Videomicroscopy in combination with evanescent field illumination is applied to study the sorption of colloidal particles from flow in a parallel plate channel on a glass surface. The experiments, carried out in the presence of a repulsive electrostatic barrier, reveal surprisingly complex results : The glass surface, though optically hat and well cleaned, is not homogeneous, but rather the sorption occurs at a limited number of preferred sites. Moreover, these sites are not static : new sites keep appearing at random positions on the observed surface and disappearing at a rate of k(d) = 1.3 x 10(-5) s(-1). These findings can be understood within a simple model that takes into account slow but inevitable dissolution of the glass surface. The bulk glass contains potential adsorbers, which are continuously being exposed by the dissolution process and act as transient adsorption sites, before being washed off by the flowing buffer solution,