The measurement of δ13C in respiratory gases based on incoherent broadband cavity enhanced absorption spectroscopy

Abstract

The change of stable isotope ratio of carbon dioxide (δ13CO2) in respiratory gases of patients before and after taking medicine can be used to judge whether Helicobacter pylori exists in patients’ intestines and stomach. The 4.3 μm band of blackbody radiation source and infrared dual path structure are selected for measurement, the incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) technology was used to change the structure of the light path on one side of 13CO2 to make sure that the absorption intensity of 13CO2 and 12CO2 was in the same order of magnitude. The influence of different types of optical cavity, coating method of lens and reflectivity of mirror on effective optical path were compared in this article and the effective optical path length was the largest when the semi-stable cavity with 90% reflectivity and Ge coating material was used. The standard deviation of the measurement results was 0.191‰, which met the requirements of the precision and accuracy of the measurement index in medical detection. The system had the advantages of high precision, small volume, and accurate measurement results, which is of great significance for medical auxiliary detection.