IR analysis of crystalline samples of some urea derivatives

The dependence of an IR spectrum of crystal samples of allantoin, barbital, chloroethylaminouracil (dopan), carbromal, 5-allyl-5-(beta-hydroxypropyl)-barbituric acid (ipronal) and theophyllin upon the method of crystals preparation was found after 3 months storage of crystals. There were no differences in the case of mephenytoin. The results obtained here demonstrate the possibility of an occurence of the majority of the analyzed substances as metastable polymorphic modifications in solid dosage forms. Furthermore, the IR identification of drugs requires crystallization of a substance from a particular solvent just before analysis.