Optimization of ultrasound assisted dispersive liquid-liquid microextraction of six antidepressants in human plasma using experimental design.

A simple Ultrasounds Assisted-Dispersive Liquid Liquid Microextraction (UA-DLLME) method is presented for the simultaneous determination of six second-generation antidepressants in plasma by Ultra Performance Liquid Chromatography with Photodiode Array Detector (UPLC-PDA). The main factors that potentially affect to DLLME were optimized by a screening design followed by a response surface design and desirability functions. The optimal conditions were 2.5 mL of acetonitrile as dispersant solvent, 0.2 mL of chloroform as extractant solvent, 3 min of ultrasounds stirring and extraction pH 9.8.Under optimized conditions, the UPLC-PDA method showed good separation of antidepressants in 2.5 min and good linearity in the range of 0.02-4 μg mL(-1), with determination coefficients higher than 0.998. The limits of detection were in the range 4-5 ng mL(-1). The method precision (n=5) was evaluated showing relative standard deviations (RSD) lower than 8.1% for all compounds. The average recoveries ranged from 92.5% for fluoxetine to 110% for mirtazapine. The applicability of DLLME/UPLC-PDA was successfully tested in twenty nine plasma samples from antidepressant consumers. Real samples were analyzed by the proposed method and the results were successfully submitted to comparison with those obtained by a Liquid Liquid Extraction-Gas Chromatography - Mass Spectrometry (LLE-GC-MS) method. The results confirmed the presence of venlafaxine in most cases (19 cases), followed by sertraline (3 cases) and fluoxetine (3 cases) at concentrations below toxic levels.