Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film samples were surface-modified by exposure to a UV-activated mercury/ammonia environment (called the "mercat reaction"), yielding a hydrophilic surface with a diversity of functional groups. We describe herein the functionality of mercat-modified FEP and ultimately hope to use these defined surfaces in biomedical applications, specifically to enhance the interaction of cells at the FEP interface. Following the mercat reaction, advancing and receding water contact angles decreased from 120 degrees/101 degrees for FEP to 71 degrees/27 degrees for mercat-modified FEP. By comparison to small molecule chemistry, we had expected the film samples to have imine and nitrile functional groups; however, XPS analysis of mercat-modified film samples indicated the presence of both nitrogen and oxygen functional groups. From a series of labeling reactions, the surface functional groups were found to include nitrile, amine, carboxylic acid, hydroxyl, and carbon-carbon double bonds. Hydrolysis of nitrile functional groups resulted in an increased carboxylic acid concentration from 10% to 38% and decreased water contact angles from 71 degrees/27 degrees to 61 degrees/30 degrees. Bromination/amination of carbon-carbon double bonds resulted in an increased amine concentration from 8% to 10% and decreased water contact angles from 71 degrees/27 degrees to 54 degrees/24 degrees. Future studies will correlate surface chemistry of these defined mercat-modified FEP film samples with neuronal cellular response.