Determination of acidic drugs in biological and environmental matrices by membrane-based dual emulsification liquid-phase microextraction followed by high-performance liquid chromatography.

A simple method is introduced providing a highly clean microextraction for the determination of some anti-inflammatory drugs as the model analytes in human urine and environmental matrices. This method is based upon the implementation of two consecutive emulsification liquid-phase microextractions, which are separated by a syringe filtration step. In this method, the organic extraction solvent (dihexyl ether) is dispersed into the aqueous sample solution (20 mL), and the resulting cloudy mixture is passed through a hydrophilic polytetrafluoroethylene syringe filter. By this action, the extraction phase containing the analytes and many interfering species that could be transferred into the organic phase is retained behind the hydrophilic membrane. The filter is then detached from the syringe and attached to another syringe containing an aqueous solution (pH 12.0, 150 μL), and by the in-syringe dispersion of the organic phase into the aqueous phase, the analytes are selectively back-extracted into the aqueous phase. The developed method is centrifuge-free and very simple, and provides a high sample clean-up in a few minutes. Under the optimized experimental conditions, the developed method provided a linearity in the range of 2.0-2000 ng/mL, a low limit of detection (0.5 ng/mL), and enrichment factors of 47-53.