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Addition of trace amount of EDTA (0.04 mM) in plasma samples and the mobile phase to prevent the formation of iron complexes of deferasirox with ferric ion.Validated LC–MS/MS method for evaluation of pharmacokinetics and therapeutic drug monitoring of deferasirox in human plasma.As an orally active iron chelator, deferasirox forms its ion complexes in the prepared plasma samples and LC–MS mobile phase where ferric ion exists, and then comparing with the nominal concentration level, a lower detected concentration level of deferasirox would be obtained after LC–MS analysis, if no proper treatment was adopted. Meanwhile, the phenomenon would be observed that multiple repeat injections of the same deferasirox plasma sample in the same tube would show the lower and lower detected concentration levels of deferasirox, which caused by more and more ferric ions from the injection needle dissolved in the sample solution as multiple repeated injections. The addition of a proper concentration of EDTA in the mobile phase and the sample will competitively inhibit deferasirox from complexing with ferric ion, and prevent the decrease of deferasirox concentration. In this paper, an LC–MS/MS method was developed and validated for the determination of deferasirox in human plasma. To achieve the protein precipitation, the analytes were extracted from aliquots of 200 μL human plasma with acetonitrile. Chromatographic separation was performed on an ODS-C18 column with the mobile phase consisted of methanol and 0.1% formic acid containing 0.04 mM ethylenediamine tetraacetate dihydrate (EDTA) (80:20, v/v) at a flow rate of 0.5 mL/min. Deferasirox and the internal standard (IS, mifepristone) were detected using electrospray ionization in positive ion multiple reaction monitoring mode by monitoring the precursor-to-product ion transitions m/z 374.2 → 108.1 for deferasirox and m/z 430.1 → 372.2 for the IS. The method exhibited good linearity over the concentration range of 0.04–40 μg/mL for deferasirox. The method was successfully applied to a pharmacokinetic study in 10 Chinese healthy volunteers after oral administration of deferasirox.