As you know, one of the complementary test methods in inhibitor's investigations is to perform FTIR analysis on the film which can be formed on the surface of the metal in laboratory tests.

Since the aforementioned film would be very thin, So how we can take sample of this thin film in order to conduct FTIR analysis to find out the possibility of formation of the inhibitor-metal ion complex and related functional groups of the inhibitor molecules on the surface of the metal ?

What would be the limitations of this method and how reliable is the results of FTIR by this way of sampling ?