Detection Of Several Drug/Biological Small Molecules By High-performance Liquid Chromatography And Electrochemical Techniques

Because of its high sensitivity, good selectivity, fast response, low cost, high performance liquid chromatography-electrochemical detector (HPLC-ECD) has been widely used in the fields of medicine, biology, chemistry and the environment science. Graphene as a relatively new carbon nanomaterial has been widely used in electrochemical biosensing due to its excellent electrochemical properties. In this thesis, we briefly review the applications of HPLC-ECD in pharmaceutical analysis and of graphene composites in biosensing and prepared a wall-jet/thin-layer electrochemical detector and several graphene composites for analysis of several drug/biological small molecules.1. High-performance liquid chromatography (HPLC) with gradient elution was coupled to a glassy carbon electrode (GCE)-based wall-jet/thin-layer electrochemical detector (ECD) for the simultaneous analysis of isoniazid (INH) and rifampicin (RIF). The simultaneous HPLC-ECD analysis of INH and RIF was performed on a reversed phase C18column (150mm×4.6mm,5μm) using a gradient elution program at a flow rate of1.0mL min-1, by HPLC-UV detector at a wavelength of268nm and by HPLC-ECD with a working potential of0.9V vs SCE. Linear calibration plots for INH and RIF were obtained in the range of0.01-100μM for INH and RIF. Our wall-jet/thin-layer ECD gave limits of detection (LODs) of0.3and0.5nM (S/N=3) for INH and RIF, respectively, which are lower than those obtained with the UV-vis detector and a commercial electrochemical detector. Our method was successfully applied for the simultaneous determination of INH and RIF in an antitubercolosis drug and urine substrate samples.2. An ERGO/GCE was prepared by cyclic voltammetric deposition of electroreduced graphene oxide (ERGO) on a glassy carbon electrode (GCE), and the Aucs/ERGO/GCE were then fabricated via Au-Cu co-electrodeposition followed by electrochemical stripping of Cu. The modified electrode with wall-jet/thin-layer electrochemical detector was coupled to HPLC for simultaneous analysis of INH and RIF. Linear calibration plots for INH and RIF were obtained in the range of0.01-60μM for INH and RIF. Our wall-jet/thin-layer ECD gave LODs of0.2and0.6nM (S/N=3) for INH and RIF, respectively. The overpotential of INH was significantly reduced and the peak current of INH and RIF were increased on the modified electrode. The modified electrode exhibited good reproducibility and stability in wall-jet/thin-layer ECD and was successfully applied for the simultaneous determination of INH and RIF in an antitubercolosis drug3. Simultaneous electroanalysis of isoniazid and uric acid (UA) was achieved at a glassy carbon electrode (GCE) modified with electroreduced carboxylated graphene (ERCG) and electrosynthesized poly(sulfosalicylic acid)(PSA). Electrochemical quartz crystal microbalance was used to investigate the electrodeposition processes. The surface morphologies and electrochemical properties of the PSA/ERCG/GCE were studied by scanning electron microscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy. The electrochemical behaviors of isoniazid and UA at PSA/ERCG/GCE were investigated by CV and differential pulse voltammetry (DPV), giving well defined and mutually separated oxidation peaks of isoniazid and UA. The PSA/ERCG/GCE exhibited notably enhanced electro-oxidation signals of isoniazid and UA in NH3-NH4Cl buffer solution (pH9.0), as compared with bare GCE and PSA/GCE. Under optimum conditions, the DPV peak currents at PSA/ERCG/GCE responded linearly to isoniazid concentrations from0.05to15μM and to UA concentrations from0.02to15pM, with limits of detection of12nM for isoniazid and UA, which is better than many of reported analogues. The PSA/ERCG/GCE was successfully applied to the simultaneous determination of isoniazid and UA in urine substrate samples.