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Updated: Jun 28, 2025
05:00
Measuring Dissolved Methane in Aquatic Ecosystems Using An Optical Spectroscopy Gas Analyzer
Published on: July 26, 2024
435
13CH4/12CH4 sensing using Raman spectroscopy.
Dmitry V Petrov1, Aleksandr S Tanichev2
1Institute of Monitoring of Climatic and Ecological Systems, 634055 Tomsk, Russia; Tomsk State University, 634050 Tomsk, Russia.
Summary
This study introduces a Raman spectroscopy method to measure 13CH4 concentration in natural methane. The technique achieves a 10‰ measurement error for δ13C, enhancing mud gas logging capabilities.
Area of Science:
- Analytical Chemistry
- Spectroscopy
- Geochemistry
Background:
- Accurate measurement of methane isotopes is crucial for various applications, including natural gas exploration and environmental monitoring.
- Traditional methods for isotopic analysis can be complex and time-consuming.
- Raman spectroscopy offers a potential alternative for rapid and precise isotopic composition determination.
Purpose of the Study:
- To develop and validate a Raman spectroscopy technique for quantifying 13CH4 concentration in natural methane.
- To determine the peak positions and relative scattering cross-sections of key vibrational bands for 13CH4.
- To assess the feasibility of using simulated spectra for 13CH4/12CH4 ratio determination.
Main Methods:
- Utilized Raman spectroscopy to measure the concentration of 13CH4 in natural methane samples.
- Determined peak positions and relative scattering cross-sections of Q-branches for intense vibrational bands of 13CH4.
- Investigated measurement methods for the 13CH4/12CH4 ratio using Q-branches of ν1 and ν3 bands.
- Employed spectral simulation of ν3 bands for ratio determination without experimental spectra.
- Recorded Raman spectra of alkanes (up to n-hexane) and their integrated intensities.
Main Results:
- Established a Raman spectroscopy technique for measuring 13CH4 concentration with a δ13C measurement error of 10‰.
- Determined spectral characteristics (peak positions, scattering cross-sections) of 13CH4 vibrational bands.
- Demonstrated that the 13CH4/12CH4 ratio can be accurately determined via simulation of ν3 bands.
- Provided integrated intensities for alkanes in characteristic 13CH4 and 12CH4 band regions.
- Achieved a spectral resolution of 0.4 cm-1 and 100-s exposure time at near 1 atm pressure.
Conclusions:
- The developed Raman spectroscopy method provides a precise and efficient way to measure 13CH4 concentration in natural methane.
- The ability to determine the 13CH4/12CH4 ratio through spectral simulation simplifies the analysis process.
- The findings expand the application range of Raman gas analyzers, particularly in mud gas logging.
- The presented data on alkanes further supports the utility of Raman spectroscopy for complex gas mixture analysis.
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