Optimization of Electrode Alignment for Electrochemical Detection in Capillary Electrophoresis Using a Scanning Electrochemical Microscope

Electrochemical detection in capillary electrophoresis requires decoupling the voltage applied to the working electrode from the separation voltage applied across the capillary. End‐capillary electrochemical detection achieves this by placing the electrode just outside the ground end of the separation capillary. Obtaining adequate signal‐to‐noise in this arrangement requires using small inner diameter capillaries. Decreasing the inner diameter of the separation capillary, however, increases the difficulty of aligning the microelectrode with the open end of the capillary. Using scanning electrochemical microscopy (SECM), the position of the capillary opening is determined while electroactive material is continuously emerging from the end of the capillary. The SECM instrument is then used to place the electrode at the position of maximum current for subsequent separations. Subsequent measurements found that the best signal‐to‐noise is obtained when the detection electrode is placed directly opposite the capillary opening and just outside of the capillary opening. When the electrode is further above the opening (but still opposite the capillary opening), the signal‐to‐noise does not dramatically decrease until the electrode is more than 30 μm above the 10 μm inner‐diameter capillary.     

Performance evaluation of a capillary electrophoresis electrochemical chip integrated with gold nanoelectrode ensemble working and decoupler electrodes

This paper presents a capillary electrophoresis poly(methyl methacrylate) (PMMA) based microchip for electrochemical detection applications featuring embedded gold nanoelectrode ensemble (GNEE) working and decoupler electrodes. In fabricating the microchip, the GNEE films are pressed directly onto the metallic electrode structures using a hot embossing technique, and the microfluidic channels are then sealed using a low-temperature azeotropic solvent bonding method. The detection performance of the microchip is evaluated using dopamine and catechol analytes for illustration purposes. The experimental results show that the GNEE working electrode provides a significantly higher signal response than that obtained from a bulk gold electrode when applied to the detection of dopamine analyte. Compared to a conventional bulk palladium decoupler electrode, the GNEE decoupler electrode reduces both the amplitude of the charge current (3.5 nA vs. 18.7 nA) and the baseline drift at higher separation voltages. The measured baseline current drift for the microchip equipped the proposed GNEE decoupler electrode is around three times smaller than the microchip with the palladium decoupler electrode under the applied separation electric field from 40 V/cm to 240 V/cm. Finally, when detecting a mixture of 1mM dopamine and 1mM catechol, the calculated signal response of the microchip with a GNEE decoupler electrode is approximately five times higher than that obtained from a microchip with a bulk Pd decoupler electrode, resulting in the detection limit of 1 microM for the proposed GNEE-based microchip device. Overall, the results indicate that the proposed capillary electrophoresis-electrochemical detection (CE-ED) microchip with embedded GNEE working and decoupler electrodes provides an ideal solution for sample detection in lab-on-a-chip and micro total analysis applications.     

毛细管电泳-柱端电化学检测池的设计

在射壁式检测器的基规上,设计了一种用于毛细管电泳-电化学检测装置的检测池,巧妙地利用因表面张力现象而留驻波滴曲面的放大作用,直接调整毛细管与电极之间的相对位置,无需显微镜-微调节器装置,具有空间体积小,操作更简便的优点。     

芯片毛细管电泳电化学检测

评述了芯片毛细管电泳各种电化学检测尤其是安培检测中工作模式、工作电极、分离电流的消除、应用等方面的进展,并进行了展望。     

Incorporation of Disposable Screen‐Printed Electrodes for Use in Capillary Electrophoresis End‐Column Amperometric Detection System

The development and performance of an end‐column amperometric detection system integrated with disposable screen‐printed electrodes for capillary electrophoresis is presented. In this system, the electrode and capillary can be easily replaced and the capillary/electrode alignment procedure is straightforward. The use of easily replaceable screen‐printed electrodes offers a tremendous benefit for capillary electrophoresis applications requiring frequent replacement of the working electrode due to fouling. This simple and convenient system is very attractive for routine analyses by capillary electrophoresis with electrochemical detection. The separation and determination of uric acid in human urine is presented.     

毛细管电泳多脉冲溶出安培检测方法的研究

 摘要：将用于电化学检测的三电极与驱动电泳分离的电化学系统的接地电极在毛细管出口处的外面作适当的布置,可最大程度地减少高压电场对安培检测的干扰。多阶脉冲溶出安培检测方式提高了电流检测灵敏度,并可在一定程度上通过不同的溶出电位鉴别分离组分。将该方法应用于铜、锌、铅、铊、镉等离子的毛细管电泳分离,得到了较满意的结果。     

一种新型毛细管电泳柱端喷壁安培检测池

提出一种新型毛细管电泳柱端喷壁安培检测池。它制作简单，操作容易，具有很好的重现性和灵敏度。用这种安培检测池，可以不使用微动平台很容易地将工作电极与分离毛细管出口对准。为评价该安培检测池的分析性能，用毛细管电泳柱端安培检测法分别检测了酚、儿茶酚胺和芳香胺。考察了电动进样时间、分离电压以及毛细管出口与电极的间距对响应电流和分离效能的影响。通过对酚和儿茶酚胺测定的重现性、浓度线性范围及检出限的考察，结果表明该安培池是精密可靠的。同时，用该安培池对标准加入于血浆样品中的多巴胺（ＤＡ）、去甲基肾上腺素（ＮＥ）和原儿茶醛（ＰＡ）进行了测定，结果令人满意。     

Capillary electrophoresis coupled with electrochemical detection using porous etched joint for determination of antioxidants

Capillary electrophoresis coupled with electrochemical detection (CE-EC) for determination of antioxidants, propyl gallate (PG) and tert-butylhydroquinone (TBHQ), in cosmetic samples was proposed in this work. A porous etched joint was used to isolate the electrochemical detection from the electrophoretic high voltage. Compared with the 25 microm i.d. capillary without a decoupler in a CE-EC system, a 75 microm i.d. capillary applied in the present system gave an improvement in both sample injection and sensitivity. Moreover, the carbon fiber working electrode could be directly in touch with the end of separation capillary due to the elimination of the effect of separation voltage on the EC detection, so the alignment of working electrode and capillary became easy and the dead volume was also decreased. Baseline separation of the two antioxidants was achieved by CE in a 50 cm long x 75 microm i.d. capillary at 20 kV using 5.0 mmol L(-1) phosphate buffer (pH 8.00). 0.7 V (versus Ag/AgCl) was applied to the carbon fiber electrode for electrochemical detection. Under the optimal condition, the precisions (RSD, n=4) of peak height and migration time of PG and TBHQ were 2.39-3.59% and 0.34-0.44%, respectively. The detection limits of PG and TBHQ were 2.51x10(-6) and 4.88 x 10(-6) mol L(-1) for standard solution and 0.0751 and 0.0328 mg g(-1) for the real cosmetic samples with consumption of 0.3g sample. Analysis of TBHQ and PG in cosmetics samples was also achieved with the present system and the spiked recoveries of two analytes in cosmetics samples were in the range of 93.6-98.8%.     

Indirect Measurement of Yoctomole Alkaline Phosphatase by Capillary Electrophoresis with Electrochemical Detection

A method for indirectly detecting yoctomole (ymol) alkaline phosphatase was developed by capillary electrophoresis with electrochemical detection. In this method, disodium phenyl phosphate was used as the enzyme substrate and the product (phenol) of its hydrolysis reaction catalyzed by alkaline phosphatase was detected at the carbon fiber electrode. The optimum conditions of detection are 1.0×10^?2 mol/L Na₂B₄O₇ (pH 9.8) for the running buffer; 1.00×10^?3 mol/L disodium phenyl phosphate for the enzyme substrate; 20.0 kV for the separation voltage; 5 kV and 10 s for the injection voltage and injection time; 1.05 V (vs. saturated calomel electrode) for the detection potential and 10 min for the incubation time, respectively. In order to enhance the ratio of signal to noise, the shape and size of the working electrode, the shape of detection end of the capillary, and the capillary/electrode alignment method were studied in detail. When a single carbon fiber microcylinder electrode of 6 μm, a capillary of 10 μm ID with the etched detection end and the in‐capillary alignment were used, a ymol mass limit of detection for alkaline phosphatase was achieved.     

Capillary electrophoresis and capillary flow injection analysis with electrochemical detection

Measurements by capillary flow injection analysis (CFIA) and capillary electrophoresis (CE) in conjunction with electrochemical detection are described. The detection is based on an end-column electrode arrangement. Several novel electrodes, such as a spherical gold electrode and a dual-microdisk electrode, are presented and characterized regarding their analytical utility. In order to improve the selectivity of CFIA, dual-electrode and multiple-pulse detection are studied using couples of cyanometallates or metallocenes. Capillary electrophoretic experiments with amperometric detection are performed using 50 m i.d. capillaries without any electrical-field decoupler. The practicality and analytical characteristics of this detection strategy are illustrated for the separation of serotonin and some biological precursors and metabolites of neurotransmitter substances.     

毛细管电泳多道电化学检测器的研制及其应用

报道了毛细管电泳多道电化学检测器的研制及其应用，安培检测器和电导检测器并联在同一毛细管电泳检测系统中，在同一缓冲体系，同一工作电极下对同一复杂的分析体系同时进行电导和安培检测；整个装置综合了电导检测和安培检测两种检测器的优点，性能优良，造价低廉，对实际样品的检测取得了令人满意的结果。     

柱前衍生毛细管电泳-电化学检测组胺

本文采用邻苯二甲醛（OPA）为柱前衍生化试剂,用毛细管电泳-电化学检测（CE—ED）法测定酱油中组胺的含量。以直径300μm的碳圆盘电极为工作电极,50mmol／L硼砂（pH8．7）为运行缓冲液,对组胺和组氨酸的分离检测条件进行优化。在优化条件下,组胺和组氨酸二组分可在12min内完全分离,检出限分别为7．5×10^-7g／mL和5．0×10^-4g／mL。该方法已经成功用于实际样品的检测。     

毛细管电泳安培检测技术进展

对毛细管电泳离柱和柱端安培检测方式、不同形式电极在安培检测中的应用、安培检测在芯片毛细管电泳中的应用、安培检测池等内容进行了总结和讨论 ,并预测了安培检测技术未来发展方向     

一种基于双工作电极-双通道的毛细管电泳电化学检测系统

报道了一种双工作电极-双通道毛细管电泳电化学检测系统，实现电导和安培 同时检测或者安培与安培检测联用，使两种方法相互补充，发挥各自的优势。其中 ，工作电极与检测池的制作工艺简单，操作简便，通过不锈钢针管和毛细管作为套 管，无需三维微调装置即可简单实现双工作电极的准确放置及分离毛细管与工作电 极的准确对接，并根据分析体系的需要采用不同类型的工作电极和检测器；同时采 用复式滤波电路解决了不同检测器之间的电场叠加对输出信号的干扰问题。采用该 装置可以同时检测复杂体系中的电活性和惰性物质，或同时测定只能氧化或只能还 原的物质，还可以对具有氧化还原性质的物质进行纯度的确证。将该装置应用于实 际样品的测定，节约了分析时间，提高了分析速度，扩大了检测范围，结果令人满 意。     

A New Dual-electrode and Multi-channel Electrochemical Detection System for Capillary Electrophoresis

A new type of dual-electrode and multi-channel electrochemical detection technology for capillary electrophoresis is described in this paper.Two detectors(the amperometric detector and the conductometric detector) or two conductometric detectors are connected to the same capillary electrophoresis system.The whole system possesses the advantages of the two electrochemical detectors including sparing time,improving the analytical speed and expanding the sample range.The working electrode and detector cell are handled easily.The system was applied to sample detection with satisfactory results.     

毛细管电泳-柱端安培检测测定莲子心中荷叶碱、芦丁和金丝桃甙的含量

采用毛细管电泳-柱端安培检测测定莲子心中荷叶碱、芦丁和金丝桃甙的含量．研究了检测电位、运行缓冲液浓度和pH值,分离电压和进样时间对分离和检测的影响．以微碳圆盘电极（Ф=0.5ram）为工作电极,检测电位为＋0．95V（vs．Ag／AgCl）,pH为7．25的50mmol／L Na2B4O7和100mmol／L NaH2PO4缓冲液为运行液,当分离电压为15kV时,3种分析物在15min内完全分离．荷叶碱、芦丁和金丝桃甙的检出限（S／N=3）分别为0．02μg／mL、0．05μg／mL和0．04μg／mL．该方法已成功地应用于莲子心中上述3种活性成分的测定．     

毛细管电泳-柱端喷壁式电化学检测法用于利尿剂氢氯噻嗪和氨苯喋啶的研究

应用毛细管电泳-电化学检测法对利尿剂氢氯噻嗪和氨苯喋啶进行了研究。考察了电化学检测和电泳分离条件对氢氯噻嗪和氨苯喋啶分离、检测的影响,结果表明在最佳分离、检测条件下,两种待测物在8 min内达到基线分离。氨苯喋啶和氢氯噻嗪的检测限分别达到0.29和0.25 mg/L。对两物质于日内和日间重复测定7次,迁移时间的日内相对标准偏差(RSD)不大于1.6％,峰电流的日内RSD不大于 3.1％; 迁移时间的日间RSD不大于1.7％,峰电流的日间RSD不大于 4.9％。 将该方法用于复方氨苯喋啶成药中氨苯喋啶和氢氯噻嗪的分离和测定,成药的检测结果与标示量比较,相对误差小于4.6％。在模拟尿样中对氢氯噻嗪和氨苯喋啶进行标准溶液添加回收实验,其回收率分别为93.5%~96.7%和96.6%~97.2%,结果令人满意。     

毛细管电泳-柱端安培检测中分离毛细管与检测电极对接方式比较的研究

针对目前毛细管电泳中普遍采用的水平式和直立式两种柱端安培检测形式,在各种可能的对接角度下,以邻苯二酚、间苯二酚和对苯二酚3种二酚作为分离分析测试对象,对分离毛细管与检测电极的对接方式进行了优化比较,并对每一种对接方式的分析特性进行了测试。结果表明：在以3种典型的方式对接时,分离毛细管与检测电极为倒直立式对接时,获得的检测灵敏度最高,响应电流最大,水平式次之,直立式最小。     

Application of a Square‐Wave Potential Program for Time‐Dependent Amperometric Detection in Capillary Electrophoresis

Use of a square‐wave potential program for time‐dependent amperometric detection of analyte zones in capillary electrophoresis (CE) is described. Electrochemical detection for CE requires that the separation field be isolated from that of the electrochemical detection. This is generally done by physically separating the CE separation field from that of the detection. By applying a time variant potential program to the detection electrode, the detector current has a time dependence that can be used to help isolate the electrochemical detection current from that of the separation. When using a 20 μm inner‐diameter capillary, we find that a square‐wave potential program decreases the RMS baseline current from 4.5×10^?10 A, found with a constant potential amperometric detection, to 1.1×10^?10 A when using a square‐wave potential program. With a 75 μm inner‐diameter capillary, the improvement is even more dramatic, from 2.3×10^?9 A with amperometric detection to 2.06×10^?10 A when using a 1 Hz square‐wave potential program. When not using the time‐dependent detection with the 75 μm capillary, the analyte zones were beneath the S/N for the system and not detected. With the square‐wave potential program and time‐dependent detection, however, the analyte zones for an electrokinetic injection of 200 μM solution of 2,3‐dihydroxybenzoic acid were observed with the 75 μm inner‐diameter capillary. The improvement in the ability to discriminate the analytical signal from the background found experimentally is consistent with modeling studies.     

带有可更换半自准工作电极的集成化毛细管电泳安培检测芯片

自Woolley等首次报道集成于玻璃芯片上的微型毛细管电泳-安培检测(Chip-based capillary electrophoresis with amperometric detection,CE-AD)系统以来,CE-AD以其高效、高速、高灵敏度以及易微型化集成化等特点引起研究者的关注．在芯片上实现柱端安培检测可用直接制作在芯片上的喷(镀)膜工作电极,或采用外置的壁喷式电极。前者集成化程度高,后者的工作电极可以更换,大大提高了芯片的重复利用率。