QUANTITATIVE-DETERMINATION OF SEVERAL SYNTHETIC CORTICOSTEROIDS BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY AFTER PURIFICATION BY IMMUNOAFFINITY CHROMATOGRAPHY

A study was conducted to test a multiresidue analytical procedure for detecting and quantifying several corticosteroids on which the Europea n Union imposes maximum residue limits (MRLs). Primary extracts from d ifferent matrices (liver, milk, urine, faeces) were first purified on C-18 cartridges. A new immunoaffinity clean-up step was included. The immunoaffinity gel was used to purify several corticosteroids simultan eously with enrichment of the corresponding fractions. The extracts we re treated with an aqueous solution of pyridinium chlorochromate to fu lly oxidise all corticosteroids and to facilitate their extraction wit h dichloromethane. After evaporation, the final extract was reconstitu ted with toluene before injection into the GC-MS apparatus, The analys is was performed in the CI-negative ionisation mode using ammonia as t he reactant gas. The estimated detection and quantification limits wer e, respectively, 0.25 and 0.5 ppb or lower. Overall, the method is rep roducible to within 20%. Recovery is between 50 and 80% according to t he corticosteroid. (C) 1997 Elsevier Science B.V.