An Economical Online Solid-Phase Extraction LC-MS/MS Method for Quantifying Methylprednisolone.

An economical, reproducible and automated online solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry method was developed to quantify methylprednisolone in human plasma. The method was validated in terms of selectivity, precision/accuracy, process efficiency, stability, cartridge reproducibility and carryover studies. Sample pretreatment was performed by protein precipitation and elimination using methanol followed by water dilution. Then, the mixture was passed onto the HySphere C-8 EC-SE online solid-phase extraction cartridge followed by the separation of the analytes on an Agilent Eclipse XDB column. Electrospray ionization in positive ion mode and multiple reaction monitoring were used to monitor the ion transitions at m/z 375.4/160.8 for methylprednisolone, and m/z 361.2/147.0 for prednisolone. The calibration curve ranged from 5.25 to 525 ng/mL. Meanwhile both the intra-day and inter-day precision values (relative standard deviation) were within 4.45%. The method which turns out to be less laborious, faster and lower consumable cost per sample has already been successfully applied to a pharmacokinetic study in which the oral administration of 16 mg methylprednisolone was conducted in Chinese volunteers.