Fourier Transform Infra-Red Spectroscopy

Fourier-transform infra red spectroscopyis a vibrational spectroscopic technique which allows compositional analysis of liquids, solids and gases.

The technique is typically used to assess organic samples, though it can be used for certain inorganic samples too. It can also report on aspects of the structure of biological molecules, particularly proteins.

By utilising a KBr press or the ATR (attenuated total reflection) accessory a wide range of sample types can be analysed using this investigative technique.

Molecules absorb infra-red light at wavelengths that correspond to molecular vibrational energies (e.g. bond stretching). The actual energies of light absorbed depends on the strength of the bond and, in turn, on the atoms at either end of the bond and the bond order.

Thus, the pattern of lioght absorbed by a molecule is a composit of all bonds within that molecule and the result is a unique absorption spectrum for each molecule of interest.

Other aspects of molecule geometry that impinge on bond strengths and rigidity, such as intra- and inter-molecular interactions, alter the wavelength of light absorbed and hence can be probed by FT-IR

FT-IR is used primarily for the identification of organic compounds due to the readiness of bonds within these molecules to vibrate upon interaction with infra-red radiation. Thus FT-IR is well-suited for the analysis of unknown organic materials such as polymers.

By linking FT-IR to thermal analysis (simultaneous thermal analyser (STA)) a multi-pronged approach to sample identification can be performed to increase confidence and reliability.

In addition, thermal stability (e.g. for pharmaceutical studies) can be assessed by measuring the volatiles released during thermal analysis.

By using appropriate sample probes or an attenuated total reflectance (ATR) stage, solids, liquids and gases can all be analysed by FT-IR, often with minimal sample preparation required.

If linking FT-IR with thermal analysis, samples should be available in milligram quantities with care taken to ensure the samples are representative of the bulk sample.