Absorbance Linearity and Repeatability in Cylindrical Internal Reflectance FT-IR Spectroscopy of Liquids

Abstract

This paper reports the results of a program aimed at eliminating the sources of performance variability and excessive nonlinearity that have limited the effectiveness of the cylindrical internal reflectance technique for use in quantitative FT-IR analysis. After discussing the various optical factors that can affect performance, it describes a new adjustment-free optical design which promises to eliminate those factors which lead to data unpredictability. Finally, it summarizes the results of a series of experiments carried out to test the effectiveness of the new design. These confirm the achievement of three significant improvements: an enhancement of band strengths by factors of typically 2.5 to 3, significantly improved absorbance linearity, and a high degree of data repeatability under varied experimental conditions.