PROCEDURE FOR THE CLASSIFICATION OF FULVIC-ACIDS AND SIMILAR SUBSTANCES BASED ON THE VARIATION WITH PH OF THEIR SYNCHRONOUS FLUORESCENCE-SPECTRA

A method for the classification of fulvic acids (FA) and similar subst ances Is presented, It consists of three steps: (i) for each sample, s ets of synchronous molecular fluorescence spect ra as the pH is change d are acquired; (ii) the spectral set is reduced to a small number of spectra and concentration profiles of the detected components by evolv ing factor analysis with a gradient concentration window (EFA-GCW) are obtained; (iii) the spectra of the components of the samples are subj ected to pattern recognition analysis by cluster analysis and multi-di mensional scaling. The procedure was tested with 13 samples of FA of n atural and anthropogenic origin. Classification rules as a function of the origin and acid-base properties of the samples, in the form of fi gures with spectra and tables with spectral characteristics, were obta ined. The classification according to the origin of the FA samples is useful for the evaluation of the 'extent of humification of FA, The fo llowing information on the acid-base properties of the fluorescent fra ctions of FA was obtained: only FA extracted from soil have fluorescen t fractions with relatively strong acid character (pK(a) approximate t o 3.2); all FA extracted from different origins have similar fluoresce nt structures with relatively weak acid character (pK(a) approximate t o 6.2); in addition, FA extracted from low humified materials (leaf li tter and composted wastes) have another set of similar fluorescent str uctures with weak acid character (pK(a) = 9.2).