Development of a separation/determination method based on the quantitative controlled potential electrolysis at the aqueous/organic solution interface and its application to coulometry of ions

在此之前，库仑法仅用于易还原或氧化的物质。本工作的目的是借鉴最近发展起来的电化学方法——伏安法在水(W)和有机(O)溶液界面上的离子转移，将库仑法的领域扩展到不易还原或氧化的离子种类。(1)理论考虑快速电解被认为是精确和准确的库仑电解的必要条件，因为当电解快速时，由背景电流引起的不准确性可以减少。在这里，当W/O界面的面积(A)与样品溶液（W和/或O）的体积(V)之比(A)较大，界面处扩散层的厚度（δ）较薄时，进行快速电解。(2)电解池的发展研究发现，当W/O界面直接搅拌时，A/V比非常大，δ相当小，因此研制出了“界面搅拌电解池”。另一种电池是“流动型电解电池”。ETFC由内径1mm，外径2mm，长50cm的多孔聚四氟乙烯【〇R】管组成。将外径0.8 mm、长60 cm的镀有氯化银的银线插入Teflon^【〇R】管中。银线作为工作/参比电极。反电极是一根缠绕在管子上的银线。电解是通过将带有银电极的管浸入有机溶液(O)并迫使含水样品溶液(W)流入管和银工作/参比电极之间的间隙来进行的。四苯基硼酸盐离子选择电极设置在O中作为O中的参比电极。由于W在ECFT中流动，因此ECFT中的V/A比大，δ 6较薄。(3) ECIS和ecft的性能评价。通过改变客观离子、有机溶剂、支撑电解质、电池尺寸等条件，对ECIS和ecft的性能进行了评价，发现在o中加入离子载体，不仅可以实现疏水离子和亲水离子从W到0的库伦转移，当W中客观离子的浓度为10^<-3> M时；定量电解（超过99%的离子从W转移到O）可以在ECIS和ECFT在20分钟和1分钟内以小于1%的精度实现。这一结果表明库仑测量的范围已经扩展到离子在W/O界面上的转移。少

The coulometric determination had been applied only to species which are easily reduced or oxidized before the present work. The purpose of the present work was to expand the field of coulometry to ionic species which are not easily reduced or oxidized by referring to the recently developed electrochemical method, voltammetry for ion transfer at the interface between aqueous (W) and organic (O) solutions.(1) Theoretical considerationThe rapid electrolysis was considered to be essential for the precise and accurate coulometric electrolysis, since the inaccuracy due to the background current could be reduced when the electrolysis was rapid. Here, the rapid electrolysis is performed when the ratio of the area (A) of the W/O interface to the volume (V) of the sample solution (W and/or O) is large and the thickness (δ) of the diffusion layer at the interface is thin.(2) Development of electrolytic cellsIt was found that the ratio of A/V was extremely large and δ was considerably small when … More the W/O interface was stirred directly, and an "electrolytic cell with interfacial stirring (ECIS)" was developed. Another cell developed was a "electrolytic cell of flow type (ECFT)". The ETFC was composed of a porous Teflon【○R】 tube of 1 mm in inner diameter, 2 mm in outer diameter and 50 cm in length. A silver wire of 0.8 mm in outer diameter and 60 cm in length which was coated with silver chloride was inserted into Teflon^【○R】 tube. The silver wire worked as a working/reference electrode. The counter electrode was a silver wire wound around the tube. The electrolysis was carried out by dipping the tube with silver electrodes in an organic solution (O) and forcing an aqueous sample solution (W) to flow into the gap between the tube and the silver working/reference electrode. A tetraphenylborate ion selective electrode set in O near to the tube worked as a reference electrode in O. The V/A ratio is large with ECFT and δ 6 is thin since W flows in ECFT.(3) Evaluation of capabilities of ECIS and ECFTThe capabilities were evaluated under various conditions by changing objective ions, organic solvents, supporting electrolytes, dimensions of cells, etc, and it was found that the coulometric transfer of not only hydrophobic ions but also hydrophilic ions from W to 0 could be attained when ionophors were added in O. When the concentration of an objective ion in W was 10^<-3> M, the quantitative electrolysis (the transfer of more than 99 % of the ion from W to O) could be attained with a precision of less than 1 % within 20 min by ECIS and within 1 min by ECFT. This result indicates that the field of coulometry has been expanded to the ion transfer at the W/O interface. Less