Abstract
The microscopic study of crystalline substances using a polarizing microscope and the immersion media was shown to have an advantage of simple and rapid identification of drugs, especially in polymorphs or solvates. Examples of the application of this technique were given for four crystal forms of thiamine hydrochloride, two forms of each bromvalerylurea and ampicillin. The accuracy and reproducibility of the measured refractive indices are discussed with its relation to crystal habit.