Measurement of CO2 Isotopologue Ratios Using a Hollow Waveguide-Based Mid-Infrared Dispersion Spectrometer

Haojie Zhang, Tao Wu*, Qiang Wu, Weidong Chen, Chenwen Ye, Mengyu Wang, Xingdao He

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We demonstrate for the first time the measurement of CO2 isotope ratios (13C/12C and 18O/16O) in a hollow waveguide (HWG) fiber using a mid-infrared heterodyne phase sensitive dispersion spectrometer (HPSDS). A 4.329 μm interband cascade laser (ICL) is used to target the absorption lines of three CO2 isotopes (13C16O2, 18O12C16O, and 12C16O2) in a 1 m long and 1mm inner diameter HWG fiber. The detection limits are 0.29 ppm, 65.78 ppb and 14.65 ppm with an integration time of 218 s for13C16O2, 18O12C16O, and 12C16O2, respectively, at a modulation frequency of 160 MHz and a pressure of 230 mbar. The measurement precisions of δ13C and δ18O are 0.89 ‰ and 0.88 ‰, respectively, corresponding to an integration time of 167 s. An experimental comparison between a HPSDS and a built wavelength modulation system with second-harmonic detection (WMS-2f) is conducted. The results show that compared to the WMS-2f, the developed HPSDS exhibits a greater linear dynamic range and excellent longterm stability. This work aims to demonstrate a detection technique of CO2 isotope dispersion spectroscopy with a large dynamic range for relevant applications focusing on samples with high concentrations of CO2 (% volume fraction), such as respiratory analysis in medical diagnostics.
Original languageEnglish
Pages (from-to)18479–18486
Number of pages9
JournalAnalytical Chemistry
Issue number50
Early online date6 Dec 2023
Publication statusPublished - 19 Dec 2023

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