A study of the basic characteristics of the hybrid anilinesilica xerogel, which shows promising metal sorption properties, was carried out. A simplified approach to describe the protonization affinity of the immobilized aniline was developed, and it was compared with the known values for free aniline. The proton chemisorption process may be described properly by a model based on the Langmuir equation, and the immobilized groups have less affinity to the H+ than to the free aniline. (c) 2004 Elsevier Inc. All rights reserved.