Comparison of Attenuated Total Reflectance and Photoacoustic Sampling for Surface Analysis of Polymer Mixtures by Fourier Transform Infrared Spectroscopy

Two methods are compared for improvement of the surface sensitivity in FT-IR analysis of polymer surfaces with commercially available biocompatible polymer mixtures. Attenuated total reflectance (ATR) sampling yields results directly related to absorbance and can sample over a range of depths by varying the angle of incidence. Focusing and sample preparation requirements limit the best results to smooth surfaces. Photoacoustic (PA) methods are Insensitive to surface scattering and roughness contributions from different sample morphologies, but PA suffers from low signal intensities and saturation which can contribute to photometric Inaccuracies. Sampling depths in both methods are wavelength dependent, introducing problems when utilizing ratios of peaks to Internal standards for quantitation of surface concentrations. Results from the analysis by both methods of Blomer and Avcothane, two commercially available biocompatible polymer mixtures, and their homopolymer constituents allow the detection of surface Impurities and segregation of specific polymer components in a near surface region. The degree of surface segregation can be estimated by using the different means of varying the sampling depth of each method.