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Restan MS, Jensen H, Shen X, et al. Comprehensive study of buffer systems and local pH effects in electromembrane extraction. Anal Chim Acta. 2017;984:116-123doi: 10.1016/j.aca.2017.06.049.
Restan, M. S., Jensen, H., Shen, X., Huang, C., Martinsen, �. �. G., Kubáň, P., Gjelstad, A., & Pedersen-Bjergaard, S. (2017). Comprehensive study of buffer systems and local pH effects in electromembrane extraction. Analytica chimica acta, 984116-123. https://doi.org/10.1016/j.aca.2017.06.049
Restan, Magnus Saed, et al. "Comprehensive study of buffer systems and local pH effects in electromembrane extraction." Analytica chimica acta vol. 984 (2017): 116-123. doi: https://doi.org/10.1016/j.aca.2017.06.049
Restan MS, Jensen H, Shen X, Huang C, Martinsen ØG, Kubáň P, Gjelstad A, Pedersen-Bjergaard S. Comprehensive study of buffer systems and local pH effects in electromembrane extraction. Anal Chim Acta. 2017 Sep 01;984:116-123. doi: 10.1016/j.aca.2017.06.049. Epub 2017 Jun 30. PMID: 28843554.
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Anal Chim Acta. 2017 Sep 01;984:116-123. doi: 10.1016/j.aca.2017.06.049. Epub 2017 Jun 30.

Comprehensive study of buffer systems and local pH effects in electromembrane extraction.

Analytica chimica acta

Magnus Saed Restan, Henrik Jensen, Xiantao Shen, Chuixiu Huang, Ørjan Grøttem Martinsen, Pavel Kubáň, Astrid Gjelstad, Stig Pedersen-Bjergaard

Affiliations

  1. School of Pharmacy, University of Oslo, P.O. Box 1068 Blindern, 0316 Oslo, Norway.
  2. Faculty of Health and Medical Sciences, School of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark.
  3. Institute of Environmental Medicine, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Hangkong Road #13, Wuhan 430030, China.
  4. Department of Forensic Medicine, Huazhong University of Science and Technology, Hangkong Road #13, Wuhan 430030, China; School of Pharmacy, University of Oslo, P.O. Box 1068 Blindern, 0316 Oslo, Norway.
  5. Department of Physics, University of Oslo, P.O. Box 1048 Blindern, 0316 Oslo, Norway; Department of Clinical and Biomedical Engineering, Oslo University Hospital, 0027 Oslo, Norway.
  6. Institute of Analytical Chemistry of the Czech Academy of Sciences, v.v.i., Veve?í 97, CZ-60200 Brno, Czech Republic.
  7. School of Pharmacy, University of Oslo, P.O. Box 1068 Blindern, 0316 Oslo, Norway; Faculty of Health and Medical Sciences, School of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark. Electronic address: [email protected].

PMID: 28843554 DOI: 10.1016/j.aca.2017.06.049

Abstract

Different phosphate-, acetate- and formate buffers in the pH range 2.0-6.8 were tested for electromembrane extraction (EME) in a 96-well system. The five basic drugs haloperidol, loperamide, methadone, nortriptyline, and pethidine were selected as model analytes. The EME performance was tested with respect to extraction recovery, extraction current and pH-stability. The analytes were extracted from 200 μL buffer, through a 100 μm thick supported liquid membrane (SLM) of 2-nitrophenyl octyl ether (NPOE) immobilized in the pores of filters in a 96-well plate, and into 100 μL buffer acceptor phase. The extraction voltage was 50 V and the extraction time was 10 min. The acceptor phase was analyzed by HPLC-UV. The extraction current was ≤6 μA with all buffers, and pH was effectively stabilized during EME using buffers as donor (sample) and acceptor phase. For buffers with pH ≤ 4.8 as acceptor phase, the extraction recoveries were in the range 66-97% and with RSD <15%. With pH in the range 5.8-6.8 in the acceptor phase, the extraction recoveries decreased and were in the range 21-62%. This was attributed to elevated pH conditions in the acceptor/SLM interface. The presence of elevated pH conditions was visualized with phenolphthalein as pH sensitive color indicator. Increasing the buffer strength from 10 to 500 mM in an attempt to offset the elevated pH conditions gave no improvement, and elevated pH conditions remained. Elevated pH conditions in the acceptor/SLM interface were also observed when voltage was increased, and when NPOE was replaced with tributyl phosphate as SLM. The presence of elevated pH conditions close to the SLM in EME was discussed for the first time, and this information is highly important for future development of EME.

Copyright © 2017 Elsevier B.V. All rights reserved.

Keywords: Boundary layer; Buffers; Electrolysis; Electromembrane extraction (EME); Sample preparation

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