Analysis of gas mixtures by means of Fourier transform infrared spectroscopy

Abstract

FT-IR spectroscopy as a rapid and sensitive method for on-line gas analysis was investigated. Background knowledge of the IR spectroscopy of carbon dioxide and methane was obtained by undertaking a study of their high-resolution spectra. As a result of the CO2 molecule conforming to Einstein-Bose statistics the uneven rotational lines are absent. An excellent correlation between a theoretically calculated spectrum of the methane v4 band and an experimental spectrum was found, by taking the first and second order Coriolis coupling into account. Once the theoretical interpretation of the FT-IR spectra was well understood, quantitative analysis on gas mixtures were done. Results of on-line measurements are reported and discussed. Two types of gas-cells, originally designed in our laboratories are discussed. These cells can be used to selectively enhance the signal of a low concentration component, in the presence of an overlapping signal, by way of condensation as well as polar absorption.