Simultaneous electrochemical determination of three sunscreens using cetyltrimethylammonium bromide

This paper proposes a methodology based on electrochemical reduction for the simultaneous determination of three sunscreen agents, namely 4-methylbenzylidene camphor (MBC), benzophenone-3 (BENZO) and 2-ethylhexyl-4-methoxycinnamate (EHMC) by differential-pulse polarography (DPP). The highest peak currents and optimal separation of reduction peaks were obtained by using a supporting electrolyte consisted of Britton-Robinson buffer-methanol (8:2) solution at pH 4.0 and cationic surfactant 3.0 x 10(-4)mol L(-1) cetyltrimethylammonium bromide (CTAB). The methodology was validated using four commercial sunscreen preparation as a sample and the results showed high recovery rates. The efficiency of the proposed methodology was demonstrated by comparing the results obtained by DPP with those obtained by the high-performance liquid chromatography (HPLC) method.     

Polarographic determination of deltamethrin

The electrochemical characteristics of deltamethrin have been determined by means of electrochemical techniques such as d.c. polarography, cyclic voltammetry and differential pulse polarography over a wide range of pH from 2.0-12.0. The title compound exhibits a single well defined peak due to the reduction of the CC moiety present in deltamethrin. The overall reduction process is diffusion-controlled and adsorption free in nature. The variation of half-wave potential with the pH, concentration of the title compound, and other experimental conditions is described. A possible mechanism for the reduction is suggested. The number of electrons involved in the electrode reduction is two. Investigation was also undertaken for the determination of deltamethrin in vegetables and in storage bags of rice and wheat under FCI's storage system.     

Differential-pulse polarography (DPP) determination of betamethasone valerate in dosage form

The electrochemical reduction of betamethasone valerate (BV) in a pharmaceutical formulation containing neomycin has been carried out in Britton-Robinson buffer (BRB) (0.04 mol L(-1)) by differential-pulse polarography (DPP). BV exhibits a well-defined irreversible reduction peak at -1.03 V/ref. The influence of pH on the reduction of BV was studied in Britton-Robinson buffer (pH range 1.7-10). A method for the analysis of BV in BRB (0.04 mol L(-1)), which allows quantification over the range 3.9x10(-6)-1.1x10(-4) mol L(-1), was proposed and successfully applied to the determination of BV in tablets with mean recovery and relative standard deviation of 100.81% and 0.45%, respectively.     

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.     

Voltammetric determination of benazepril and ramipril in dosage forms and biological fluids through nitrosation

A simple and highly sensitive voltammetric method was developed for the determination of benazepril (I) and ramipril (II). The compounds were treated with nitrous acid, and the cathodic current produced by the resulting nitroso derivatives was measured. The voltammetric behavior was studied by adopting direct current (DCt), differential pulse (DPP), and alternating current (ACt) polarography. Both compounds produced well-defined, diffusion-controlled cathodic waves over the whole pH range in Britton-Robinson buffers (BRb). At pH 3 and 5, the values of diffusion-current constants (Id), were 5.90 +/- 0.40 and 6.66 +/- 0.61 for I and II, respectively. The current concentration plots for I were rectilinear over the range of 1.5-40 and 0.1-30 microg/mL in the DCt and DPP modes, respectively; for II, the range was 2-30 and 0.1-20 microg/mL in the DCt and DPP modes, respectively. The minimum detectabilities (S/N = 2) were 0.015 microg/mL (about 3.25 x 10(-8)M) and 0.012 microg/mL (about 2.88 x 10(-8)M) for I and II, respectively, adopting the DPP mode. Results obtained for the proposed method when applied to the determination of both compounds in dosage forms were in good agreement with those obtained using reference methods. Hydrochlorthiazide, which is frequently co-formulated with these drugs, did not interfere with the assay. The method was also applied to the determination of benazepril in spiked human urine and plasma. The percentage recoveries adopting the DPP mode were 96.2 +/- 1.21 and 95.7 +/- 1.61, respectively.     

Adsorptive stripping voltammetric assay of phenazopyridine hydrochloride in biological fluids and pharmaceutical preparations

A sensitive method for the measurement of phenazopyridine hydrochloride (PAP) by differential pulse polarography (DPP) based on adsorptive stripping technique, using a hanging mercury drop electrode (HMDE) is described. The voltammetric peak is obtained at -0.760 V, which corresponds to the reduction of the azo group in Britton-Robinson buffer. The redox behaviour is reversible. Optimum conditions were found to be: accumulation potential -50 mV (vs. Ag/AgCl), accumulation time 60 s, scan rate 5 mV s(-1), pulse amplitude -100 mV and supporting electrolyte Britton-Robinson buffer (0.04 M, pH=11). The relative standard deviation (at 20 ng ml(-1) level) was +/-0.6% for six measurements. The calculated detection limit was 0.0299 ng ml(-1) with a 60-s accumulation time. The applicability of such a method was evaluated through the assay of PAP in human plasma and urine samples after a simple extraction procedure and in pharmaceutical preparation. The mean recovery was 97+/-2 (100 ng ml(-1) plasma).     

Differential pulse polarography and electron spin resonance spectroscopy of nitroxyl free radicals used as ESR-spin probes

Differential pulse polarography (DPP) and electron spin resonance (ESR) were used to study the influence of substituents and of the pH of the medium on DPP peak potentials (electrochemical reduction) resp. kreduction (chemical reduction) of nitroxyl free radicals. The DPP peak potentials can be used to select the appropriate nitroxide spin label for relevant biochemical and biophysical applications.     

紫草素的电化学伏安行为研究

紫草素在0.2 mol/L HAc-NaAc缓冲溶液(pH4.3)中,产生灵敏的线性扫描极谱峰,峰电位EP=-0.186 V(vs.Ag/AgCl)。峰电流与紫草素浓度在5×10-7~1×10-5mol/L范围内呈良好的线性关系。可用于紫草中紫草素含量的测定。用线性扫描和循环伏安法测试表明,该体系属具有反应物吸附性的可逆过程体系。     

Complexation of cadmium by the C-terminal hexapeptide Lys-Cys-Thr-Cys-Cys-Ala from mouse metallothionein: study by differential pulse polarography and circular dichroism spectroscopy with multivariate curve resolution analysis

The cadmium-binding properties of the C-terminal hexapeptide of mouse metallothionein I, Lys-Cys-Thr-Cys-Cys-Ala, were studied by circular dichroism spectroscopy (CD), differential pulse polarography (DPP) and ¹¹³Cd-nuclear magnetic resonance (NMR).

The structure of the multiple cadmium binding sites could not be determined by ¹¹³Cd-NMR because of the insolubility of the Cd–peptide samples at the high concentrations required for NMR. Therefore, alternative approaches were used: CD and DPP. The data were analyzed using a multivariate curve resolution (MCR) approach, based on factor analysis techniques, which allows the identification of the signal corresponding to different metal ions bound in different chemical environments. The CD study confirmed that the binding of Cd²⁺ induces important conformational changes in the structure of the peptidic complex, including the formation of a binuclear cluster. The DPP results obtained at various Cd²⁺-to-peptide concentration ratios and pH values, under conditions where electrode adsorption is low, if not negligible, indicated the formation of different Cd²⁺–peptide complexes, and a scheme for the electrochemical reduction of the complexed Cd²⁺ ions is proposed.

These results show that the application of MCR to complex data, such as those from DPP, allows to reach valuable information which is not possible to be obtained by univariate approaches.     

芦丁的电化学伏安行为及其应用

芦丁在0.1mol/L Tris-HCl缓冲溶液(pH=8.3)中产生灵敏的线性扫描极谱峰,峰电位EP=-1.10V(vs.Ag/AgCl).峰电流与芦丁浓度在7×10-7~9.8×10-6mol/L范围内呈良好的线性关系.可用于乌拉尔甘草内黄酮含量的测定.线性扫描和循环伏安法测试表明,该体系属具有吸附性的准可逆过程体系.     

Electroreduction and determination of Pipril (Piperacillin) in both aqueous and biological samples

The electrochemical behavior of the relatively new antibacterial antibiotic Pipril (Piperacillin) at the dropping mercury electrode is investigated using both direct current polarography (DCP) and differential pulse polarography (DPP). At the hanging mercury electrode (HMDE), the reduction mechanism has been elucidated using cyclic voltammetric technique in the pH range from 2 to 10. The effect of some metal ions, e.g. Cu(II) and Pb(II) has been also tested. Determination of the drug using adsorptive stripping analysis was assessed in both aqueous and urine samples. The effect of the different experimental parameters affecting the drug determination, e.g. pH, supporting electrolyte nature, accumulation potential, accumulation time and other operational parameters are also mentioned. Detection limits of 5 × 10⁻⁹ and 1 × 10⁻⁸M Pipril in aqueous and urine samples, respectively, are achieved.     

Voltammetric reduction of finasteride at mercury electrode and its determination in tablets

Finasteride in hydroalcoholic solutions (ethanol/Britton-Robinson buffer, 30/70) exhibits cathodic response in a wide range of pH (-0.5 to 12) using differential pulse (DPP) and test polarography (TP). The reduction peak of finasteride at acidic pH, is a catalytic proton peak resulting from a mechanism involving a first protonation of finasteride followed by the reduction of the protons combined with finasteride in order to regenerate finasteride and liberate hydrogen. Based on the catalytic hydrogen wave, a novel method for the determination of finasteride can be proposed. For analytical purposes we selected DPP technique in an ethanol/0.0625 mol L(-1) H(2)SO(4) (30/70) solution medium. In this condition the I(p) varied linearly with finasteride concentration between 5 x 10(-5) and 5 x 10(-4) mol L(-1). Within-day and inter-day reproducibility's were adequate with R.S.D. values lower than 2%. The selectivity of the method was checked with both accelerated degradation trials and typical excipients formulations. The developed method was applied to the assay and the uniformity content of finasteride tablets and compared with the standard HPLC method. The DPP-developed method was adequate for the finasteride determination in pharmaceutical forms as that exhibited an adequate accuracy, reproducibility and selectivity. Furthermore, treatment of the sample was not required as in HPLC; the method is not time-consuming and less expensive than the HPLC ones.     

Redox behaviour of the dicobalt cofacial porphyrin Co2FTF4 and related complexes adsorbed on graphite electrodes

Adsorbed on graphite electrodes, Co₂FTF4 in a potent catalyst for O₂ reduction by a four-electron mechanism. The two observable redox surface waves have been previously assigned to the two cobalt centres. Using differential pulse polarography (DPP), the behaviour of this dicobalt cofacial dimer was re-examined at different pH values in aqueous solutions and in the presence of potential axial ligands for cobalt. From these observations and from a comparison with other adsorbed porphyrins it can be concluded that (a) the porphyrins are probably adsorbed by strong interactions between graphite and the aromatic rings, and (b) the more negative surface wave is cobalt-based but the more positive one is instead a porphyrin ring oxidation. This implies that the catalyst is in the Co^IICo^IIIFTF4 state when catalytic oxygen reduction begins.     

Biamperometric and Differential Pulse Polarographic Methods for the Assay of Nomifensine Maleate

Abstract

Biamperometric titration and differential pulse polarography (DPP) are described for the analysis of nomifensine maleate powder and commercial capsules (Merital^R -50 mg). The biamperometric method involved the titration in cold dil. HCl medium against 0.01 M - NaN0₂ and electrometric detection of end point. The mean percent recoveries obtained were 100.0 ± 0.87 and 99.2 ± 0.95 for the authentic powder and capsules, respectively. The DPP method was performed by measuring the peak current, i_P, obtained from the recorded differential polarogram under constant 50mV modulation amplitude. The peak current was measured at the peak potential of ? 1.02 V on the dropping mercury electrode (DME) versus Ag/AgCl/KCl (sat.) reference electrode at pH 5.0 (acetate buffer). A linear relationship between peak current and concentration was demonstrated in the range 3 to 30μg ml^?1. The mean percent recovery for the capsules was 103.1 ± 1.26.     

8—氮鸟嘌呤的极谱伏安行为

用循环伏安法（ＣＶ）、电流采样极诸法（ＳＣＰ，即ＴＡＳＴ）、常规脉冲极谱法（ＮＰＰ）、微分脉冲极谱法（ＤＰＰ）、线性扫描伏安法（ＬＳＶ）、Ｏｓｔｅｒｙｏｕｎｇ方波伏安法（ＯＳＷＶ）和计时库仑法（ＣＣ）等电化学技术研究了抗癌药物８－氮鸟嘌呤（８－ａｚａｇｕａｎｉｎｅ，ｇｕａｎａｚｏｌｏ，简称８－ＡＧ）的极谱伏安行为．在 ０． １ｍｏｌ／Ｌ Ｈ２ＳＯ４底液中，８－ＡＧ有一良好的还原峰，峰电位（Ｅｐ）在－０． ９５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ，下同）附近，８－ＡＧ浓度在４×１０－６～８×１０－４ｍｏｌ／Ｌ范围内．峰高与浓度有良好的线性关系，线性相关系数ｒ＝０．９９９９～０．９９１０，检出限为１× １０－６ｍｏｌ／Ｌ．实验证明了该峰具有吸附性．本文提出了电极反应机理，它包括：酸性介质中８－ＡＧ的质子化、质子化的８－ＡＧ在汞电极上吸附以及完全不可逆的两电子还原过程．同时用量子化学计算方法（全略微分重叠法即ＣＮＤＯ／２）对８－ＡＧ和鸟嘌呤的各原子的净电荷以及Ｗｉｂｅｒｇ键级进行了计算，从理论上解释了８－ＡＧ的电化学还原机理。     

Electrochemical behaviour of some neuroleptics: Haloperidol and its derivatives

The electrochemical characteristics of Haloperidol and related compounds, representative neuroleptics of the butyrophenone family, have been investigated as a function of pH and concentration by direct-current, alternating-current and differential-pulse polarography and cyclic voltammetry at a hanging mercury drop electrode. A single cathodic wave representing an irreversible two-electron reduction is obtained, and its half-wave potential differs from that characteristic of aromatic ketone reduction. Adsorption processes disturb the wave behaviour and an adsorption prewave is observed at high concentrations. Quantitative measurements were successful in the concentration range 1 x 10(-4)-1 x 10(-6)M (0.4 mg/l.), the lower concentration representing the detection limit by differential-pulse polarography.     

Electrochemical behavior and detection of plant hormone 6-benzyl adenine in acetate buffer at mercury electrode.

The electrochemical behavior of 6-benzyl adenine (6-BA) has been studied in 0.1 mol L(-1) HAc-NaAc solution (pH 3.8). Cyclic voltammetry, single-sweep polarography and direct current polarography were employed to clarify the mechanism of the electrode process; the kinetic parameters of the rate-determining step were determined. Reduction of 6-BA involves two pH-dependent processes, corresponding to the overall irreversible reduction of the 1,6 and 3,2 N=C bonds. Each reduction stage consists a preprotonation of the nitrogen atom at the electroactive site and a rapid two-electron transfer. In the presence of 6-BA, the reduction potentials of some ions were shifted. Under the given conditions, 6-BA displays one irreversible reduction peak controlled by adsorption. Two linear response were observed in the range 2.0 x 10(-8) - 8.0 x 10(-7) mol L(-1) and the range 1.0 x 10(-6) - 8.0 x 10(-6) mol L(-1), with correlation coefficients of 0.9995 and 0.9998, respectively. The detection limit is 7.1 x 10(-9) mol L(-1). The method had been applied to the determination of 6-BA in bean sprout samples with satisfactory results.     

Polarographic Behaviour of Orotic Acid (Vitamin B13). Anodic Wave

Abstract

The electroanalytical anodic behaviour of orotic acid has been studied at several pH values, using DPP and CV techniques. The orotic acid undergoes an anodic wave in both techniques.

The best conditions for the determination of orotic acid with the mentioned techniques was studied.

The determination of Hg(II) by classic polarography, DC, was performed.     

Reactant adsorption in analytical pulse polarography: An outline in terms of the concentration profile

The consequences of adsorption of the electroactive species in analytical pulse polarography are discussed. For both normal pulse polarography (NPP) and differential pulse polarography (DPP) explanations are given in terms of the concentration profiles as they are developed upon adsorption before pulse application. An approximate interpretation of the depressed NPP limiting current is sometimes possible by taking its dependence on pulse duration into account. In a number of cases NPP offers the possibility of avoiding adsorption effects by choosing a suitable initial potential. In DPP reactant adsorption generally causes peak enlargement, but the theoretical approach is complex and practical means for checking or eliminating adsorption effects in DPP are limited. Analytical calibration curves start with a linear portion corresponding with the linear adsorption regime; at higher concentrations the DPP curve bends downwards, whereas the NPP curve bends slightly upwards, before reaching the linear region of diffusion control. Several analytical pitfalls connected with the adsorption phenomena are indicated.     

Cathodic adsorptive stripping voltammetric studies on lamivudine: an antiretroviral drug

The electrochemical reduction and adsorption of lamivudine, a systemic antiviral drug, were studied in a phosphate buffer medium at a hanging mercury drop electrode (HMDE). Cyclic voltammetry studies showed one well-defined reduction peak in the potential range from -1.2 to -1.8 V under different pH conditions, but the best results were obtained at pH 3.4. The reduction was irreversible and exhibited diffusion-controlled adsorption. The response was evaluated with respect to preconcentration time, pH effect, accumulation potential, accumulation time, and scan rate. The number of electrons transferred in the reduction process was calculated and the probable reduction mechanism was proposed. A systemic study of the experimental parameters that affect the square-wave stripping response was carried out and experimental conditions were optimized.