Electroanalytical Studies On Several Active Components Of Natural Medicine At Ploy-L-lysine Modified Electrode And Glass Carbon Electrode

In this work,an electrode modified with poly-L-lysine(PLL) and glass carbon electrode was applied to the determination of several active components of natural medicine.The major contents are described as follows:Part 1.At frist,the electrochemical behavior of baicalein(BAI) was investigated at glass carbon electrode(GCE) and poly-L-lysine modified glass carbon electrode (PLL/GCE).The result was shown that a pair reversible redox peak which wasn't emerged at GCE was observed at PLL/GCE.This indicated that PLL/GCE performed effective electrochemical response to BAI.Under optimal conditions,a good linear relationship between anodic peak current and concentration was obtained in the range of with the detection limit of 4.8×10^-8mol/L(S/N=3).The responses of repeated measurements at the renewed surface of the PLL/GCE were examined with relative standard deviation of 4.3%(n=10),respectively,indicating that the chemically modified electrode showed excellent reproducibility.The proposed method has been used to determine baicalein concentration in urine sample with satisfactory results.Part 2.The electrochemical behavior of Lu at PLL/GCE has been studied by CV. The experiments showed the good effect of accumulation on luteolin in this modified electrode.On optimal conditions,a good linear relationship between anodic peak current and Lu concentration was obtained in the range of 8.0×10^-8～1.2×10^-6mol/L and 2.0×10^-6～1.1×10^-4mol/L with the detection limit of 5.5×10^-9mol/L(S/N=3) by differential pulse voltammetry(DPV).The responses of repeated measurements at the identical and the remodified surface of PLL/GCE were examined with relative standard deviation of 3.7%(n=25) and 4.7%(n=10),respectively,indicating that the chemically modified electrode showed excellent reproducibility.The proposed method has been used to determine Lu concentration in urine samples with satisfactory results.Part 3.A new method applied to the electrochemical determination of coumarin derivatives was described by investigation of electrochemical behavior of hymecromone(Hy),coumarin-3-carboxylic acid and pteryxin at GCE in alkaline solution.The proposed method was based on the reaction of degradation in 0.2M sodium hydroxide solution at 60℃for 20 min.The electrochemical behavior of degradation product of coumain was investigated by CV at GCE.An irreversible oxidation peak was obtained in Britton-Robinson buffer solution(pH 10.6).The diffusion coefficient of Hy was calculated in pH 10.6 B-R buffer solution to be D₀= 4.84×10^-6 cm² s^-1.It can be conferred that the electrochemical oxidation of degradation product of coumarin consisted of two successive one-electron irreversible reactions at GCE and the possible reaction mechanism in the alkaline solution was proposed.Using DPV,the peak current was proportional to the concentration of Hy over the range of 8.7×10^-6～7.0×10^-4 mol/L and this method was applied to practical sample analysis.