Fourier Transform Infrared Spectroscopy for Biophysical Applications: Technical Aspects

FTIR spectroscopy has become an important non-destructive tool in gathering structural information of biological macromolecules at atomic resolution and under functional conditions. Modern instrumentation allows recording high resolution IR spectra of biomolecules in liquids, thin films, and adsorbed monolayers without chemical modification. The time-course of structural changes of biomolecules can be followed easily down to ~20 ms time resolution with rapidly scanning interferometers. If such reactions are highly reproducible, molecular mechanisms can be studied at a time resolution down to ns by step scan interferometers. Despite the advanced user-friendliness in operating modern FTIR spectrometers, the use of the adequate detector type, the correct adjustment of the signal to noise ratio, the setting of optical and electronic filters to physically restrict the band width and the corresponding choice of the interferometer scanning speed are crucial parameters in the hand of the user. Their prudential use is essential for gaining high quality spectra by proper signal averaging procedures in static as well as time-resolved experiments and for avoiding spectral artefacts inherent to improper sampling of both the optical path and the intensity of the IR interferogram.