Determination of 2-chlorodeoxyadenosine (cladribine, 2-CdA) in human plasma by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

Abstract A sensitive and specific assay based on combined liquid chromatography mass spectrometry (LCMS) has been developed and validated for the quantification of 2-chlorodeoxyadenosine (cladribine, 2-CdA) in human plasma. Sample preparation consisted of an extraction with ethyl acetate under basic conditions. The organic solvent was evaporated and the residue re-dissolved for analysis. The extracts were chromatographed on a base deactivated C-8 column interfaced via the heated nebulizer probe to a corona discharge chemical ionization source. The mass spectrometer was operated in the positive ion tandem mode. Typical retention times were 1.5 and 2.0 min for 2-CdA and a fluorinated analog internal standard (IS), respectively. The standard curve was linear from 0.1 to 20 ng ml −1 using a 1.0 ml sample volume. The resulting chromatograms produced sharp peaks for 2-CdA and the IS and showed no endogenous peaks from blank plasma. Peak area ratios of 2-CdA to IS were used for standard curve regression analysis. This assay procedure gave interday mean accuracy results for the standards and quality controls that were within 4.9% of target concentrations and interday precision results (RSDs) that were less than 5.3%.