Buhlmann P, Umezawa Y, Rondinini S, Vertova A, Pigliucci A, Bertesago L
Department of Chemistry, School of Science, The University of Tokyo, Japan.
Anal Chem. 2000 Apr 15;72(8):1843-52. doi: 10.1021/ac991130x.
The lifetime of solvent polymeric ion-selective electrodes (ISEs) is limited by leaching of the membrane components into the sample solutions. In this article, leaching of charged ionophores is discussed. Because of the electroneutrality principle, the loss of the charged ionophore into the sample must be accompanied by parallel transport of an ion of the opposite charge sign into the sample or by ion exchange with a sample ion of the same charge sign. Because ionic sites of high lipophilicity are available, the loss of ionic sites is, in general, not a concern. Therefore, it is assumed here that the cotransported or ion-exchanging ions are primary or interfering ions forming complexes with the ionophore. A general theory that allows quantification of ionophore lipophilicities and a discussion of changes in the membrane composition and selectivity with time is presented. A high complex stability and high analyte concentrations diminish the rate of ionophore loss into the sample if a charged ionophore is coextracted from the membrane into the sample together with an analyte ion of opposite charge. On the other hand, if the charged ionophore has the same charge sign as the ion that it binds, a large binding constant and high analyte concentrations enhance ionophore leaching into the sample. The model is applied to interpret results for an electrically charged ionophore, for which selectivity changes as a function of the leaching time were observed and the lipophilicity was determined with potentiometric measurements. Using the lipophilicities of neutral ionophores, as described previously, and the lipophilicities of charged ionophores, as described here, a direct comparison of the expected leaching rates of charged and neutral ionophores has become possible.
溶剂聚合离子选择电极（ISEs）的使用寿命受到膜成分向样品溶液中浸出的限制。在本文中，将讨论带电离子载体的浸出问题。由于电中性原理，带电离子载体向样品中的损失必然伴随着相反电荷离子向样品中的平行传输，或者与相同电荷的样品离子进行离子交换。由于存在高亲脂性的离子位点，一般来说，离子位点的损失并不令人担忧。因此，这里假设共运输或离子交换的离子是与离子载体形成络合物的主要离子或干扰离子。本文提出了一种通用理论，该理论可以对离子载体的亲脂性进行量化，并讨论膜组成和选择性随时间的变化。如果带电离子载体与相反电荷的分析物离子一起从膜中共萃取到样品中，高络合物稳定性和高分析物浓度会降低离子载体向样品中的损失速率。另一方面，如果带电离子载体与它所结合的离子具有相同的电荷符号，大的结合常数和高分析物浓度会增强离子载体向样品中的浸出。该模型用于解释一种带电离子载体的结果，观察到其选择性随浸出时间而变化，并通过电位测量确定了其亲脂性。利用如前所述的中性离子载体的亲脂性以及本文所述的带电离子载体的亲脂性，现在可以直接比较带电和中性离子载体的预期浸出速率。
