College of Chemical Engineering, Sichuan University, Chengdu, China.
Anal Chem. 2012 Sep 18;84(18):7771-8. doi: 10.1021/ac3011507. Epub 2012 Aug 28.
Liquid-junction-free reference electrodes that contact the sample through an ionic-liquid-doped, hydrophobic polymer membrane have attracted attention because they offer an alternative to reference electrodes with conventional salt bridges. In this work, liquid-junction-free reference electrodes were developed using plasticized poly(vinyl chloride) membranes doped with the ionic liquid (IL) 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide. Three-dimensionally ordered macroporous (3DOM) carbon substrates infused with this ionic liquid phase were used as solid contacts for these reference membranes. As in prior work with ionophore-based 3DOM carbon-contact ion-selective electrodes, the long-term stability of the liquid-junction-free reference electrodes was excellent, with potential drifts as low as 42 μV/h over 26 days. Successful measurements of pH in milk were performed and, to the best of our knowledge, are the first example of the use of liquid-junction-free reference electrodes in complex real-life samples. A thorough analysis of their performance at low pH revealed protonation of the ionic liquid anion (L(-)) and formation of LHL(-) type of associates in the reference electrode membrane, effects not observed in prior work. Also, when reference membranes were mounted into conventional electrode bodies with inner filling solutions that contained no ionic liquid ions, zero-current ion fluxes across the sample/membrane interface occurred, as previously only seen for ionophore-doped ion-selective membranes. Understanding these effects will be crucial to the design of liquid-junction-free reference electrodes suitable for other applications.
无液接界参考电极通过离子液体掺杂疏水性聚合物膜与样品接触，引起了人们的关注，因为它们提供了一种替代传统盐桥参考电极的方法。在这项工作中，使用掺杂离子液体（IL）1-甲基-3-辛基咪唑双（三氟甲烷磺酰基）亚胺的增塑聚氯乙烯（PVC）膜开发了无液接界参考电极。这种离子液相注入的三维有序大孔（3DOM）碳基质被用作这些参考膜的固体接触。与基于离子载体的 3DOM 碳接触离子选择性电极的先前工作一样，无液接界参考电极的长期稳定性非常出色，在 26 天内电位漂移低至 42 μV/h。成功地对牛奶中的 pH 值进行了测量，据我们所知，这是首次在复杂的实际样品中使用无液接界参考电极。对其在低 pH 值下的性能进行了彻底分析，结果表明在参考电极膜中离子液体阴离子（L(-)）质子化并形成 LHL(-)型缔合物，这是在先前工作中未观察到的现象。此外，当参考膜安装到常规电极体中，内部填充溶液中不含离子液体离子时，样品/膜界面会发生零电流离子通量，这与之前仅在离子载体掺杂的离子选择性膜中看到的情况相同。理解这些效应对于设计适用于其他应用的无液接界参考电极至关重要。
