Gel-electromembrane extraction of peptides: Determination of five hypothalamic agents in human plasma samples

Agarose gel as a green membrane has been proposed for use in electromembrane extraction of five hypothalamic-related peptides without an ionic carrier. Octreotide, goserelin, triptorelin, cetrorelix, and somatostatin were extracted from 5.0 mL of sample solution (adjusted to pH 5.0) into a microvolume acceptor solution (HCl, 100 mM) under the applied voltage of 30 V in 15 min. The pH of the agarose gel 3.0% (w/v) was adjusted to 4.0 to facilitate the movement of peptides through the membrane. Quantification was performed using an HPLC-UV system on a C18 column. Quantification and detection limits were found to be in the range of 15.0-20.0 ng mL^-1 and 4.5-6.0 ng mL^-1, respectively. Dynamic linear ranges were found to be in the range of 15.0-1000 ng mL^-1 (R² > 0.995) and recoveries were in the range of 62.3-77.6%. The optimized method was applied to spiked human plasma samples. The method showed relative recoveries in the range of 44.8-66.0%. Finally, the proposed method was compared with and shown to have higher recoveries than, the conventional electromembrane extraction method for the peptides under study.