A micro-gas column assisted in situ laser-induced breakdown spectroscopy system: Development and field testing

Abstract

Laser-induced breakdown spectroscopy (LIBS) has attracted extensive attention as a new technique for in situ marine applications. In this paper, a high-sensitivity underwater micro-gas column assisted in situ LIBS system (MGC-LIBSea) was designed and implemented. The system creates a stable millimeter-scale gas column in water and a pulsed laser is focused on the gas–liquid interface of the micro-gas column to obtain enhanced LIBS signals. To improve its resistance in underwater complex conditions, a protective water flow layer is set on the outer surface of the gas colum. A pressure-balancing airbag was also designed to ensure a stable gas supply at all depths. Both the laboratory and nearshore testing results demonstrated the enhancement feasibility of the MGC-LIBSea system. Particularly, the ion lines of Mg and Ca exhibit remarkable enhancement compared to those without MGC. Moreover, clear signals of H and O could be excited by adoption of the MGC metho, making in situ calibration for LIBS more convenient. By using H as an internal standard, the RSD decreased from 5.21% to 2.95% in laboratory experiments, and a RSD of 4.58% was obtained in sea trial in Qingdao Jiaozhou Bay. A profiling sea trial was carried out at an 18 m depth, proving the potential of MGC-LIBSea for high-pressure environments.