Department of Chemistry , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States.
Anal Chem. 2018 Sep 18;90(18):11000-11007. doi: 10.1021/acs.analchem.8b02595. Epub 2018 Sep 6.
While ion-selective electrodes (ISEs) with inner filling solutions are used widely, solid-contact ISEs are better suited for miniaturization and mass manufacturing. Calibration-free measurements with such electrodes require the reproducible control of the phase boundary potential between the ion-selective membrane and the underlying electron conductor. The most promising approach to achieve this goal is based on redox buffers incorporated into the ion-selective membrane. Here we introduce the theory and present experimental data for Co(III), Co(II), Ru(II), Fe(II), and Os(II) compounds that show quantitatively how the phase boundary potential at a solid contact doped with redox-active compounds is affected by weighing errors, reagent impurities, and redox-active interferents. Perhaps surprisingly, theory predicts that there is only a minimal dependence of the phase boundary potential on the ratio of the concentrations of a pure oxidized and a pure reduced compounds if those two compounds are not a redox couple. However, theory predicts that even small redox-active impurities of those compounds shift the phase boundary potential drastically. Experimentally, a surprisingly good in-batch reproducibility was observed by us and others for solid contacts prepared to contain either only the reduced or only the oxidized species of a redox couple. This can be explained by redox-active impurities and is unlikely to be repeatable when different suppliers of reagents are used or long-term experiments are performed. This work confirms that the preferred approach to calibration-free sensing is based on redox buffers that comprise the reduced and oxidized species of a redox couple in well-controlled concentrations.
虽然内充液离子选择性电极 (ISEs) 应用广泛，但固态接触 ISEs 更适合小型化和大规模制造。此类电极进行无校准测量需要可重现地控制离子选择性膜与底层电子导体之间的相界电位。实现这一目标最有前途的方法是基于整合到离子选择性膜中的氧化还原缓冲剂。在这里，我们介绍了理论和实验数据，这些数据表明 Co(III)、Co(II)、Ru(II)、Fe(II) 和 Os(II) 化合物如何定量地影响掺杂有氧化还原活性化合物的固态接触的相界电位，包括称重误差、试剂杂质和氧化还原活性干扰物。也许令人惊讶的是，理论预测，如果两种化合物不是氧化还原对，掺杂有氧化还原活性化合物的固态接触的相界电位仅与纯氧化和纯还原化合物的浓度比存在最小的依赖关系。然而，理论预测即使是这些化合物的少量氧化还原活性杂质也会剧烈地移动相界电位。实验上，我们和其他人观察到，对于仅包含氧化还原对的还原或氧化物种的固态接触，在批次内具有令人惊讶的良好重现性。这可以用氧化还原活性杂质来解释，并且当使用不同试剂供应商或进行长期实验时，这种重现性不太可能重复。这项工作证实，无校准传感的首选方法是基于氧化还原缓冲剂，其以可控制的浓度包含氧化还原对的还原和氧化物种。
