Quantitative comparison of ATR-IR spectra of LB and bulk layers of 22-tricosenic acid on inorganic supports

Abstract

The availability of ATR devices equipped with a diamond internal reflection element makes it possible to obtain IR absorption spectra of organic substances deposited on inorganic substrates, for example, metals, glass or quartz. The quantitative comparison of these spectra performing mass calibration by Langmuir-Blodgett (LB) layers are reported. The measurements were made in the common configuration with the specimen placed between the internal reflection element and the non-transparent support and in a second configuration with a thin transparent substrate (silicon) placed between the specimen and the internal reflection element. The band areas of the CH₂ bands near 2900 cm^–1 measured for the two ATR configurations were compared with those obtained from transmission measurements. The results can be partially interpreted by the equation for the effective thickness of thin layers on internal reflection elements. The relative absorbances of several bands of the TSE spectra obtained under different measuring conditions were also investigated.