Spectrophotometric determination of components of real materials usually has to be preceded by their chemical separation. This time-consuming step of a procedure sometimes can be avoided, if absorption spectra of substances of interest are of specific shape or characteristic points are advantageously situated. In these cases numerical evaluation of the data allows to simplify analysis. Spectrum of the examined mixture is recorded under standard conditions and percentages of individual species are calculated on the basis of their spectra taken from the database. For these calculations many algorithms are recommended, e.g. CLS, ILS, PLS, PLS-2, PCR or PCA, but the universal approach is still under development.