EFFECT OF THE PH ON THE COMPLEXATION OF CU(II), NI(II) AND FE(III) IONS BY A VINE LEAF-LITTER EXTRACT BY FLUORESCENCE QUENCHING

An extract of dead vine leaves (vitis viniferal) (VLE) was obtained by the extraction procedure for fulvic acids and its interaction (at a c oncentration of 25 mg/L in 0.1 M KNO3) with the Cu(II), Ni(II) and Fe( III) ions was studied in the pH range between 3 and 6. This interactio n was monitored by synchronous molecular fluorescence, since bands due to the fluorescent ligands undergo quenching upon complex formation. After the chemometric isolation of the quenching profiles from the raw spectra by a self-modeling mixture analysis, SIMPLISMA, they were ana lyzed by two methods: (i) graphical procedures based on the Stem-Volme r model; and (ii) a non-linear least-squares procedure. For the Cu(II) and Ni(II) ions, the treatment by these two methods provided similar values both for the logarithm of the conditional stability constants ( log Kc) and the percentage of fluorescent structures that do not parti cipate in the complexation. The log Kc were (standard deviations in pa renthesis): Cu(II) ion, 2.4(3), 3.37(3), 4.4(1) and 4.92(9), respectiv ely, for pH = 3, 4, 5 and 6; Ni(II)ion, 2.9(1), 3.3(2), and 4.09(3), r espectively, for pH = 4, 5 and 6. For Fe(III) an interaction with VLE was observed, but no values for Kc could be obtained.