difference spectrophotometry

A simple, precise, economical and accurate difference spectroscopic method has been developed for the valacyclovir in bulk and in pharmaceutical dosage form. The proposed method is based on the principle that valacyclovir exhibits two different chemical forms that differs in the absorption spectra in acidic and basic solution. The absorptions were measured in acidic and basic solution separately against reagent blank. Valacyclovir has exhibited maximum absorbance at 252 and 262nm in acidic and basic solution respectively. Difference in absorbance between these two maxima was calculated to find out the amplitude. The amplitude plotted against concentration showed linear response in the concentration range of 0.5 – 2.5μg/mL with linear regression value 0.999. The proposed method was applied to pharmaceutical formulation and the common excipient present in the formulation does not interfere in the analysis of the drug. The method was validated as per ICH guidelines and statistical results of analysis were found to be satisfactory.