A rapid microextraction by packed sorbent - liquid chromatography tandem mass spectrometry method for the determination of dexamethasone disodium phosphate and dexamethasone in aqueous humor of patients with uveitis

A new method based on microextraction by packed sorbent(MEPS) coupled with liquid chromatographytandem mass spectrometry (LC–MS/MS) was developed and validated for the determination of dexamethasone and dexamethasone disodium phosphate in human aqueous humor. A central composite design was applied to investigate the effects of both loading and eluting cycles in the MEPS procedure; subsequently the multicriteria method of the desirability functions allowed to find the best conditions for the simultaneous extraction of both the analytes. Detection was performed on a LTQ XL linear ion trap mass spectrometer operating in the positive electrospray ionization mode applying multiple reaction monitoring mode. The assay was validated in accordance with the guidelines bioanalytical method validation obtaining quantitation limits in the low g/L range, a precision characterized by RSD ≤ 16% and recovery rates in the 91–119% range