Department of Chemistry, Nanochemistry Research Institute, Curtin University of Technology, Perth, WA 6845, Australia.
Anal Chem. 2010 Jun 1;82(11):4537-42. doi: 10.1021/ac100524z.
We are demonstrating here for the first time a thin layer coulometric detection mode for ionophore based liquid ion-selective membranes. Coulometry promises to achieve the design of robust, calibration free sensors that are especially attractive for applications where recalibration in situ is difficult or undesirable. This readout principle is here achieved with porous polypropylene tubing doped with the membrane material and which contains a chlorinated silver wire in the inner compartment, together with the fluidically delivered sample solution. The membrane material consists of the lipophilic plasticizer dodecyl 2-nitrophenyl ether, the lipophilic electrolyte ETH 500, and the calcium ionophore ETH 5234. Importantly and in contrast to earlier work on voltammetric liquid membrane electrodes, the membrane also contains a cation-exchanger salt, KTFPB. This renders the membrane permselective and allows one to observe open circuit potentiometric responses for the device, which is confirmed to follow the expected Nernstian equation. Moreover, as the same cationic species is now potential determining at both interfaces of the membrane, it is possible to use rapidly diffusing and/or thin membrane systems where transport processes at the inner and outer interface of the membrane do not perturb each other or the overall composition of the membrane. The tubing is immersed in an electrolyte solution where the counter and working electrode are placed, and the potentials are applied relative to the measured open circuit potentials. Exhaustive current decays are observed in the range of 10 to 100 muM calcium chloride. The observed charge, calculated as integrated currents, is linearly dependent on concentration and forms the basis for the coulometric readout of ion-selective membrane electrodes.
我们首次展示了基于载体的液膜离子选择性电极的薄层库仑检测模式。库仑法有望实现稳健、无需校准的传感器设计，这对于现场难以或不希望进行重新校准的应用特别有吸引力。这种读出原理是通过用掺杂有膜材料的多孔聚丙烯管来实现的，管内有一个氯银丝，并在内腔中输送流体样品溶液。膜材料由亲脂性增塑剂十二烷基 2-硝基苯醚、亲脂性电解质 ETH 500 和钙离子载体 ETH 5234 组成。重要的是，与早期关于伏安法液膜电极的工作相比，该膜还包含一种阳离子交换剂盐 KTFPB。这使得膜具有选择性，并允许观察到设备的开路电位响应，这被证实符合预期的能斯特方程。此外，由于相同的阳离子现在在膜的两个界面处都是电位决定的，因此可以使用快速扩散和/或薄膜系统，其中膜内和外界面的传输过程不会相互干扰或改变膜的整体组成。该管浸入电解质溶液中，其中放置了对电极和工作电极，并相对于测量的开路电位施加电势。在 10 到 100 μM 氯化钙范围内观察到了详尽的电流衰减。观察到的电荷，通过积分电流计算得出，与浓度呈线性相关，这是离子选择性膜电极的库仑读出的基础。
