Towards real-time quantification of seawater composition using laser-induced breakdown spectroscopy

Laser-Induced Breakdown Spectroscopy (LIBS) is being investigated as a technique to perform in situ multielement chemical analysis of liquids at sea. The purpose of this study is to develop a method to quantify the concentration of ions dissolved in seawater using LIBS. LIBS signals suffer from shot-to-shot variations which often limit their application to qualitative or semi-quantitative analysis. In this work, we investigate the effects of fluctuations in laser energy on LIBS spectra as a possible cause for this instability, and perform experiments using a LIBS device that has been modified to register the energy of each laser pulse along with the spectral measurements. The experiments demonstrate that the intensity of the LIBS spectra observed for each element are proportionate to energy of the laser pulse of over the range of fluctuation, and based on the findings, we propose a method to improve the stability of LIBS measurements using co-registered laser pulse energy as a filtering criterion. Significant improvements in the linearity of calibration curves generated using 15 artificial seawater and hydrothermal vent fluid samples containing dissolved ions at various concentrations are achieved, and we demonstrate that the proposed method can improve the quantitative performance of LIBS for application to oceanic liquids.