Abstract
Laser-induced breakdown spectroscopy (LIBS) is a simple and straightforward technique of atomic emission spectroscopy that can provide multi-element detection and quantification in any material, in-situ and in real time because all elements emit in the 200–900 nm spectral range of the LIBS optical emission. This study evaluated two practical applications of LIBS—validation of labels assigned to garnets in museum collections and discrimination of LCT (lithium-cesium-tantalum) and NYF (niobium, yttrium and fluorine) pegmatites based on garnet geochemical fingerprinting, both of which could be implemented on site in a museum or field setting with a handheld LIBS analyzer. Major element compositions were determined using electron microprobe analysis for a suite of 208 garnets from 24 countries to determine garnet type. Both commercial laboratory and handheld analyzers were then used to acquire LIBS broadband spectra that were chemometrically processed by partial least squares discriminant analysis (PLSDA) and linear support vector machine classification (SVM). High attribution success rates (>98%) were obtained using PLSDA and SVM for the handheld data suggesting that LIBS could be used in a museum setting to assign garnet type quickly and accurately. LIBS also identifies changes in garnet composition associated with increasing mineral and chemical complexity of LCT and NYF pegmatites.
Highlights
This study evaluated two practical applications of the Laser-induced breakdown spectroscopy (LIBS)—the validation of labels assigned to garnets in museum collections and the discrimination of LCT and NYF granitic pegmatites based on garnet geochemical fingerprinting
In cases where there is not voting unanimity, those samples should be examined for quantitative compositional analysis. If this metric were applied to the present study, there are only two samples (Table 4, entries 5 and 18) that would have been incorrectly assigned as false positives with an additional 19 samples requiring further analysis. These results suggest that a hybrid LIBS/electron microprobe (EMP) approach would provide approximately 99% correct labels, which is a significant improvement over the ~82% level observed in this study, while offering substantial time and cost savings compared to having to prepare and compositionally analyze over 200 samples
Laser-induced breakdown spectroscopy (LIBS) is an established technique of analytical atomic spectrometry that today offers, in handheld analyzer form, a convenient, reliable, and versatile technique for localized material analysis. The application of both laboratory and handheld LIBS across multiple domains of the geosciences has been described in the literature
Summary
Commercial LIBS technology has recently progressed from bespoke and commercial laboratory systems to handheld analyzers for field use. This new capability offers the possibility for using LIBS as a survey tool for distinguishing different geological materials through rapid compositional analysis outside the laboratory under ambient environmental conditions with little to no sample preparation. Because many electron orbital transitions occur for most elements, a LIBS emission intensity spectrum consists of multiple peaks for the majority of elements and, for most geological materials, normally contains tens to hundreds of spectral lines. LIBS analysis has been used in four distinct ways: (i) as an elemental detector, (ii) for quantitative chemical analysis, (iii) for microscale elemental mapping, and (iv) qualitatively to rapidly distinguish between samples of similar character through chemometric analysis, e.g., via spectral matching against a pre-assembled library
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