维生素B2的极谱催化波研究及应用

维生素B2是人和动物维持机体正常结构与功能的必需营养物质,具有广泛的生理功能。目前,测定维生素B2的方法有高效液相色谱法、荧光分析法、化学发光分析法、紫外分光光度法及电化学分析法等,而其中电化学分析法大都需要采用化学修饰电极,对电极需特殊处理,比较麻烦和费时。本文发现在KH2PO4-Na2HPO4缓冲介质中,维生素B2在-0．43V（vs．SCE）电位附近产生的还原波可被H2O2催化,产生一新的极谱催化波。通过伏安分析并结合光谱分析,本文研究并推导了该极谱催化波的产生机理,并建立了测定维生素B2的新方法。该方法简单,操作简便快速,无需对电极进行特殊处理,而灵敏度与其他电化学测定方法相当。     

Voltammetric behaviour of hyponitrite ion and its analytical applications

Hyponitrite is electrochemically oxidized at a platinized platinum microelectrode. The overall process is characterized by an appreciable overvoltage; in alkaline solution nitrite and nitrous oxide are the ultimate products. The wave is well shaped and diffusion-controlled, and can be used for the voltammetric determination of microamounts of hyponitrite. Alternatively, the oxidation of hyponitrite by hypochlorite in basic solution can be used for the direct determination of hyponitrite with amperometric end-point detection. The limits of determination of the voltammetric and amperometric methods are about 10^-4 M and 5 · 10^-4 M, respectively.     

Voltammetric behaviour of copper(iii) and its analytical applications

Copper(II) and copper(III) complexes with periodate or tellurate ligands are electroactive at a smooth platinum electrode, giving an anodic, cathodic or cathanodic wave in the presence of alkaline hydroxide solutions containing copper(II), copper(III), or copper(II)-copper(III) species, respectively. The corresponding limiting currents are diffusion-controlled. The following analytical applications are proposed: (a) amperometric titration of copper(III) solutions; (b) voltammetric determination of copper. Results of amperometric titrations of copper(III) were similar to those by an established procedure. Voltammetry of copper(II) allows the metal to be determined down to concentrations of 1·10^-5M, even in the presence of different ions; the procedure can be applied to such heat-transfer media for nuclear reactors as sodium and potassium metals and their hydroxides.     

Polarographic behaviour and hydrolysis of midazolam and its metabolites

The electrochemical behaviour of midazolam [7-chloro-5-(o-fluorophenyl)-3H-(2′- methyllimidazo) [1,5-a]-benzodiazepine was studied by polarography and cyclic voltammetry. The irreversible two-electron were is not strongly affected by the imidazole ring or the 5-o-fluorophenyl substituent, but the latter increases the rate of the hydrolysis in acidic media. Kinetic parameters are evaluated for midazolam and three of its hydroxylated metabolites. The hydrolysis is a first-order reaction initially but becomes second order. The 3-hydroxy matabolites are more easily hydrolyzed than midazolam. Midazolam (10^?4–10^?7 M) can be quanitified by using differential-pulse polarography; the detection limit is 6 × 10^?8 M.     

钼(Ⅵ)-水杨基荧光酮络合物吸附波的研究与应用

在邻苯二甲酸氢钾 HCl 乙醇 水溶液中,钼(Ⅵ) 水杨基荧光酮体系在滴汞电极上,于-1.10V(vs.SCE)处有一良好的极谱波,其二阶导数峰电流与钼(Ⅵ)在8×10-10～6×10-8mol L范围内有良好的线性关系,检出限为5×10-10mol L。研究了极谱波的性质和电极反应机理。该方法已用于水及生物样品的测定。     

Polarographic behaviour of phenothiazine

Summary Phenothiazine oxidizes at the dropping mercury electrode in waterethanolic solutions, containing 7 N sulphuric acid, giving a wave corresponding to the formation of free cation radicals.The normal potential of the system phenothiazine/radical, against the reference electrode formed from mercuric sulphate in the presence of 10 N H₂SO₄ and 30% ethanol, is –240±20 mV.In alkaline solutions of pH 12.5 phenothiazine also gives a polarographic wave. This wave corresponds to the insoluble anions of compounds formed with mercury. The conditions for the quantitative polarographic determination of phenothiazine are also given.

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Zusammenfassung Es wurde bewiesen, daß in äthanolisch-wäßrigen Lösungen, die 7 n H₂SO₄ enthalten, Phenothiazin an der Quecksilber-Tropfelektrode oxydiert wird. Als Reaktionsprodukt entsteht ein freies Kation-Radikal. Das Normalpotential des Systems Phenothiazin/Radikal gegen die gesättigte Quecksilbersulfatelektrode, die 10 n H₂SO₄ und 30% C₂H₅OH enthält, beträgt –240 ± 20 mV.In alkalischen Lösungen bei pH 12,5 konnte man eine polarographische Welle registrieren, deren Eigenschaften schwerlöslichen Anionen einer Quecksilberverbindung entsprechen.Die Bedingungen für eine quantitative polarographische Phenothiazinbestimmung werden angegeben.

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Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.     

Polarographic study of hydrogen peroxide anodic current and its application to antioxidant activity determination

Behavior of hydrogen peroxide in alkaline medium has been studied by direct current (DC) polarography with dropping mercury electrode (DME) aiming to apply it in antioxidant (AO) activity determination. Development of a peroxide anodic current having form of a peak, instead of common polarographic wave, has been investigated. As a base for this investigation the interaction of H₂O₂ with anodically dissolved mercury was followed. Formation of mercury complex [Hg(O₂H)(OH)] has been confirmed. The relevant experimental conditions, such as temperature, concentration and pH dependence, as well as time stability of hydrogen peroxide anodic current, have been assessed. Development of an AO assay based on decrease of anodic current of hydrogen peroxide in the presence of antioxidants (AOs) has been described. Under optimized working conditions, a series of benzoic acids along with corresponding cinnamate analogues have been tested for hydrogen peroxide scavenging activity. In addition, the assay versatility has been confirmed on various complex samples.     

Polarographic behaviour and determination of spironolactone

The polarographic behaviour of spironolactone in Britton-Robinson buffers containing 40% methanol as a solubilizer was studied. Over the pH range 3-12 a cathodic wave was produced. The wave was characterized as irreversible, diffusion-controlled and partially affected by adsorption phenomena. The number of electrons involved in the reduction was found by coulometric measurements at a controlled potential. A method was developed for the determination of spironolactone in tablets and the results obtained were in agreement with those obtained by the B.P. 1988 method. The mechanism of the electrode reaction is discussed.AvH scholar: 1989–1991     

Polarographic behaviour and determination of azintamide

Azintamide was found to be reduced at the dropping mercury electrode over the pH range 1.8–9.4 in Britton Robinson buffers containing 20% methanol. At pH 7.42 a well defined diffusion-controlled cathodic wave was produced. The limiting current versus concentration plot was linear over the range 0.025–1.0 mM and 0.005–1.0 mM in the DC_t and DPP modes, respectively, with a lower detection limit of 1 × 10^–7 M by the latter technique. A mechanism for the electrode reaction has been proposed. The method has been applied to the determination of azintamide in tablets, and the results obtained were in agreement with those obtained by a reference method.AvH Scholar 1989–1991.     

Polarographic behaviour of some o-hydroxyketoximes

The polarographic behaviour of three o-hydroxyketoximes, CH(3)C(6)H(3)(OH)CRNOH, where R CH(3), C(2)H(5) and C(3)H(7), has been studied in 5% ethanolic medium, with potassium chloride as supporting electrolyte. A single four-electron reduction wave is obtained which diminishes with increase in pH, being replaced by a new wave in alkaline media. A trough is formed on the limiting-current plateau at higher negative potentials. A mechanism has been proposed for the reduction at the dropping mercury electrode.     

Polarographic behaviour of n-butyl thioglycolate

The polarographic behaviour of n-butyl thioglycolate, [HSCH₂OOC(C₄H₉)] has been studied in 25% ethanol, 0.1M-KNO₃ and 0.002% Triton X-100 in the pH range 1.96–11.84 at the d.m.e. The polarograms consist of two waves, a pre-wave of constant height followed by a normal anodic wave. The electrode reaction is reversible and diffusion controlled involving one electron transfer process. The maximum number of moles adsorbed per unit area is 1.30×10^–9 mole/cm², i.e. 7.82×10¹⁴ molecules/cm², which corresponds to an area 12.84 Å per adsorbed molecule. The adsorption coefficient and molar adsorption energy have been calculated to be 43.4×10⁴ and 142.8 kcal/mole respectively. The dissociation constant (pK) of the sulphydryl group is found to be 9.4.With 1 Figure     

Polarographic catalytic wave of hydrogen

A polarographic catalytic hydrogen wave of bovine serum albumin (BSA) at about-1.80 V (vs. SCE) in NH₄Cl-NH₃ · H₂O buffer is further catalyzed by such oxidants as iodate, persulfate and hydrogen peroxide, producing a kinetic wave. Studies show that the kinetic wave is a parallel catalytic wave of hydrogen, which resulted from that hydrogen ion is electrochemically reduced and chemically regenerated through oxidation of its reduction product, atomic hydrogen, by oxidants mentioned above. It is a new type of poralographic catalytic wave of protein, which is suggested to be named as a parallel catalytic hydrogen wave.     

Polarographic behaviour and determination of beclomethasone dipropionate

The polarographic behaviour of beclomethasone dipropionate in Britton-Robinson buffers containing 40% methanol as a solubilizer has been studied. Over the pH range 1.8–12, a cathodic wave was produced, which was characterised as being irreversible, diffusion controlled and free from adsorption phenomena. The number of electrons involved in the reduction was found through comparative study with spironolactone. Using direct current polarographic mode, the limiting current concentration plot is rectilinear over the range 2.5 × 10^–5 to 4 × 10^–4 mol/1 with a detection limit of 2.5 × 10^–6 mol/1. A method has been developed for the determination of the drug in aerosols and creams, the results being in agreement with those obtained by the official method.