Instrumental technique:

UV-VIS spectrometry is an instrumental technique that provides ideal methods for the determination of micro and semi-micro quantities of analytes in a sample. The UV- VIS spectrum arises due to the transitions amongst the electronic energy levels of the absorbing species. For the sample in gaseous phase, the spectrum consists of a number of closely spaced lines whereas in the solution phase, the spectrum has the shape of a smooth and continuous absorption peak. This is due to the collisions and the interactions among the absorbing species and the solvent molecules. A typical UV spectrum is a plot of wavelength versus the intensity of absorption and is characterized by two major parameters-the position of the maximum of the absorption band (λ_max) and the intensity.

There are three types of species that absorb in the UV-VIS region. These are organic molecules, inorganic salts containing the ions of the transition and inner transition elements and the species that involve formation of charge transfer complexes. The relationship of the absorption with the concentration and the path length of the absorbing sample is expressed in terms of Beer-Lambert's law. This law forms the basis of quantitative determinations of the analyte. A number of factors like pH, concentration of electrolytes, wavelength, the possibility of association and dissociation etc may cause deviations from the law. These need to be considered in such determinations.