Study Of Separationand Detection Of Quercetin And Rutin

Quercetinand rutin, the latter beingthe rutinoside ofthe former, are the most abundantnatural flavonoidantioxidants which usually coexist in some plants. There have been some reports on their electrochemical detection, but the simultaneous determination is hindered by the overlapping of their oxidation peaks. This thesisattempts to simultaneouslydetermine quercetin and rutin by using two strategies.The first one is improvement of conventional voltammetric methods by activating the electrode material or changing the solution polarity, and the second is development ofa new bipolar electrochemical method based on the gradient potential difference between the bipolar electrode and the solution.Aflake graphite electrode was pre-activated by voltammetric oxidation in Na2HCO3 solution, and used to study the redox processes of quercetin, rutin and their mixtures. In addition, we attempted to improve the adsorption and voltammetric signals of quercetin and rutin, by increasing the concentration of the supporting electrolyte and then the polarity of the solution. These measures wereadoptedin order to obtain more detailed information for the separation and detection of quercetin and rutin, and on the other hand, to aid in understanding their antioxidant activity and related pharmacological mechanisms. Four anodic peaks and six reverse cathodic peaks were observed for the multi-step redox processes of quercetinon the electrochemically pretreated flake graphite electrode, which are more than the voltammetric peaks reported in literature. The voltammetric response to the anodic switching potential, electrolyte pH, preconcentration time, scan rate and quercetin concentration were examined. A consecutive oxidation mechanism is proposed for the reactions of quercetin at the first and third anodic peaks. This study provides a significant step forward in clarifying the complex multi-step oxidation process of quercetin.Theoxidationof rutin on the pre-activated electrode showed twoenhancedanodic peaks.The results show that the pre-activated treatment improved the performance of the graphite electrode.Also, the voltammetric signals of quercetin and rutin were indeed enhanced by increasing the concentration of the supporting electrolyte. However, the problem of the peak overlapping of the two samplesremained andwas not substantially solved.A new thin-layer microfluidic microchannel bipolar electrode cell was designed according to the bipolar electrochemical principle, in order toseparate and detect the quercetin and rutin by using the gradient potential difference between the bipolar electrode and the solution in a microchannel. According to the test results, the structure of the bipolar electrochemical microchannel cell was continuously updated,and some technical problems in therunning processes of the bipolar cell were solved.The final objective of this work isnot currently achieveddue to the high exploratorynature of the research, but the results of this work provide usefulexperience and confidence for the further improvement of themicrochannel bipolar electrode cell in application of separation and detection of multicomponents.