Fabrication and Optimization of Electrochemical Detector for HPLC by Use of Microhole Array Electrodes

采用碳纤维-环氧复合材料电化学刻蚀制备的微孔阵列电极作为高效液相色谱或流动注射分析的电化学检测器。对流动电池的制造和优化进行了研究。用市售的流动电池结合嵌入在环氧圆盘板上的微孔阵列电极进行检测，结果表明，对于六氰高铁离子，可以获得与流速无关的稳态电流响应，这表明，如果已知扩散系数值，则可以从电流值直接测定分析物，而无需任何校准曲线。结果表明，该探测器可用于电活性有机物质，如儿茶酚胺，如多巴胺。然而，观察到电流值的逐渐下降，因为电池的使用时间很长。为了提高探测器的灵敏度，尝试了由几十根或上百根甚至上千根碳纤维组成的微孔阵列电极的制造。结果表明，电位控制刻蚀比恒流刻蚀更有利于碳纤维的均匀刻蚀。虽然得到了蚀刻电极电位、电解时间和微孔深度之间的关系，但为了得到均匀的微孔，还需要进一步的研究。研究了用脉冲伏安法检测样品的方法，但发现双层充电电流对总电流的贡献很大，必须对蚀刻碳的表面调理进行研究。研究还发现，将某些酶固定在微孔阵列电极上，可以对流动细胞中的特定物质进行选择性检测。

Microhole array electrodes, which can be fabricated by electrochemical etching of a carbon fiber-epoxy composite, were employed as electrochemical detectors for HPLC or flow injection analysis. Fabrication and optimization of the flow cells were pursued. Examination with a commercially available flow cell in combination with a microhole array electrode embedded in an epoxy disk plate revealed that steady state current responses which are independent of the flow rate are obtained for hexacyanoferrate ions, indicating that direct determination of analyte is possible from the current value without any calibration curves if the diffusion coefficient value is known. It was shown that the detectors can be used for electroactive organic species like catecholamines such as dopamine. However, gradual depression of current values was observed for the use of the cell for a long duration. In order to increase the sensitivity of the detector, fabrication of microhole array electrodes consisting of tens of or a hundred of a thousand carbon fibers was tried. It was found that potential controlled etching is preferable for uniform etching of these carbon fibers to galvanostatic etching. Though a relation between electrode potential for etching, electrolysis time and depth of the microholes has been obtained, further study for getting uniform microholes would be required. Use of pulse voltammetry for the detection of species was also investigated but it was found that contribution of double layer charging current to the total current is large and surface conditioning of the etched carbon must be studied. It was also found that immobilization of some enzyme to the microhole array electrode makes possible a selective detection of specified species in the flow cell.