Rapid and real-time analysis of multi-component dissolved gas in seawater by Raman spectroscopy combined with continuous gas−liquid separator

Rapid and sensitive detection of dissolved gases in seawater is quite essential for the investigation of the global carbon cycle. Large quantities of in situ optical detection techniques showed restricted measurement efficiency, owing to the single gas sensor without the identification ability of multiple gases. In this work, a novel gas−liquid Raman detection method of monitoring the multi-component dissolved gases was proposed based on a continuous gas−liquid separator under a large difference of partial pressure. The limit of detection (LOD) of the gas Raman spectrometer could arrive at about 14 μl·L⁻¹ for N₂ gas. Moreover, based on the continuous gas−liquid separation process, the detection time of the dissolved gases could be largely decreased to about 200 s compared with that of the traditional detection method (30 min). Effect of equilibrium time on gas−liquid separation process indicated that the extracted efficiency and decay time of these dissolved gases was CO₂ >O₂ >N₂. In addition, the analysis of the relationship between equilibrium time and flow speed indicated that the decay time decreased with the increase of the flow speed. The validation and application of the developed system presented its great potential for studying the components and spatiotemporal distribution of dissolved gases in seawater.