Chronoamperometry at micropipet electrodes for determination of diffusion coefficients and transferred charges at liquid/liquid interfaces.
Chronoamperometry at micropipet electrodes for determination of diffusion coefficients and transferred charges at liquid/liquid interfaces.
复制标题
微量移液器电极上的计时电流分析法用于测定液/液界面处的扩散系数和转移电荷。
DOI：
10.1021/ac0493774
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发表时间：
2004
影响因子：
7.4
通讯作者：
S. Amemiya
中科院分区：
文献类型：
--
作者：
Yi Yuan;Lei Wang;S. Amemiya
计时电流法进行了支持在微量移液器电极的尖端的液体/液体的界面，用于直接测定的物种在外部溶液中的扩散系数。的扩散系数用于随后的测定从扩散限制的稳态电流的每个物种的转移电荷。微量移液管的大尖端电阻导致延长的充电电流，使得仅在长时间状态（通常t > 5 ms）下才能准确地测量法拉第电流。同时，在由移液管的薄玻璃壁包围的界面处的长时间电流响应通过从移液管尖端后面的物质扩散而增强。因此，长时间计时电流响应的数值模拟进行了使用有限元方法准确测定的扩散系数。通过对四乙基铵离子简单迁移的研究，验证了模拟结果的有效性。该技术被应用于天然多肽鱼精蛋白的转移/吸附反应，也为Ca 2+和Mg 2+转移促进离子载体ETH 129。鱼精蛋白的扩散系数测定为（1.2 +/- 0.1）× 10（-6）cm（2）/s，每个鱼精蛋白分子转移的离子电荷为+20 +/- 1，接近鱼精蛋白的过量正电荷。此外，测定ETH 129的扩散系数，以证明每个离子载体分子分别转移+0.67和+1电荷/Ca 2+和Mg 2+转移，这对应于与相应离子形成1：3和1：2复合物。
Chronoamperometry was carried out at liquid/liquid interfaces supported at the tip of micropipet electrodes for direct determination of the diffusion coefficient of a species in the outer solution. The diffusion coefficient was used for subsequent determination of the transferred charges per species from the diffusion-limited steady-state current. A large tip resistance of the micropipets causes prolonged charging current so that the faradic current can be measured accurately only at a long-time regime (typically t > 5 ms). At the same time, the long-time current response at the interfaces surrounded by a thin glass wall of the pipets is enhanced by diffusion of the species from behind the pipet tip. Therefore, numerical simulations of the long-time chronoamperometric response were carried out using the finite element method for accurate determination of diffusion coefficients. Validity of the simulation results was confirmed by studying simple transfer of tetraethylammonium ion. The technique was applied for transfer/adsorption reactions of the natural polypeptide protamine and also for Ca2+ and Mg2+ transfers facilitated by ionophore ETH 129. With the diffusion coefficient of protamine determined to be (1.2 +/- 0.1) x 10(-6) cm(2)/s, the ionic charge transferred by each protamine molecule was obtained as +20 +/- 1, which is close to the excess positive charge of protamine. Also, the diffusion coefficient of ETH 129 was determined to demonstrate that each ionophore molecule transfers +0.67 and +1 charge per Ca2+ and Mg2+ transfer, respectively, which corresponds to formation of 1:3 and 1:2 complexes with the respective ions.