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Guidelines for improving the lower detection limit of ion-selective electrodes: A systematic approach

机译：改善离子选择电极下限的指南：系统方法

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摘要

Zero-current membrane fluxes are the principal source of bias that has prohibited researchers from obtaining true, thermodynamic selectivity coefficients for membrane-based ion-selective electrodes (ISEs). They are also responsible for the mediocre detection limits historically seen with these types of potentiometric sensors. By choosing an experimental protocol that suppresses these fluxes, it becomes possible to obtain unbiased thermodynamic selectivity coefficients that are needed to produce ISEs with greatly improved detection limits. In this work, a Cs+-selective electrode based on calix[6]arene-hexaacetic acid hexaethyl ester (Cs 1) is used to systematically demonstrate how unbiased selectivity coefficients can be obtained, and how they can be used to optimize inner filling solutions for low detection limit measurements. A comparison of biased selectivity methods (e.g., classical separate solution method (SSM), fixed interference method (FIM), matched potential method (MPM)) with the unbiased modified separate solution method (MSSM) found that selectivity coefficients were underestimated in several cases by more than 4 orders of magnitude (logK(CsMg)(pot,MSSM) = - 8.7; log K-Cs,Mg(pot,SSM) = -4.5). The importance of key experimental parameters, including diffusion coefficients and diffusion layer thicknesses in the aqueous and organic phases, on the minimization of ion fluxes and the improvement of lower detection limits is also described. A dramatic reduction of membrane fluxes by the covalent attachment of a Ca2+-selective ionophore to a methyl methacrylate-decyl methacrylate (MMA-DMA) copolymer matrix is also demonstrated. The ionophore-immobilized ISE exhibited no super-Nernstian response and yielded a detection limit of 40 ppt (109 a(Ca) = - 9-0) with an inner filling solution of 1 x 10(-3) M KCl. Finally, a set of guidelines for experimental protocols leading to obtaining unbiased selectivity coefficients and producing ISEs for trace level analyses is given.
机译：零电流膜通量是产生偏差的主要来源，这已阻止研究人员获得基于膜的离子选择电极（ISE）的真实热力学选择性系数。他们还负责这些类型的电位传感器在历史上所见的中等检测极限。通过选择抑制这些通量的实验方案，可以获得具有显着提高的检测限的ISE所需的无偏热力学选择性系数。在这项工作中，使用基于杯[6]芳烃-六乙酸六乙酯（Cs 1）的Cs +选择电极来系统地证明如何获得无偏的选择性系数，以及如何将它们用于优化内填充液。低检测限测量。将有偏选择性方法（例如，经典分离方法（SSM），固定干扰方法（FIM），匹配电位方法（MPM））与无偏改进分离方法（MSSM）进行比较发现，在某些情况下选择性系数被低估了超过4个数量级（logK（CsMg）（pot，MSSM）=-8.7; log K-Cs，Mg（pot，SSM）= -4.5）。还描述了关键实验参数的重要性，包括在水相和有机相中的扩散系数和扩散层厚度，对最小化离子通量和改善较低检测限的重要性。还证明了通过将Ca2 +选择性离子载体共价附接到甲基丙烯酸甲酯-甲基丙烯酸癸酯（MMA-DMA）共聚物基质上，膜通量显着降低。离子载体固定的ISE没有超能斯特反应，检测限为40 ppt（109 a（Ca）=-9-0），内部填充溶液为1 x 10（-3）M KCl。最后，给出了一组用于获得无偏选择性系数并产生痕量水平分析的ISE的实验方案指南。

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