High-performance liquid chromatographic determination of diltiazem in human plasma after solid-phase and liquid-liquid extraction.

A selective, sensitive, and accurate high-performance liquid chromatographic method for determination of diltiazem in plasma samples has been developed and validated. The effects of mobile phase composition, buffer concentration, mobile phase pH, and concentration of organic modifiers on retention of diltiazem and internal standard were investigated. Solid-phase and liquid-liquid extraction were examined and proposed for isolation of the drug and elimination of endogenous plasma interferences. A 5 microm Lichrocart Lichrospher 60 RP-select B chromatographic column was used; the mobile phase was acetonitrile-0.025 mol L(-1) KH(2)PO(4) (pH 5.5), 35:65 ( v/ v) at a flow-rate of 1.5 mL min(-1). The detection wavelength was 215 nm. The calibration plots were linear in the concentration range 20.0-500.0 ng mL(-1). The method has been implemented to monitor diltiazem levels in patient samples.