Study And Application Of Catalytic Voltammetry Of Oganic Compound

This paper involves two parts: Part one Documents ReviewPolarographic catalytic wave is an important branch of electroanalytical chemistry. From the literatures reported, the catalytic waves of inorganic metal ions mainly include parallel catalytic wave, catalytic wave of inorganic complex and catalytic hydrogen wave of platinum-group elements. Recently, the researching range of catalytic wave extends to organic compound. From the production mechanisms, the catalytic waves of organic compounds are divided into catalytic hydrogen wave, parallel catalytic hydrogen wave and parallel catalytic wave. The study on the catalytic wave of organic compound plays an important role in increasing analytical sensitivity, and studying electrode process and chemical reaction kinetics. The development, types and production mechanisms of the polarographic catalytic wave, and the achievement of voltammetric catalytic study of organic compound were reviewed in this part.Part two Research reportsAll the former studies on the catalytic wave were performed at mercury electrode. Mercury electrode is idea electrochemical transducer, which can realize polarization easily and have higher over-potential for hydrogen. However, mercury is toxic and would be oxidized if the potential exceed +0.4 V, which accordingly limit the uses of this kind of electrode in the study aspect of organic catalytic wave. Carbon paste electrode made of graphite powder and organic solvent has lots of merits such as low cost, convenience, nontoxicity, wider practicable potential area, properties of renewable and modifiable easily, stability in the presence of oxidant and so on. Consequently it becomes the suitable instrument to study the catalytic votammetric behavior of organic compound in the presence of oxidant.The four studies were mainly performed in this paper. Firstly, the voltammetric catalytic behavior of methyl red and oxidation of the intermediate product of its reduction in the presence of dissolved oxygen, hydrogen peroxide were studied at carbon paste electrode. It was the first time to find and study the catalytic wave of azocompound. Secondly, the voltammetric catalytic behavior of vitamin K3 bisulfite (VK3b) was studied at carbon paste electrode. The production mechanism of the catalytic wave was explored, and a novel method for the determination of VK^b was proposed. Thirdly, the polarographic behaviors and the catalytic behavior of fenofibrate under acidic, basic conditions, and in the presence of oxidant were studied at mercury electrode. Base on the catalytic wave in the presence of oxidant, a novel method for the determination of fenofibrate was established. Finally, the production mechanisms of the catalytic hydrogen wave and the parallel catalytic hydrogen wave of quaternary ammonium cationic surfactant dodecyltrimethyl ammonium chloride in the presence of H2O2 were examined at mercury electrode. The concrete contents and results as follow:1. Study on catalytic voltammetry of methyl red.In 0.2 mol/L HAc-NaAc buffer (pH 4.4), the pseudo-reversible reduction of methyl red in red quinonoid form in a 2e", 2H+ addition ended to the colorless corresponding hydrazo compound, 4'-dimethylamino hydroazobenzene-2-carboxylic acid (DAHA). When oxidant such as dissolved oxygen, hydrogen peroxide was present, DAHA was oxidized to reform the original, producing a parallel catalytic wave. The apparent rate constant k{ of the oxidation reaction of DAHA with hydrogen peroxide was 744 mol"1 L s"l. This study especially the oxidation kinetics of the reduction product of methyl red in the presence of oxidant provided some valuable information to understanding the reduction degradation process of azo compound under anaerobic/aerobic condition, which was helpful for the optimization of the degradation operation conditions.2. Study on catalytic voltammetry of vitamin K3 bisulfite(VK3b).In 0.25 mol/L HAc-NaAc (pH 4.7) buffer, when accumulation potential was +0.6 V and accumulation time was 60 s, VK^b produced a reduction wave with peak potential -0.16 V (vs. SCE) at carbon paste electrode. When H2O2 was present, the reduction wave could be catalyzed, producing a parallel catalytic wave. A catalytic square wave adsorptive stripping voltammetry, adsorptive stripping voltammetry combined with the catalytic wave and the square wave technology, for the determination of VK^b was proposed. The method could be applied to the direct determination of VK3b in clinical injections and the detection limit was 2.0xl0"7 mol/L.3. Study on polarographic catalytic wave of fenofibrate.Fenofibrate and fenofibric acid salt, its hydrolysate, contain carbonyl groups. Theywere reduced in a 2e\ 2H+ process to the corresponding alcohols and produced two reduction waves under acidic conditions. Under basic conditions, fenofibrate hydrolyzed completely to the fenofibric acid salt, only one reduction wave was observed. When K2S2O8 was present, the peak current of the reduction wave increased about 25 times, producing one sensitive catalytic wave. The detection limit of the proposed method was 4.0xl0"5 mg/mL.4. Parallel catalytic hydrogen wave of quaternary ammonium cationic surfactant.A palarographic catalytic hydrogen wave appeared at -1.49 V (vs. SCE) in the presence of quaternary ammonium cationic surfactant dodecyltrimethyl ammonium chloride in 0.4 mol/LNH3-H2O-NH4Cl (pH 9.1) buffer. When H202was present, the peak current of the catalytic hydrogen wave increased about 30 times, while the peak potential was nearly unchanged, producing a parallel catalytic hydrogen wave.5. Determination of piroxicam with 0.5th derivative anodic stripping voltammetry.In 0.4 mol/L HC1 supporting electrolyte, piroxicam produced an oxidation wave with peak potential +0.74 V (vs. SCE) at carbon paste electrode. A new method, 0.5th derivative anodic stripping voltammetry, for the determination of piroxicam based on the oxidation wave was proposed. When accumulation potential was -0.4 V and accumulation time was 30 s, the 0.5th derivative peak current of piroxicam was proportional to its concentration in the range of 4.0X10"4 ~ 2.0xl0"2 mg/mL (r = 0.999 4, n = 7). The detection limit was 2.0X10"4 mg/mL.