By applying the regular solution model (RS) to the determination of composition in a mixed surfactant layer adsorbed at a hydrophilic solid/aqueous interfaceand combining it with the measurement of composition by NR gives us a means of measuring the surface CMC (CAC) of a surfactant, which approximately measures the concentration of the onset of cooperative adsorption. For most surfactants this will be greater than the CMC if their charge and the surface charge are identical, i.e. it is inaccessible to direct measurement. We propose to make systematic measurements on zwitterionic/charged mixtures to widen the range of known CACs. At the same time, there seem to be categories of systems for which the RS model is inappropriate and preliminary measurements suggest that zwitterionic/charged systems sometimes fall into this category. We propose to explore the reasons.