Fabrication Of Carbon Nanomaterial-based Composite Electrodes And Their Applications In The Analysis Of Pharmaceuticals And Cosmetics

New facile approaches and two kinds of carbon-based nano-material have been successfully developed for the rapid preparation of new graphene-coated AER microspheres, graphene/EVA composite and MWCNTs/PET composite for electrochemical sensing. In our study, novel methods have been employed for the synthesis of the new carbon-based composites as well as the fabrication of electrodes. The analytical performance of these carbon-based electrodes have been demonstrated by measuring cosmetics or Chinese herbal medicine samples in connection with capillary electrophoresis (CE) and electrochemical detection (ED).In Chapter One, the types of the current carbon-based nanocomposites were briefly reviewed. Recent studies and developments on the characteristics and preparation methods of Graphene-based and CNTs-based composites and electrochemical applications of these composite electrodes were mainly discussed.In Chapter Two, Graphene-coated anion exchange resin (AER) spheres were facilely prepared based on the electrostatic interaction between graphene oxide and AER and subsequent chemical reduction. The prepared graphene-coated AER microspheres were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, etc. Moreover, they were embedded in the bores of pipette tips to fabricate disposable electrodes for electrochemical sensing and biosensing. The feasibility and performance of the novel electrodes were demonstrated by investigating the electrochemical behaviours of ascorbic acid, dopamine, uric acid, acetaminophen, aniline and glucose in combination with cyclic voltammetry and amperometry. Besides, these novel electrodes were also used for measuring parabens in combination with micellar electrokinetic chromatography. The advantages of the electrodes include ease of fabrication, low cost, pronounced electrocatalytic activity and rapid response, indicating great promise for a wide range of applications.In Chapter Three, a graphene/poly (ethylene-co-vinyl acetate) composite electrode was fabricated by melt compounding for the amperometric detection of capillary electrophoresis. The composite electrode was fabricated by packing a mixture of graphene and melted poly (ethylene-co-vinyl acetate) in a piece of fused silica capillary under heat. The structure of the composite was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy. The results indicated that graphene sheets were well dispersed in the composite to form an interconnected conducting network. The performance of this unique graphene-based detector has been demonstrated by separating and detecting rutin, quercitrin, kaempferol and quercetin in Cacumen Platycladi in combination with capillary electrophoresis. The four flavones have been well separated within 9 min in a 50 cm long capillary at a separation voltage of 12 kV using a 50 mM sodium borate buffer (pH 9.2). It showed long-term stability and repeatability with relative standard deviations of less than 5% for the peak current (n=15).In Chapter Four, a novel multiwall carbon nanotube/poly (ethylene terephthalate) (MWCNTs/PET) composite electrode was fabricated by packing a mixture of MWCNTs and melted PET in a piece of fused-silica capillary under heat. This electrode was developed for the determination of 5,7-dihydroxychromone and luteolin in peanut hulls in combination with capillary electrophoresis (CE). The results indicated that 5,7-dihydroxychromone and luteolin were well separated within 12 min in a 40 cm long capillary at a separation voltage of 12 kV using a 50 mM borate buffer (pH 9.2). It showed long-term stability and reproducibility with a relative standard deviation of 2.6% for the peak current (n=15). The relation between peak current and analyte concentration was linear over about three orders of magnitude.