Salinity effects on elemental analysis in bulk water by laser-induced breakdown spectroscopy.

The effects of salinity on underwater laser-induced breakdown spectroscopy (LIBS) were investigated with salinities ranging from 2‰ to 50‰. Both spectroscopic and fast imaging techniques were used to observe plasma emission. It was shown that as the salinity increased, emission intensities of the atomic lines increased, while intensities of the ionic lines were suppressed. The signal-to-background ratios of the spectral lines decreased as a function of salinity, but the signal-to-noise ratios changed irregularly with salinity. Image results demonstrated that brighter and longer plasma could be produced at higher salinity with higher plasma temperature and electron density. The calibration curves at different salinities indicated that the high salinity environment did not limit the detection capability of LIBS. The obtained results reveal the significant influences of salinity on underwater LIBS detection, which plays an important role in promoting applications of LIBS in the ocean.