Resonance-enhanced laser-induced breakdown spectroscopy (RELIBS) was investigated with the aim to improve the limit of detection of trace elements in the context of elemental analysis of aluminium alloys. A Q-switched Nd:YAG laser pulse (7 ns, 1064 nm) was used for ablation of the samples and was followed, after a suitable delay, by an Optical Parametric Oscillator (OPO) laser pulse (7 ns), tuned at 396.15 nm, to resonantly excite the aluminium host atoms. In particular, the Mg I 285.21 nm and Si I 288.16 nm lines were observed in the acquisition spectral window. We investigated the influence of the main experimental parameters, namely, the excitation wavelength, the interpulse delay and the ablation and excitation fluences, on the signal-to-noise ratio for the Mg I 285.21 nm line. We found that, at low ablation fluences, typically less than a few J cm À2 , the Mg signal at 285.21 nm achieved using RELIBS was significantly enhanced when compared to LIBS using the same ablation fluence. At fluences higher than 8 J cm À2 , the effect of the excitation pulse became unnoticeable and similar results were observed for both approaches. The optimum conditions were achieved for an interpulse delay of about 30 ns, an ablation fluence of about 3.8 J cm À2 and an excitation fluence of about 1.1 J cm À2 . The corresponding absolute LoDs were 0.7 and 50 fg, for Mg and Si, respectively, using RELIBS. When using LIBS, they were 4 and 128 fg, instead. Finally, the applicability of RELIBS in the context of a minimally destructive elemental analysis is discussed.

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Leakage of injected carbon dioxide (CO2) or resident fluids, such as brine, is a major concern associated with the injection of large volumes of CO2 into deep saline formations. Migration of brine could contaminate drinking water resources by increasing their salinity or endanger vegetation and animal life as well as human health. The main objective of this study was to investigate the effect of sodium chloride (NaCl) concentration on the detection of calcium and potassium in brine samples using laser-induced breakdown spectroscopy (LIBS). The ultimate goals were to determine the suitability of the LIBS technique for in situ measurements of metal ion concentrations in NaCl-rich solution and to develop a chemical sensor that can provide the early detection of brine intrusion into formations used for domestic or agricultural water production. Several brine samples of NaCl-CaCl2 and NaCl-KCl were prepared at NaCl concentrations between 0.0 and 3.0 M. The effect of NaCl concentration on the signal-to-background ratio (SBR) and signal-to-noise ratio (SNR) for calcium (422.67 nm) and potassium (769.49 nm) emission lines was evaluated. Results show that, for a delay time of 300 ns and a gate width of 3 μs, the presence of and changes in NaCl concentration significantly affect the SBR and SNR for both emission lines. An increase in NaCl concentration from 0.0 to 3.0 M produced an increase in the SNR, whereas the SBR dropped continuously. The detection limits obtained for both elements were in the milligrams per liter range, suggesting that a NaCl-rich solution does not severely limit the ability of LIBS to detect trace amount of metal ions.

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Laser-induced breakdown spectroscopy (LIBS) was used to detect rare earth elements (REEs) in natural geological samples. Low and high intensity emission lines of Ce, La, Nd, Y, Pr, Sm, Eu, Gd, and Dy were identified in the spectra recorded from the samples to claim the presence of these REEs. Multivariate analysis was executed by developing partial least squares regression (PLS-R) models for the quantification of Ce, La, and Nd. Analysis of unknown samples indicated that the prediction results of these samples were found comparable to those obtained by inductively coupled plasma mass spectrometry analysis. Data support that LIBS has potential to quantify REEs in geological minerals/ores.

Geologic carbon storage in deep saline aquifers is considered a feasible and possible approach of mitigating the problem of increasing greenhouse gas emissions. However, there are latent risks in which carbon dioxide (CO2) could migrate from the deep saline formations to shallower aquifers. In the event of a significant CO2 leakage to an underground source of drinking water, CO2 will dissolve in the water, thereby increasing its acidity, which could potentially enhance the solubility of various aquifer constituents, including hazardous compounds, subsequently compromising groundwater quality due to increased concentration of aqueous metals. In this paper we explore the possibility of detecting such leakage by the use of laser-induced breakdown spectroscopy (LIBS). The experiments were conducted in calcium chloride solution at three pressures of 10, 50, and 120 bar. To evaluate the direct effect of elevated CO2 on the intensity of calcium emission lines (422.67 and 393.37 nm), we also performed experiments with pure nitrogen (N2) gas, offering large water solubility contrast. We found that when performed in presence of CO2, LIBS showed only a modest decrease in Ca emission intensity from 10 to 120 bar compared to N2. These results indicate that LIBS is a viable tool for measuring brine/water contents in high-pressure CO2 environment and can be applied for monitoring CO2 leakage and displaced brine migration.

A significant portion of the carbon sequestration research being performed in the United States involves the risk assessment of injecting large quantities of carbon dioxide into deep saline aquifers. Leakage of CO2 has the potential to affect the quality of groundwater supplies in case contaminants migrate through underlying conduits. New remote sensing and near-surface monitoring technologies are needed to ensure that injection, abandoned, and monitoring wells are structurally sound, and that CO2 remains within the geologic storage reservoir. In this paper, we propose underwater laser-induced breakdown spectroscopy (underwater LIBS) as an analytical method for monitoring naturally occurring elements that can act as tracers to detect a CO2 leak from storage sites. Laboratory-scale experiments were conducted to measure Sr2+, Ca2+, K(+), and Li(+) in bulk solutions to ascertain the analytical performance of underwater LIBS. We compared the effect of NaCl, Na2CO3, and Na2SO4 on the analytes calibration curves to determine underwater LIBS' ability to analyze samples of sodium compounds. In all cases, the calibration curves showed a good linearity within 2 orders of magnitude. The limit of detections (LODs) obtained for K(+) (30±1  ppb) and Li(+) (60±2  ppb) were in ppb range, while higher LODs were observed for Ca(2+) (0.94±0.14  ppm) and Sr(2+) (2.89±0.11  ppm). Evaluation of the calibration curves for the analytes in mixed solutions showed dependence of the lines' intensity with the sodium compounds. The intensities increased respectively in the presence of dissolved NaCl and Na2SO4, whereas the intensities slightly decreased in the presence of Na2CO3. Finally, the capabilities of underwater LIBS to detect certain elements in the ppb or in the low ppm range make it particularly appealing for in situ monitoring of a CO2 leak.

Underwater laser-induced breakdown spectroscopy was applied for rapid in situ measurements of CaCO3 dissolution in CO2-saturated water at high pressure.