5.0. FTIR ( Fourier Transform Infrared ) Spectroscopy:

5.1. Infrared spectrometry is one of the most powerful tools available for identifying pure organic and inorganic compounds because, with few exceptions, all molecular species absorb infrared radiation, and each molecular species has a unique infrared absorption spectrum. An exact match between the spectrum of known structure and that of an analyte unambiguously identifies the latter.              FTIR ( Fourier Transform Infrared ) Spectroscopy offers a unique "fingerprint" spectrum for organic materials. Each specific chemical characteristic or structural group of an organic molecule provides a specific absorption peak in the spectrum. The relative peak intensities, shapes, spectral background, and absorption frequencies are extremely reproducible and commonly accepted as the primary method of identifying materials. When the material is a mixture, these ratios and peaks can even provide confirmation that the formulation of a material involves the same amounts of each component.

5.2. The number of ways a molecule can vibrate and rotate is related to  the number of atoms, and thus the number of bonds, it contains.  Infrared spectra exhibit narrow, closely spaced absorption  peaks resulting from transitions among the various vibrational quantum levels. Variations in rotational levels may also give rise to a series of peaks for each vibrational state. There are also hundreds of thousands of reference IR spectra available from which comparisons and identifications can be made. 5.3. Infrared absorption occurs not only with organic molecules but also with covalently bonded metal complexes, which are generally active in the longer-wavelength infrared region. 5.4. Fourier-transform infrared (FTIR) spectrometry is used for obtaining complete spectra for quantitative identification. FTIR spectrometers offer the advantages of unusually high sensitivity, resolution, and speed of data acquisition. A moderately sophisticated dedicated computer is needed to decode the output data. Virtually every kind of organic material can be sample and run by FTIR in some way. This may include liquid samples, gas samples, and solids. It may include large amounts of material or even samples smaller than the diameter of a human hair. Whereas the later types of samples are run using an FTIR equipped with a microscope to align the IR beam, there are many different methods and devices used to assist FTIR analysis.

5.5. Another extremely useful method of FTIR analysis included a special cell which allows one to obtain a spectrum by reflection of the infrared beam from the surface of a solid material. This method, called ATR ( Attenuated Total Reflection ) , provides IR data about the outer few hundred Angstroms of a solid.

5.6. Fourier-transform instruments contain no dispersing element (grating or prism), and all wavelengths are detected and measured simultaneously. In order to separate wavelengths, it is necessary to modulate the source signal in such a way that it can subsequently be decoded by a Fourier transformation, a mathematical operation that requires a high-speed computer.

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