Matrix effect of sodium compounds on the determination of metal ions in aqueous solutions by underwater laser-induced breakdown spectroscopy

Abstract

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.

Detection of Low Lithium Concentrations Using Laser-Induced Breakdown Spectroscopy (LIBS) in High-Pressure and High-Flow Conditions

“…The limits of detection were estimated to be 44, 50, 36, and 38 mg L �1 for measurements performed in the following conditions: (1 bar and static), (1 bar and 6.7 mL min �1 ), (210 bar and static), and (210 bar and 6.7 mL min �1 ), respectively. These detection limits are very similar to 60 mg L �1 described by Goueguel et al, 18 13 mg L �1 reported by Knopp et al, 19 and slightly higher than those obtained with the double pulse approach, e.g., 0.8 mg L �1 and 6 mg L �1 . 19,20 The evaluation for the determination of Li in 2.5% NaCl solution was carried out in the concentration range of 0 to 1.0 mg L �1 , employing the same experimental conditions for measurements in water.…”

Rapid, direct determination of strontium in natural waters by laser-induced breakdown spectroscopy

“…19). More recently, Goueguel et al 35 demonstrated that the LOD of strontium determination in water with the use of the resonance atomic line would be decreased to 2.89 mg L À1 by signal accumulation over 500 spectra. The poor sensitivity of the atomic line is related to the excitation conditions inside plasma, which do not promote sufficient intensity from strontium atoms.…”

A Review of Underwater Laser-induced Breakdown Spectroscopy of Submerged Solids

“…The analysis of the dissolved species has been performed intensively by laser-induced breakdown in bulk solutions (for example, references [141][142][143] ). On the other hand, the ablation of submerged solids has the advantage that the position of the plasma ignition is comparatively stable, and that the plasma can be generated with lower energy, i.e., the ablation threshold of solids is extremely lower than the breakdown threshold in bulk water.…”