Dissolved organic species, identification

The interaction of UV and visible radiation with matter can provide qualitative identification of molecules and polyatomic species, including ions and complexes. Structural information about molecules and polyatomic species, especially organic molecules, can be acquired. This qualitative information is usually obtained by observing the UV /VIS spectrum, the absorption of UV and visible radiation as a function of wavelength by molecules. A typical UV absorption spectrum is shown in Fig. 5.1. The spectrum may be plotted as wavelength vs. absorbance, transmittance, or molar absorptivity, s. The molar absorptivity is defined subsequently. In Fig. 5.1, the absorption spectrum of pyridine dissolved in ethanol is plotted as log s vs. wavelength in angstroms (A). 

NMR has proven to be one of the most valuable spectroscopic techniques for the identification and characterization of a wide range of organic and inorganic species. It can provide unparalleled information about the chemical composition and structure of molecules. The newer two-dimensional pulse techniques [20] are expanding the capabilities of NMR even further so that in some cases structural prediction can approach that of x-ray crystallography. The use of NMR has traditionally been associated with chemical structure determination or characterization of new compounds produced by synthetic chemists or as an aid in the identification of unknown compounds in the solving of analytical problems. In most instances the compound is dissolved in an appropriate solvent and the spectrum is obtained in the solution state. For materials analysis or surface characterization, it is often impossible or impractical to dissolve the sample. Therefore, the ability to obtain NMR spectra in the solid state is crucial to the extension of this most important spectral technique to the study of surfaces. 

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