A microcalorimetric study on the role of moisture in photolysis of nifedipine powder

A well-known photolabile substance, nifedipine, was used as a sample materi al to test self-constructed irradiation cells and demonstrate their usefuln ess in photostability studies. The devices were made as accessories for a c ommercial isothermal microcalorimeter. Several powder samples containing va rious amounts of moisture were irradiated with monochromatic light as a sca n measurement from 700 to 280 nm, and the heat flow evolved in the photodeg radation of nifedipine was determined. According to the results, light does not affect the nifedipine molecule directly, but the photodegradation is a result of the combined effects of moisture and light.