Two high-performance liquid chromatographic assays for the determination of free and total silibinin diastereomers in plasma using column switching with electrochemical detection and reversed-phase chromatography with ultraviolet detection.

A combination of two stereoselective assays was developed using column-switching HPLC with electrochemical detection for the determination of free (unconjugated) silibinin and RP-HPLC with UV detection for the measurement of total (free and conjugated) silibinin in human plasma. After extraction of free silibinin and the internal standard hesperetin with diethyl ether the compounds were pre-separated on a RP-CN column. A cut fraction of eluate containing the analytes was then transferred to the RP-18 main column by means of a switching valve for final separation of the compounds.