A specular reflectance system for the infrared analysis of micro size samples is described and its advantages and limitations compared to other micro infrared techniques. Samples are mounted on small metal mirrors which reflect the light beam back through the sample. A transmission spectrum of the sample is thereby obtained but the effective path length is twice that of the actual thickness. A given absorption band therefore has twice the absorbance obtained by conventional transmission measurements The system has been applied mainly to gas chromatographic fractions but should be suitable to a variety of other analyses. Major limitations include a "stray light" artifact, polymorphism effects, and difficulties in achieving sample uniformity.
H. J. Sloane, T. Johns, W. F. Ulrich, and W. J. Cadman, "Infrared Examination of Micro Samples—Application of a Specular Reflectance System," Appl. Spectrosc. 19, 130-135 (1965)