A method is presented for comparative analysis of absorption line properties in the case of interference between rotation-vibration bands of the gas to be detected and a foreign gas. It can be applied to high-sensitivity analysis of complex gas mixtures, when detection of a weak analytical line is hampered by closely located more intense interfering lines of foreign gases. Disappearance of analytical line extremes in the studied spectrum is proposed to be used as a criterion of assessment. The concentration ratio of the analyzed and foreign gases can be used for quantitative analysis and comparison of properties if this criterion is fulfilled. The criterion can be applied to the first and second derivatives of the absorption spectra as well. Equations are obtained that relate line parameters to concentrations of the detected and foreign gases, at which analytical line extremes disappear from the absorption spectrum. The relationship is found between the concentration of the detected gas under this condition and its first and second derivatives, as well as the dependence of the conditions of extreme disappearance on the total pressure of the gas mixture.