A quantitative evaluation of spurious results in the infrared spectroscopic measurement of CO2 isotope ratios

Mansfield, C.D. and Rutt, H.N. (2002) A quantitative evaluation of spurious results in the infrared spectroscopic measurement of CO2 isotope ratios. Physics in Medicine and Biology, 47 (4), 689-696. (doi:10.1088/0031-9155/47/4/310).

Abstract

The possible generation of spurious results, arising from the application of infrared spectroscopic techniques to the measurement of carbon isotope ratios in breath, due to coincident absorption bands has been re-examined. An earlier investigation, which approached the problem qualitatively, fulfilled its aspirations in providing an unambiguous assurance that ¹³C¹⁶O₂/¹²C¹⁶O₂ ratios can be confidently measured for isotopic breath tests using instruments based on infrared absorption. Although this conclusion still stands, subsequent quantitative investigation has revealed an important exception that necessitates a strict adherence to sample collection protocol. The results show that concentrations and decay rates of the coincident breath trace compounds acetonitrile and carbon monoxide, found in the breath sample of a heavy smoker, can produce spurious results. Hence, findings from this investigation justify the concern that breath trace compounds present a risk to the accurate measurement of carbon isotope ratios in breath when using broadband, non-dispersive, ground state absorption infrared spectroscopy. It provides recommendations on the length of smoking abstention required to avoid generation of spurious results and also reaffirms, through quantitative argument, the validity of using infrared absorption spectroscopy to measure CO₂ isotope ratios in breath.

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