Nondestructive Determination of the Degree of Saponification Using Concentration Depth Profiling of Functional Groups by FT-IR/ATR Spectroscopy

Abstract

Concentration depth profiling of functional groups using FT-IR/ATR spectroscopy has been applied to the nondestructive determination of the degree of saponification. A two-layered film, which had acetyl groups in its surface layer distributed inhomogeneously in the depth direction, was prepared. The dependence of its FT-IR/ATR spectra on incident angles was measured. The degree of saponification was determined on the basis of the concentration depth profile of the acetyl groups obtained from the angular dependency. The results obtained showed good agreement with micro FT-IR and neutralization titration results. This method is judged able to determine functional groups within the range of a few micrometers from the sample surface.