Underwater In Situ Dissolved Gas Detection Based on Multi-Reflection Raman Spectroscopy

Area of Science:

• Oceanography
• Analytical Chemistry
• Spectroscopy

Background:

• Dissolved gas detection is vital for oceanic exploration.
• Raman spectroscopy shows promise but lacks sensitivity for common seawater analysis.

Purpose of the Study:

• To develop a highly sensitive underwater in situ Raman spectroscopy system for detecting dissolved gases in common seawater.
• To overcome the limitations of previous techniques in oceanic applications.

Main Methods:

• Designed a near-concentric cavity with a miniature 1 mL gas sample chamber for enhanced sensitivity.
• Integrated a hollow fiber membrane degasser for efficient underwater degassing.
• Calculated detection limits for CO2, O2, and H2 using the 3σ criteria.

Main Results:

• Achieved detection limits of 72.8 ppm for CO2, 44.0 ppm for O2, and 27.7 ppm for H2.
• Demonstrated clear CO2 signal detection within 30 s at a flow rate of 550 mL/min.
• Successfully deployed the system for simultaneous in situ detection of multiple dissolved gases in offshore seawater.

Conclusions:

• The developed Raman spectroscopy system offers high sensitivity for underwater dissolved gas detection.
• The system is suitable for practical oceanic observations and exploration.
• Enables simultaneous, in situ measurement of multiple dissolved gases in seawater.