A novel and sensitive method for ethinylestradiol quantification in human plasma by high-performance liquid chromatography coupled to atmospheric pressure photoionization (APPI) tandem mass spectrometry: application to a comparative pharmacokinetics study.

In the present study, a novel, fast, sensitive and robust method to quantify ethinylestradiol in human plasma using 17alpha-ethinylestradiol-d4 as the internal standard (IS) is described. The analyte and the IS were extracted from acidified plasma by liquid-liquid extraction (LLE) using diethyl ether-hexane followed by online solid phase extraction (SPE) using online C18 cartridges. Extracted samples were analyzed by high-performance liquid chromatography coupled to atmospheric pressure photoionization tandem mass spectrometry (HPLC-APPI-MS/MS).