Studies On The Adsorption Voltammetry And Adsorption Catalytic Voltammetry Of Origanic Drugs At Carbon Paste Electrodes

Carbon paste electrodes (CPE) are characteristics of low background currents and flat measure baseline over a range of the large positive potentials in aqueous solution. The paper investigates for the oxidation peaks of ofloxacin and Pipemidic acid at a CPE by adsorptive stripping voltammetry , and the electrode reaction mechanism of them was investigated. A new adsorptive catalytic voltammetry is developed for the determination of Aloe-emodin at a CPE and dissolved oxygen takes part in the reaction as an oxidant.The paper consists of three chapters.In the first chapter, a highly selective and rapid new anodic adsorptive voltammetric method has been developed for the determination of ultra trace amount of ofloxacin at a carbon paste electrode (CPE) in the current paper. The ofloxacin is adsorbed on the surface of a CPE in 0.096 mol/L KHP-NaOH buffer solution (pH5.6) yielding one oxidation peak at 0.92 V (vs.SCE) when scanning from 0.4 to 1.4 V. The relationship between the peak current and ofloxacin concentration is linear in the ranges of 5.5×10-9～5.5×10-8 mol/L(75 s accumulation) and 3.3×10-8～3.3×10-7 mol/L(30 s accumulation). The correlation coefficients are 0.9962 and 0.9983, respectively. Its detection limit is 9.0×10-10 mol/L (S/N=3) for 150 s accumulation. The relative standard deviation is 4.0﹪ for 15 successive determinations of 2.2×10-7 mol/L ofloxacin on the same electrode surface. The electrode reaction mechanism of oflocacin was investigated. The proposed method was applied to direct determinion of trace ofloxacin in the urine sample in good agreement with the results of the spectrophometric determination.In the second chapter, pipemidic acid is adsorbed on the surface of the CPE in 0.64 mol/L NH4Ac-HAc buffer solution (pH4.90) yielding one oxidation peak at 1.05 V (vs.SCE),when scanning from 0.8 to 1.8 V. The relationship between the peak current and pipemidic acid concentration is linear in the range of 2.0×10-9 to 2.0×10-7 mol/L. The correlation coefficient is 0.9964. Its detection limit is 6.0×10-10 mol/L (S/N=3) for 150 s accumulation. The RSD of 3.9﹪ is obtained for 15 determinations of pipemidic acid at 4.0×10-8 mol/L level on the same CPE surface. The electrode processes of pipemidic acid were investigated. The proposed method was applied to direct determine trace of pipemidic acid in the skipped urine samples with satisfactory results. In the third chapter, a new adsorptive catalytic voltammetry was developed for the determination of aloe-emodin at a CPE in the current paper and the oxidant of the reaction is dissolved oxygen. The second–order derivative linearly scan voltammograms of the aloe-emodin are recorded by model JP-303 polarographic analyzer from 0.0 to –1.0 V (versus, SCE). Optimal conditions are found to be: 0.56 mol/L NH4Cl-NH3.H2O buffer (pH=8.9); the accumulation potential, 0.0 V; the accumulation time, 30 s; the rest time, 10 s; the scan rate, 300 mVs-1. The peak current was linear to the aloe-emodin concentration in the range of 4.0×10-10～4.0×10-8 mol/L for 30 s accumulation. The correlation coefficient is 0.9979. The limit of detection is 9.0×10-11 mol/L(S/N=3) for 120 s accumulation. The mechanism of the electrode reaction was discussed in detail. The method was applied to the determination of aloe-emodin in the Radix rhei with satisfactory results. The experiment results were identical with the results obtained by the HPLCFrom the above, adsorption voltammetry and adsorptive catalytic voltammetry are effective methods to the determination of organic drugs at a CPE and can be applied in clinical trial. Its sensitivity is high. Discussion of the electrode processes may help to study the distribution of drugs in vivo, the regular of the charge transfer, the pharmacokinetics and structure-activity relationships of drugs and obtain the important data for the development of pharmacology.