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This study investigated the capability of electromembrane extraction (EME) as a general technique for peptides, by extracting complex pools of peptides comprising in total of 5953 different substances, varying in size from seven to 16 amino acids. Electromembrane extraction was conducted from a sample adjusted to pH 3.0 and utilized a liquid membrane consisting of 2-nitrophenyl octyl ether and carvacrol (1:1 w/w), containing 2% (w/w) di(2-ethylhexyl) phosphate. The acceptor phase was 50 mM phosphoric acid (pH 1.8), the extraction time was 45 min, and 10 V was used. High extraction efficiency, defined as a higher peptide signal in the acceptor than the sample after extraction, was achieved for 3706 different peptides. Extraction efficiencies were predominantly influenced by the hydrophobicity of the peptides and their net charge in the sample. Hydrophobic peptides were extracted with a net charge of +1, while hydrophilic peptides were extracted when the net charge was +2 or higher. A computational model based on machine learning was developed to predict the extractability of peptides based on peptide descriptors, including the grand average of hydropathy index and net charge at pH 3.0 (sample pH). This research shows that EME has general applicability for peptides and represents the first steps toward in silico prediction of extraction efficiency., (© 2024 The Author(s). Journal of Separation Science published by Wiley‐VCH GmbH.)

Background: Electromembrane extraction (EME) involves the process of mass transfer of charged analytes from an aqueous sample through an organic liquid membrane into an aqueous acceptor medium under the influence of an electrical field. Successful solvation of the analyte within the liquid membrane is of paramount importance and involves molecular interactions with the liquid membrane. In this comprehensive investigation, parallel EME was examined using a training set of 13 model peptides employing deep eutectic solvents as the liquid membrane. These deep eutectic solvents were formulated by mixing specific monoterpenes (thymol, menthol, camphor) with medium-chain fatty acids (1-octanoic acid and 1-decanoic acid)., Results: From an array of different liquid membrane compositions explored, it was revealed that the combination of camphor and 1-decanoic acid (in a 1:1 w/w ratio) with 2% di (2-ethylhexyl) phosphate (DEHP) delivered the most efficient extraction system. The solvation of the model peptides within this liquid membrane predominantly relied on ionic interactions between protonated basic functionalities and DEHP, along with hydrogen bond interactions between the deprotonated acid functionalities (hydrogen bond acceptor) and 1-decanoic acid (hydrogen bond donor). Selectivity was modulated by the pH of the sample and acceptor solutions, with a direct correlation to the polarity and net charge of the model peptides. The ionization of 1-decanoic acid in the interfacial region between the sample and liquid membrane emerged as an important factor influencing the selectivity., Significance and Novelty: Although parallel EME of peptides has been reported previously, the current liquid membrane provides an extraction system with sufficient stability for the first time. Selective extraction of peptides through EME holds substantial promise within the realm of next-generation environmentally-friendly sample preparation methodologies. The findings presented in this paper contribute significantly to our fundamental understanding of these processes, and may serve as an important reference for the development of future methods in this field., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

This article reviews the scientific literature on electromembrane extraction (EME) of peptides and amino acids. In EME, target analytes are extracted from aqueous sample, through a supported liquid membrane (organic) and into a microliter volume of aqueous buffer (acceptor). Experimental conditions and performance for EME of peptides and amino acids are reviewed and discussed in detail, providing readers with an overview and basic understanding of the subject. In addition, this review discuss the potential for future applications, and scientific questions that need to be addressed for EME of peptides and amino acids to be generally accepted. EME is under commercialization, and therefore we expect it will be an active area of research in the near future.

A triple-flow electromembrane extraction (EME) probe was developed and coupled directly to electrospray-ionization mass spectrometry (ESI-MS). Metabolic reaction mixtures (pH 7.4) containing drug substances and related metabolites were continuously drawn (20 μL/min) into the EME probe in one flow channel, and mixed inside the probe with 7.5 μL min -1 of 1 M formic acid as make-up flow from a second flow channel. Following this acidification, the drug substances and their related metabolites were continuously extracted by EME at 400 V, across a supported liquid membrane (SLM) comprising 2-nitrophenyl octyl ether (and for some experiments containing 30% triphenyl phosphate (TPP)), and into 20 μL min -1 of formic acid as acceptor phase, which was introduced through a third flow channel. The acceptor phase was pumped directly to the MS system, and the ion intensity of extracted analytes was followed continuously as function of time. The triple-flow EME probe was used for co-extraction of positively charged parent drugs and their zwitterionic drug metabolites (hydroxyzine and its carboxylic acid metabolite cetirizine; and vortioxetine and its carboxylic acid metabolite Lu AA34443). While the zwitterionic metabolites could not be extracted at pH 7.4, it was shown that by acidifying the sample solution the zwitterionic metabolites could be extracted effectively. Various extraction parameters like make-up flow, extraction voltage and SLM composition were optimized for simultaneous extraction of parent drugs and metabolites. It was found that TPP added to the SLM improved extraction efficiencies of certain drug metabolites. Finally the optimized and characterized triple-flow EME probe was used for online studying the in-vitro metabolism of hydroxyzine and vortioxetine by rat liver microsomes. Due to the automated pre-extraction acidification of the rat liver microsomal solutions, it was possible to continuously monitor formation of the zwitterionic drug metabolites. As the triple-flow EME probe allowed modification of the pH of the sample without changing the pH in the bulk sample, the system can potentially be used for direct analysis of various kinds of chemical reactions that have to be run at pH conditions unfavorable for direct analyte extractions., (Copyright © 2017 Elsevier B.V. All rights reserved.)