Dowlatshah Samira, Hansen Frederik André, Zhou Chen, Ramos-Payán María, Halvorsen Trine Grønhaug, Pedersen-Bjergaard Stig
Department of Pharmacy, University of Oslo, P.O Box 1068 Blindern, 0316, Oslo, Norway.
Department of Pharmacy, University of Oslo, P.O Box 1068 Blindern, 0316, Oslo, Norway; West China School of Public Health and West China Fourth Hospital, Sichuan University, Chengdu, 610041, China.
Anal Chim Acta. 2023 Sep 22;1275:341610. doi: 10.1016/j.aca.2023.341610. Epub 2023 Jul 10.
Electromembrane extraction (EME) of peptides reported in the scientific literature involve transfer of net positively charged peptides from an aqueous sample, through a liquid membrane, and into an aqueous acceptor solution, under the influence of an electrical field. The liquid membrane comprises an organic solvent, containing an ionic carrier. The purpose of the ionic carrier is to facilitate peptide solvation in the organic solvent based on ionic interactions. Unfortunately, ionic carriers increase the conductivity of the liquid membrane; the current in the system increases, the electrolysis in sample and acceptor is accelerated, and the extraction system tend to be unstable and suffers from drifting pH.
In the present work, a broad selection of organic solvents were tested as pure liquid membrane for EME of peptides, without ionic carrier. Several phosphates provided high mass transfer, and tri(pentyl) phosphate was selected since this solvent also provided high operational stability. Among 16 different peptides used as model analytes, tri(pentyl) phosphate extracted those with net charge +1 and with no more than two polar side chains. Tri(pentyl) phosphate served as a very strong hydrogen bond acceptor, while the protonated peptides were hydrogen bond donors. By such, hydrogen bonding served as the primary interactions responsible for mass transfer. Tri(pentyl) phosphate as liquid membrane, could exhaustively extract leu-enkephalin, met-enkephalin, and endomorphin from human blood plasma and detected by LC-MS/MS. Calibration curves were linear (r > 0.99) within a concentration range from 1 to 500 ng/mL, and a relative standard deviation within 12% was observed for precision studies.
The current experiments are important because they indicate that small peptides of low polarity may be extracted selectively in EME based on hydrogen bond interactions, in systems not suffering from electrolysis.
科学文献中报道的肽的电膜萃取（EME）涉及在电场影响下，将带正电的净电荷肽从水性样品中通过液膜转移到水性接受溶液中。液膜由含有离子载体的有机溶剂组成。离子载体的目的是基于离子相互作用促进肽在有机溶剂中的溶剂化。不幸的是，离子载体增加了液膜的电导率；系统中的电流增加，样品和接受体中的电解加速，萃取系统往往不稳定且pH值会漂移。
在本研究中，测试了多种有机溶剂作为无离子载体的肽EME纯液膜。几种磷酸盐提供了高传质率，选择了磷酸三（戊基）酯，因为这种溶剂还提供了高操作稳定性。在用作模型分析物的16种不同肽中，磷酸三（戊基）酯萃取了那些净电荷为 +1 且极性侧链不超过两个的肽。磷酸三（戊基）酯作为非常强的氢键受体，而质子化肽是氢键供体。由此，氢键作为负责传质的主要相互作用。以磷酸三（戊基）酯作为液膜，可以从人血浆中彻底萃取亮氨酸脑啡肽、甲硫氨酸脑啡肽和内吗啡肽，并通过LC-MS/MS进行检测。校准曲线在1至500 ng/mL的浓度范围内呈线性（r > 0.99），精密度研究的相对标准偏差在12%以内。
当前的实验很重要，因为它们表明在不涉及电解的系统中，基于氢键相互作用，低极性的小肽可以在EME中被选择性萃取。
