Accurate concentration measurements using infrared absorption without determination of the baselines

Infrared absorption spectra have become widely used for in situ determinati on of concentrations in complex mixtures. However, experimental accuracy is often limited by lack of knowledge of the baselines. The mathematical trea tment described below allows the spectra to be superimposed on any backgrou nd with a shape as complex as a parabolic one. The concentrations are thus accurately determined whatever the baseline of the mixture spectrum and eve n those of the calibration spectra. A mathematical proof of this property i s given within the framework of the presently used method, and tests of the efficiency of the method are presented.