Electromembrane extraction of polar substances - Status and perspectives.

In this article, the scientific literature on electromembrane extraction (EME) of polar substances (log P < 2) is reviewed. EME is an extraction technique based on electrokinetic migration of analyte ions from an aqueous sample, across an organic supported liquid membrane (SLM), and into an aqueous acceptor solution. Because extraction is based on voltage-assisted partitioning, EME is fundamentally suitable for extraction of polar and ionizable substances that are challenging in many other extraction techniques. The article provides an exhaustive overview of papers on EME of polar substances. From this, different strategies to improve the mass transfer of polar substances are reviewed and critically discussed. These strategies include different SLM chemistries, modification of supporting membranes, sorbent additives, aqueous solution chemistry, and voltage/current related strategies. Finally, the future applicability of EME for polar substances is discussed. We expect EME in the coming years to be developed towards both very selective targeted analysis, as well as untargeted analysis of polar substances in biomedical applications such as metabolomics and peptidomics.

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.

Electromembrane extraction of peptides and amino acids - status and perspectives.

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.