear discriminant analysis of the spatially resolved LIBS hyperspectral data set. On a swine (porcine) brain sample, we successfully performed this matrix recognition with an accuracy of 98% for the grey and white matter and we converted a LIBS intensity map of a tissue sample to a correct concentration map for the elements Na, K and Mg. Found concentrations in the grey and white matter agreed the element concentrations published in the literature and our reference measurements. Our results revealed that the actual concentration distribution in tissues can be quite different from what is suggested by the LIBS signal intensity map, therefore this conversion is always suggested to be performed if an accurate concentration distribution is to be assessed

An Innovative Approach to Meteorite Analysis by Laser-Induced Breakdown Spectroscopy (LIBS)

An innovative approach of double pulse laser-induced breakdown spectroscopy (DP-LIBS) coupled with optical microscopy was applied to the characterisation and quantitative analysis of the Agoudal iron meteorite in bulk sample and in petrographic thin section. Qualitative analysis identified the elements Ca, Co, Fe, Ga, Li and Ni in the thin section and the whole meteorite. Two different methods, calibration-free LIBS and one-point calibration LIBS, were used as complementary methodologies for quantitative LIBS analysis. The elemental composition data obtained by LIBS were in good agreement with the compositional analyses obtained by traditional methods generally applied for the analysis of meteorites, such as ICP-MS and EDS-SEM. Besides the recognised advantages of LIBS over traditional techniques, including versatility, minimal destructivity, lack of waste production, low operating costs, rapidity of analysis, availability of transportable or portable systems, etc., additional advantages of this technique in the analysis of meteorites are precision and accuracy, sensitivity to low atomic number elements such as Li and the capacity to detect and quantify Co contents that cannot be obtained by EDS-SEM