Compositional Analysis of Chalcopyrite Using Calibration-Free Laser-Induced Breakdown Spectroscopy

This article presents elemental analysis of an economically important mineral (chalcopyrite) of local origin. Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) methodology based on the assumption of optically thin plasma and local thermodynamic equilibrium was employed for quantitative analysis. Plasma on the surface of the chalcopyrite target was generated by an Nd:YAG laser beam of wavelength 532 nm, pulse width 5 ns, and operated at repetition rate of 10 Hz. A LIBS2000+ detection system, comprised of five spectrometers, covering the spectral range from 200–720 nm, was used to record the signal of the optical emission from the chalcopyrite plasma. Recorded optical spectrum revealed the presence of Cu and Fe as the major elements while Ca and Na were recognized as the minor elements in the target sample. Quantitative analysis has shown that the relative concentrations of Cu, Fe, and Ca in the sample under study were 58.9%, 40.2%, and 0.9% by weight respectively. However, Na was not quantified due to the unavailability of suitable spectral lines, required for CF-LIBS analysis. Results obtained by CF-LIBS were validated by X-ray fluorescence (XRF) analysis, which showed the presence of five compositional elements viz. Cu, Fe, Si, Se and Ag with weight percentages of 58.1%, 35.4%, 5.7%, 0.7%, and 0.1% respectively. These results endorse the effectiveness of the CF-LIBS technique for quantitative analysis of major elements, however, its usefulness in case of minor and trace elements needs further improvement.

Calibration-free laser-induced breakdown spectroscopic analysis of copper-rich mineral collected from the Gilgit-Baltistan region of Pakistan

In this paper, we present the results of compositional analysis of a copper-rich mineral known as malachite, collected from the Gilgit-Baltistan region of Pakistan. A calibration-free laser-induced breakdown spectroscopy (CF-LIBS) technique is employed for determination of elemental composition of the sample. The study aims at the investigation of the presence of precious elements, if any, in minerals of local origin. The laser beam of a 1064 nm wavelength from a nanosecond pulsed $Q$Q-switched Nd:YAG laser was focused on the surface of the sample, and an emission spectrum was obtained with the help of a LIBS2000 spectrometer covering the spectral range between 200 to 700 nm. Results obtained through analyzing the characteristic emission lines of different elements have confirmed the presence of sixteen (16) elements in the investigated sample, viz. Cu, Si, Al, K, Fe, Mn, Ag, Ti, Ba, Sr, Ca, Mg, Na, Li, C, and H. For quantification of the detected elements in the sample, a calibration-free method based on local thermodynamic equilibrium and optically thin plasma model was employed. Plasma parameters, such as electron number density and temperature, were calculated for the purpose of subsequent calculations. Seven elements, viz. Cu, Fe, Si, Ca, Mg, Mn, and Al, were quantified out of 16 initially detected elements, and their concentration in terms of weight percentage was 43.15%, 20.13%, 18.31%, 9.46%, 3.28%, 3.16%, and 2.51%, respectively. The presence of all seven elements quantified by CF-LIBS was confirmed by x-ray fluorescence analysis.

Percussive Rock Surface Remover Driven by Solenoid with Planer Motion for Lunar Exploration

This paper deals with a percussive rock surface crusher driven with a solenoid to smoothen the sample surface by a 2-axis planar motion. The weathered rock surface should be removed and smoothened before analyzing its structure and composition precisely. The solenoid, which generates a large vibration amplitude and a large impulsive force, was used to vibrate a tool bit with engineered 1-mm pyramids made of tungsten carbide. The tool bit was fixed parallel to the feed direction or with a skew. A rock sample was moved by a stage with movable ranges for the machining of 10 mm and 20 mm in the x- and y-directions, respectively. The sample paths were randomly generated in 1 or 2 directions. In the comparisons of the surface roughness, the 2-axis motion and tool skew not only allowed isotropic and small roughness but also the removal of more amount due to the removed debris. The roughness reached several tens of micrometers without a certain special frequency component. This level allows for component analysis by X-ray fluorescence or laser-induced breakdown spectrometer.

Improved intact soil-core carbon determination applying regression shrinkage and variable selection techniques to complete spectrum laser-induced breakdown spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS) provides a potential method for rapid, in situ soil C measurement. In previous research on the application of LIBS to intact soil cores, we hypothesized that ultraviolet (UV) spectrum LIBS (200-300 nm) might not provide sufficient elemental information to reliably discriminate between soil organic C (SOC) and inorganic C (IC). In this study, using a custom complete spectrum (245-925 nm) core-scanning LIBS instrument, we analyzed 60 intact soil cores from six wheat fields. Predictive multi-response partial least squares (PLS2) models using full and reduced spectrum LIBS were compared for directly determining soil total C (TC), IC, and SOC. Two regression shrinkage and variable selection approaches, the least absolute shrinkage and selection operator (LASSO) and sparse multivariate regression with covariance estimation (MRCE), were tested for soil C predictions and the identification of wavelengths important for soil C prediction. Using complete spectrum LIBS for PLS2 modeling reduced the calibration standard error of prediction (SEP) 15 and 19% for TC and IC, respectively, compared to UV spectrum LIBS. The LASSO and MRCE approaches provided significantly improved calibration accuracy and reduced SEP 32-55% over UV spectrum PLS2 models. We conclude that (1) complete spectrum LIBS is superior to UV spectrum LIBS for predicting soil C for intact soil cores without pretreatment; (2) LASSO and MRCE approaches provide improved calibration prediction accuracy over PLS2 but require additional testing with increased soil and target analyte diversity; and (3) measurement errors associated with analyzing intact cores (e.g., sample density and surface roughness) require further study and quantification.

Laser induced breakdown spectroscopy for elemental analysis in environmental, cultural heritage and space applications: a review of methods and results

Analytical applications of Laser Induced Breakdown Spectroscopy (LIBS), namely optical emission spectroscopy of laser-induced plasmas, have been constantly growing thanks to its intrinsic conceptual simplicity and versatility. Qualitative and quantitative analysis can be performed by LIBS both by drawing calibration lines and by using calibration-free methods and some of its features, so as fast multi-elemental response, micro-destructiveness, instrumentation portability, have rendered it particularly suitable for analytical applications in the field of environmental science, space exploration and cultural heritage. This review reports and discusses LIBS achievements in these areas and results obtained for soils and aqueous samples, meteorites and terrestrial samples simulating extraterrestrial planets, and cultural heritage samples, including buildings and objects of various kinds.