ABSTRACT
Electrochemical detection, with limits of detection (LODs) in the subnanomolar range, is one of the most sensitive detection methods for capillary electrophoresis (CE) and microuidic chip (MC). Recent integration of MC
CONTENTS
8.1 Introduction ................................................................................................ 133 8.2 Needs and Requirements for Polyphenol Determination ................... 134 8.3 Analytical Techniques for Polyphenol Determination ......................... 135 8.4 Electrochemical Detection for CE and MC Devices ............................. 136 8.5 Recent Advancement in MC-CE Devices ............................................... 138 8.6 Design and Assembly of DOCME Detection Cell ................................ 138 8.7 Integrating DOCME with MC-CE Device for Determining
Polyphenols in Red Wine .......................................................................... 141 8.7.1 Challenges for Determining Polyphenols in Red Wine ......... 141 8.7.2 Optimization of MC-CE/DOCME Devices for Determining
Polyphenols in Red Wine ..................................................................142 8.7.3 Real Sample Application of MC-CE/DOCME Devices for
Determining Polyphenols in Red Wine .................................... 143 8.8 Summary ..................................................................................................... 146 References ............................................................................................................. 147
and CE for the development of microuidic chip-capillary electrophoresis (MC-CE) devices greatly enhances the power of either technique alone to provide the most promising detection mode for portable application. Normally, an amperometric detection mode by holding the detecting electrode at a constant potential is employed for detecting electrochemically active analytes after electrophoretic separation. The identication of an analyte depends on the migration time and repeatability of the operational conditions for CE separation. For determination of trace analytes in complex real samples, such as biouid or food containing interfering substances, additional parameters are needed for peak conrmation to reduce falsepositive results. The use of the two working electrodes operating at different potentials provides additional information based on the current ratio to assist in the identication of specic analytes eluted out from the separation capillary at the same time, hence reducing false-positive results due to comigration impurities. This enhancement is made possible by the integration of MC with separation capillary to enable repeatable alignment of the detection electrodes with the separation capillary to achieve identical environmental and operational conditions for each of the two detection electrodes. In this way, the current ratio obtained is mainly due to the difference in potential imposed on each of the two electrodes. As each substance has its specic voltage-current prole, it is possible to assess the peak purity for a specic analyte coming out from the capillary based on the ratio of the peak currents at two different potentials. Thus, detection selectivity of the dual-electrode detector is enhanced compared to single-electrode detection. The capability to detect interfering, comigrating impurities in real samples is illustrated by the detection of polyphenols in red wine by integrating dual-electrode detection with CE in the MC-CE devices fabricated.
