Observation of a penetration depth gradient in attenuated total reflection Fourier transform infrared spectroscopic imaging applications

The Fourier Transform-Infrared (FT-IR) spectroscopic macro-Attenuated Total Reflection (ATR) imaging measurements of homogeneous liquid samples for observing penetration depth gradient were conducted. ATR imaging measurements were taken using a Bruker imaging system and were performed on paraffin oil, the backing of two adhesive tapes, and an oil-in-water emulsion. During the measurements on paraffin oil, a gradient as a function of the Z direction which is the direction of the IR beam from the source to the detector was observed in the image. For heterogeneous samples, this gradient does not become obvious in the imaging data. Result shows an absorbance gradient for absorption bands in the Z direction of the imaged area, although a perfect contact between the sample and the ATR crystal is ensured.