Simultaneous Sensitive Determination of δ(13)C, δ(18)O, and δ(17)O in Human Breath CO(2) Based on ICL Direct Absorption Spectroscopy

Previous research revealed that isotopes (13)C and (18)O of exhaled CO(2) have the potential link with Helicobacter pylori; however, the (17)O isotope has received very little attention. We developed a sensitive spectroscopic sensor for simultaneous δ(13)C, δ(18)O, and δ(17)O analysis of human breath CO(2) based on mid-infrared laser direct absorption spectroscopy with an interband cascade laser (ICL) at 4.33 μm. There was a gas cell with a small volume of less than 5 mL, and the pressure in the gas cell was precisely controlled with a standard deviation of 0.0035 Torr. Moreover, real-time breath sampling and batch operation were achieved in gas inlets. The theoretical drifts for δ(13)C, δ(18)O, and δ(17)O measurement caused by temperature were minimized to 0.017‰, 0.024‰, and 0.021‰, respectively, thanks to the precise temperature control with a standard deviation of 0.0013 °C. After absolute temperature correction, the error between the system responded δ-value and the reference is less than 0.3‰. According to Allan variance analysis, the system precisions for δ(13)C, δ(18)O, and δ(17)O were 0.12‰, 0.18‰, and 0.47‰, respectively, at 1 s integration time, which were close to the real-time measurement errors of six repeated exhalations.