A simple method is described for determining of the contribution of hydrodynamically coupled solvent to the adsorbed film mass determined in a quartz crystal microbalance (QCM) when operated in liquid. The method requires no additional apparatus and utilizes the change in QCM resonant frequency response between measurements made in nondeuterated and deuterated solvents. The mass of coupled water in a polymer film has been determined and is found to agree with that determined by XPS analysis of the dried polymer film. (C) 2003 Elsevier Science (USA). All rights reserved.