CONTINUOUS MULTILIGAND DISTRIBUTION MODEL USED TO PREDICT THE STABILITY CONSTANT OF CU(II) METAL COMPLEXATION WITH HUMIC MATERIAL FROM FLUORESCENCE QUENCHING DATA

We report the use of a pH-dependent continuous multiligand distribution model to determine the stability constant between Cu(II) and dissolved humic material. Fluorescence quenching of the humic material by Cu(II) is used to produce spectral titration curves. The values from the titration curves are then fit, by use of a least-squares fitting routine, to the calculated values produced by the model. Three titrations at pH 2.5, 3.5, and 4.5 were conducted using this method, and the observed and calculated values are compared. A single stability constant for Cu(II) with the humic material is reported. The results of these titrations are compared with the results of experiments carried out using a new technique that relies on the spectral properties of the Eu(III) ion to probe metal binding sites in humic material.