Журнал аналитических и биоаналитических методов

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Identification and Reduction of Matrix Effects Caused by Cremophor EL in Bioanalysis Using Liquid Chromatography/Tandem Mass Spectrometry

Vijaya Bhaskar V, Anil Middha, Sudhir Tiwari and Savithiri Shivakumar

Ion suppression effect of dosing vehicle excipient Cremophor EL (CrEL) on the accuracy of liquid chromatography/ tandem mass spectrometry (LC-MS/MS) measurements was studied. Ion suppression cause significant errors in accuracy of the measured concentrations of test compounds, thereby invalidating the assessment of pharmacokinetic results. Using CrEL as a probe compound, the concentration-time profile of the excipient in plasma from rats dosed both orally and intravenously was determined. The most abundant molecular ions corresponding to PEG oligomers at m/z 828, 872, 916 and 960 with daughter ion at m/z 89 were selected for multiple reaction monitoring (MRM) in electrospray mode of ionization. Plasma concentrations of CrEL ranging from 0.50-1.0 mg/mL in the initial sampling points caused 2-10 fold ion suppression on most of the analytes studied. This can result in false rejection of compounds in a drug discovery screen. In this paper, various sample preparation methods, enhanced chromatographic selectivity, and alternative ionization methods were investigated as means to avoid or minimize ion suppression effects. The elimination of ion suppression effects was achieved by Liquid-Liquid Extraction (LLE) with hexane, TBME in Electrospray Ionisation (ESI) mode as sample preparation method. In contrast to ESI mode that had severe suppression effects from CrEL, atmospheric pressure chemical ionisation (APCI) mode is totally free of suppression effects. The mechanism of ion suppression caused by CrEL in relation to both liquid and gas phase reactions was discussed.