Research Article Electromembrane extraction of peptides – Fundamental studies on the supported liquid membrane A large screening of different components in the supported liquid membrane (SLM) in electromembrane extraction (EME) was performed to test the extraction efficiency on eight model peptides. Electromembrane extraction from a 500 mL acidified aqueous sample containing the model peptides in the concentration 10 mg/mL was used. Extraction time was 5 min with an electric potential of 10 V and 900 rpm agitation of the sample vial. The samples were extracted through a hollow fiber-based SLM with different compositions of organic solvents and carriers. A small volume of acidified acceptor solution (25 mL) was after extraction analyzed directly, or with some dilution, on CE or HPLC. This article has identified mono- or di-substituted phosphate groups as the prominent group of carrier molecules needed to obtain acceptable recoveries. For the organic solvents, primary alco- hols and ketones have shown promise regarding recovery and reproducibility, with some differences in selectivity. A new composition of the SLM, namely 2-octanone and tridecyl phosphate (90:10w/w) has proved to give higher extraction recoveries and lower standard deviation than SLMs previously reported in the literature. Keywords: Electrokinetic migration / Electromembrane extraction / Peptides / Sample preparation / Supported liquid membrane DOI 10.1002/jssc.201100558 1 Introduction The analysis of peptides is a growing field of importance, based on the increased use in medical diagnostics, therapeutic drug monitoring, pharmaceutical industry, doping control, proteomics, and in medical/pharmaceutical research [1, 2]. An important aspect regarding peptide analysis is to have good sample preparation methods to get clean extracts from biological samples, and good enrich- ment to enable the detection of substances in low concentrations. Conventional methods such as SPE and LLE are often time consuming, require several steps, and have a rather high usage of organic solvents. These reasons have been some of the drive for the development of microextraction techniques. One such technique, called hollow fiber liquid-phase microextraction (HF-LPME), has proved to be a good alternative to the more conventional procedures in several sample preparation methods, prior to analysis [3–7]. In one configuration, HF-LPME is a three- phase liquid extraction system where the sample passes from a donor compartment, through a hollow fiber-based supported liquid membrane (SLM) and into a small volume of acceptor solution. The acceptor solution can often be analyzed directly on HPLC, LC-MS, or CE. The hollow fiber is usually based on a porous polymer material, i.e. polypropylene, impregnated with an organic solution, and hence it will function as an SLM that separates the aqueous phases. HF-LPME has proven to give clean extracts and good recovery for several applications, with minimal use of organic solvents and a simple setup [5, 8, 9]. However, the method is based on passive diffusion and thus suffers from long extraction times, usually around 15–60 min, with limited potential for faster extractions [10]. To overcome this drawback, a new technique, called electromembrane extraction (EME), was developed [11]. This differs from HF- LPME by the addition of an electrical field across the SLM, and has shown a vast improvement in the extraction time needed to get a similar amount of recovery. EME has shown promising results in the extraction of several basic and acidic drugs with high recoveries, good enrichment, and clean extracts from several matrices [12–15]. The extraction time is usually around 1–10 min with varying strengths of the electric field, typically in the range from 9 to 300 V [11–13, 16, 17]. Knut Fredrik Seip 1à Jeanette Stigsson 1 Astrid Gjelstad 1 Marte Balchen 1 Stig Pedersen-Bjergaard 1,2 1 Department of Pharmaceutical Chemistry, School of Pharmacy, University of Oslo, Oslo, Norway 2 Department of Pharmaceutics, Analytical Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark Received June 29, 2011 Revised August 8, 2011 Accepted September 9, 2011 Abbreviations: AT 1, angiotensin 1; AT 2, angiotensin 2; AT 2 AP, angiotensin 2 antipeptide; BK, bradykinin; DBP, dibutyl phosphate; DEHP, di-(2-ethylhexyl)-phosphate; EME, electromembrane extraction; Endom., endomorphin; Enkeph., enkephalin; HF-LPME, hollow fiber liquid-phase microextraction; NT, neurotensin; SLM, supported liquid membrane; TDP, tridecyl phosphate; VP, vasopressin à Additional correspondence: Knut Fredrik Seip, M.Sc. E-mail: k.f.seip@farmasi.uio.no Correspondence: Professor Stig Pedersen-Bjergaard, Depart- ment of Pharmaceutical Chemistry, School of Pharmacy, University of Oslo, P.O. Box 1068 Blindern, 0316 Oslo, Norway E-mail: stig.pedersen-bjergaard@farmasi.uio.no Fax: 147-22854402 & 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com J. Sep. Sci. 2011, 34, 3410–3417 3410