Computer emulation of the method for comparing the isotopic composition of CO2 in gas mixtures based on laser spectral analysis at the 2.05-µm line

Abstract

An algorithm for processing spectral data in order to determine the isotopic composition of gas mixtures is proposed and simulated using emulated transmission spectra of CO2 in exhaled air tests. It is shown that the ratio of the optical-density spectra of the analyzed and reference gas mixtures is a contrast spectrum with resonant features and a fixed depth of their amplitude modulation. Based on the simulation results several spectral ranges are found to be optimal for analyzing the relative 12CO2 and 13CO2 contents in exhaled air. The effect of random noise on the isotopic analysis result is estimated, and the correlation between the optical density of analyzed gas media, level of random noise, and sensitivity of isotopic analysis is determined. The use of the algorithm proposed reduces the effect of such noises as interference at optical elements, absorption in open atmosphere, drift of the laser pulse envelope, and disbalance of spectral channels. This algorithm is valid for comparative isotopic analysis of any other gas molecules with similar spectral properties.