Determination of dexamethasone in milk by high pressure liquid chromatography

A rapid and sensitive high pressure liquid chromatographic method for the analysis of dexamethasone (9 alpha - fluoro - 11 beta, 17 alpha, 21 - trihydroxy - 16 alpha - methylpregna - 1,4-diene-3,20-dione) in milk has been developed. The corticosteroid can be quantitated at 20 ppb, with the limit of detectability estimated at 5 ppb. Recoveries ranged from 72 to 94%. After dexamethasone was injected into 5 Holstein-Friesian cows, no residues were dound in milk, even after the first milking.