The application of infrared spectroscopy to breath CO₂isotope ratio measurements and the risk of spurious results

Abstract

Stable CO2 isotope breath tests are established as a valuable tool in diagnostic and investigative medicine with the potential to become more prominent in the future. However, their development and widespread clinical use is limited by the requirement of isotope ratio mass spectroscopic analysis. To overcome this restriction alternative analytical techniques have been developed; the most promising, offering relative simplicity and lower costs, are those instruments using infrared spectroscopy. Clinical investigations using such instruments show them to perform well but very little attention has been given to the possibility of interference from the infrared absorption spectrum of other compounds in the breath. To provide an unambiguous answer to this concern we have analysed literature on over 200 detected breath compounds and their infrared absorption spectra to identify any absorption bands coincident with the nu3 absorption band of CO2. It was found that only five breath trace compounds possess coincident fundamental absorption bands, none of which pose the risk of spurious results. We conclude that the 13C16O2/12C16O2 ratio can confidently be measured for isotopic breath tests using an infrared spectrometer, the position of the nu3 absorption band of CO2 in the infrared spectrum precluding any discernible risk of spurious measurements due to coincidental absorption bands.

Mass spectrometric studies on brain metabolism, using stable isotopes

“…Infrared (IR) spectroscopy has frequently been employed for the determination of isotope ratio 13 C/ 12 C for CO 2 in breath tests (Mansfield & Rutt, 1998; Adamek et al, 1999; Braden, Caspary, & Lembcke, 1999; Esler et al, 2000; Crosson et al, 2002). IR spectroscopy provides a simple method for isotope ratio measurement, but it has a narrow window to detect isotopes.…”

Major Influence of Oxygen Supply on 13CO2 : 12CO2 Ratio Measurement by Nondispersive Isotope‐Selective Infrared Spectroscopy

“…They evaluate differences in thermal expansion within reference chambers containing 13 CO 2 and 12 CO 2 , respectively, which is induced by absorption of infrared radiation. According to this, NDIRS‐based devices are described more accurately as infrared ratiometers [7]. The infrared radiation has to pass the chamber containing the gas sample before reaching the 13 CO 2 or 12 CO 2 measuring chambers, respectively, where it induces thermal expansion because of absorption.…”

“…Thus, not only influences from spectral interference by breath test compounds with an absorption band that coincides with the band of interest, but changes in gas compounds or their concentrations may be misinterpreted as a variation in the carbon isotope ratio. Mansfield and Rutt reviewed systematically the literature for influences of more than 200 detected breath compounds on infrared spectroscopy for CO 2 isotope ratio measurement [7]. They identified five compounds which could influence the measurement but with little significance in clinical practice (including the well‐known effect of N 2 O).…”

“…Since the NDIRS-based devices give information regarding the total absorption over a certain wave number region, they are influenced by other breath sample compounds with an absorption band that coincides with the band of interest. There are few agents known to interfere with the absorption of 13 CO 2 or 12 CO 2 , respectively [7]. Influence from any spectral interference effect may be misinterpreted as a variation in the carbon isotope ratio.…”

Development of low cost instrumentation for non-invasive detection of Helicobacter pylori

“…The IR window of 4.3 µm was chosen for performing measurements due to the strong absorption of CO 2 ν 3 mode. A comprehensive study of the various possible interfering compounds present in human exhaled breath was published by Mansfield 19 and it showed that this particular IR region was free from all coincident absorption bands. Figure 1 presents an overall schematic of the instrument.…”