Dispersive liquid-liquid microextraction based on solidification of floating organic droplets followed by high performance liquid chromatography for the determination of duloxetine in human plasma.

A novel dispersive liquid-liquid microextraction method based on solidification of floating organic droplets (DLLME-SFO) technique was developed for the determination of duloxetine in human plasma samples by high performance liquid chromatography with fluorescence detection (HPLC-FLD). During the extraction procedure, plasma protein was precipitated by using a mixture of zinc sulfate solution and acetonitrile. After the protein precipitation step, duloxetine in an alkaline sample solution was quickly extracted by DLLME-SFO with 50 μL of 1-undecanol (extractant). Disperser was unnecessary because the small amount of remaining acetonitrile, which acts as a protein precipitating reagent, was also employed as a disperser; therefore, organic solvent consumption was reduced as much as possible. The emulsion was centrifuged and then fine droplets were floated to the top of the sample solution. The floated droplets were solidified in an ice bath and easily transferred. Various DLLME-SFO parameters such as extractant type, extractant amount, ionic strength, pH and extraction time were optimized. The chromatographic separation of duloxetine was carried out using ethanol as mobile phase. Validation of the method was performed with respect to linearity, intra- and inter-day accuracy and precision, limit of quantification (LOQ), and recovery. Calibration curves for duloxetine showed good linearity with correlation coefficients (r²) higher than 0.99. The method showed good precision and accuracy, with intra- and inter-assay coefficients of variation less than 15% (LOQ: less than 20%) at all concentrations. The recovery was carried out following the standard addition procedure with yields ranging from 59.6 to 65.5%. A newly developed environmentally friendly method was successfully applied to the pharmacokinetic study of duloxetine in human plasma and was shown to be an alternative green approach compared with the conventional solid-phase microextraction (SPME) and dispersive liquid-liquid microextraction (DLLME) techniques. Copyright © 2012 Elsevier B.V. All rights reserved.