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Improving δ13C Measurement Accuracy of Off-Axis Integrated Cavity Output Spectroscopy with a Weighted Feedforward
Yixuan Liu1,2, Kun Liu1,2, Guishi Wang1
1Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China.
Analytical Chemistry
|June 15, 2026
Summary
A new dual-gas isotope analyzer for methane and carbon dioxide uses a neural network to correct for concentration-dependent errors. This method significantly improves measurement accuracy for precise isotope analysis.
Area of Science:
- Environmental Science
- Analytical Chemistry
- Spectroscopy
Background:
- Laser absorption spectroscopy offers high sensitivity for isotope measurements but suffers from concentration dependence and nonlinear errors.
- These limitations hinder accurate isotope analysis, especially over wide concentration ranges and at low signal-to-noise ratios.
Purpose of the Study:
- To develop a dual-gas carbon isotope analyzer for methane (CH4) and carbon dioxide (CO2).
- To implement a feature-enhanced weighted feedforward neural network (FNN) for correcting concentration-dependent effects in isotope measurements.
Main Methods:
- Utilized off-axis integrated cavity output spectroscopy (OA-ICOS) for isotope analysis.
- Developed a 9-dimensional feature space incorporating high-order interaction terms.
- Applied boundary-constrained data augmentation and region-of-interest weighting for error correction.
Main Results:
- Successfully eliminated concentration dependence, achieving residual errors within ±0.4‰.
- Demonstrated excellent agreement with reference values (R² > 0.999) across various isotopic compositions.
- Achieved high measurement precision: 0.19‰ for CH4 and 0.075‰ for CO2 at low concentrations.
- Showed high consistency with a commercial analyzer in field comparisons for dynamic atmospheric isotope variations.
Conclusions:
- The proposed neural network-based correction effectively mitigates concentration dependence in high-precision laser isotope spectroscopy.
- This approach enhances the accuracy and reliability of isotope analyzers for environmental and scientific applications.
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