Determination of betamethasone and dexamethasone in plasma by fluorogenic derivatization and liquid chromatography

A simple and sensitive liquid chromatographic method is described for the determination of betamethasone and dexamethasone in plasma as fluorogenic derivatives. Betamethasone or dexamethasone in plasma after separation with a Sep-Pak C18 cartridge was derivatized with l-ethoxy-4-(dichloro-s-triazinyl)naphthalene. The resulting derivatives were separated on a reversed-phase C18 column with acetonitrile-water (60:40, vv) as the mobile phase. The linear range for the determination of each glucocorticoid in spiked plasma was over 2.5–50.0 pmol. The limit of detection for betamethasone or dexamethasone was 80.0 fmol per 20 μl injection (SN = 5). The intraday relative standard deviations (n = 5) and the interday relative standard deviations (n = 3) were all less than 11% for both glucocorticoids. Recoveries for both glucocorticoids were greater than 90%.