Preparation Of Carbon Nano-Composite Modified Electrodes And Their Application In Pharmaceutical Analysis

In this paper, the fabrication of carbon nano-composite modified elecrtrodes and their applications in the analysis of pharmaceutical ingredients have been studied. The reaction mechanisms of pharmaceutical ingredients at the modified electrodes were discussed. The main work was as the follows:1. Graphene (GR) sample was prepared according to the literature in this paper, and graphite raw material, graphite oxide and graphene were characterazied by infrared spectroscopy. Based on the reaction between the carboxyl groups in L-cysteine(L-Cys) and the hydroxyl radicals in graphene surface, the graphene and L-cysteine composite was pepared and dropped to the surface of a glassy carbon electrode to form a new chemical modified electrode (GR-L-Cys/GCE). The electrochemical behavior of bergenin at the modified electrode was studied. Based on this, the new method for electrochemical determination of bergenin using was established.The experimental results showed that, in0.20mol·L-1NaH2PO4-Na2HPO4(pH6.7) buffer solution, GR-L-Cys/GCE demonstrated significant catalytical effect on the oxidation reaction of bergenin, and the peak current increased about9times compared to that obtained at a bare GCE. Under the optimal conditions, a linear response of GR-L-Cys/GCE to bergenin was observed in the concentration range from3.0×10-6to1.2×10-4mol·L-1, the linear regression equation was Ip (uA)=0.3919C (μmol·L-1)+0.3236, correlation coefficient was r=0.9988, and the detection limit (S/N=3) was6.7×10-7mol·L-1. The electrocatalytic process and reaction mechanism of bergenin at GR-L-Cys/GCE was also investigated. It was showed that the electrode reaction of bergenin involved one electron and one proton transfer. This proposed method was sucessfully applied to the determination of bergenin in tablets with the recovery between97.6%-102%.2. The graphene-L-cysteine composite film modified electrode (GR-L-Cys/GCE) was prepared by electrochemical deposition method. The electrochemical behavior of levodopa at the modified electrode in the presence of the surfactants was investigated. The experimental conditions were optimized, and the method for the determination of levodopa using the modified electrode was established.It was shown that, in0.10mol·L-1Na2HPO4-citric acid buffer solution (pH2.2), GR-L-Cys/GCE demonstrated significant catalytic effect on the oxidation reaction of levodopa, and the oxidation peak current was increased about15times compared to that obtained at a bare GCE. Under the optimal conditions, a linear response of GR-L-Cys/GCE to levodopa was observed in the concentration range from4.0×10-6to2.0×10-4mol·L-1, the linear regression equation was Ipa (uA)=-0.0568C (μmol·L-1)-0.6628, the correlation coefficient was r=0.9958, and the detection limit (S/N=3) was8.7×10-7mol·L-1.The electrocatalytic process and reaction mechanism of levodopa at GR-L-Cys/GCE was also investigated. It was showed that the electrode reaction of levodopa involved one electron and one proton transfer. The proposed method was sucessfully applied to the determination of levodopa in tablets with the recovery between95.1%～104%.3. The optimal conditions of esterification reaction between graphene(GR) and L-cystine (L-CysS) was studied, and the graphene-L-cystine composite membrane formed by the esterification reaction was used to prepare glassy carbon modified electrode (GR-L-CysS/GCE), which was characterazied by infrared spectroscopy. The electrochemical behavior of isoprenaline hydrochloride at GR-L-CysS/GCE was investigated. It was shown that, in0.2mol·L-1Na2HPO4-citric acid buffer solution (pH7.4), GR-L-CysS/GCE demonstrated significant catalytic effect on the oxidation reaction of isoprenaline hydrochloride, and the oxidation peak current was increased about13times compared to that obtained at a bare GCE. Based on this the method for determination of isoprenaline hydrochloride was established.Under the optimal conditions, a linear response of GR-L-CysS/GCE to isoprenaline hydrochloride was observed in the concentration range from4.0×10-6～1.6×10-4mol·L-1, the linear regression equation was Ip (μ A)=0.3088C(μ mol·L-1)+1.4129, the correlation coefficient was r=0.9977, and the method’s detection limit (S/N=3) was8.4×10-7mol·L-1. The electrocatalytic process and reaction mechanism of isoprenaline hydrochloride at GR-L-CysS/GCE was also investigated. It was showed that the electrode reaction of isoprenaline hydrochloride involved one electron and one proton transfer. This proposed method was sucessfully applied to the determination of isoprenaline hydrochloride in injection solution with the recovery between94.9%-105%.4. The electrochemical behavior of daidzein at the multi—wall carbon nanotube modified glassy carbon electrode (MWNTs/GCE) was investigated. The experimental conditions were optimized, and the method for the determination of daidzein using the modified electrode was established.It was shown that, in NaCl(0.5mol·L-1)-H2SO4(pH=3.7) buffer solution, MWNTs/GCE demonstrated significant catalytic effect on the oxidation reaction of daidzein. Under the optimal conditions, a linear response of MWNTs/GCE to daidzein was observed in the concentration range from6.0×10-6～1.0×10-4mol-L-1, the linear regression equation was Ipa (μA)=1.4792C (μmol·L-1)+11.819, the correlation coefficient was r=0.9991, and the detection limit (S/N=3) was7.2×10-7mol·L-1. The proposed method was sucessfully applied to the determination of daidzein in tablets with the recovery between95.5%-105%.The electrocatalytic process and reaction mechanism of daidzein at MWNTs/GCE was also investigated. It was showed that the electrode reaction of daidzein involved one electron and one proton transfer.