Difference spectrophotometry pharmaceutical preparations

Wahbi et al. [32] used a spectrophotometric method for the determination of omeprazole in pharmaceutical formulations. The compensation method and other chemometric methods (derivative, orthogonal function, and difference spectrophotometry) have been applied to the direct determination of omeprazole in its pharmaceutical preparations. The method has been validated the limits of detection was 3.3 x 10 2 /ig/ml. The repeatability of the method was found to be 0.3-0.5%. The linearity range is 0.5-3.5 /ig/ml. The method has been applied to the determination of omeprazole in its gastro-resistant formulation. The difference spectrophotometric (AA) method is unaffected by the presence of acid induced degradation products, and can be used as a stability-indicating assay method. 

In turbid or cloudy solutions, in which absorbance is affected by scattering of the sample, two absorbance measurements are made one at and the other at a different wavelength where the analyte does not absorb. Then, the difference being proportional to concentration of the analyte, the analyte concentration can be calculated. Difference spectrophotometry is used in the determination of constituents in tablets, complex pharmaceutical preparations, plant extracts, syrups, biological matrices such as blood and serum, injectable oil preparations, and the like. For this technique, in addition to other general requirements such as well-matched cells that are positioned accurately, the solution should be made homogeneous, and the instrumental stray radiation at the wavelength of interest should be extremely small. 

---