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What Is Near Infrared Spectroscopy?

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  • Written By: Emma Lloyd
  • Edited By: A. Joseph
  • Last Modified Date: 15 July 2014
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Near infrared spectroscopy (NIR) is a type of spectroscopy in which the near infrared region of the electromagnetic spectrum is used as an evaluation tool. This technology is used in many different industries, including the pharmaceutical, food and agricultural industries, in certain medical diagnostic tests and in combustion and polymer science. Near infrared spectroscopy is particularly useful in diagnostic medicine because it is capable of recording state changes in hemoglobin, the oxygen-carrying molecule in blood.

Spectroscopy is the study of the way in which matter absorbs and emits light and the way it disperses emitted light into different wavelengths, which are visualized as colors. All types of matter absorb and emit light, and by studying the type of light that is absorbed or emitted, it is possible to gain clues as to the properties of the matter under examination. An object absorbs or emits light of certain colors or wavelengths depending on its temperature, mass, composition and other factors.

Near infrared spectroscopy measures the pattern of absorption of near-infrared light by a given sample. Near-infrared light refers to light of wavelengths between 800 and 2,500 nanometers (0.00003 to 0.00025 inches). This technology uses a light source to bounce light off a sample. The light that is emitted by the sample is then modified by a light-dispersing prism, which separates the light into its constituent wavelengths. Scattered light of wavelengths between 800 and 2,500 is detected, recorded, and evaluated to gain knowledge of the sample under examination.

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Near infrared spectroscopy has several advantages over other types of spectroscopy, making it a technology that is used preferentially in many situations. For example, NIR technology has a good signal-to-noise ratio, which means that background readings generally are low in comparison to results relating to the sample being tested. This makes it easier for technicians and scientists to read and evaluate the results of a given NIR test. Another advantage is that NIR is inexpensive in comparison to other spectroscopic techniques, and even high-throughput NIR experiments can be carried out relatively cheaply. Finally, this method is suitable for analyzing large samples, because near-infrared light can penetrate further than infrared light.

This technology can be used in many different ways. In astronomy, NIR can be used to study the formation of new stars and to determine the age and mass of an existing star. This information helps provide clues about how stars form. In medicine, near infrared spectroscopy is used in certain diagnostic blood tests, including pulse oximetry, used to measure the oxygen concentration of the blood. NIR can also be used as a means of assessing brain function and of measuring cardiac output in post-operative patients. There also are many industrial uses for NIR, such as sample analysis for quality control.

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