Improved extraction procedure for the assay of isosorbide-5-mononitrate in serum

A procedure is described for the extraction of isosorbide-5-mononitrate from serum with diethyl ether-n-butyl acetate (15:1, v/v). After extraction, the diethyl ether is evaporated at room temperature and the nitrate remains dissolved in the relatively non-volatile n-butyl acetate phase. Glassware must be used throughout as the recovery of isosorbide-5-mononitrate is not reproducible when plastic tubes or plastic pipettes are used. The extraction recovery of isosorbide-5-mononitrate from serum is 67 +/- 7%, measured relative to external standards.