Estimation of impurity profiles of drugs and related materials. Part VIII: Combined application of high- performance liquid chromatography and NMR spectroscopy in the impurity profiling of drugs

The usefulness of the joint application of HPLC and NMR spectroscopy in drug impurity profiling is demonstrated by the following examples: (1) identification of Z and E isomers of 17α-ethynyl-4-oestrene-3β,17-diol-3- acetate-17-(3′-acetoxy-2′-butenoate) in ethynodiol diacetate; (2) identification of the p-tolyl analogue as the impurity of enalapril maleate; (3) identification and quantification of 2′-dehydro-pipecuronium bromide in pipecuronium bromide. The possibilities of utilizing NMR spectroscopy for the identification and quantification of the impurities with and without their isolation are discussed.