STUDY OF THE ACID-BASE PROPERTIES OF LEAF-LITTER EXTRACTS

The acid-base properties of four leaf litter extracts, LLE (eucalyptus , fern, oak and chestnut coverture), were characterized by synchronous fluorescence (SyF) spectroscopy and compared with those of two fulvic acids (FA) extracted from two different horizons (0-5 and 5-15 cm) of an oak forest soil. The characterization was based on the variation w ith the pH of the properties of the fluorescent structures present in the samples, which function as probes and provide a macroscopic image of their acid-base properties. These sets of SyF spectra collected as a function of the pH show fingerprinting potential. They were treated by a self-modeling curve resolution procedure, evolving factor analysi s with a gradient concentration window (EFA-GCW), to reduce the raw sp ectral data to the number of components, their spectra, and SyF intens ity profiles (pH distribution diagrams). Four acid-base systems were d etected for all samples of LLE and FA with pKas ranging from 2.5 to 10 .0 (pKas about 3, 5, 7 and 9, except for the fern LLE sample which sho wed pKas about 5, 7, 9 and 10). A similarity analysis of the spectra o f the components, performed by cluster analysis, showed that the most acidic fluorescent structures of the LLE are not similar to those of t he soil FA, but the less acidic are.