Influence of the ligand concentration and pH on the complexation of Cu(II) by a soil fulvic acid

Anodic Stripping Voltammetry has been tested in a non-traditional, pH-variable procedure, to study the interaction between Cu(II) with a soil fulvic acid. The study was performed at 25 degrees C and I = 1.0 M, and covered wide ranges of fulvic acid concentration (5 - 20 mg L-1), Cu(II) concentration (2.10(-5) - 4.10(-6) M), and pH (3.5 - ca 8). Mean complexation equivalent weights (between 800 and 5000 g mol(-1), depending of experimental conditions) and apparent equilibrium constants (between ca. 3 and 0.02 for pH-independent constants), and their variations with pH and fulvic acid concentration were calculated through an iterative procedure. The results obtained are consistent with those published before for the implementation of the pH-variable procedure with Cu(II) ion selective electrode potentiometry, and show that Anodic Stripping Voltammetry at pH-variable conditions is suitable for the study of Cu(II) - fulvic acid interactions.