Nanostructured Base Electrochemical Sensor for Simultaneous Quantification and Voltammetric Studies of Levodopa and Carbidopa in Pharmaceutical Products and Biological Samples

A novel carbon paste electrode modified with carbon nanotubes and 5‐amino‐2′‐ethyl‐biphenyl‐2‐ol (5AEB) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electrocatalytic oxidation of levodopa (LD) and carbidopa (CD), is described. Cyclic voltammetry (CV) was used to investigate the redox properties of this modified electrode at various scan rates. The apparent charge transfer rate constant, k_s, and transfer coefficient, a, for electron transfer between 5AEB and CPE were calculated as 17.3 s^?1 and 0.5, respectively. Square wave voltammetry (SWV) exhibits a linear dynamic range from 2.5×10^?7 to 2.0×10^?4 M and a detection limit of 9.0×10^?8 M for LD.     

Cyclodextrin Host‐Guest Recognition Approach for Simultaneous Quantification and Voltammetric Studies of Levodopa and Carbidopa in Pharmaceutical Products

An electrochemical sensor for simultaneous quantification of Levodopa (L‐dopa) and Carbidopa (C‐dopa) using a β‐cyclodextrin/poly(N‐acetylaniline) (β‐CD/PNAANI) modified carbon paste electrode has been developed. Preconcentrating effect of β‐CD as well as its different inclusion complex stability with L‐dopa and C‐dopa was used to construct an electrochemical sensor for quantification of these important analytes. The overlapping anodic peaks of L‐dopa and C‐dopa at 810 mV on bare carbon paste electrode resolved in two well‐defined voltammetric peaks at 450 and 880 mV vs. Ag/AgCl, respectively, with a drastic enhancement of the anodic peak currents. Under optimized conditions, linear calibration curves were obtained in the ranges of 0.5–117 µM and 1.6–210 µM with detection limits down to 0.2 and 0.8 µM for L‐dopa and C‐dopa, respectively. The proposed electrode was successfully applied for the determination of L‐dopa /C‐dopa in pharmaceutical formulations and the results were in close agreement with the labeled values.     

Voltammetric Analysis of Naproxen in Graphite Electrodes and Its Determination in Pharmaceutical Samples

The present work discuses new findings in the electrochemistry of naproxen over graphite electrodes. This new approach, allows the proposal of a simple and competitive low‐cost method to carry out naproxen’s voltammetric quantification. Naproxen’s indirect quantification through an adsorption anodic wave was performed at a graphite bar electrode using differential pulse voltammetry. An anodic current maximum was recorded at a potential of ?0.3 V referred to a saturated Ag/AgCl reference electrode. The calibration plot having a correlation coefficient of 0.990, sensibility of 4.19±0.62 µA cm³ µg^?1, with detection and quantification limits of 0.68 and 3.3 µg cm^?3, respectively.     

铂/多壁碳纳米管修饰玻碳电极用于微分脉冲伏安法测定左旋多巴

采用微波辅助加热多元醇技术制备了载铂多壁碳纳米管复合材料,并将该复合材料分散在N,N′-二甲基甲酰胺溶液中得到悬浮液,取14μL悬浮液滴涂在玻碳电极表面,制备铂/多壁碳纳米管修饰电极(Pt/MWCNT′s/GCE)。循环伏安法研究了在0.05mol·L~(-1)硫酸支持电解质中,在0.30～0.70V(vs.SCE)电位范围内,左旋多巴在修饰电极上的电化学行为,结果表明:左旋多巴在Pt/MWCNT′s/GCE上于电位0.548V处可见明显的氧化峰,且氧化峰电流显著高于在MWCNT′s/GCE和裸玻碳电极上的氧化峰电流。提出了用微分脉冲伏安法测定左旋多巴的方法。左旋多巴的浓度在8.0×10~(-6)～2.0×10~(-1)mol·L~(-1)范围内与其氧化峰电流呈线性关系,检出限(3S/N)为1.9×10~(-6)mol·L~(-1),平均回收率为102.8%。     

Voltammetric Study and Direct Analytical Determination of the Antiparkinson Drug Benserazide

For the first time, a simple differential pulse voltammetry methodology for direct determination of benserazide in presence of levodopa in tablets was developed without any redox mediator, modified electrodes, or the aplication of mathematic deconvolution of signals. Benserazide was studied by differential pulse voltammetry using glassy carbon electrode in aqueous media. The drug exhibited a main well-defined oxidation signal in a broad pH range (2–10), and two poorly resolved signals at higher potentials. We have found that levodopa does not interfere on the electrochemical response of benserazide at pH 6.0. Thus, at this pH value, the developed analytical method exhibited adequate repeatability and reproducibility (RSD < 2%), recoveries >98.5%, which permitted its successful application to both the assay and the uniformity content of benserazide. Also, hydrolytic degradation studies of benserazide were carried out by differential pulse voltammetry.     

Voltammetric behavior of naratriptan and its determination in tablets

The electrochemical behavior and the analytical application of the selective serotonin agonist naratriptan (N-methyl-3-(1-methyl-4-piperidyl)indole-5-ethanesulfonamide) are presented herein. Naratriptan exhibits an anodic response in aqueous media over a broad pH range (pH 2-12), as determined by differential pulse voltammetry and cyclic voltammetry using glassy carbon electrodes. This response is irreversible in nature, diffusion-controlled and probably caused by the oxidation of the naratriptan indole moiety. The differential pulse voltammetry technique was performed in 0.1 mol L⁻¹ Britton-Robinson buffer (pH = 3), which elicited the most reproducible results. The percentage of naratriptan recovery was 102.1 ± 1.8%, and the limits of detection and quantitation were 9.5 × 10⁻⁶ and 2.0 × 10⁻⁵ mol L⁻¹, respectively. Selectivity trials revealed that the oxidation signal of the drug was not disturbed by the presence of excipients or degradation products. Thus, we conclude that the method presented herein is useful for the quantification of naratriptan in pharmaceutical drugs and that this method requires no separations or extractions. Finally, this voltammetric method was successfully applied to determine the quantity and the content uniformity of naratriptan in drug tablets. A comparison of this technique to the standard high-performance liquid chromatography technique was conducted at the end of our study.     

Electroreduction of Zonisamide at Hanging Mercury Drop Electrode and Its Determination in Pharmaceutical Formulations and Spiked Human Serum Samples

A simple and rapid voltammetric method has been developed for the quantitative determination of zonisamide (ZNS) in pharmaceutical formulations and spiked human serum samples. Studies with differential pulse voltammetry (DPV) were carried out using a hanging mercury drop electrode (HMDE) in 0.1 M HCl solution. A well-defined reduction peak of ZNS was obtained at ?930 mV vs. saturated calomel electrode (SCE). The current-concentration plots are linear over the range from 0.13 to 17.05 μg ml^?1 in 0.1 M HCl. The statistical parameters and the recovery study data clearly indicate good reproducibility and accuracy of the method.     

Adsorptive Stripping Voltammetric Determination of Ultra Trace of Zinc and Lead with Carbidopa as Complexing Agent in Food and Water Samples

In the present work, the cathodic stripping voltammetric methodology using a hanging mercury drop electrode was described for simultaneous determination of lead and zinc in different real samples. The method is based on adsorption of metal ions on mercury electrode using carbidopa as a suitable complexing agent. The potential was scanned to the negative direction and the differential pulse stripping voltammograms were recorded. Optimal conditions were found to be: accumulation time; 70 s, accumulation potential; 50 mV versus Ag/AgCl, scan rate; 40 mV s^?1, supporting electrolyte; 0.01 M ammonia buffer at pH 8.5, and concentration of carbidopa; 8.0 μM. The relationship between the peak current versus concentration was linear over the range of 0.1–210 and 0.2–170 nM for lead and zinc, respectively. The detection limits are 0.09 and 0.15 nM for lead and zinc ions respectively. The relative standard deviations at a concentration level of 70 nM of both metal ions are found 1.08 and 1.24% for lead and zinc ions respectively.     

Voltammetric Oxidation of Ambroxol and Application to Its Determination in Pharmaceuticals and in Drug Dissolution Studies

A detailed study of the electrochemistry of ambroxol at a glassy carbon electrode was carried out in the pH range 1.8–11.0 in aqueous solution using cyclic and differential pulse voltammetry. The compound was oxidized irreversibly at high positive potentials resulting in the formation of a chemical product at less positive potentials, which was more readily oxidized than the parent compound. In addition, a differential pulse voltammetric method was proposed for the determination of the drug in different pharmaceutical formulations, and in drug dissolution studies.     

Voltammetric Determination of α‐Tocopheryl Acetate in Pharmaceutical Dosage Forms

A simple and rapid voltammetric method has been developed for the quantitative determination of α‐tocopheryl acetate (α‐TOAc) in pharmaceutical preparations. Studies with linear scan (LSV), square‐wave (SQWV) and differential pulse voltammetry (DPV) were carried out using platinum microelectrodes. A well‐defined, irreversible oxidation wave/peak was obtained at 1.30 V (vs. Ag/AgCl reference electrode.) The use of SQWV or DPV technique provides a precise determination of α‐tocopheryl acetate using the multiple standard addition method. The statistical parameters and the recovery study data clearly indicate good reproducibility and accuracy of the method. Accuracy of the results assessed by recovery trials was found within the 99.3% to 103.5%, and 99.1% to 101.4%, for SQWV and DPV, respectively. The quantification limits for the both voltammetric techniques were found to be 6×10^?5 M (SQWV) and 7×10^?5 M (DPV). Analysis of the authentic samples containing α‐TOAc showed no interference with common additives and excipients, such as unsaturated fatty acids (co‐formulated as glycerine esters) and vitamin A (as retinol or β‐carotene). The method proposed does not require any pretreatment of the pharmaceutical dosage forms. A gas chromatography determination of α‐TOAc in real samples was also performed for comparison.     

Simultaneous Voltammetric Determination of Three Herbicides in Food and Water Samples with the Aid of Chemometrics

Differential pulse stripping voltammetry method(DPSV) was applied to the determination of three herbicides,ametryn,cyanatryn,and dimethametryn.It was found that their voltammograms overlapped strongly,and it is difficult to determine these compounds individually from their mixtures.With the aid of chemometrics,classical least squares(CLS),principal component regression(PCR) and partial least squares(PLS),voltammogram resolution and quantitative analysis of the synthetic mixtures of the three compounds were successfully performed.The proposed method was also applied to the analysis of some real samples with satisfactory results.     

微分脉冲溶出伏安法测定除草通

提出了苹果、土豆、西红柿中除草通残留量的电分析化学测定方法,研究了除草通在汞电极上的电化学行为,探讨了其电极反应机理。结果表明,除草通在汞电极上具有吸附性质,其电极反应为不可逆的还原过程。本方法的测量线性范围为0．01～0．16mg/L,检出限为9．1μg/L.     

Simultaneous Spectrophotometric Determination of Levodopa and Benserazide in a Pharmaceutical

ABSTRACT

A method based on a partial least-squares calibration (PLS) for the simultaneous spectrophotometric determination of levodopa (I) and benserazide (II) in a commercially available pharmaceutical preparation is proposed. The calibration procedure was developped by using laboratory made mixtures of I and II, and optimized by selecting the most suitable wavelength range and spectral mode. The relative standard error of prediction (RSEP %) was 0.5% and 0.9% with a limiting reproducibility (R) of 4 10^?6 M and 1.5 10^?6 M for levodopa and benserazide, respectively The proposed method is straightforward, expeditious and precise. Its results are consistent with those provided by HPLC for the two analytes.     

Voltammetric behaviour of the synthetic pyrethroid lambda-cyhalothrin and its determination in soil and well water

The pyrethroid lambda-cyhalothrin is a common insecticide which is widespread in the environment. A study of the electrochemical reduction of the pesticide on a hanging mercury drop electrode (HMDE) was performed as basis for the development of a sensitive analytical method for determination of lambda-cyhalothrin in natural samples. Two electrochemical techniques—cyclic voltammetry (CV) and differential pulse voltammetry (DPV)—were applied. The study was performed in the pH range 2-13 using Britton-Robinson (B-R) buffer to control the pH of the measuring solutions and tetrabutylammonium chloride (TBAC) salt as supporting electrolyte. In DPV, a single reduction peak was observed at both pH<4.0 and pH>10.5 while two cathodic peaks were produced in the pH range 4.0-10.5. The results showed that the reduction of lambda-cyhalothrin in the measuring solution is irreversible. The limiting current was found to be diffusion-controlled and free of adsorption of the electroactive species to HMDE over the whole pH range tested. For the analytical DPV method running at pH 2 the relationship between peak current and lambda-cyhalothrin concentration was linear up to 500 μg l⁻¹ (1.1×10⁻⁶ mol l⁻¹) with a detection limit of 2.5 μg l⁻¹. The repeatability in terms of relative standard deviation (n=10) was in the order of 3.5% at concentration levels of 5 and 10 μg l⁻¹. A DPV method for determining lambda-cyhalothrin in the agrochemical formulation Karate, spiked soil and well water was developed. The recovery was about 94% in well water and 92% in soil samples at concentration range of 0.05-0.5 μg l⁻¹ and 0.05-0.5 μg g⁻¹, respectively.     

微分脉冲阴极溶出伏安法测定呋喃唑酮

研究了呋喃唑酮在玻碳电极上的伏安行为。在 1mol LHCl底液中 ,用微分脉冲阴极溶出伏安法得到一灵敏的呋喃唑酮还原峰 ,峰电位为 0 .0 38V(vs.Ag AgCl)。峰电流与呋喃唑酮浓度在 8× 1 0 -6～ 1× 1 0 -4 mol L范围内呈线性关系 (r=0 .9984) ,检出限为 8× 1 0 -8mol L。该法已用于片剂与合成血清样品中呋喃唑酮含量的测定     

Voltammetric Determination of Azidothymidine Using Silver Solid Amalgam Electrodes

A new simple and direct electroanalytical method was developed for the determination of azidothymidine in commercial pharmaceutical preparations. It is based on differential pulse voltammetry at silver solid amalgam electrode with polished surface (p‐AgSAE) or surface modified by mercury meniscus (m‐AgSAE). The electroreduction of azidothymidine in basic media at these electrodes gives rise to one irreversible cathodic peak. Its potential in 0.05 mol L^?1 borate buffer, pH 9.3 at ca. ?1050 mV is comparable to that using hanging mercury drop electrode (HMDE). Achieved limits of quantitation are in the 10^?7 mol L^?1 concentration range for both amalgam electrodes. According to the procedure based on the standard addition technique, the recoveries of known amounts of azidothymidine contained in pharmaceutical preparations available in capsules were 101.4±1.8% (m‐AgSAE), 100.3±3.5% (p‐AgSAE) and 102.0±1.0% (HMDE) (n=10). There was no significant difference between the values gained by proposed voltammetric methods and the HPLC‐UV recommended by the United States Pharmacopoeia regarding the mean values and standard deviations.     

Voltammetric Determination of Selected Aminoquinolines Using Carbon Paste Electrode

Optimum conditions have been found for voltammetric determination of mutagenic 5‐aminoquinoline, 6‐aminoquinoline and 3‐aminoquinoline by differential pulse voltammetry and adsorptive stripping differential pulse voltammetry on carbon paste electrode. The lowest limits of determination were found for adsorptive stripping differential pulse voltammetry in 0.1 mol dm^?3 H₃PO₄ (5×10^?7 mol dm^?3 , 1×10^?7 mol dm^?3, and 1×10^?7 mol dm^?3 for 5‐aminoquinoline, 6‐aminoquinoline and 3‐aminoquinoline, respectively). The possibility to determine mixtures of 8‐aminoquinoline with 3‐aminoquinoline or 5‐aminoquinoline or 6‐aminoquinoline, and mixtures of 5‐aminoquinoline with 3‐aminoquinoline or 6‐aminoquinoline by differential pulse voltammetry was verified. Binary mixtures of 8‐aminoquinoline with 3‐aminoquinoline or 6‐aminoquinoline, and of 3‐aminoquinoline with 5‐aminoquinoline could be successfully analyzed.     

Simultaneous Differential Pulse Voltammetric Determination of Ascorbic Acid and Caffeine in Pharmaceutical Formulations Using a Boron‐Doped Diamond Electrode

A cathodically pretreated boron‐doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry. Linear calibration curves (r=0.999) were obtained from 1.9×10^?5 to 2.1×10^?4 mol L^?1 for AA and from 9.7×10^?6 to 1.1×10^?4 mol L^?1 for CAF, with detection limits of 19 μmol L^?1 and 7.0 μmol L^?1, respectively. This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations, with results equal to those obtained using a HPLC reference method.     

Differential Pulse Voltammetric Determination of L-Cysteine After Cyclic Voltammetry in Presence of Catechol with Glassy Carbon Electrode

An electrochemical method of determination of cysteine has been developed in the solution containing catechol as the indicator. Nucleophilic addition of the thiol species to the electrogenerated o-quinone results in the formation of o-quinone-cysteine adducts that easily accumulate use at the surface of the electrode in the acidic solution. Therefore, the use of cyclic voltammetry leads to the amplification of the o-quinone-cysteine adduct's reductive current. As cyclic voltammetry was performed prior to differential pulse voltammetry, the peak of o-quinone-cysteine could be separated preferentially from o-quinone in the differential pulse voltammogram and the selectivity of the method has been assessed with no interference from ascorbic acid, glycine, L-tyrosine, or L-lysine. The magnitude of o-quinone-cysteine peak is proportional to the concentration of cysteine, and thus it can be exploited to determine cysteine within the injection. The results were consistent with those obtained by means of HPLC analysis.