Electromembrane extraction of peptides using deep eutectic solvents as liquid membrane

For the first time, we report electromembrane extraction (EME) of peptides using deep eutectic solvent (DES) as supported liquid membrane (SLM). DES were mixtures of coumarin, camphor, DL-menthol and thymol. Sixteen model peptides were extracted from 100 μL 50 mM phosphate buffer solution (pH 3.0), through the SLM, and into 100 μL acceptor solution consisting of 50 mM phosphoric acid (pH 1.8). EME was performed in 96-well format with 30 V to facilitate extraction of positively charged peptides. The model peptides comprised three to 13 amino acids, and differed significantly in terms of acid/base functionalities and polarity. We found pure DES to be inefficient for EME of peptides. However, with addition of a small amount of the ionic carrier di(2-ethylhexyl) phosphate (DEHP) to the DES, the extraction efficiency increased due to ionic interactions. With the most efficient SLM; coumarin and thymol mixed in molar ratio (1:2) with 2.0% (v/v) DEHP, average recovery after 15 min was 55%; five peptides were extracted with recovery > 80%, nine peptides with recoveries in the range 40–80%, and two peptides were not extracted (recovery < 5%). When extraction time was extended to 45 min, average extraction recovery increased to 83%. Extraction recoveries with DES were higher than previously reported in the literature for the same model peptides.