Voltammetric sensor for tinidazole based on poly(carmine) film-modified electrode and its application

A poly(carmine) film-modified glassy carbon electrode (GCE) was fabricated and the electrochemical behavior of tinidazole at the modified electrode was investigated by electrochemical methods. A well-defined reduction peak was observed at 0.61 V and was applied for the determination of tinidazole. Compared with that at a bare GCE, the reduction peak potential of tinidazole shifted negatively and the reduction peak current increased significantly. The influences of some parameters on the reduction of tinidazole were also examined. Based on the experimental data, a possible mechanism was proposed for the electrochemical reaction of tinidazole at the modified electrode. It was found that the reduction peak current was proportional to the concentration of tinidazole in the range from 1.0 x 10(-7) to 5.0 x 10(-5)mol L(-1). The detection limit was about 1.0 x 10(-8)mol L(-1) after accumulation 90 s at a constant potential of 0.0 V. The proposed method was applied to determine tinidazole in drugs and the result was satisfied.     

替硝唑在离子液体-碳纳米管复合修饰电极上的电催化还原及电分析方法

目的研究替硝唑（TNZ）在玻碳电极（GCE）,多壁碳纳米管修饰电极（MWCNTs/GCE）及疏水性室温离子液体（RTIL）1-丁基-3-甲基咪唑六氟磷酸盐（BMIMPF6）-多壁碳纳米管（MWCNT）修饰电极（RTIL-MWCNTs/GCE）上的电化学行为,电化学动力学性质及电化学定量分析方法。方法运用循环伏安法（CV）、计时库仑法（CC）、计时电流法（CA）、方波伏安法（SWV）、稳态电流-时间曲线及电化学交流阻抗谱。结果与GCE相比,TNZ在RTIL-MWCNTs/GCE上的还原峰电位正移了105 mV,还原峰电流增大了约5倍;与MWCNTs/GCE相比,其还原峰电位稍有负移,但还原峰电流增大。TNZ在RTIL-MWCNTs/GCE上的还原峰电流与浓度在5.0×10^-5-1.0×10^-2 mol.L^-1内呈良好线性关系,检出限为2.4×10^-6 mol.L^-1。加标回收率在98.7%－100.2%之间,RSD在0.64%－1.65%之间。结论RTIL-MWCNTs/GCE对TNZ电化学还原具有良好的催化作用,是一受扩散控制的不可逆电极反应过程,该方法可用于TNZ含量的电化学定量测定,操作简便快捷,测定结果符合定量测定要求。     

Electrochemical study on the behavior of Morin and its interaction with DNA

Voltammetric behavior of Morin was studied in 0.1 M HAc–NaAc + 50 mM KCl (pH 3.4) solution at glassy carbon electrode (GCE) using cyclic voltammetry (CV). Morin showed an irreversible anodic peak at 0.720 V in CV which was involving two electrons and two protons. Also, the interaction of Morin with double-stranded calf thymus DNA (ctDNA) was studied by CV at GCE with an irreversible electrochemical equation. As a result of reaction with ctDNA, the voltammetric peak of Morin was a position shift and the peak current decreased. The diffusion coefficients of both free and binding Morin (D_f = 1.1086 × 10⁻⁷ cm² s⁻¹ and D_b = 8.2544 × 10⁻⁹ cm² s⁻¹), binding constant (K = 1.7765 × 10⁷ cm³ mol⁻¹), and binding site size (s = 0.8510) of the Morin–DNA complex were obtained simultaneously by non-linear fit analysis. The results demonstrate that Morin can bind to ctDNA in 0.1 M HAc–NaAc + 50 mM KCl (pH 3.4) solution and the ring B of Morin intercalates between the DNA base pairs.     

扁桃酸在玻碳电极上的电化学行为研究

本文采用现代电化学分析方法系统研究了扁桃酸在玻碳电极上的电化学行为。实验表明扁桃酸在玻碳电极上的氧化是不可逆过程,在pH=2.0的磷酸介质中．在玻碳电极上有一定的吸附性。实验研究了在pH=2．0条件下扁桃酸的各种电化学性质,并分别寻找到在不同条件下的定量方法．对实际样品进行了测定,方法简便、快速,结果令人满意。     

Electrochemical determination of the antidiabetic drug repaglinide

The electrochemical oxidation of repaglinide has been carried out in Britton-Robinson buffer at carbon paste and glassy carbon electrodes. Repaglinide exhibits a well-defined irreversible oxidation peak over the entire pH range (2-11). Differential pulse voltammetry was used to determine repaglinide in pure form. The peak current varied linearly in the following ranges: 8.0 x 10(-7)-3.2 x 10(-6) M and 4.0 x 10(-7)-4.0 x 10(-6) M in case of carbon paste electrode and glassy carbon electrode, respectively. In case of carbon paste electrode the limits of detection (LOD) and quantification (LOQ) were 1.348 x 10(-7) M and 4.494 x 10(-7) M, respectively. For glassy carbon electrode the LOD and LOQ were 1.062 x 10(-7) M and 3.54 x 10(-7) M, respectively. The percentage recoveries were found in the following ranges: 99.09-100.07% and 99.0-100.50% for carbon paste electrode and glassy carbon electrode, respectively. The relative standard deviations were found in the following ranges: 0.636-1.395% and 0.431-1.104% in case of carbon paste electrode and glassy carbon electrode, respectively. Differential pulse voltammetry was successfully applied for the determination of repaglinide in tablets and human serum.     

Voltammetric determination of promethazine hydrochloride at a multi-wall carbon nanotube modified glassy carbon electrode

A simple and sensitive method is described for voltammetric determination of promethazine hydrochloride (PMZ), a widely used phenothiazine drug, based on its electrochemical oxidation at a multi-wall carbon nanotube (MWCNT) modified glassy carbon electrode (GCE). Compared with bare GCE, the MWCNT-modified GCE exhibited excellent enhancement effect on the electrochemical oxidation of PMZ. PMZ yielded two anodic peaks at about 0.61 V and 0.78 V, and the peak at 0.61 V was applied to the determination. Under optimized conditions, the anodic peak current was linear to the concentration of PMZ in the range from 5.0 × 10(-8) to 4.0 × 10(-4) M with the detection limit of 1.0 × 10(-8) M. The relative standard deviation (RSD) was 2.28% for 8.0 × 10(-6) M PMZ (n = 10). To further validate its possible application, the proposed method was successfully used for the quantification of PMZ in pharmaceutical formulations and biological fluids with satisfactory results.     

Cheap and easy modification of glassy carbon electrode for voltammetric determination of dopamine in the presence of ascorbic acid

Background and the purpose of the study

Different methods have been proposed to modify glassy carbon electrode in order to determine dopamine (DA), as one of the most important neurotransmitters in central nervous systems of mammalian. These methods are time comsuming and in some cases expensive. In this work, a very simple and cheap pretreatment method is developed for the bare glassy carbon electrode (GCE) to determine DA in the presence of Ascorbic acid (AA).

Methods

Cyclic voltammetry as an electrochemical activation procedure was used for activation of glassy carbon electrode in order to separate diffrential pulse peaks of DA and AA. The effect of different parameters such as pH for supporting electrolyte, range of potential and the number of cycles were investigated. Finally, differential pulse voltammetry was used to determine DA in the presence of AA.

Results

On the activated electrode under optimum condition, anodic peak of AA shifted to negative potentials and peak current decreased, but the peak current of DA increased. The peak current was linearly proportional to the bulk concentration of DA in the range of 6.5×10⁻⁷–1.8×10⁻⁵ mol l⁻¹. The limit of detection was 6.2×10⁻⁷ mol l⁻¹.

Conclusion

A simple and cheap method was developed for the activation of glassy carbon electrode. It was possible to determine DA in the presence of AA on the treated electrode. The proposed method was used to determine DA in pharmacutical samples.     

己烯雌酚在多壁碳纳米管修饰电极上的电化学行为及其电化学测定己烯雌酚在多壁碳纳米管修饰电极上的电化学行为及其电化学测定

目的制作碳纳米管修饰电极,并研究己烯雌酚在该电极上的电化学行为。方法循环伏安法及线性扫描伏安法。结果与裸玻碳电极(GCE)比较,多壁碳纳米管修饰电极能显著提高己烯雌酚的氧化峰电流并降低其氧化电位。峰电流与己烯雌酚浓度在1×10^-8～2×10^-6 mol·L^-1有良好的线性关系,检测限为2.5×10^-9 mol·L^-1。1×10^-6 mol·L^-1己烯雌酚溶液的相对标准偏差为2.9%。结论多壁碳纳米管对己烯雌酚的电化学氧化有明显的催化作用。     

Electrochemical reduction of metronidazole at activated glassy carbon electrode and its determination in pharmaceutical dosage forms

A voltammetric method has been developed for the determination of metronidazole in dosage forms. The method is based on the electrochemical reduction of the drug at a glassy carbon electrode activated by applying a new pretreatment. The influence of pH, concentration, scan rate and presence of organic solvent and surfactant has been studied. The current is proportional to the concentration and permits the drug to be determined in the concentration range 2×10⁻⁶–6×10⁻⁴ M in Britton-Robinson buffer (pH 10). Furthermore, results obtained by the proposed method have been compared with USP XXIII procedure which involves a HPLC method.     

磺胺甲噁唑在多壁碳纳米管-Nafion修饰电极上的电催化氧化及电分析方法

运用循环伏安法(CV)、计时库仑法(CC)、计时电流法(CA)、线性扫描伏安法(LSV)及电流-时间曲线研究了磺胺甲噁唑(SMZ)在玻碳电极(GCE)及碳纳米管-Nafion修饰电极(MWCNTs-Nafion/GCE)上的电化学行为，电化学动力学性质以及电分析方法。研究结果表明，与GCE相比，SMZ在MWCNTs-Nafion/GCE上氧化峰电位负移140 mV，氧化峰电流明显增大约6倍，表明MWCNTs-Nafion/GCE对SMZ电化学氧化具有良好的催化作用。在扫描速度10～1 000 mV·s^-1时其氧化峰电流与扫描速度平方根(ν^1/2)呈良好的线性关系，表明SMZ在GCE及MWCNTs-Nafion/GCE上的伏安行为是受扩散控制的电化学过程。研究了SMZ在GCE及MWCNTs-Nafion/GCE上氧化峰电流与浓度分别在5.0×10^-5～2.5×10^-3和1.0×10^-5～6.0×10^-3 mol·L^-1呈良好线性关系，检测限分别为1.0×10^-5和5.0×10^-7 mol·L^-1。RSD在0.85%～1.98%，加样回收率在98%～101.2%。建立的SMZ含量的电化学测定方法简便快捷，测定结果令人满意。     

Differential pulse voltammetric determination of the dopaminergic agonist bromocriptine at glassy carbon electrode

The electrochemical oxidation of bromocriptine at glassy carbon electrode has been carried out in Britton-Robinson (B-R) buffer solutions in the pH range 2.0-11.0 employing cyclic, linear sweep and differential pulse voltammetry (DPV). Bromocriptine showed one well-defined oxidation peak accompanied by a smaller one. The oxidation process was found irreversible. For analytical purposes, the well-resolved diffusion controlled voltammetric peak at pH 5 was critically investigated. The linear relationship between peak current height and bromocriptine concentration allowed the differential pulse voltammetric determination of the drug over a wide concentration range, from 0.04 to 5.00 microg ml(-1) with a detection limit of 0.01 microg ml(-1). A relative standard deviation of 1.44% at 0.1 microg ml(-1) level was obtained. The proposed DPV method was successfully applied for the individual tablet assay to verify the uniformity content of bromocriptine in commercial tablets.     

Differential pulse voltammetric determination of carvedilol in tablets dosage form using glassy carbon electrode

The electrochemical oxidation of antihypertensive drug carvedilol has been studied in pH range 2.0-11.0 at a glassy carbon electrode by cyclic and differential pulse voltammetry. Two oxidation processes were produced in different supporting electrolyte media. Both oxidation processes were irreversible and diffusion-controlled. The first oxidation process was chosen for the analysis of carvedilol. A very resolved voltammetric peak was obtained in Britton-Robinson buffer at pH 8.0 using differential pulse mode. The linear response was obtained in the range of 0.25-10.00 microg ml(-1). The limit of detection was found to be 0.10 microg ml(-1). The developed method was used for the determination of carvedilol in tablet dosage form.     

Determination of olsalazine sodium in pharmaceuticals by differential pulse voltammetry

The electrochemical oxidation of olsalazine sodium was investigated by cyclic, linear sweep, differential pulse and square wave voltammetry using glassy carbon disc electrode in different buffer systems. Best results were obtained for the determination of olsalazine using the differential pulse voltammetric technique in phosphate buffer at pH 7.0. The electroactive species exhibits a diffusion-controlled voltammetric wave and its differential pulse peak current shows a linear dependence on olsalazine concentration in the range between 2 x 10(-6) M and 2 x 10(-4) M. This relationship has been applied to the determination of olsalazine in commercial capsule dosage forms. The recovery study shows good accuracy and precision for the assay developed. A UV spectrophotometric assay is also reported for comparison.     

多巴胺在导电聚合物膜修饰电极上的电化学行为及其测定

目的 建立测定神经递质药物多巴胺(DA)含量的电化学新方法 .方法 采用循环伏安法研究DA在溴百里香酚蓝(BTB)导电聚合膜修饰玻碳电极上的电化学行为,以差示脉冲伏安(DPV)法建立DA含量测定方法 .结果 在pH 5.0磷酸盐缓冲液(PBS)中,溴百里香酚蓝导电聚合物膜DA很强电催化作用,明显增强了电极反应的可逆性.在实验优化条件下,DA氧化峰电流与其浓度在8.0×10-7～6.0×10-6mol·L-1范围内呈良好的线性关系,检测限为1.0×10-8mol·L-1.结论 建立了DA定量检测的电化学新方法,并将此方法用于实际样品盐酸多巴胺注射液的含量检测,结果令人满意.     

Electrochemical study of hydroxychloroquine and its determination in plaquenil by differential pulse voltammetry

Hydroxychloroquine (HCQ) is a halogenated aminoquinoline that presents wide biological activity, often being used as an antimalarial drug. The electrochemical reduction of HCQ was investigated by cyclic voltammetry and chronoamperometry using glassy carbon electrodes. By cyclic voltammetry, in acid medium, only the cathodic peak was observed. The electrochemical behavior of this peak is dependent on pH and the electrodic process occurs through an E(r)C(i) mechanism. The electron number (1e) consumed in the reduction of HCQ was obtained by chronoamperometry. A method for the electrochemical determination of HCQ in pharmaceutical tablets was developed using differential pulse voltammetry. The detection limit reached was 11.2 microg ml(-1) of HCQ with a relative standard deviation of 0.46%. A spectrophotometric study of HCQ has been also carried out utilizing a band at 343 nm. The obtained detection limit and the relative standard deviation were 0.1 microg ml(-1) and 0.36%, respectively. The electrochemical methods are sufficiently accurate and precise to be applied for HCQ determination, in laboratorial routine, which can be used to determine the drug at low level.     

Electroanalysis of trimethoprim on metalloporphyrin incorporated glassy carbon electrode

Trimethoprim (TMP) is a bacteriostatic antibiotic mainly used in the prophylaxis and treatment of urinary tract infections. It belongs to the class of chemotherapeutic agents known as dihydrofolate reductase inhibitors. Its use is associated with idiosyncratic reactions, including liver toxicity and agranulocytosis. In order to determine TMP electrochemically, a metalloporphyrin modified glassy carbon electrode was prepared by coating [5,10,15,20‐ tetrakis(4‐methoxyphenyl) porphyrinato]Mn (III)chloride (TMOPPMn(III)Cl) solution on the surface of the electrode. The electrochemical behaviour of TMP in Phosphate buffer solution (PBS) on TMOPPMn(III)Cl modified glassy carbon electrode (TMOPPMn(III)Cl/GCE) was explored using differential pulse voltammetry (DPV). The voltammograms showed enhanced oxidation response at the TMOPPMn (III)Cl/GCE with respect to the bare GCE for TMP, attributable to the electrocatalytic activity of TMOPPMn(III)Cl. Electrochemical parameters of the oxidation of TMP on the modified electrode were analyzed. The electro‐oxidation of TMP was found to be irreversible, pH dependent and adsorption controlled on the modified electrode. It is found that the oxidation peak current is proportional to the concentration of TMP over the range 6 × 10^?8 ? 1 × 10^?6 M with a very low detection limit of 3 × 10^?9 M at 2 min open circuit accumulation. The repeatability expressed as relative standard deviation (RSD) for n = 9 was 3.2% and the operational stability was found to be 20 days. Another striking feature is that equimolar concentration of sulfamethoxazole did not interfere in the determination of TMP. Applicability to assay the drug in urine and tablet samples has also been studied. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrochemical characteristics of zafirlukast and its determination in pharmaceutical formulations by voltammetric methods

Simple, rapid, reliable and fully validated voltammetric methods were developed for the determination of zafirlukast in pharmaceutical formulations, based on its electrochemical reduction at a hanging mercury drop electrode. Its electrochemical behavior in borate buffer (pH 8.0) was investigated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The linear sweep voltammetric study of zafirlukast was carried out using glassy carbon electrode. A well-defined cathodic peak at -1326 mV without the adsorptive accumulation time and at -1312 mV with 20 s of accumulation time versus Ag/AgCl reference electrode in square-wave and square-wave adsorptive stripping voltammetric methods, respectively, was observed. The experimental and instrumental parameters affecting the peak current of zafirlukast were investigated and optimized for the zafirlukast determination. The detection limits of square-wave and square-wave adsorptive stripping voltammetric methods were 50 and 5 ngmL(-1) with R.S.D. of 6.79 and 5.72%, respectively. The methods showed good sensitivity, accuracy, precision, selectivity, robustness and ruggedness. The proposed methods were applied for the determination of zafirlukast in its pharmaceutical formulations. The results obtained from developed methods were compared with a spectrophotometric method reported in the literature and no significant difference was found statistically.     

玻碳电极吸附伏安法测定泰尔登

泰尔登,化学名2-氯-N,N-二甲基噻吨-△~9丙胺,为噻吨类抗精神病药物的主要品种,临床治疗精神分裂症,效果较好,但有关该药物的分析报道甚少。本文首次提出了泰尔登的电化学分析方法——玻碳电极吸附伏安法。作者曾用碳糊电极测定了吩噻嗪类药物,但用该电极测定泰尔登时,却因不能有效富集而未获成功。实验中发现,泰尔登在玻碳表面有强烈的吸附作用,并能在电极上发生氧化反应,溶出峰电流和浓度呈线性关系。本文     

Voltammetric determination of chlorogenic acid in pharmaceutical products using poly(aminosulfonic acid) modified glassy carbon electrode

In this work, a poly(aminosulfonic acid) modified glassy carbon electrode was fabricated and the electrochemical behavior of chlorogenic acid (CGA) was studied by cyclic voltammetry. Compared with a bare glassy carbon electrode, the modified electrode exhibits excellent catalytic effect on the electrochemical redox of CGA. Utilizing this catalytic effect, a sensitive and selective electrochemical method for the determination of CGA was developed. The analytical parameters were optimized. Under the optimized conditions, the oxidation peak current is linearly proportional to the concentration of CGA in the range from 4.00 × 10⁻⁷ to 1.20 × 10⁻⁵ mol/L and the detection limit is 4.00 × 10⁻⁸ mol/L. Further, the performance of the proposed method has been validated in terms of linearity (r = 0.9995), recovery (96.3–102.8%), reproducibility (RSD ＜ 4.0%, n = 6) and robustness. The developed method has been successfully applied for the determination of CGA in a variety of pharmaceutical products.     

Electrochemical and Spectroelectrochemical Behavior of the Main Photodegradation Product of Nifedipine: The Nitrosopyridine Derivative

Purpose. To characterize the electrochemical behavior of the photodegradation product of nifedipine, i.e., 2,6-dimethyl-4-(2-nitrosophenyl)-3,5-pyridine-carboxylic acid dimethyl ester (NPD) in different electrolytic media. We also evaluated the interaction between free radicals generated from NPD and xeno/endobiotics. Methods. Tast polarography, differential pulse polarography, and cyclic voltammetry were used for the characterization. Controlled potential electrolysis and ultraviolet-visible spectroscopy were used to generate and to detect the nitroso radical anion. Results. In protic media, the NPD derivative gave a reversible well-defined peak either on Hg or glassy carbon electrodes in a reaction involving two electrons and two protons to give the hydroxylamine derivative. In mixed aqueous-organic media (pH 9) and in aprotic media, nitroso radical anion was isolated and characterized, exhibiting second-order dimerization rate constant (k₂) values of 11,300 ± 210 [Ms]^–1 and 8,820 ± 78 [Ms]^–1, respectively. Reactivity of the nitroso radical anion with relevant pharmacologic targets revealed a significant interaction with the tested endo/xenobiotics (cysteamine, GSH, N-acetylcysteine, and adenine). Conclusions. Both in mixed and aprotic media, NPD generated free-radical species, the nitroso radical anion. Taking into account their respective interaction rate constants, the following tentative rank order of reactivity can be established as follows: cysteamine > N-acetylcysteine > GSH > adenine.