Analysis of Infrared spectroscopy (IR)

Infrared spectroscopy (IR) is an ideal technique to analyze chemical structural properties of natural materials, since the frequencies of several vibrational modes of organic and inorganic molecules are active in the infrared. This method has become one of the major analytical techniques used because of its quality screening, quickness, and cost of analysis.

Compounds with a dipole moment selectively absorb IR radiation according to their characteristic functional groups—hydroxyl, nitirle, amide, for example. An IR spectrogram plots the absorbance versus the wavelengths ranging from 700 to 400 000 nm and wave numbers from 14 000 to 25 cm−1. As the compounds absorb energy the molecule vibrates more–stretching and bending–depending on its geometry. 

The pattern of the absorption spectrum is like a fingerprint that identifies the molecule, which lends itself to both quantitative and qualitative analysis. The IR absorption frequency depends on the vibrational modes, whereas the intensity depends on: (a) how effectively energy is transferred to the molecule, which depends on the change in the dipole moment that occurs during the molecular vibration, (b) how much is transmitted (or reflected), and (c) the detector.  

Fig 1. Range of IR spectroscopic stretching bands