Ionic liquid-based reference electrodes for miniaturized ion sensors: What can go wrong?
Ionic liquid-based reference electrodes for miniaturized ion sensors: What can go wrong?
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DOI：
10.1016/j.snb.2019.127112
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发表时间：
2019-12-12
影响因子：
8.4
通讯作者：
Buhlmann, Philippe
中科院分区：
文献类型：
--
作者：
Mousavi, Maral P. S.;Abd El-Rahman, Mohamed K.;Buhlmann, Philippe
基于离子液体的参比电极，特别是含有1-辛基-3-甲基咪唑鎓双（三氟甲基磺酰基）酰亚胺（MeOctIm TFSI）的参比电极，越来越多地用于电位测量。它们取代了传统的盐桥，并通过在参比膜和样品溶液之间局部分配离子液体的离子来建立参比电位。除非电化学电池和测量协议被适当地设计，否则这些离子可以干扰具有聚合物膜的离子选择性电极（ISE）的响应。本文研究了MeOctIm TFSI对K+、Na+和Cl-离子选择性电极的影响。用紫外-可见光谱监测MeOctIm TFSI从参比膜到样品溶液的浸出。MeOctIm TFSI在水相中的浓度逐渐增加，并在约1.0 mM处达到稳定。低至100 μ M的MeOctIm TFSI浓度引起K+、Na+和Cl-ISE的电动势（50-150 mV）的巨大变化。10 μ M的TESI-的存在足以引起以缬氨霉素作为离子载体的K+ ISE的唐南失效（即，和K+ TESI-共萃取到传感膜中）。使用亲脂性较低的阴离子，如四氟硼酸根（BF 4-）或三氟甲磺酸根（OTf-）推迟了阳离子选择性离子交换膜的唐南失效的发生，以更高浓度的阴离子，但降低了参比电极的参比电位和寿命的稳定性。这些结果意味着，虽然MeOctIm TFSI为基础的参考电极提供样品独立和稳定的电位，他们应该谨慎使用与聚合物膜离子选择电极的测量，由于强烈的干扰MeOctIm（+）和TESI-与测量值的电动势。
Ionic liquid-based reference electrodes, especially those containing 1-octyl-3-methylimidazolium bis(tri-fluoromethylsulfonyl)imide (MeOctIm TFSI), are increasingly used in potentiometric measurements. They replace the conventional salt bridges and establish the reference potential through local partitioning of the ions of the ionic liquid between the reference membrane and the sample solution. Unless the electrochemical cell and the measurement protocol are designed appropriately, these ions can interfere with the response of ion-selective electrodes (ISEs) with polymeric membranes. This work characterizes the effect of MeOctIm TFSI on the response of K+, Na+, and Cl- ISEs with polymeric membranes. The leaching of MeOctIm TFSI from the reference membrane to the sample solution was monitored with UV-vis spectroscopy. The concentration of MeOctIm TFSI in the aqueous phase increased gradually and plateaued at approximately 1.0 mM. Concentrations as low as 100 mu M of MeOctIm TFSI caused large changes to the emf (50-150 mV) of K+, Na+, and Cl- ISEs. The presence of 10 mu M of TESI- was enough to cause Donnan failure of K+ ISEs with valinomycin as ionophore (that is, co-extraction of and K+ TESI- into the sensing membrane). Use of less lipophilic anions such as tetrafluoroborate (BF4-) or triflate (OTf-) postponed the onset of Donnan failure of cation-selective ISEs to higher concentrations of the anion, but decreased the stability in the reference potential and lifetime of the reference electrode. These results imply that although MeOctIm TFSI-based reference electrodes provide sample-independent and stable electrical potentials, they should be used with caution for measurements with polymeric-membrane ISEs, due to strong interference of both MeOctIm(+) and TESI- with measured values of emf.