In this work, we proposed a double moving redox boundary (MROB) model to realize the colorless analyte electrophoresis titration (ET) by the two steps of the redox reaction. Single MROB has been proposed for the development of ET sensing (Analyst, 2013, 138, 1137. ACS Sensor, 2019, 4, 126.), and faces great challenges in detecting the analyte without color change during redox reaction. Herein, a novel model of double-MROB electrophoresis, including its mechanisms, equations, and procedures, was developed for titration by using ascorbic acid as a model analyte. The first MROB was created with ferric iron (Fe³⁺) and iodide ion (I⁻) in which Fe³⁺ was reduced as Fe²⁺ and I⁻ was oxidized as molecular iodine (I₂) used as an indicator of visible MROB due to blue starch–iodine complex. The second boundary was then formed between the molecular iodine and model analyte of ascorbic acid. Under given conditions, there was a quantitative relationship between velocity of MROB (V_MROB(ii)) and ascorbic acid concentration (C_{Vit C}) in the double-MROB system (1/V_MROB(ii) = 0.6502C_{Vit C} + 4.5165, and R = 0.9939). The relevant relative standard deviation values of intraday and inter-day were less than ∼5.55% and ∼6.64%, respectively. Finally, the titration of ascorbic acid in chewable vitamin C tablets was performed by the developed method, the titration results agreed with those via the classic iodometric titration. All the results briefly demonstrated the validity of the double MROB model, in which Vit C was used as a model analyte. The developed method had potential use in quantitative analysis of redox-active species in biomedical samples.

中文翻译：

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用于抗坏血酸可视电泳滴定的简易双移动氧化还原边界模型

在这项工作中，我们提出了双移动氧化还原边界（MROB）模型，通过氧化还原反应的两步实现无色分析物电泳滴定（ET）。单个 MROB 已被提议用于 ET 传感的开发（Analyst, 2013, 138, 1137. ACS Sensor, 2019, 4, 126.），并且在氧化还原反应过程中检测不发生颜色变化的分析物方面面临着巨大的挑战。在此，开发了一种新的双 MROB 电泳模型，包括其机制、方程和程序，用于使用抗坏血酸作为模型分析物进行滴定。第一个 MROB 是用三价铁 (Fe ³⁺ ) 和碘离子 (I ⁻ ) 创建的，其中 Fe ³⁺被还原为 Fe ²⁺，I ⁻被氧化为分子碘 (I ₂ )，用作可见 MROB 的指示剂由于蓝色淀粉-碘复合物。然后在分子碘和抗坏血酸模型分析物之间形成第二个边界。在给定条件下，双MROB系统中MROB速度( V _MROB(ii) )与抗坏血酸浓度( C _{Vit C} )之间存在定量关系(1/ V _MROB(ii)  = 0.6502 C _{Vit C}  + 4.5165 ，R  = 0.9939）。日内和日间相关相对标准差值分别小于～5.55%和～6.64%。最后，采用所建立的方法对维生素C咀嚼片中抗坏血酸进行滴定，滴定结果与经典碘量滴定法的结果一致。所有结果简要证明了双 MROB 模型的有效性，其中使用维生素 C 作为模型分析物。所开发的方法在生物医学样品中氧化还原活性物质的定量分析中具有潜在用途。