Qin Y, Bakker E
Department of Chemistry, Auburn University, Alabama 36849, USA.
Anal Chem. 2001 Sep 1;73(17):4262-7. doi: 10.1021/ac0104126.
Ionic impurities in solvent polymeric membranes have been the main reason early ion-selective electrodes (ISEs) without added ion exchanger exhibited a functional potentiometric response. Today, knowledge of such impurities and their elimination becomes important in view of designing ISEs with low detection limits and voltammetric ion-selective electrodes, to increase operational lifetime, and to optimize sensing selectivity. Here, a potentiometric segmented sandwich membrane technique is used to study the amount and properties of impurities in situ directly in the membrane phase. This technique can be used with a number of ionophores and with different membrane matrixes and does not require specialized equipment. The concentration of anionic impurities in PVC-DOS (bis(2-ethylhexyl) sebacate) and PVC-NPOE (o-nitrophenyloctyl ether) was found to be on the order of 100 micromol/kg with membranes containing weakly binding potassium ionophores. The concentration of cation-exchanger sites of carboxylated PVC-NPOE was found to be higher (1.62 mmol/kg). Addition of the neutral lipophilic salt ETH 500 to both membrane segments had only a marginal effect on the results for PVC-NPOE membranes but had a large impact on the observed membrane potential for PVC-DOS membranes. Theory explains that the addition of such salt to membranes where ion pairing is predominant is essential for the accurate assessment of ionic impurities with this technique.
溶剂聚合膜中的离子杂质一直是早期未添加离子交换剂的离子选择性电极（ISE）呈现功能性电位响应的主要原因。如今，鉴于设计具有低检测限的ISE和伏安型离子选择性电极、延长使用寿命以及优化传感选择性，了解此类杂质及其去除方法变得至关重要。在此，采用电位分段夹心膜技术直接原位研究膜相中杂质的含量和性质。该技术可与多种离子载体以及不同的膜基质配合使用，且无需专门设备。对于含有弱结合钾离子载体的膜，发现PVC-DOS（癸二酸二（2-乙基己基）酯）和PVC-NPOE（邻硝基苯基辛基醚）中阴离子杂质的浓度约为100 μmol/kg。发现羧化PVC-NPOE的阳离子交换位点浓度更高（1.62 mmol/kg）。向两个膜段添加中性亲脂性盐ETH 500对PVC-NPOE膜的结果影响甚微，但对PVC-DOS膜观察到的膜电位有很大影响。理论解释称，向离子配对占主导的膜中添加此类盐对于用该技术准确评估离子杂质至关重要。
