Infra red spectrometry:

Infra red spectrometry is one of the most general spectroscopic methods used for structural elucidation and compound identification. The IR spectrum is a consequence of excitation between the quantised vibrational energy stages of the molecules and is characterized through three main parameters, namely the number of bands in the spectrum, the positions of the bands and the intensities of the bands. It is necessary in which the molecule has a fluctuating or oscillating dipole moment in the course of a vibration for it to absorb IR radiation.

The IR spectrum for a molecule of a reasonable size is quite complex and it is not desirable to interpret all the signals acquired.

The primary components of an IR instrument include a stable source of radiation, a suitable sampling device, a monochromator or frequency modulator, a transducer and signal processing and output device.

Within IR spectrometry, glass or quartz cannot be used as a material for making cuvettes as it tightly absorbs the IR radiation. Thus IR windows made from the salts like NaCl and KBr that are transparent in the IR region are used for the reasons.  Because most of the general solvents absorb in several regions of the IR spectrum, it becomes hard to run spectra of the solutions.

There are three kinds of IR instruments. These are dispersive, FT and non dispersive kinds. The dispersive IR instruments are somewhat outdated but could be used for qualitative work as these are quite inexpensive. These instruments use reflection grating for dispersing the radiation emerging out of the sample cell.

In compare to the dispersive IR spectrometers, the FT instruments collect the response at all the wavelengths concurrently.  In these instruments the monochromator is replaced through an interferometer and response of the sample is suitably modulated and collected in time domain that is then decoded using the Fourier transformation.

The FT spectrometers have certain benefits over dispersive instruments such as it saves time and gives a better signal to noise (S/N) ratio, better frequency resolution reproducibility and a higher sensitivity, etc.

IR spectroscopy searches applications in quite diverse areas like drugs and pharmaceuticals, chemical industry, polymer industry, forensic determinations, air pollution monitoring, agriculture, semiconductor microelectronics, clinical and biomedical determinations etc.