Simultaneous Sensitive Determination of C, O, and O in Human Breath CO Based on ICL Direct Absorption Spectroscopy.

Previous research revealed that isotopes C and O of exhaled CO have the potential link with ; however, the O isotope has received very little attention. We developed a sensitive spectroscopic sensor for simultaneous C, O, and O analysis of human breath CO 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 C, O, and 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 -value and the reference is less than 0.3‱. According to Allan variance analysis, the system precisions for C, O, and 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.