Determination of cadralazine in human plasma and urine by high-performance liquid chromatography.

A high-performance liquid chromatographic method is described for the determination of cadralazine in human plasma and urine. To 1 g of plasma (pH 7) or urine (adjusted to pH 11), internal standard was added and the samples were extracted with chloroform-ethanol (95:5, v/v). The substances were then back-extracted into acid (pH 2) and 100 microliter of the aqueous phase were injected. Chromatography was performed on a 10-micron LiChrosorb RP-8 column with acetonitrile-phosphate buffer pH 6 (15:85, v/v) as eluent at a flow-rate of 2.7 ml/min. The substances were detected by UV spectrophotometry at 254 nm. Concentrations down to 0.141 nmol/g in plasma or 10.59 nmol/g in urine could be measured with very good precision. This method was applied to samples from two healthy volunteers given a single oral dose of 10 mg or 20 mg of cadralazine .