Highly sensitive Raman system for dissolved gas analysis in water.

Area of Science:

• Oceanography
• Analytical Chemistry
• Spectroscopy

Background:

• Dissolved gas detection in seawater is crucial for ocean observation.
• Raman spectroscopy offers simultaneous multi-species detection but faces sensitivity limitations for undersea dissolved gases.

Purpose of the Study:

• To develop a highly sensitive Raman spectroscopy (HSRS) system for detecting small amounts of underwater dissolved gases.
• To improve the sensitivity of Raman measurements for oceanic applications.

Main Methods:

• Designed a specialized gas chamber integrated with a near-concentric cavity for enhanced Raman signal collection.
• Evaluated system performance through systematic experiments, including lab-based detection limits and a field test with a gas-liquid separator.

Main Results:

• Achieved approximately 21 times stronger Raman signals compared to conventional side-scattering methods.
• Established low limits of detection: 2.32 μmol/L for CO2 and 0.44 μmol/L for CH4 in laboratory settings.
• Successfully detected O2 and CO2 signals in a test-out experiment after 1 hour of degasification.

Conclusions:

• The developed HSRS system demonstrates significant potential for sensitive underwater dissolved gas detection.
• Further improvements are needed for robust in situ detection capabilities in oceanic environments.