Near infrared spectroscopy

Encyclopedia : N : NE : NEA : Near infrared spectroscopy

Near infrared spectroscopy (NIRS) is a spectroscopic method utilising the near infra-red region of the electromagnetic spectrum (from about 1000nm to 2500nm). Common incandescent or quartz halogen light bulbs are most often used as broadband sources of near infrared radiation. In fact light bulbs are the most common radiation sources for the NIR based analytical applications. It is becoming more common to employ LEDs as well. Typical applications include pharmaceutical, food and agrochemical quality control, as well as combustion research.

Molecular overtone and combination vibrations are probed by near infrared spectroscopy. Such transitions are quantum mechanically forbidden, leading to weak molar absorptivities. This results in greater depth of penetration of near infrared radiation compared to mid infrared radiation. Near infrared spectroscopy is therefore not a particularly sensitive technique, but it can be very useful in probing bulk material with little or no sample preparation. Because of the complexity of interpreting molecular overtone and combination absorption bands, multivariate multiwavelength calibration techniques are often employed to extract the desired chemical information. Careful development of a set of calibration samples and application of multivariate calibration techniques is essential for near infrared analytical methods.

When NIRS is used as a method to image hemodynamics of the human brain, the term NIRSI (Near Infrared Spectroscopic Imaging) or fNIR (functional near-infrared imaging) is used.

Near infrared spectroscopy

See also