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.
Anal Chim Acta. 2017 Sep 1;984:116-123. doi: 10.1016/j.aca.2017.06.049. Epub 2017 Jun 30.
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.
不同的磷酸盐、乙酸盐和甲酸盐缓冲液在 pH 值 2.0-6.8 范围内进行了测试，以用于 96 孔系统中的电膜萃取（EME）。选择了五种基本药物氟哌啶醇、洛哌丁胺、美沙酮、去甲替林和哌替啶作为模型分析物。根据萃取回收率、萃取电流和 pH 稳定性测试了 EME 性能。将分析物从 200μL 缓冲液中萃取出来，通过 2-硝基苯基辛基醚（NPOE）的 100μm 厚支撑液膜（SLM）萃取，该 SLM 固定在 96 孔板的过滤器孔中，进入 100μL 缓冲液接受相。萃取电压为 50V，萃取时间为 10min。接受相通过 HPLC-UV 进行分析。所有缓冲液的萃取电流均≤6μA，并且在使用缓冲液作为供体（样品）和接受相时，有效地稳定了 pH 值。对于 pH 值≤4.8 的缓冲液作为接受相，萃取回收率在 66-97%范围内，RSD<15%。在接受相 pH 值为 5.8-6.8 的范围内，萃取回收率降低，范围为 21-62%。这归因于接受/SLM 界面处 pH 值升高的条件。使用酚酞作为 pH 敏感显色指示剂可以观察到接受/SLM 界面处 pH 值升高的情况。试图通过增加缓冲液强度从 10mM 增加到 500mM 来抵消升高的 pH 条件没有得到改善，并且仍然存在升高的 pH 条件。当电压增加时，当 NPOE 被三丁基磷酸盐代替为 SLM 时，也观察到接受/SLM 界面处 pH 值升高的情况。首次讨论了 EME 中靠近 SLM 处存在升高的 pH 条件的情况，这对于 EME 的未来发展非常重要。
