The nature of interactions between metal ions Ag(I), Hg(II), Cu(II) and chitosan derivative of 1.2-ethanedithiol, QTDT, was investigated by isothermal calorimetry using the membrane breaking technique. Simultaneous determination of thermal effects, Q(int), and amount of cation that interacts, n(int), are described. The experimental data have been interpreted in terms of the Langmuir equation to determine the maximum adsorption capacity to form a monolayer, N-mon, and the energy of interaction for a saturated monolayer per gram of QTDT, Q(mon). With Nmon and Qmon, the molar enthalpy of interaction for formation of a monolayer of anchored cations per gram of QTDT, Delta(mon)H(m), was determined. The Delta(mon)H(m) values for A,(I), Hg(II), and Cu(II) were -60.56, -58.05, and -84.36 kJ mol(-1), respectively. Negative values of Delta G show the spontaneity of the interaction processes. The least entropically favourable processes, i.e., those which present more negative Delta S values, seem to be compensated by the more favourable enthalpic parameter. (c) 2005 Elsevier Inc. All rights reserved.