Bakker Eric, Bhakthavatsalam Vishnupriya, Gemene Kebede L
Department of Chemistry, 560 Oval Drive, Purdue University, West Lafayette, IN 47907, USA.
Talanta. 2008 May 15;75(3):629-35. doi: 10.1016/j.talanta.2007.10.021. Epub 2007 Oct 18.
For about 100 years, potentiometry with ion-selective electrodes has been one of the dominating electroanalytical techniques. While great advances in terms of selective chemistries and materials have been achieved in recent years, the basic manner in which ion-selective membranes are used has not fundamentally changed. The potential readings are directly co-dependent on the potential at the reference electrode, which requires maintenance and for which very few accepted alternatives have been proposed. Fouling or clogging of the exposed electrode surfaces will lead to changes in the observed potential. At the same time, the Nernst equation predicts quite small potential changes, on the order of millivolts for concentration changes on the order of a factor two, making frequent recalibration, accurate temperature control and electrode maintenance key requirements of routine analytical measurements. While the relatively advanced selective materials developed for ion-selective sensors would be highly attractive for low power remote sensing application, one should consider solutions beyond classical potentiometry to make this technology practically feasible. This paper evaluates some recent examples that may be attractive solutions to the stated problems that face potentiometric measurements. These include high-amplitude sensing approaches, with sensitivities that are an order of magnitude larger than predicted by the Nernst equation; backside calibration potentiometry, where knowledge of the magnitude of the potential is irrelevant and the system is evaluated from the backside of the membrane; controlled current coulometry with ion-selective membranes, an attractive technique for calibration-free reagent delivery without the need for standards or volumetry; localized electrochemical titrations at ion-selective membranes, making it possible to design sensors that directly monitor parameters such as total acidity for which volumetric techniques were traditionally used; and controlled potential coulometry, where all ions of interest are selectively transferred into the ion-selective organic phase, forming a calibration-free technique that would be exquisitely suitable for remote sensing applications.
在大约100年的时间里，离子选择性电极电位分析法一直是主导的电分析技术之一。尽管近年来在选择性化学和材料方面取得了巨大进展，但离子选择性膜的基本使用方式并未发生根本性改变。电位读数直接与参比电极的电位相互依赖，这需要进行维护，并且几乎没有提出被广泛接受的替代方案。暴露电极表面的污垢或堵塞会导致观测电位发生变化。同时，能斯特方程预测的电位变化非常小，对于浓度变化两倍左右的情况，电位变化在毫伏量级，这使得频繁重新校准、精确的温度控制和电极维护成为常规分析测量的关键要求。虽然为离子选择性传感器开发的相对先进的选择性材料对于低功耗遥感应用极具吸引力，但人们应该考虑超越传统电位分析法的解决方案，以使这项技术切实可行。本文评估了一些最近的例子，它们可能是解决电位测量所面临上述问题的有吸引力的解决方案。这些方案包括高振幅传感方法，其灵敏度比能斯特方程预测的高一个数量级；背面校准电位分析法，其中电位大小的知识无关紧要，并且从膜的背面评估系统；离子选择性膜控制电流库仑分析法，这是一种无需标准或容量分析即可进行免校准试剂输送的有吸引力的技术；离子选择性膜处的局部电化学滴定，使得能够设计直接监测诸如总酸度等参数的传感器，而传统上使用容量技术来监测这些参数；以及控制电位库仑分析法，其中所有感兴趣的离子被选择性地转移到离子选择性有机相中，形成一种非常适合遥感应用的免校准技术。
