With the advent of TS-II, there is a drive to probe more complex and multicomponent systems using neutron reflectivity. In such studies, confidence associated with model Nb fits will be significantly enhanced by auxillary or supporting measurements to assay different aspects of a system. These will be particularly useful where an interface is being formed or compositionally manipulated during the course of an NR experiment. To date we have made good use of electrochemical and spectroscopic assays when probing polymers undergoing (electro)chemical transformations or bond forming biomolecule immobilisations and in this proposal we seek to develop a methodology of more general benefit. This will combine surface acoustic wave based gravimetry-the most general probe of all-to determine the mass of material in contact with the NR reflecting surface, with NR that probe the compositional profile