Many mass-transfer applications have used chitosan membranes in separation processes (e.g. filtration and adsorption). Chitosan can be crosslinked easily by dialdehydes, such as glutaraldehyde, and this process is able to change drastically some macro and micro properties: water absorption, ion permeability, chemical and mechanical properties. Dense membranes were produced by casting and drying of chitosan solution. Potentiometric titration, infrared spectroscopy (FTIR-ATR) and thermal gravimetric analyses (TGA) were used for chemical characterization, and to identify differences between pristine and crosslinked chitosan membranes. Diffusion experiments confirm some subtle changes in permeability of ions. All results indicate that chemical modification with glutaraldehyde turns chitosan more hydrophobic. (c) 2007 Elsevier B.V. All rights reserved.