Simultaneous determination of dexamethasone and lenalidomide in rat plasma by solid phase extraction and ultra-performance liquid chromatography-tandem mass spectrometry: application to pharmacokinetic studiesElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ra22339c

An ultra-performance liquid chromatography method with tandem mass spectrometric detection (UPLC-MS/MS) has been developed and validated for the simultaneous determination of lenalidomide (LND) and dexamethasone (DEX) in rat plasma using domperidone (DOM) as an internal standard (IS). Sample preparation was performed using solid phase extraction methodology (SPE) followed by chromatographic analysis on a C 18 column (100 × 1.0 mm, i.d., 1.7 μm particle size) and a mobile phase composed of (0.1% formic acid in water) and (0.1% formic acid in acetonitrile) in the ratio of (20 : 80, v/v) at the flow rate of 0.2 mL min −1 . Electrospray ionization (EI) in the positive ionization mode using multiple reaction monitoring (MRM) was applied to detect the transitions of DEX at m / z 393 > 147, LND at m / z 260 > 149 (LND), and DOM at m / z 426 > 175. The method was validated over the concentration range of 0.01-5 ng mL −1 with a very low limit of quantitation of 0.01 ng mL −1 for both LND and DEX. Recoveries of both analytes from plasma samples ranged from 86-106% throughout their linear ranges. Intra-day and inter-day precision was evaluated and in all cases, the RSD values were within the acceptance values (