FT -IR Spectroscopy has widespread applications in molecular structural confirmation and characterization of solids, liquids and gases. FT-IR imaging complements the technique for chemical mapping of surfaces. This permits study of surfaces of materials for contamination or manufacturing defects and is ideally suited for pharmaceutical granules and finished dosage forms. In the field of polymers it is indispensable for characterization of multilayered laminates.
The FT-IR images complement images taken by other microscopic techniques such as visible microscopy, scanning electron microscopy and atomic force microscopy. Such techniques provide information at atomic or elemental level but IR imaging is capable of providing information at the molecular level.
Detectors in FT – IR Imaging
Focal Plane array detectors permit rapid scan of a surface to acquire several thousand spectra per minute but suffer from limitations such as low sensitivity and limited spectral range. The linear mercury cadmium telluride detector offers a viable alternative. It provides images of variable sizes and aspect ratios instead of fixed size images.
Imaging systems are capable of achieving resolutions down to about 10μm. Depending on the nature of specimen under observation the resolution can be varied. For a rapid scan of the surface higher resolutions of the order of 50μm can be used and subsequently areas requiring closer scrutiny can be scanned at higher resolutions.
ATR imaging which is reflection-based does not require thin slicing of sections. Samples are mounted in an embedding resin and polished to get a smooth flat surface. Images produced are sharp and show fewer artefacts due to divergence of beams. ATR images result in images having superior spatial resolution than the transmission mode images.
Samples studied include films, fibers, laminates, crystals, filled polymers and black rubbers. This is a unique technique which can help in academic R&D and improvements in manufacturing processes.
Almost all major FT-IR manufactures have ventured into FT-IR imaging systems. Links to offerings of some major manufacturers are provided below :