EVOLVING FACTOR-ANALYSIS OF SYNCHRONOUS FLUORESCENCE-SPECTRA OF HUMICSUBSTANCES IN THE PRESENCE OF CU(II)

Synchronous fluorescence spectra of soil and marine fulvic acids and o f a commercial humic acid collected by varying Cu(II) concentration at constant pH (quenching experiments) were analyzed by evolving factor analysis (EFA). The number of components in each data set were related to different binding sites on the molecules of the corresponding humi c substances. Two binding sites were found for the marine fulvic acid (mfua) and humic acid (hua) samples and two or three binding sites, de pending on the pH, for the soil fulvic acid (sfua) sample. Rules were developed for the EFA procedure to obtain, in a self-modeling base, sp ectra and fluorescence intensity profiles for the detected binding sit es. From the calculated fluorescence intensity profiles, and using a 1 : 1 stoichiometry for the Cu(II)/binding site complex formation, the conditional stability constants (K) and complexing capacities for the detected stronger binding sites were calculated. The following values for log K (standard deviation) were obtained: mfua (pH=6), log K-1=5.2 (0.3); sfua (pH=6), log K-1=5.57 (0.06) and log K-2=4.92 (0.04); and hua (pH=7), log K-1=5.38 (0.07).