Quantitative determination of corticosteroids in bovine milk using mixed-mode polymeric strong cation exchange solid-phase extraction and liquid chromatography-tandem mass spectrometry.

A new method was developed to identify and quantify corticosteroids (prednisolone, methylprednisone, flumetasone, dexamethasone, and methylprednisolone) in raw bovine milk by liquid chromatography-tandem mass spectrometry (LC-MS/MS) utilizing mixed-mode polymeric strong cation exchange and reversed-phase (MCX) solid-phase extraction (SPE) to reduce ion effects in a multimode ion (MMI) source. The main advantage of this method over other commonly used methods includes the use of a single SPE cartridge with a low volume for sample preparation and fast separation on the HPLC system with reduced ion suppression. This study is the first to report the determination of methylprednisone, a metabolite of methylprednisolone, in bovine milk. This method was validated in accordance with the European Union (EU) Commission Decision 2002/657/EC. The recoveries vary between 90% and 105%. The within-laboratory reproducibility (precision) is less than 30%. The decision limits and detection capabilities were calculated along with LODs, which ranged from 0.02 to 0.07 microg/kg. The method was further enhanced by its successful adaptation to other LC-MS/MS systems equipped with the newly developed ion source, Agilent Jet Stream (AJS). After optimization of the AJS ion source and MS parameters, even lower LOD values were achieved (0.001-0.006 microg/kg) for the corticosteroids. Analytical results obtained with the AJS were characterized by an enhanced area response and similar noise level comparable to those obtained with conventional orthogonal atmospheric ionization (API).