Quantification of dissolved metals in high-pressure CO2-water solutions by underwater laser-induced breakdown spectroscopy

Underwater laser-induced breakdown spectroscopy has been employed for the measurement of dissolved metals (Mg, Ca, Sr, Ba and Mn) in high-pressure CO2-water solutions. The CO2 pressure was varied over the range from 10 to 400 bars and the concentrations of Mg, Ca, Sr, Ba and Mn were determined by spectral analysis and establishing the calibration curves. Limit of detection (LOD) for Mg, Ca, Sr, Ba, and Mn at 10 bars were found to be 31.7 ppm, 2.5 ppm, 3.3 ppm, 4.4 ppm, and 10.5 ppm, respectively. The LOD for Mg, Ca, Sr, and Ba were unaffected by the pressure however, a 2-fold decrease in LOD of Mn was observed with an increasing pressure from 10 to 400 bars. The results demonstrate that low-ppm range concentrations of Mg, Ca, Sr, Ba and Mn can be precisely measured in CO2-charged water at varied pressure conditions by using underwater LIBS. The study has implications in monitoring of CO2 leak in carbon sequestration.