SIMULTANEOUS USE OF EVOLVING FACTOR-ANALYSIS OF FLUORESCENCE SPECTRALDATA AND ANALYSIS OF PH TITRATION DATA FOR COMPARISON OF THE ACID-BASE PROPERTIES OF FULVIC-ACIDS

Three fulvic acids (fua) extracted from a Portuguese pinewood soil (dr y pine needles, fua1, leaf litter, fua2, and lower soil horizon, fua3) have been studied by synchronous molecular fluorescence spectroscopy (SyF) at variable pH and by potentiometric pH titrations. The number o f macroscopic acid-base systems and their pK(a)s were calculated by an alysis of the SyF-pH hyphenated data with a self-modeling curve resolu tion technique (evolving factor analysis, EFA). Four macroscopic acid- base systems were detected in the fulvic acid samples (with pK(a)s aro und 3.0, 4.5, 7.0 and 9.0). The concentrations of the groups responsib le for the acid-base systems were calculated by a standard non-linear least squares adjustment of pH potentiometric titration curves using t he pK(a) values obtained by EFA. The procedure detected differences be tween the three fua: the concentration of carboxylic groups increased from fua1 to fua3 but, in contrast, the concentration of the phenolic groups decreased. These results correlate well with the expected exten t of humification of the samples.