The polarographic and voltammetric behaviour of acetylacetonato and hexafluoroacetylacetonato complexes in acetonitrile

The polarographic behaviour of Ce(acac)₄, Ce(acac)₃, Eu(acac)₃, Fe(acac)₃, Cr(acac)₃, Co(acac)₃, Mn(acac)₃, NaMn(acac)₃, Mn(acac)₂, Ni(acac)₂, Cu(acac)₂, VO(acac)₂, Fe(hfacac)₃, Cr(hfacac)₃ and Cu(hfacac)₂ has been studied in acetonitrile on the dropping mercury electrode. Half-wave potentials versus bisbiphenylchromium(I)/(0), the reversibility of the electrode reaction and the number of electrons participating in the electrode processes measured by coulometry are reported. Cyclovoltammetric measurements have been performed on the hanging mercury drop electrode and on the stationary platinum electrode, the data of these studies are given. quite different behaviour has been observed on the platinum electrode compared to the dropping mercury electrode. Large scale electrolysis was employed to obtain information on the reaction products. The influence of the electrode material and the reaction mechanisms are discussed.     

The polarographic and voltammetric behaviour of the copper(II) mitoxantrone complex and its analytical application

The polarographic and voltammetric behaviour of the copper(II)-mitoxantrone complex have been studied. A well-defined linear sweep voltammetric peak was obtained at -0.275 V (vs. Ag AgCl ) or -0.325 V (vs. SCE) in ammonia-ammonium chloride (20 mmoll(-1), pH 9.0). The characteristics of the peak have been examined in detail. The experimental results show that the reduction of the copper(II) mitoxantrone complex is irreversible and the peak displays adsorption characteristics at the dropping mercury electrode. A mechanism is proposed for the reduction of the complex, comprising one-electron reduction of the copper(II) of the complex, is reduced directly in the complex form. A single-sweep oscillopolarographic method was develped for the determination of copper(II). The peak current is proportional to the concentration over the range 5 x 10(-8)-2 x 10(-5) mol l(-1). The method reported here has the advantage that the interference of many common metal ions is small.     

A study of HPLC separation and spectrophotometric, polarographic and voltammetric detection of 4-substituted derivatives of N-nitroso-N-methylaniline

Optimised conditions have been found for the separation of N-nitroso-N-methylaniline derivatives substituted in the position 4 (4-R-NMA, where R =- H,- CH₃, - OCH₃, - Cl, - CN, - OH and - NO₂), using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of aqueous 0.01 mol l^–1 KH₂PO₄ with methanol (4+6) or acetonitrile (7+3), or a mixture of water, methanol, acetonitrile and 80% H₃PO₄ (200+200+200+3). Four detection techniques have been investigated: Direct UV photometry, polarography on a hanging mercury drop electrode, anodic voltammetry on a glassy carbon fibre array electrode and indirect anodic voltammetric detection after photolytic denitrosation of the analytes. The UV photometry is the most universal and yields limits of detection around 10^–6 mol l^–1. Polarography exhibits the poorest sensitivity (with a limit of detection of ca. 10^–5 mol l^–1) but it can be used for selective detection of 4-NO₂-NMA. Direct voltammetric detection is selective for the oxidizable derivatives and the limits of detection attained are lower than those obtained by UV photometry (for 4-OH-NMA) or comparable with (for 4-OCH₃-NMA). When the analytes are photolytically denitrosated to yield oxidizable derivatives, the voltammetric detection of 4-H-NMA, 4-Cl-NMA, 4-CH₃-NMA and 4-NO₂-NMA has limits of detection one order of magnitude lower than those obtained UV photometrically.     

Electrochemical behavior of atomoxetine and its voltammetric determination in capsules

In this work, the electrochemical behavior and the analytical application of atomoxetine, a selective noradrenaline reuptake inhibitor, are studied. Atomoxetine, studied by differential pulse voltammetry and cyclic voltammetry on a glassy carbon electrode, exhibited an anodic response in aqueous media with pH between 1.5 and 7. In non-aqueous medium (acetonitrile), the drug exhibited two irreversible oxidation peaks that are diffusion controlled. From chronocoulometric studies in acetonitrile, it was determined that each oxidation signal involves two and four electrons, respectively. For analytical purposes, a differential pulse voltammetry technique in 0.1 mol L⁻¹ perchloric acid was selected, which exhibited adequate figures of merit. The percent recovery was 96.6 ± 1.2 and the detection and quantitation limits were 6.9 × 10⁻⁵ and 1.0 × 10⁻⁴ mol L⁻¹, respectively. Also, results indicate that excipients do not interfere with the oxidation signal of atomoxetine, which leads to the conclusion that the developed method is satisfactorily selective for atomoxetine quantification in pharmaceuticals with no prior separation or extraction necessary. Finally, the proposed voltammetric method was successfully applied to both the assay and the uniformity content of atomoxetine in capsules. For comparison, high-performance liquid chromatography analysis was also performed.     

Voltammetric behavior of zaleplon and its differential pulse polarographic determination in capsules

In this work both the electrochemical behavior and the analysis of the hypnotic pyrazolopyrimidine derivative zaleplon were studied. Zaleplon in ethanol-0.1M Britton Robinson buffer solution (30-70) showed 2 irreversible, well-defined cathodic responses in the pH range of 2-12 using differential pulse polarography (DPP), tast polarography, and cyclic voltammetry. From chronocoulometric studies, it was possible to conclude that one electron was transferred in each reduction peak or wave. For analytical purposes, the DPP technique working at pH 4.5 for peak I was selected, which exhibited adequate repeatability, reproducibility, and selectivity. The recovery was 99.97 +/- 1.52%, and the detection and quantitation limits were 5.13 x 10(-7)M and 1.11 x 10(-6)M, respectively. The DPP method was applied successfully to the individual assay of capsules in order to verify the content uniformity of zaleplon. Treatment of the sample is not required because the excipients do not interfere, the method is not time consuming, and it is less expensive than column liquid chromatography.     

Simultaneous determination of hyoscine butylbromide and ketoprofen in pharmaceutical preparations by spectrophotometric and liquid chromatographic methods

A binary mixture of hyoscine butylbromide and ketoprofen was determined by 4 different methods. The first involved determination of hyoscine butylbromide and ketoprofen using the ratio-spectra first-derivative spectrophotometric technique at 211 and 234 nm over the concentration ranges of 2-14 and 5-45 microg/mL with mean accuracies 99.84 +/-0.92 and 99.98+/- 0.64%, respectively. The second method utilized second-derivative spectrophotometry over the concentration ranges of 2-14 and 5-35 microg/mL with mean accuracies 99.32+/- 1.06 and 99.55+/-1.15%, respectively. The third method was based on the resolution of the 2 components by bivariate calibration depending on a simple and rapid mathematical algorithm and quantitative evaluation of the absorbances at 206 and 254 nm over concentration ranges of 2-16 and 5-35 microg/mL; mean accuracies of 100.21+/-1.30 and 100.19 +/-1.07% were obtained for hyoscine butylbromide and ketoprofen, respectively. The fourth method was reversed-phase liquid chromatography using 0.05 M ammonium dihydrogen phosphate-acetonitrile-methanol (20 + 30 + 6, v/v) as the mobile phase with ultraviolet detection at 220 nm over concentration ranges of 1-90 and 5-70 microg/mL; mean accuracies were 99.92+/-1.02 and 99.61+/- 0.98%, respectively. The suggested procedures were checked using laboratory-prepared mixtures and were successfully applied for the analysis of pharmaceutical preparations. The methods retained their accuracy and precision when the standard addition technique was applied. The results obtained by applying the proposed methods were statistically analyzed and compared with those obtained by the manufacturer's method.     

New techniques in radiochemical determinations using polarographic methods

This work was undertaken as part of a research program on the development of new radio-chemical procedures. The techniques used are those of standard polarographic practices. Radio-isotopes that can be polarographically reduced to the zero oxidation state amalgamate with the mercury, are removed from the solution, and the radioactivity determined. Reproducible curves of activity vs. Ede are found to be in every way analogous to polarograms obtained under the same experimental condition. The requirements necessary for any radio-ihotope to be determined quantitatively by this method are that the radio-isotope be polarographically reduced to the zero oxidation state and that no other radio-isotope be polarographically reduced at the same potential. This type of analysis has been successfully applied to several radio-isotopes and mixtures of radio-isotopes.     

The polarographic behaviour of the antidepressant drug chlorimipramine

The polarograpbic activity of chlorimipramine is due to surface catalytic hydrogen evolution; there is no reduction of the chlorimipramine itself at the d.m.e. The occurrence of the catalytic process is confirmed by the effects of the supporting electrolyte and of the buffer pH and composition.     

Rapid titrimetric and spectrophotometric assay methods for the determination of lamivudine in pharmaceuticals using iodate and two dyes

One titrimetric and two spectrophotometric methods, which are simple, sensitive and rapid, are described for the assay of lamivudine in bulk drug and in tablet dosage forms using potassium iodate and two dyes, methyl orange and indigocarmine, as reagents. In titrimetry, an aqueous solution of lamivudine is titrated directly with iodate in an acidic medium, and in the presence of an excess of bromide using methyl orange as an indicator. After the decoloration of the red color of methyl orange, the residual bromine is titrated iodometrically to a starch endpoint. Spectrophotometric methods involve the addition of a known excess of iodate in an acidic medium and in the presence of an excess of bromide followed by the determination of residual bromine by the reaction with a fixed amount of either methyl orange and measuring the absorbance at 520 nm (method A), or indigo carmine and measuring the absorbance at 610 nm (method B). In all methods, the amount of iodate which reacted corresponds to the amount of lamivudine content. The titrimetric method is applicable over the 1.5–8.0 mg range. The systems obey Beer’s law for 0.5–5.0 μg/mL (method A) and 1.25–12.5 μg/mL (method B). The calculated apparent molar absorptivity values are found to be 3.3 × 10⁴ and 9.3 × 10³ L mol⁻¹ cm⁻¹, for method A and method B, respectively, and the corresponding Sandell sensitivity values are 6.94 and 24.62 ng/cm². The limits of detection and quantification are also reported for both spectrophotometric methods. Intra-and interday precision and accuracy for the developed methods have been evaluated. The methods were successfully applied to the assay of lamivudine in tablet form and the results were compared with those of a reference method by applying the Student’s t-test and F-test. No interference was observed from common tablet adjuvants. The accuracy and reliability of the methods were further ascertained by recovery experiments using the standard addition technique. The text was submitted by the authors in English.     

马兜铃酸A的伏安及示波极谱行为研究

马兜铃酸A(简称从)为关木通、朱砂莲等多种常用中药的主要成分。马兜铃酸A具有抗癌、抗感染、抗早孕及增强吞噬细胞活性等方面的药理作用,可作为含量测定指标,其对肝、肾的毒性为有效剂量的1000倍,在医药上它已得到广泛的药理应用。鉴于生物体内的氧化还原过程和电化学过程都具有电子传递的共性,研究马兜铃酸A的电化学性能具有特殊重要的意义。     

A spectrophotometric and polarographic investigation of three new cyclohexene-substituted benzodiazepines

Three recently introduced benzodiazepine derivatives, tetrazepam (I), nortetrazepam (II) and menitrazepam (III) have been subjected to spectral and polarographic investigation. From the ultraviolet spectral data their pK(a)-values have been determined: 4.28 (I), 4.3 (II) and 3.5 (III). From the polarographic measurements it can be concluded that in I and II the 4,5 CN double bond is reduced with 2 electrons. For the first time for the benzodiazepine series it has been observed that in slightly alkaline solutions this process takes place in two separate 1-electron steps. In III, first the aromatic nitro group is reduced to a hydroxylamine group, then at more negative potentials the CN double bond is also reduced; its reduction wave mostly coalesces with that for the 6-electron reduction of the nitro group to an amino group. A differential pulse polarographic method is presented, for the determination of I, II, III at concentrations as low as 10(-7)M.     

Different spectrophotometric methods for antioxidant activity assay of four Romanian herbs

The present study investigates the antioxidant activities of some Romanian plants, using different spectrophotometric methods (FRAP I, FRAP II, and CUPRAC). The plants investigated are hawthorn (Crataegus oxyacantha), bilberry (Vaccinium myrtillus L.), rosehip (Rosa canina), and chokeberries (Aronia melanocarpa). Hawthorn is used to treat a wide variety of inflammatory conditions, but the primary use is generally restricted for treating hypertension, ischemic heart disease, congestive heart failure, and arrhythmia. Investigations have proved the safe and reliable use of plant and plant extracts for treatment of cardiovascular disorders.     

Modulated polarographic and voltammetric techniques in the study of natural water chemistry

Modulated polarographic and voltammetric techniques are of particular importance in natural water chemistry because of their sensitivity not only to very low concentrations of electroactive components but also to their chemical form. Direct polarographic techniques are most useful for the analysis of non-metallic components at low concentrations since metal levels are only rarely high enough for the analysis of untreated samples. Preconcentration by chemical or electrochemical techniques have both been employed. Potentially the most productive field of application of polarographic and voltammetric methods is in determining the chemical speciation of electroactive components in natural waters. Some clarification is required of the chemical and biological significance of operational classifications currently employed. Intermetallic interferences and the influence of surface films on electrode behaviour need to be more thoroughly investigated before analyses or speciation studies on untreated samples can be routinely undertaken. Chemical and electrochemical understanding rather than increased sophistication in the instrumentation is required at this stage if full advantage is to be taken of the capabilities of modulated polarographic and voltammetric methods in natural water chemistry.     

紫外分光光度法表征Lipozyme TL IM脂肪酶转酯化活性

建立了一种新的有机相脂肪酶转酯化活性测定方法. 以正己烷为溶剂,脂肪酶催化棕榈酸对硝基苯酯和正丁醇的转酯化反应为模型反应,通过测定反应液中310 nm下吸光值的变化计算反应转化率. 以气相色谱法对新建的紫外分光光度法进行验证,分别采用这两种方法测定了七种商品化脂肪酶的转酯化活性,两种方法所得实验结果基本一致. 利用紫外分光光度检测法考察了Lipozyme TL IM脂肪酶催化转酯化的时间进程及合成活性与酶量的关系,并对Lipozyme TL IM催化转酯化的性质（最适溶剂、酰基受体特异性、醇耐受性、最优反应温度和热力学稳定性）进行了表征.     

Adsorptive voltammetric behaviour of immunoglobulin M

The adsorptive voltammetric behaviour of immunoglobulin M (IgM) has been investigated at the static mercury drop electrode. The stripping process yields an analytically useful signal and the detection limit is 1.2 x 10(-10)M. The adsorptive voltammetric behaviour of IgM has been compared with that of IgG and streptavidin.     

The polarographic behaviour of tungstate at the dropping mercury electrode

Summary The polarographic behaviour of W(VI) is investigated in some supporting electrolytes of varying H⁺ concentration. In HCl solution the reduction yields two waves; the first one is essentially reversible and corresponds to the process W(VI) W(V). The second one is irreversible and composed of two strongly overlapping waves representing the stepwise reduction of W(V) to W(III). In H₂SO₄ solution, three irreversible waves of almost equal heights are observed. The reduction in H₃PO₄ solution indicated that different types of phosphotungstic acid (PTA) are formed which change to either a mixture of 9- and 12-PTA or to 9-PTA only, depending on the H₃PO₄ concentration. In HCl or H₃PO₄ solutions i _l is a linear function of the W(VI) concentration.

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Zusammenfassung Das polarographische Verhalten von Wolframat ist in einigen Trägerlösungen verschiedener H⁺-Konzentration untersucht worden. In HCl-Lösung ergibt die Reduktion zwei Stufen. Die erste Stufe ist reversibel und stellt die Reduktion W(VI) W(V) dar, während die zweite dem Reduktionsverlauf W(V) W(III) entspricht und aus zwei stark über-lappenden Stufen besteht. In H₂SO₄-Lösung sind drei Stufen mit fast gleichen Höhen zu erkennen. In H₃PO₄-Lösung scheint aus dem polarographischen Verhalten von Wolframat hervorzugehen, daß verschiedene Formen der Wolframatophosphorsäure (WPS) gebildet werden, welche sich entweder in eine Mischung der 9- und 12-WPS oder nur in die 9-WPS umwandlen. Die Art der Umwandlung hängt von der H₃PO₄-Konzentration ab. Der Grenzstrom in HCl- und H₃PO₄-Lösungen ist eine lineare Funktion der W(VI)-Konzentration.