• , -..'.2 ELSEVIER Talanta 42 (1995) 1919-1923 Talanta Conductimetric analysis of the ion binding pToperties of three leaf extracts of chestnut (Castanea sativa), Eucalyptus (Eucalyptus globulus) and oak (Quercus robur) F. Reya'*, M. P6rez-Asenjo", A.A.S.C. Machado u, P. FacaP, M.A. Ferreira", A. Toja a Area de Quimica Fisica, Universidad de Vigo, Torrecedeira 86, Vigo, Spain b LAQU1PAI, Departamento de Qulmica, Faculdade de Ciencias, P-4050 Porto, Portugal Received 10 March 1995; revised 23 May 1995; accepted 8 June 1995 Abstract Humic materials extracted from tree leaves of chestnut (Castanea sativa), eucalyptus (Eucalyptus globulus) and oak (Quercus robur) were analyzed by performing conductimetric titrations. Values between about 84 and 236 ~tScm -I for the molar conductivity and between 0.42 and 0.74 for the charge distribution parameter were obtained when the concentrations of the extract are increased from 40 to 100 mg I-I. These variations were explained by using the counterion condensation theory, and the distance between the charged groups of the polyions, the volume of the counterion condensation and the Debye-Hiickel potential were also calculated. Keywords: Conductimetry; Humic acids; Leaf extract 1. Introduction The organic matter of soils is constituted mainly from humic materials (humic acids (HA) and fulvic acids (FA)), polyelectrolyte compounds which play an important role in the behaviour of metals in soils and aquatic environments, due to their ability to complex metal ions. On the other hand, these humic materials are formed by microbial degradation and percolation of water through leaves and other organic litter, so a knowledge of the behaviour and structural properties of leaf ex- tracts in solution may be of interest in under- standing the chemical behaviour of humic materials. In order to study these polyelectrolyte mate- * Corresponding author. 0039-9140/95/$09.50 © 1995 Elsevier Science B.V. All rights SS D I 0039-9140(95)01663-5 TAL ~ l t 1 | 4 rials in solution, many different techniques (i.e. potentiometry, dialysis, fluorescence spec- troscopy, etc.) have been used. Conductimetric titrations are an important tool in the study of these types of compounds, because they provide information on association phenomena and on the nature and behaviour of charged groups [1-11]. However, interpretation of the experimental results has been difficult. The de- velopment of the condensation theory [12] was an important advance in the explanation of the polyelectrolyte properties of solutions [13-16], and recently van Leeuwen et al. [17] sum- marised existing theories of association phe- nomena and reviewed the literature relating to conductimetric analysis of polyelectrolyte sys- tems. These authors stressed the difficulty of understanding the concentration dependence of the conductivity of polyelectrolyte solutions. reserved