Though based on the same physical phenomena regarding the interaction between radiation and matter, today’s IR spectrometers have evolved in the way they irradiate the sample, replacing the former monochromators for interferometers, giving rise to the faster FT-IR spectroscopy.
Besides its classical application in chemical characterization, the use of infrared radiation has evolved giving rise to new techniques that go further:
VCD (Vibrational Circular Dichroism) is a technique that gives 3D information of molecules. It can be applied for determining the secondary structure of proteins and peptides, the purity of enantiomers and also their absolute configuration by comparison with previously reported data or with data obtained through theoretical simulations.
PM-IRRAS (Polarization Modulation-IR Reflection-Adsorption Spectroscopy) is a very useful technique for the analysis of ultrathin layers and coatings, monolayers and submonolayers and biomolecules, deposited on surfaces, especially for conductors (Au, Cu, Pd, alloys, etc). It allows for the study of not only the composition but also the organization, conformation and orientation of molecules on a given substrate. In addition, it is also useful for analysing phenomena affecting such surfaces, as could be corrosion processes. Thanks to the characteristics of this technique, samples can be measured without reference, giving rise to spectra free from atmospheric interferences such as carbon dioxide and water vapour
FT-IR Microscopy which allows for visible inspection of samples and to obtain FT-IR spectra by coupling all-reflective Vis-IR microscopes to a FT-IR spectrometer. It is useful for performing chemical characterisation in concrete points, and also for obtaining chemical maps of larger areas, with minimum spot sizes of 25-30 μm using conventional IR sources. Diffraction-limited resolution can be achieved exploiting the brightness advantage of IR Synchrotron Radiation (SR), for unveiling vibrational details at few microns in the Mid-IR regime. The non-damaging nature of IR SR and the use of IR-transparent fluidic devices permit the analysis of hydrated species, to follow sample dynamics and to work under physiological conditions at single cell level.
FT-IR Imaging is a very versatile toll for chemical imaging of large sample areas, that takes advantage from bi-dimensional Focal Plane Arrays (FPA) detectors. The technique is ideally suited for the rapid analysis of a large variety of chemically heterogeneous samples, from slice tissues to polymer blends, in transmission, reflection and ATR mode.