![]() Therefore, the spacer thickness should be reduced to avoid saturation effects. Because of a non-linear detector response the subtraction is useless. Furthermore, bands in this region, are fully overlapped with usually much broader and intense OH stretching modes and hence are lost for further exploitation. ![]() In other words, the region between 2800 cm - cm -1 is void of useful information. The smallest commercially available cell spacers, which are 6 m m thick, produce an absorbance near 3 absorbance units, where a linearity of all commercial known detectors is corrupted. Water is an extremely strong absorber (molar absorptivity 104.4 M -1cm -1 near 3 m m wavelength) a characteristic it shares with most compounds containing OH groups and often leads to signal saturation. This is of overwhelming importance when a solvent such as water is used. This is ideal, but the reproducibility of the path length is hard to guarantee. In the transmission technique the angle of incidence of the radiation at the cell is a narrow cone around normal. These difficulties are usually expressed using liquid samples. However, there are a number of technical difficulties commonly encountered with this technique that can make collection of high quality spectra difficult. Transmission FTIR spectroscopy is the IR method most commonly used in biophysical studies. ™CIRCLE is trademark of Thermo Spectra-Tech. * Abbreviations: ATR attenuated total reflection, The pure absorbance spectrum is calculated and shown to be fully comparable with transmission spectra. Also shown is the optical constant method of calculation, using the CIRCLE™ ATR liquid cell, and from optical constants the calculation of the dielectric constants e‘ and e”. The main differences between the transmission infrared spectroscopy and ATR are pointed out. As examples, the ATR spectra of liquid phase water and a water solution of bovine serum albumin are used. E-mail: this article the main advantages and limitations of the ATR * technique are presented.
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