Residues and Resource Reclamation Centre (R3C), Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, 637141 Singapore.
School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore.
ACS Sens. 2024 Aug 23;9(8):3870-3876. doi: 10.1021/acssensors.4c01673. Epub 2024 Aug 8.
Ion-selective electrodes (ISEs) have widespread use in the fields of clinical and environmental analyses. Tetrahydrofuran (THF) is the most used solvent for the preparation of modern ISEs, equipped with ion-selective membranes (ISMs). Until now, the influence of impurities in THF toward potentiometric instability of ion-selective membrane based ISEs was probably associated with the presence of either residual water or peroxide. To address this issue, most literature recommends redistilling THF prior to use in the preparation of the potentiometric membranes. Current study reveals that the actual THF impurity that is responsible for potential instability in the ISM includes products from the oxidation of THF, which contains the hydroxyl group and possibly carbonyl group with a boiling point of above 200 °C. The density functional theory calculation supported pathway of the chemical reaction of THF oxidation, hence, the chemical structure of the uncertain impurities was predicted. The underlying reason for the deteriorating potential stability of the ISEs is proposed as the significant hydrophilicity of these impurities that affect the partitioning of the ion sensing components in the membrane, thus enhancing the leaching of the membrane components from the membrane phase. This finding explains why redistillation of aged THF is advised.
离子选择性电极（ISEs）在临床和环境分析领域得到了广泛的应用。四氢呋喃（THF）是制备现代 ISE 所使用的最常用的溶剂，配备有离子选择性膜（ISMs）。到目前为止，THF 中的杂质对基于离子选择性膜的 ISE 电化学不稳定性的影响可能与残留水或过氧化物的存在有关。为了解决这个问题，大多数文献建议在制备电位膜之前对 THF 进行再蒸馏。本研究表明，导致 ISM 中潜在不稳定性的实际 THF 杂质包括 THF 氧化产物，其中含有沸点高于 200°C 的羟基和可能的羰基。密度泛函理论计算支持 THF 氧化的化学反应途径，因此预测了不确定杂质的化学结构。提出 ISE 电位稳定性恶化的根本原因是这些杂质具有显著的亲水性，这会影响膜中离子传感成分的分配，从而增强膜成分从膜相中的浸出。这一发现解释了为什么建议对老化的 THF 进行再蒸馏。
