Determination of sunitinib in human plasma using liquid chromatography coupled with mass spectrometry

An original method based on liquid chromatography with single quadrupole electrospray ionization mass spectrometry was developed for the determination of sunitinib in human plasma. The quantitation limit of the method at 0.10 ng/mL is comparable to that of tandem mass spectrometry assays. The handling of all solutions containing sunitinib was performed under low-intensity red light to avoid the isomerization of sunitinib and enable quantitation using a single peak. Liquid-liquid extraction with a mixture of n-hexane/isopropanol (90:10 v/v) allowed recoveries at the level of 70%. Measurements were performed using a Zorbax SB-C18 column (3.0 mm × 150 mm, 3.5 μm) and isocratic elution with (A) 0.1% aqueous formic acid and (B) acetonitrile/methanol (80:20 v/v) in an A/B ratio of 55:45 at 35°C. Under these conditions, sunitinib is eluted at 3.8 min in 6 min of the total run time. The linearity of the calibration curve ranges from 0.10 to 150 ng/mL. The baseline separation of sunitinib and its primary metabolite, N-des-ethyl sunitinib (SU12662), as well as sharp peak shapes, suggest a possibility of extending the applied methodology to the quantitative determination of both compounds. Isotopically labeled sunitinib was used as the internal standard. All required validation tests met the acceptance criteria and proved the method's reliability and robustness. The method may be conveniently applied to study the pharmacokinetics of sunitinib in humans.