Mid-infrared spectroscopy (MIR) is a vibrational spectroscopy technique that identifies chemicals based on the interaction of molecules with electromagnetic radiation in the mid-infrared region (400-4000 cm-1). Infrared spectroscopy identifies chemicals based on the absorption of specific wavelengths of mid-infrared light by a molecule. Molecular absorbances of mid-infrared light cause molecular rotations and vibrations and are classified by chemical functional groups. The resulting MIR spectrum produced is characteristic for a given molecule.
Point analysis (“benchtop”) systems are used for analyzing condensed phase materials such as biological samples. Attenuated total reflection (ATR-MIR) is the most popular sampling technique used in most laboratories today, and can be used to sample solid samples (e.g., bacterial spores), or aqueous media (e.g., blood serum). MIR spectra of biological can be searched against reference spectral databases, however, most samples have strong resemblences to one another due to similar carbohydrate, protein and aqueous content. For biological samples, the major limitations of MIR are the presence of water (this tends to swamp aqueous media sample spectra) and the lack of diversity in chemical moieties that absorb MIR light. Distinction of most biological samples from one another requires a chemometric approach configured by an expert spectroscopist.