The adsorption of bovine serum albumin (BSA) on a passivated chromium surface in deaerated pH 4 sulphate solution was studied in situ using a switch-flow cell in combination with an electrochemical quartz crystal microbalance (EQCM) and ex situ by X-ray photoelectron spectroscopy (XPS). EQCM measurements showed that the kinetics of BSA adsorption was fast, and that a steady-state was reached about 10 min after introducing the protein. They also showed that BSA adsorption was an irreversible process, or that the kinetics of desorption was very slow. The equivalent thicknesses of the adsorbed BSA layer estimated in situ by EQCM and ex situ by XPS are in excellent agreement, and are equal to 3.5 +/- 0.7 nm, which corresponds to one horizontally orientated monolayer. (c) 2007 Elsevier Ltd. All riahts reserved.