Spectrophotometry Essay

1.1. UV-SPECTROPHOTOMETRY Spectroscopy is the measurement and interpretation of electromagnetic radiation absorbed or emitted when the molecules or atoms or ions of a sample move from one energy state to another energy state. Spectroscopy is a general methodology that can be adapted in many ways to extract the information you need (energies of electronic, vibrational, rotational states, structure and symmetry of molecules, dynamic information). Ultraviolet-Visible Spectrophotometry is one of the most frequently employed techniques in Pharmaceutical analysis. It involves the measurement of the amount of Ultraviolet (190-380nm) radiation by a substance in a solution. A compound or drug which posses conjugated double bond absorbs UV radiation

The concentration of the analyte in the sample solution is read from the graph as the concentration corresponding to the absorbance of the solution.
Assay of Multi-Component samples: The assay of components of mixture sample can be done by following methods:
1) Simultaneous Equation method
2) Absorbance Ratio method
3) Geometric Correction method
4) Difference spectrophotometry
5) Derivative spectrophotometry The basis of all the spectrophotometric techniques for multicomponent samples is the property that at all wavelengths,
a) The absorbance of a solution is the sum of absorbances f the individual components or
b) To measure the absorbnce of sample solution with that of reference standard solution.

Simultaneous Equation method If a sample contains two absorbing drugs (X and Y) each of which absorbs at the λmax of the other, it may be possible to determine both drugs by the technique of simultaneous equation.
The information required is:
a) The absorptivities of X at λ1 and λ2, ax1 and ax2 respectively.
b) The absorptivities of Y at λ1 and λ2, ay1 and ay2