DETERMINATION FOR ACIDITY AND METAL-ION COMPLEXING CONSTANTS FOR EUCALYPTUS AND OAK EXTRACTS

The acidity constants for Eucalyptus (Eucalyptus globulus) (pK 3.83+/- 0.02) and oak (Quercus robur) (pK 3.46+/-0.07) aqueous extracts were d etermined by potentiometric titration at mu = 0.5 M using the Bjerrum method. The complexation of these extracts with copper (Cu), zinc (Zn) , lead (Pb), and cadmium (Cd) show two different behaviours in the vol tammetric titrations depending on the nature of the cation. For Cu, tw o regions were obtained in the plot of the peak height versus metal ad ded which allows the calculation of the complexing capacity (2337+/-14 9 and 281+/-17 mu g/L, respectively) and the stability constants of th e 1:1 complex (Log beta' = 4.26+/-0.20 for Eucalyptus at pH 4.6 and 5. 32+/0.02 for oak at pH = 5.5). For the rest of the cations, only a lin ear response was obtained. A possible explanation for these results is based on the Irving-William's rule and the IR spectra that was obtain ed.