NIR is the abbreviation for near infrared. The near infrared spectroscopy is a physical method for the determination of mostly organic molecular bonds. The NIR-spectroscopy operates with light of a wavelength of between 800 and 2.500 nanometres; this makes it lie between the visible spectral range (VIS) and middle infrared (MIR).
During the absorption of NIR radiation, molecular vibration is excited – similar to MIR. Information about the molecular structure can be taken from the reflected spectra. They can serve for the identification (“fingerprint”) or quantification of substances.
Other than MIR, NIR covers the measurement of overtone and combination vibrations of molecule groups, which result as the sum of the ground vibration occurring there. The resulting spectra are more difficult to interpret analytically due to the strong band overlap: Thus, software with mathematical-statistical and chemometrical methods (e.g. PCA, PLS) are used for evaluation. An important advantage of the NIR-spectroscopy is the easy handling – light can be transported through air or glass fibre almost everywhere.
The numerous areas of application of the NIR-spectroscopy range from agriculture and the food industry to the chemical and pharmaceutical industries, biotechnology, polymer production, petrochemistry, etc. to the sorting of plastic materials during recycling.