Single pulse laser-induced breakdown spectroscopy of bulk aqueous solutions at oceanic pressures: interrelationship of gate delay and pulse energy

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 2.76x107 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 approx. 60 mJ) for detection of analytes at high pressure is also established. Na, Mn, and Ca are detectable at pressures up to 2.76x107 Pa at 50, 500, and 50 ppm, respectively, using an Echelle spectrometer