Photolytic degradation pharmaceuticals

Pharmaceutical preparations containing riboflavin have been analyzed by TLC using concentrated ethanolic extracts on silica gel plates developed in butanol-benzene-acetic acid-water (8 7 S 3) or butanol-acetic acid-water (9 4 5) (7). Foods, tissue samples and urine each require particular methods of sample preparation and these, together with a number of solvent systems have been reviewed (8). A darkroom is required for sample preparation and chromatography of flavins to prevent photolytic degradation. The fluorescent property of flavins provides a convenient means of detection and spots have been located under radiation at 254 and 366nm (4). HPTLC followed by fiberoptic fluorimetry has been used to quantitate riboflavin in vitamin mixtures and can detect 48-320 ng (6). Recently, a method has been described using mixed-layer plates of GDX-102 and silica gel G (1 1) precoated with hexadecyl-trimethylammonium bromide developed in 60-70% ethanol (9). 

Pereira VJ, Linden KG, Weinberg HS (2007) Evaluation of UV irradiation for photolytic and oxidative degradation of pharmaceutical compounds in water. Water Res 41 4413 1423... 

There are four major degradation pathways that an analytical chemists must focus on for pharmaceutical analysis thermolytic (heat), hydrolytic (water), oxidative (oxygen, light, peroxide), and photolytic (UV and Vis light). 

The key to the strategy outlined above is to have well-designed stress testing studies that form all potential degradation products. Thorough stress testing studies need to evaluate the four main degradation pathways of pharmaceuticals (1) hydrolytic, (2) thermolytic, (3) photolytic, and (4) oxidative. 

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