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Laser-induced breakdown spectroscopy (LIBS) has been identified as an analytical chemistry technique suitable for field use. We use double pulse LIBS to detect five analytes (sodium, manganese, calcium, magnesium, and potassium) that are of key importance in understanding the chemistry of deep ocean hydrothermal vent fluids as well as mixtures of vent fluids and seawater. The high pressure aqueous environment of the deep ocean is simulated in the laboratory, and the key double pulse experimental parameters (laser pulse energies, gate delay time, and interpulse delay time) are studied at pressures up to 2.76x10(7) Pa. Each element is found to have a unique optimal set of parameters for detection. For all pressures and energies, a short (< or = 100 ns) gate delay is necessary. As pressure increases, a shorter interpulse delay is needed and the double pulse conditions effectively become single pulse for both the 1.38x10(7) Pa and the 2.76x10(7) Pa conditions tested. Calibration curves reveal the limits of detection of the elements (5000 ppm Mg, 500 ppm K, 500 ppm Ca, 1000 ppm Mn, and 50 ppm Na) in aqueous solutions at 2.76x10(7) Pa for the experimental setup used. When compared to our previous single pulse LIBS work for Ca, Mn, and Na, the use of double pulse LIBS for analyte detection in high pressure aqueous solutions did not improve the limits of detection.

The ability of oceanographers to make sustained measurements of ocean processes is limited by the number of available sensors for long-term in situ analysis. In recent years, laser-induced breakdown spectroscopy (LIBS) has been identified as a viable technique to develop into an oceanic chemical sensor. We performed single pulse laser-induced breakdown spectroscopy of high pressure bulk aqueous solutions to detect three analytes (sodium, manganese, and calcium) that are of key importance in hydrothermal vent fluids, an ocean environment that would greatly benefit from the development of an oceanic LIBS sensor. The interrelationship of the key experimental parameters, pulse energy and gate delay, for a range of pressures up to 2.76x10(7) Pa, is studied. A minimal effect of pressure on the peak intensity is observed. A short gate delay (less than 200 ns) must be used at all pressures. The ability to use a relatively low laser pulse energy (less than approximately 60 mJ) for detection of analytes at high pressure is also established. Na, Mn, and Ca are detectable at pressures up to 2.76x10(7) Pa at 50, 500, and 50 ppm, respectively, using an Echelle spectrometer.

The development of in situ chemical sensors is critical for present-day expeditionary oceanography and the new mode of ocean observing systems that we are entering. New sensors take a significant amount of time to develop; therefore, validation of techniques in the laboratory for use in the ocean environment is necessary. Laser-induced breakdown spectroscopy (LIBS) is a promising in situ technique for oceanography. Laboratory investigations on the feasibility of using LIBS to detect analytes in bulk liquids at oceanic pressures were carried out. LIBS was successfully used to detect dissolved Na, Mn, Ca, K, and Li at pressures up to 2.76 x 10(7) Pa. The effects of pressure, laser-pulse energy, interpulse delay, gate delay, temperature, and NaCl concentration on the LIBS signal were examined. An optimal range of laser-pulse energies was found to exist for analyte detection in bulk aqueous solutions at both low and high pressures. No pressure effect was seen on the emission intensity for Ca and Na, and an increase in emission intensity with increased pressure was seen for Mn. Using the dual-pulse technique for several analytes, a very short interpulse delay resulted in the greatest emission intensity. The presence of NaCl enhanced the emission intensity for Ca, but had no effect on peak intensity of Mn or K. Overall, increased pressure, the addition of NaCl to a solution, and temperature did not inhibit detection of analytes in solution and sometimes even enhanced the ability to detect the analytes. The results suggest that LIBS is a viable chemical sensing method for in situ analyte detection in high-pressure environments such as the deep ocean.