Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used to follow qualitatively and quantitatively the displacement of gelatin by a fluorosurfactant from an interface over a wide concentration range from zero to beyond monolayer coverage of the fluorosurfactant. The ToF-SIMS results are in good agreement with published wettability data and also show a good correlation with previously reported measurements using X-ray photoelectron spectroscopy (XPS). The ToF-SIMS results indicate no change in the outermost surface chemistry above the point of monolayer coverage as defined according to the Gibbs adsorption model and that the surface displacement of gelatin by the fluorosurfactant is effectively complete.