Fourier-Transform Infrared Spectroscopy (FTIR) For Chemical Analysis

Fourier transform infrared spectroscopy makes use of the infrared region of the electromagnetic spectrum. This spectroscopic technique is mainly used to determine with accuracy the composition of materials (bulk and surface analysis). Certain configurations of new FTIR systems (like FTIR microscopy and grazing-angle FTIR spectroscopy) are especially suitable for the analysis of materials surfaces and chemical mapping/imaging. FTIR is very useful for the analysis of many types of materials (organic compounds, polymers, etc) because this instrument gives molecular information on the compound.

Working principle

Infrared spectroscopy exploits the fact that molecules vibrate at specific frequencies that correspond to discrete energy levels (vibrational modes). These vibrational modes are specific to each molecule, which can be used to identify them accurately.

Fourier-transform infrared spectroscopy consists in passing through a sample a beam containing many infrared optical frequencies or in reflecting the beam off the sample surface, and simultaneously measuring the light absorbed at each frequency. The infrared signal detected is an interferogram. If needed, this process can be repeated a few times to improve the signal quality and the noise-signal ratio of the final spectrum. An algorithm called the Fourier transform is then used to transform the raw data (interferograms) in a graph (i.e., FTIR spectrum) showing the absorption as a function of the wavenumber. This spectrum contains the “molecular fingerprint” of the sample, which is unique for each material. A comparison of the experimental spectrum with database spectra can then be used to identify or classify the sample.

Industrial applications

FTIR is widely available in the private sector due to its reliability and versatility to analyse many types of samples (solids, liquids, gels, powders). As a matter of fact, FTIR is often the first instrument used to identify a polymer or an unknown organic compound. In electronics and optics, FTIR can identify resins, residues or powders on printed circuits or on lens. In the field of surface coatings, FTIR can confirm the molecular structure of a coating.

Benefits:

– Analyse any type of sample (solids, liquids, gels, powders)
– Bulk and surface analysis
– Gives the molecular composition

Applications:

– Identify unknowns
– Analyse contaminants
– Determine the presence of organic compounds
– Quantitative analysis of concentrations and sample thickness
– Quality control