High-performance liquid chromatographic determination of diltiazem and two of its metabolites in plasma using a short alkyl chain silanol deactivated column.

A simple and reproducible method for the determination of diltiazem and its two major metabolites, demethyl- and deacetyldiltiazem, is presented using a new column containing a short alkyl chain silanol deactivated support. This method involves the extraction of alkalinized plasma with a hexane-isopropanol mixture (95:5, v/v) followed by back-extraction 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 less than 10%. The lower limits of detection are 4, 2 and 4 ng/ml for diltiazem, deacetyl- and demethyldiltiazem, respectively. Samples can be stored for up to thirty days with no significant degradation. The assay has clinical applicability.