Direct injection analysis of melphalan in plasma using column-switching high-performance liquid chromatography

An automated column-switching high-performance liquid chromatographic (HPLC) method with ultraviolet detection is described for a simple and rapid determination of melphalan, an alkylating agent, in human plasma following direct sample injection. The system consists of a pretreatment column and an analytical column connected in series via a switching valve. Plasma samples are loaded onto a pretreatment column with an aqueous mobile phase, with which the sample to be analyzed is retained and the solubilized plasma proteins are flushed to be discarded. The retained compound is eluted from the pretreatment column onto the analytical column by using the chromatographic mobile phase with a higher elution capacity. The column-switching technique can be used to achieve an automated assay. Analytical recovery of the compound was 99.1%, and the coefficients of both intra- and interday variations did not exceed 3.5%. The detection limit was 10 ng/ml for the compound. Recovery of melphalan in plasma was only 2.1% after 4 weeks at 25 degrees C, as compared to 24.5% at 5 degrees C and 100.1% at -20 degrees C.