13CO 2/ 12CO 2 isotopic ratio measurements with a continuous-wave quantum cascade laser in exhaled breath

Vasili L. Kasyutich, Philip A. Martin

    Research output: Contribution to journalArticlepeer-review

    Abstract

    A laser spectrometer based on a continuous-wave thermoelectrically-cooled distributed feedback quantum cascade laser at ∼2308 cm -1 has been evaluated for measurement of 13CO 2/ 12CO 2 isotopic ratio (δ 13C) changes in exhaled breath samples and in CO 2 gas flows in the concentration range 1-5%. Mid-infrared CO 2 absorption spectra were measured in a 54.2-cm long optical cell using balanced detection whereby the beam passing through the cell was ratioed against a reference beam split-off from the main beam before the cell. Signal-to-noise ratios (SNR) were estimated for CO 2 concentration measurements determined from either absorption peak amplitude or absorption peak area. The highest SNR were achieved in the measurements based upon a fitted absorption peak area. Typical short-term δ 13C precisions of 1.1 0/ 00 (1-s integration time) and 0.5 0/ 00 (8-12-s integration time) were estimated from the two-sample (Allan) variance plots of data recorded in the optical cell at a pressure of 20 Torr and with no active temperature stabilization of the cell and gas flow. The best precision of 0.12 0/ 00 was achieved for averaging 80 successive 1-s integration time measurements. © 2011 Elsevier B.V. All rights reserved.
    Original languageEnglish
    Pages (from-to)60-66
    Number of pages6
    JournalInfrared Physics and Technology
    Volume55
    Issue number1
    DOIs
    Publication statusPublished - Jan 2012

    Keywords

    • Breath analysis
    • Carbon dioxide
    • Direct absorption spectroscopy
    • Gas sensor
    • Isotopic ratio
    • Quantum cascade laser

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