Abstract
The reaction of vitamin A with maleic anhydride in benzene solution was applied for studying the isomerization of vitamin A in commercial drugs. The change of maleic anhydride value was measured using their unsaponifiable fractions, kept at high humidity, high temperature and at highly diluted solution. The values for sugar-coated tablet were 20-32,and those for other preparations were 30-35,when kept at 40℃ for one month. In oily solution kept in cold place, the isomerization was not recognized for one year.
