Bruker FTIR gas analyzer provide a spectrum fitting algorithm to analyze, extract, combine and match the spectrum of target gas, to obtain the concentration and spectrum information of each compound This method is different from the traditional CLS and PLS methods which only use the characteristic peak integral value as the basis for concentration evaluation, instead, it fits and analyzes the spectrum shape of the characteristic area, combines and matches the measured spectrum, realizes the qual. and quant. anal. of each compounds in the complex gas. The spectrum fit method based on Lambert Beer′s law, the spectrum shape of all interfering gases in the characteristic area of the target gas is fitted, the spectrum of each compound and its contribution to the total spectrum is also accurately fitted. The measured spectrum is resolved into the target gas spectrum and various impurity spectrum, with the unique characteristics of the peak shape of the IR spectrum, concentration of each compound is obtained. In addition, because this method can analyze the contribution of water vapor and carbon dioxide to the target spectrum in real time, the Bruker FTIR gas analyzer can directly analyze the single-channel spectrum without any background. Compared with basic quantification methods such as traditional CLS, PLS linear math. model anal. or nonlinear least squares method, the spectral fitting algorithm is more applicable to complex gas mixtures, low concentration gases, and homogeneous gas mixtures