2-Nitrobenzaldehyde: a convenient UV-A and UV-B chemical actinometer for drug photostability testing.

We report the development of a new 'photochemical titration' actinometric method for measurement of UV-B (290-320 nm) and UV-A (320-400 nm) light dose during drug photostability testing. It is based upon photolysis of aqueous 2-nitrobenzaldehyde solution, a well-characterized reaction that has been previously demonstrated to be useful as an accurate and reliable actinometric method. Our new method can be performed by a chemical technician using only common reagents. It has been developed for use with xenon arc lamp illumination chambers which are commonly employed for drug photostability testing, but can be readily modified for use with the other illumination sources.