Liquid chromatographic assay using electrochemical detection for the quantitation of indoramin in human plasma

An automated high-performance liquid chromatographic method with electrochemical detection is described for the determination of indoramin, a new antihypertensive drug. The procedure involves a single extraction of the drug from alkaline plasma with chlorobutane. The chlorobutane extract is evaporated to dryness, reconstituted in methanol and injected into the chromatograph. Separation is achieved using a CN-bonded silica column and an isocratic elution with 0.01 M sodium phosphate in 50% acetonitrile. Detection is at 0.95 V applied potential on a glassy carbon electrode versus an Ag/AgCl electrode. Electrochemical methods that depend on a high oxidation potential suffer from rapid electrode passivation by significant amounts of impurities extracted from plasma. Therefore, the instrumentation includes a valve-switching unit to divert most of the impurities away from the electrode compartment; thus, maintaining sensitivity during the automated analysis of a large number of samples. An RSD of 5-15% was obtained in the concentration range of 0.5-100 ng/mL plasma. The limit of detection is 0.5 ng/mL. The method has been successfully used for the determination of indoramin in plasma samples from human subjects given a 50-mg oral dose of the drug.