Spectral properties of gaseous biomarkers and choice of the optimal analytical line at interference of the spectra of detected gases

Abstract

A method for comparative investigation of the absorption line properties at interference of vibration-rotation bands of the detected and interfering gases is proposed. This method is intended for highly sensitive analysis of complex gas mixtures when measurement of absorption in a weak analytical line is hindered by a stronger, closely located interfering line. Disappearance of the analytical line extrema in the spectrum studied is proposed as an assessment criterion. The concentration ratio of the analytical and interfering gases under this condition could be used for quantitative analysis and comparison of the properties. This criterion can be applied to the first and second derivatives of the absorption spectra. To demonstrate the potential of the approach proposed, it was applied to the NO and NH3 lines that are promising for monitoring the contents of these compounds in atmospheric and exhaled air. The interference of the absorption bands of H2O, CO2, and several gaseous biomarkers was analyzed in the near-IR spectral region using the HITRAN2000 database. It was demonstrated that the problem of the vibration-rotation band interference for detected and interfering gases is aggravated in this spectral region. This aggravation is caused not only by the decrease in the absolute band intensity for overtones and combination bands of the molecular vibrations but also by the relative increase in the absorption in H2O lines and high density of CO2 lines in the near-IR spectral region.