Effect of lipophilic ion-exchanger leaching on the detection limit of carrier-based ion-selective electrodes.
Effect of lipophilic ion-exchanger leaching on the detection limit of carrier-based ion-selective electrodes.
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DOI：
10.1021/ac010526h
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发表时间：
2001-10
影响因子：
7.4
通讯作者：
Martin Telting-Diaz and;Eric Bakker
中科院分区：
文献类型：
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作者：
Martin Telting-Diaz and;Eric Bakker
描述了亲脂性离子交换盐与离子选择性聚合物膜电极 (ISE) 的平衡分配及其对这些传感器检测下限的可能影响。基于各种参数进行预测，包括四苯硼酸钾盐分配常数的知识、无离子载体的离子交换膜的选择性以及膜中离子载体的稳定性常数。如果膜含有强烈结合初级离子的离子载体，则离子交换剂的亲脂性会显着增加。对于无离子载体的膜，预测检测限约为 10(-5)-10(-8) M，如果膜中有足够的离子载体，则可能达到低至 10(-18) M 的水平。对含有不同四苯硼酸盐衍生物的良好描述的铅选择性膜进行了实验，检测限似乎与所使用的离子交换剂无关。然而，如果膜中加入更亲水的碳硼烷阳离子交换剂，则它们会高得多。第一个发现证实了最近的理论，该理论指出，由干扰离子在样品侧进行的小水平离子交换给出的跨膜离子通量通常决定了这些传感系统的检测极限。这里列出了仅基于离子交换剂浸出的预测检测限，用于许多分析相关的情况。对于含有 BME-44 和四苯硼酸盐作为离子交换剂的钾选择性电极，实验检测限与预测值一致。这些结果表明，在最佳情况下，许多当前用于超痕量水平分析的 ISE 的检测限是由跨膜离子通量决定的。然而，由于正在开发改进的化学溶液来减少这种影响，简单的离子交换剂分配确实可能成为一种重要的机制，可以提供比实际所需更高的检测限，并且不应被排除。
The equilibrium partitioning of lipophilic ion-exchanger salts from ion-selective polymeric membrane electrodes (ISEs) and its possible effect on the lower detection limit of these sensors is described. Predictions are made on the basis of various parameters, including the knowledge of tetraphenylborate potassium salt partitioning constants, the selectivity of ionophore-free ion-exchanger membranes, and ionophore stability constants in the membrane. Ion-exchanger lipophilicities are significantly increased if the membrane contains an ionophore that strongly binds the primary ion. Predicted detection limits are on the order of 10(-5)-10(-8) M for ionophore-free membranes, and may reach levels as low as 10(-18) M with adequate ionophores in the membrane. Experiments are performed for well-described lead-selective membranes containing different tetraphenylborate derivatives, and detection limits appear to be independent of the ion-exchanger used. However, they are much higher if a more hydrophilic carborane cation-exchanger is incorporated in the membrane. The first finding confirms recent theory, which states that transmembrane ion fluxes, given by a small level of ion-exchange at the sample side by interfering ions, normally dictate the detection limit of these sensing systems. Predicted detection limits on the basis of ion-exchanger leaching alone are here listed for a number of analytically relevant cases. For potassium-selective electrodes containing BME-44 and tetraphenylborate as ion-exchanger, the experimental detection limits are in agreement with predicted values. These results suggest that the detection limit of many current ISEs for ultratrace level analysis are, in optimal cases, dictated by transmembrane ion fluxes; however, because improved chemical solutions are being developed to reduce such effects, simple ion-exchanger partitioning may indeed become an important mechanism that can give higher detection limits than practically desired, and should not be ruled out.