Rapid High-Sensitivity Analysis of Methane Clumped Isotopes (Δ¹³CH₃D and Δ¹²CH₂D₂) Using Mid-Infrared Laser...

Area of Science:

• Geochemistry
• Analytical Chemistry
• Spectroscopy

Background:

• Mid-infrared laser absorption spectroscopy is a rapid, nondestructive method for methane clumped isotope analysis.
• Current methods require large sample volumes (20 mL STP), limiting applications with natural samples.

Purpose of the Study:

• To develop a laser spectroscopic platform for methane clumped isotope analysis with reduced sample size requirements.
• To improve the precision and efficiency of methane clumped isotope measurements.

Main Methods:

• Established a laser spectroscopic platform using newly identified spectral windows (1076.97 cm⁻¹ for ¹²CH₂D₂ and 1163.47 cm⁻¹ for ¹³CH₃D).
• Utilized a custom-built gas inlet system and extensive spectral surveys on high-resolution FTIR spectra.
• Implemented technological advances for superior sample injection and analysis control, including a recycle-refilling system.

Main Results:

• Achieved measurement precision comparable to mass spectrometry for Δ¹²CH₂D₂ (∼1.5‰) with small samples (3–10 mL) in a few hours.
• Quantified larger samples (>10 mL) in under 20 minutes.
• Realized a repeatability of 0.05‰ for Δ¹³CH₃D analysis, surpassing mass spectrometry.

Conclusions:

• The developed spectroscopic platform significantly reduces methane sample size requirements for clumped isotope analysis.
• The advancements enhance the practicality of spectroscopic techniques for natural methane samples, especially those with low concentrations or requiring sequential analyses.
• This method offers a more accessible and efficient approach to determining methane clumped isotope signatures.