Photosensitivity of Internal Standard Valerophenone Used in USP Ibuprofen Bulk Drug and Tablet Assay

In the ibuprofen (IBP) bulk drug (1) and tablet (2) assay methods (high-performance liquid chromatography [HPLC]) of the United States Pharmacopeia (USP), valerophenone (ISTD) is used in standard solutions for system-suitability determination and as an internal standard for the quantitation of ibuprofen in bulk drug and tablets. ISTD is prepared in a solution of 1% chloroacetic acid (pH 3.0
0.05):acetonitrile (40:60). This ISTD solution is used as an extraction solvent for IBP tablets (tablet assay preparation) and for IBP bulk drug substances (bulk drug assay preparation) as well as for the preparation of system-suitability standard solutions. The HPLC mobile phase for this method is 1% chloroacetic acid (pH 3.0
0.05):acetonitrile (40:60). The peak response ratios of IBP and 4-isobutylacetophenone (4-IBAP) to ISTD are factored in the quantitation of IBP and 4-IBAP in bulk drug and tablet assay samples. ISTD has been found to be sensitive to light during use in standard solutions and assay preparations in the laboratory (unprotected use), and has been shown to degrade extensively  in samples exposed to light stress during the forced degradation studies (3). In this study, we examined the degradation of ISTD under different light sources in various solutions used in the ibuprofen assay methods (i.e., system-suitability standard solution, extraction solution, and assay preparations of bulk drug and tablets) to assess the stability of ISTD and its potential effect on the quantitation of IBP and the limit of 4-IBAP in bulk drug and tablets

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