Position-Specific Isotope Analysis of Propane by Mid-IR Laser Absorption Spectroscopy

Area of Science:

• Analytical Chemistry
• Geochemistry
• Spectroscopy

Background:

• Position-specific carbon isotope analysis of propane provides insights into its formation and thermal history.
• Current methods for detecting propane isotopomers are complex, time-consuming, and require extensive sample preparation.

Purpose of the Study:

• To present a direct, non-destructive analytical technique for quantifying terminal (¹³C_t) and central (¹³C_c) propane isotopomers.
• To establish a high-precision method for site-specific carbon isotope analysis of propane using laser absorption spectroscopy.

Main Methods:

• Utilized quantum cascade laser absorption spectroscopy (QCLAS) for high-resolution spectral measurements.
• Employed a Fourier-transform infrared (FTIR) spectrometer to identify optimal spectral regions for minimal interference.
• Developed a reference template fitting method using spectral data acquired at 300 K and 155 K.

Main Results:

• Achieved high precision for natural abundance propane: 0.33 ‰ for δ¹³C_t and 0.73 ‰ for δ¹³C_c within 100 seconds.
• Successfully demonstrated site-specific, high-precision measurements of isotopically substituted non-methane hydrocarbons.
• Validated the technique's sensitivity and selectivity through spectral analysis.

Conclusions:

• The developed QCLAS technique offers a direct and non-destructive approach for analyzing propane isotopomers.
• This method significantly advances the capability for site-specific isotopic analysis of non-methane hydrocarbons.
• The technique's versatility holds potential for isotopic studies of other organic compounds.