Dexamethasone cleanup

A generic enzyme immunoassay for the determination of several synthetic corticosteroids including dexamethasone, betamethasone, flumethasone, triamcinolone, prednisolone, and methylprednisolone in milk, liver, kidney, and muscle samples was recently developed (156). Antibodies raised against dexamethasone-21-hemisuccinate-bovine serum albumin were used in this assay, whereas dexa-methasone-horseradish peroxidase was the label conjugate. Skimmed milk could be directly screened for the presence of corticosteroids at limits of detection of 0.1 ppb for dexamethasone, betamethasone, and flumethasone, 0.3 ppb for triamcinolone and 0.5 ppb for prednisolone. Tissue samples were submitted, prior to the immunoassay, to an extraction/cleanup procedure involving liquid-liquid partitions with acetonitrile-water followed by hexane-chloroform. Background values for bovine liver, swine kidney, and calf muscle were determined to be 0.26, 0.26, and 0.07 ppb, respectively, of dexamethasone equivalents. 

In addition, column-switching between three columns coupled together for sample cleanup, concentration of analyte, and analytical separation proved to be a rugged, automated means of isolating dexamethasone from bovine tissues (528). The analyte, along with co-eluting matrix components, was heart-cut from the first, phenyl-silica, column and collected on a second, silica, column. The second column was then backflushed with a stronger eluent onto the third, cyanopropyl-silica, column where the analyte was finally resolved from matrix components. 

Following solid-phase extraction, all extracts are adjusted in the pH range 7-7.5, and submitted to additional cleanup on an immunoaffinity column containing a mixture of dexamethasone- and prednisolone-specific gels. Column washing is performed with water, while elution of the analytes with 3 ml methanol/water (80 20). Aliquots of the eluates are submitted to oxidative reaction with pyridin-ium chlorochromate, and the oxidized corticosteroid derivatives are then analyzed by gas chromatography-mass spectrometry under the conditions shown in Table... 

East sample preparation without cleanup. Separation of the two isomers betamethasone and dexamethasone Performance fit-for-purpose for low concentrations of corticosteroids. 

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