The variations observed in the synchronous fluorescence spectra of a soil fulvic acid, collected in the north of Portugal, with pH (between 2 and 7) and with C&I) concentration (at pH 3, 4, 5 and 6 and total copper concentrations between 0.005 and 4 mM depending on the pH) were studied by SIMPLISMA, a self-modelling mixture analysis technique. Three components were detected when varying the pH, corresponding to three acid-base equilibria with pK, values around 3.0, 5.0 and 6.0, and their individual spectra were obtained. lko components were detected when varying the C&I) concentration, corresponding to two different ligand sites, and their spectra and concentration profiles (based on the two detected pure variables) were obtained. The spectrum of one binding site is similar to the component associated with the acid-base equilibrium with pK, = 3.0 and that of the other binding site is similar to the sum of the spectra of the components associated with the other two acid-base equilibria. Using a 1: 1 stoichiometry for complex formation, complexation capacities (C,) and stability constants (K) were calculated for the two binding sites at the four pH values. The calculated stability constants were log K, = 3.4X4), log K, = 3.05(5) at pH 3, log K, = 4.17(3), log K, = 3.71(l) at pH 4, log K, = 4.51(3), log K, = 3.95(2) at pH 5 and log K, = 4.57(3), log K2 = 4.03(l) at pH 6. Key work Fluorimetry; Copper; Fulvic acid; Soils; Self-modelling mixture analysis (SIMPLISMA) * Corresponding author. sumed for complex formation, the stability constant and complex@ capacity of the ligand can be calculated. In these calculations, only one type of binding site is defined and only one fluorescence intensity value, the maximum of the emission fluorescence spectrum, is used, because the excitation and emission fluorescence spectra of FA usually show only one band. More recently, synchronous fluorescence (SyF) spectra were obtained for FA, which are characterized by several overlapped bands [9,10], and the information was treated by multi-wavelength