Three-phase, liquid-phase microextraction combined with high performance liquid chromatography-fluorescence detection for the simultaneous determination of fluoxetine and norfluoxetine in human plasma

A three-phase, liquid-phase microextraction using a hollow fibre (HF-LPME) combined with high performance liquid chromatography-fluorescence detection (HPLC-FL) was developed for the analysis of fluoxetine (FLX) and its active metabolite, norfluoxetine (NFLX), in human plasma. An HF-LPME system using a disposable 7-cm polypropylene porous hollow fibre, 5 mL of alkaline plasma solution (donor phase), n-hexyl ether (extraction solvent) and 20 mM hydrochloric acid (acceptor phase) was used in the extraction. The method was validated after optimisation of several parameters that influence LPME efficiency. A reverse-phase LiChrospher 60 RP-Select B column (125 mm × 4 mm, 5 μm particle size) was used with 0.005 M sodium acetate buffer (pH 4.5) and acetonitrile at a 50:50 (v/v) as the mobile phase at a flow rate of 0.6 mL min−1. In these conditions satisfactory chromatographic resolution and efficiency for the analytes were obtained. Fluorescence detection at 230 nm excitation wavelength and 290 nm emission wavelength was performed. Linearity over a range of 5–500 ng mL−1, with determination coefficients (R2) of 0.9999 and 0.9962 for FLX and NFLX, respectively, was established. Venlafaxine was used as the internal standard for both analytes. Extraction recoveries from plasma samples were 70.9% for FLX and 59.7% for NFLX. The intra-day coefficients of variation (CVs) were below 5.4%, and inter-day CVs were below 13.0%, for both analytes at concentrations of 20, 80 and 160 ng mL−1. HF-LPME extraction followed by HPLC-FL detection for FLX and NFLX analyses demonstrated excellent sample clean-up and selectivity. This method was simple, cheap, and easy to perform, yielding substantial analytes enrichment. The method was applied to the analysis of samples from 12 patients under fluoxetine treatment and proved suitable for routine therapeutic drug monitoring for this antidepressant.