HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION OF DILTIAZEM AND 2 OF ITS METABOLITES IN PLASMA USING A SHORT ALKYL CHAIN SILANOL DEACTIVATED COLUMN

A simple and reproducible method for the determination of diltiazem an d its two major metabolites, demethyl- and deacetyldiltiazem, is prese nted using a new column containing a short alkyl chain silanol deactiv ated support. This method involves the extraction of alkalinized plasm a with a hexane-isopropanol mixture (95:5, v/v) followed by back-extra ction into 5 mM sulfuric acid. Reversed-phase liquid chromatography is used with ultraviolet detection at 237 nm over a concentration range of 20-400 ng/ml for the compounds. Imipramine is used as the internal standard. Within-day and between-day coefficients of variation are les s than 10%. The lower limits of detection are 4, 2 and 4 ng/ml for dil tiazem, deacetyl- and demethyldiltiazem, respectively. Samples can be stored for up to thirty days with no significant degradation. The assa y has clinical applicability.