**3.2. Usage of IR-based technologies in petroleum industry**

One key area that utilizes IR has been the refinement of petroleum products. In the production of rubber, relatively simple techniques have been used for the analysis of C4 hydrocarbons. NIR spectroscopy has been used for petroleum refining, especially for petrochemicals and polymers. The major advantages of NIR spectroscopy include its fast, non-destructive and easy approach to extend to online analysis in conjunction with optical fibers. Based on these advantages, oil companies have used IR spectrophotometry and Raman spectrophotometry for the online control of product quality [21, 22].

Spectroscopy is a specific analytical technique used in the structure determination of organic compounds. This technique assesses the changes in the wavelength of the radiation, which was passed from the material to be examined, and measures the amount of radiation absorbed in different wavelengths by the material. As a result of the substantial number of different absorption bands in the spectra of organic substances, organic substances are facilitated to be compared with each other. The spectrum of an organic substance is similar to its fingerprints, and there are no two different substances that provide the same absorption spectrum in theory. Utilizing the originality of the IR spectrum of the substances, qualitative and quantitative analyses may be performed via IR spectrophotometry [23, 24]. IR spectrophotometry has been used in several areas of forensic sciences. NIR spectrophotometry may be used for the determination of ignitable liquids, which are used as accelerants in forensic laboratories. The use of these techniques in forensic science is subsequently described in detail in the section under "Usage of IR-Based Technologies in Forensic Sciences".
