The changing role of ultraviolet spectroscopy in drug analysis.

New applications in the identification of minor components in drugs by rapid scanning diode-array UV spectrophotometers as high-performance liquid chromatographic (HPLC) detectors are exemplified by (a) identification and quantification of alpha-chloro-4-methoxycinnamic acid methyl ester as the byproduct of the Darzens reaction between 4-methoxybenzaldehyde and chloroacetic acid methyl ester; and (b) identification of 4-androsten-17-one and 3 beta-phenyl-5 alpha-androstan-17-one as impurities in 5 alpha-androst-2-en-17-one. The advantages of the use of derivative spectrophotometry are illustrated by the following examples: (a) determination of flumecinol (3-trifluoromethyl-alpha-ethylbenzhydrol) in an oily emulsion formulation; (b) determination of RGH-6148 (2-benzylthiazolidinone) in a suspension used in toxicological studies; and (c) determination of mestranol as an impurity in norethisterone.