Components of the Net Current in Differential Pulse Polarography

As the modern (voltammetric) software packages offer ‘resolution’ of each individual net signal in differential pulse polarography (DPP) to its components, an attempt was made to test such a possibility on several model systems. Reversible and nonreversible reduction processes of simple metal ions (Cd²⁺, Eu³⁺) were included, together with some examples of the anion induced adsorption (Cd²⁺‐I^? and Pb²⁺‐Br^? systems) under conditions of partly or fully covered electrode surface. Taking into account that so called ‘backward’ current is in fact DC wave, it could be said that one technique is hidden within the other. Consequently, DPP measurements together with following of the ‘backward’ signals could give more information and save the time. ‘Forward’ component offers additional possibilities in data treatment, especially when its relationship to the ‘backward’ current (with respect to the potential and height) is taken into account. Such an approach seems promising, even when applied on a purely qualitative level, because some effects which cannot be observed if only the net signals are followed become obvious when their components are taken into consideration.     

Determination of Codeine,Dionin and Thebaine by Differential Pulse Polarography

Abstract

The method proposed for determining codeine, dionin and thebaine by differential pulse polarography is based on the reduction (in ammoniacal medium) of the nitroderivatives obtained by dissolving the substances in concentrated nitric acid. The values of the reduction potentials range between -0.45 and -0.69 V. Morphine and heroine do not interfere in the determination of the mentioned alkaloids.     

Differential Pulse Polarography of the Zn2+ Complexation by Glutathione Fragments Cys‐Gly and gamma‐Glu‐Cys

The metal binding properties of glutathione (GSH) and their fragments γ‐Glu‐Cys and Cys‐Gly are of biological and environmental interest. In this work a differential pulse polarographic study of the Zn²⁺/γ‐Glu‐Cys and Zn²⁺/Cys‐Gly systems was carried out for a better understanding of the results obtained in previous studies on the Zn²⁺‐GSH system. In the case of γ‐Glu‐Cys, complexation with Zn²⁺ was not detected. In the case of Cys‐Gly, the parallel analysis, by multivariate curve resolution with alternating least squares, of data from the titration of peptide with metal and of metal with peptide suggested the presence of two types of bound Zn²⁺. This could be attributed to Zn²⁺ strongly bound to two sulfur atoms of two peptides, to form a complex of 1 : 2 stoichiometry, and to Zn²⁺ weakly bound to carboxylate and/or amino groups.     

Voltammertric Behaviour of Clonixin and its Differential Pulse Polarographic Determination in Tablets

ABSTRACT

Clonixin, a non-steroid analgesic, can be both reduced at the mercury electrode and oxidised at the glassy carbon electrode. The anodic response shows well-defined waves in a pH range between pH 2-12. The polarographic response shows two irreversible waves or peaks in the range between pH 1-6 shifting cathodically when pH increases. Above pH 7.0 all the signals disappeared. The first signal in the dpp mode at pH 1.8 was selected for analytical use. The polarographic     

Indirect Determination of Trace Tetraborate by Differential Pulse Polarography Using Its Copper Complex and Application to Waste and Drinking Water

A new differential pulse polarographic (DPP) method has been developed for the trace determination of boron. Its most stable copper complex is used in 0.5 M KNO₃ electrolyte since boron is not electroactive. By continuous addition of tetraborate to copper solution, the copper peak decreased first but then the peak became very small and nearly constant. This point was used for the boron determination. It was found that one mole of copper used two moles of tetraborate. Using this relationship, 1×10^?5 M tetraborate could be determined. The quantification limit was 2.5×10^?6 M and detection limit was 8×10^?7 M. In the presence of complex forming ions such as Pb, Zn, and Cd, the borate found in sample was somewhat smaller because of their reaction with borate. But since their complexes were not as strong as copper, only a few percent of borate were used. No interference was observed in the presence of calcium, chloride and sulfate. This method is applied for the determination of B in borax ore, waste water of borax industries and tap water of Ankara city.     

Components of the Net Current in Differential Pulse Polarography. Part 2. Kinetics and Adsorption

Components of the net response in differential pulse polarography were studied theoretically, assuming gradually changing electrode rate constant or strength of the reactant adsorption. The difference between the maximum potential of the peak component and the half‐wave potential of the wave component appear as an important parameter. From its value, the electrode rate constant can be calculated even when the standard potential is not known. In a reversible process, effects of the reactant adsorption on the mentioned separation are less pronounced. The results were compared with experimentally obtained effects. For deeper insight into the applicability of this approach, additional experimentally obtained polarograms (that reflect different potential/timing parameters or changing character of the electrode process) should be studied in terms of their components.     

两种蒙药中锗的差示脉冲极谱测定及其红外光谱的差异

采用差示脉冲极谱法,以3,4-二羟基苯甲醛的0.072 mol·L-1硫酸溶液作为底液,在峰电位为-0.53 Ⅴ(vs．Ag/AgCl),锗(Ⅳ)浓度在1.03×10-5～1004×10-4mol·L-1范围内与峰电流呈线性关系.据此测定了阿嘎日-35和阿嘎日-8中总锗、无机锗、有机锗含量,并利用红外光谱比较了两种蒙药的红外谱图的差异,据此可对两种蒙药予以区别.     

维生素C及其制剂的一阶导数差示脉冲极谱法测定

本文建立了维生素Ｃ及其制剂的一阶导数差示脉冲极谱定量分析方法，在水溶液中，维生素Ｃ于－１．１０Ｖ（ｖｓＡｇ／ＡｇＣｌ）处出现一良好的一阶导数差示脉冲极谱峰，在１～１７５μｇ／ｍＬ范围内，维生素Ｃ浓度与其一阶导数差示脉冲极谱峰幅值呈非常显著的线性关系（Ｐ〈０．０１），方法简便，快速，灵敏，结果准确。     

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.     

Application of Net Analyte Signal Standard Addition Method (NASSAM) for Simultaneous Determination of Lead and Tin by Differential Pulse Polarography

Differential pulse polarography was used for simultaneous determination of Sn²⁺ and Pb²⁺. But there is a problem for simultaneous determination and it is high overlapped DPPs of mentioned cations that their determination is impossible in the presence of each other, so multivariate calibration methods as chemomatrics methods were used for this determination. There are some disadvantageous for multivariate calibration methods that can be solved by a new and simple method called net analyte signal standard addition method. This method has some advantages, such as: the use of a full voltammogram, realization in a single step, therefore it does not require calibration and prediction steps and only a few measurements are required for the determination.     

Differential Pulse Polarographic and UV‐Vis Spectrophotometric Study of Inclusion Complexes Formed by 1,4‐Dihydropyridine Calcium Antagonists,Nifedipine and Nicardipine with β‐Cyclodextrin

The formation of inclusion complexes of well‐known 1,4‐dihydropyridine calcium antagonists, such as nifedipine (NF) and nicardipine (NC), with β‐cyclodextrin (βCD) was investigated by differential pulse polarography (DPP) and UV‐vis spectrophotometry. The equimolar variation method indicated the formation of the NF‐βCD (1 : 1, M : M) and a NC‐βCD (1 : 1, M : M) inclusion complexes. Titrations using the DPP peak currents for NF and NC permitted one to determine formation constant values of (135±20) M^?1 and (357±41) M^?1 for NF‐βCD and NC‐βCD, respectively. For comparative purposes we have also applied phase solubility studies with spectrophotometric detection obtaining formation constant values of (129±5) M^?1 and (385±19) M^?1 for NF‐βCD and NC‐βCD, respectively. According to the DPP studies, we can postulate that the inclusion moiety were the nitroaromatic group, in the case of NF‐βCD, and the phenyl group on 3‐position of the 1,4‐DHP, in the case of NC‐βCD. The solubility of NF in water was increased about three times due to the formation of an inclusion complex with βCD. For NC the solubility was increased almost seven times.     

Sensitive Differential Pulse Polarographic Determination of Molybdenum Using The New Catalytic System Mo(VI)‐Phenantroline‐Chlorate

It was found that in acidic chloride media the complex of Mo(VI) with 1,10‐phenantroline induces catalytic reduction of KClO₃. This catalytic effect can be utilized for sensitive differential pulse polarographic determination of Mo(VI) with a low detection limit of 2.9×10^?11 M (2.8 ng/L). The optimal Mo(VI) response was obtained at pH 2.8, in the presence of (6–12)×10^?5 M 1,10‐phenantroline and 2×10^?2 M KClO₃. The sensitivity was 1.73 nA/nM and the catalytic response was linear up to 7.5×10^?7 M Mo (VI). The interferences from inorganic ions and surface‐active substances were investigated. The results of the determination of Mo(VI) in CRM water sample showed good reproducibility (R.S.D. for standard solution is below 1.2% and for water samples is 8.9%) and accuracy of the elaborated catalytic polarographic method.     

Differential Pulse Voltammetric Determination of Paraquat Using a Bismuth‐Film Electrode

A bismuth‐film electrode (BiFE) ex situ electrochemically deposited onto a copper substrate has been presented for paraquat determination. The bismuth film was electrochemically deposited at an applied potential of ?0.18 V vs. Ag/AgCl (3.0 M KCl) for 200 s. The analytical curve was linear in the paraquat concentration range from 6.6×10^?7 M to 4.8×10^?5 M with a limit of detection of 9.3×10^?8 M. The method presented satisfactory results at a confidence level of 95% and the performance was evaluated in water samples.     

Differential Pulse Voltammetric Determination and Application of Square‐Wave Voltammetry of yRNA on a CPB‐Cellulose Modified Electrode

Electrochemical behavior of remarkably low levels of Ribonucleic acid yeast (yRNA) is studied through differential pulse voltammetry (DPV), and kinetic parameters of the electrochemical reaction have also been calculated through square‐wave voltammetry (SWV), based on immobilization of yRNA on the surface of a CPB‐cellulose modified electrode. YRNA/ CPB‐cellulose/ITO conductive glass electrode is demonstrated by Infrared reflect (IR) and electrochemical impedance spectroscopy (EIS). The oxidation peak potential of yRNA shifts negatively with increasing pH. The peak currents decrease gradually in successive scans and no corresponding reduction peaks occur, indicating that oxidation process of yRNA is completely irreversible. Variables influencing DPV response of yRNA, such as pH, pulse amplitude and electrolyte concentration, are explored and optimized. Peak currents are proportional to the concentration of yRNA in the range of 0.1 μg mL^?1–1.0 μg mL^?1, and the linear regression coefficient equals 0.9923. The detection limit for yRNA is 1.0×10^?10 g mL^?1. Interferences of L ‐cysteine, L ‐alanine, Hemoglobin, Uridine 5′‐monophosphate, Guanosine 5′‐monophosphate, Adenosine 5′‐triphosphate and some metal ions (Co³⁺, Cr³⁺, Ni²⁺, Hg²⁺, Zn²⁺, etc) are negligible. The methods adopted here are more sensitive and selective than currently applied techniques and overcome the drawback of absorption spectroscopy arising from a strong interference due to other UV‐absorbing substances.     

Voltammetric and Differential Pulse Stripping Study of Adenine on a Sol‐gel Derived Carbon Composite Electrode

This communication reports on the electrochemical investigation of adenine on a sol‐gel carbon composite electrode (CCE). Cyclic voltammetric (CV) technique is used to characterize the redox behavior of adenine at CCE. The peak current and peak potentials are dependent on the pH of the buffer solution. From the scan rate and peak current study, there is evidence of adsorption of adenine on the CCE. The parameters affecting the differential pulse stripping adsorption peak were systematically optimized. Under optimum conditions of E_acc=?0.10 and t_acc=60 s, a linear calibration plot was obtained, 2×10^?7–1×10^?6 M. This CCE is useful for the simultaneous analysis of adenine and guanine from denatured DNA.     

Differential Pulse Voltammetric Determination of Selenocystine Using Selenium‐gold Film Modified Electrode

Differential pulse voltammetric determination of selenocystine (SeC) using selenium‐gold film modified glassy carbon electrode ((Se‐Au)/GC) is presented. In 0.10 mol?L^?1 KNO₃ (pH 3.20) solution, SeC yields a sensitive reduction peak at ?740 mV on (Se‐Au)/GC electrode. The peak current has a linear relationship with the concentration of SeC in the range of 5.0×10^?8–7.0×10^?4 mol?L^?1, and a 3σ detection limit of SeC is 3.0×10^?8 mol?L^?1. The relative standard deviation of the reduction current at SeC concentration of 10^?6 mol?L^?1 is 3.88% (n=8) using the same electrode, and 4.19% when using three modified electrodes prepared at different times. The content of SeC in the selenium‐enriched yeast and selenium‐enriched tea is determined. The total selenium in ordinary or selenium‐enriched tea is determined by DAN fluorescence method. The results indicate that in selenium‐enriched yeast about 20% of total selenium is present as SeC and in selenium‐enriched tea SeC is the major form of selenoamino acids. The total selenium content in selenium‐enriched tea soup is 0.09 μgSe/g accounting by 7% compared with that in selenium‐enriched tea. Hence, only a little amount of selenium is utilized by drinking tea, and most selenium still stay in tealeaf. Uncertainty are 22.4% and 16.1% for determination of SeC in selenium‐enriched yeast and selenium‐enriched tea by differential pulse voltammetry (DPV) on (Se‐Au)/GC electrode, respectively.     

Differential Pulse Polarographic Determination of Cd(II) and Pb(II) in Milk Samples after Solid‐Phase Extraction Using Amberlite XAD‐2 Resin Modified with 2,2′‐DPED3P

In the present paper novel column solid phase extraction procedure was developed for the determination of Cd(II) and Pb(II) in cows', goats', ewes', buffalos' and humans' milk samples using newly synthesized reagent 2,2′‐DPED₃P (2,2′‐{[1,2‐diphenylethane‐1,2‐diylidene]dinitrilo}diphenol) for preconcentration and separation prior to differential pulse polarography using amberlite XAD‐2 in the ranges of pH 4.0–5.0. The sorbed elements were subsequently eluted with 10 mL of 2 M HCl elutes were analysed by differential pulse polarography (DPP). The interference of foreign ions has also been studied. Effects of various instrumental parameters are investigated and received conditions are optimized. The total metal concentration of the milk samples in the study area were in the following ranges 0.030–0.090 μg L^?1 of Cd(II), 0.009–0.026 μg L^?1 of Pb(II) respectively. The limits of detections were found to be 0.020 and 0.024 μg L^?1 for Cd(II) and Pb(II) respectively by applying a preconcentration factor ～40. The proposed enrichment method was applied successfully for the determination of metal ions in cows', goats', ewes', buffalos' and humans' milk samples.     

Simultaneous Differential Pulse Voltammetric Determination of Sulfamethoxazole and Trimethoprim on a Boron‐Doped Diamond Electrode

The performance of hydrogen‐ (HT) and oxygen‐terminated (OT) boron‐doped diamond (BDD) electrodes (electrochemically pretreated) on the simultaneous differential pulse voltammetric determination of sulfamethoxazole and trimethoprim in pharmaceutical products is presented. Under the optimum analytical experimental conditions, the HT‐BDD electrode presented two well‐defined oxidation peaks at 920 and 1100 mV vs. Ag/AgCl for sulfamethoxazole and trimethoprim, respectively. On the other hand, when the OT‐BDD electrode was used, the sulfamethoxazole oxidation current peak was decreased twenty fold. The calculated LOD values for sulfamethoxazole and trimethoprim using the HT‐BDD electrode were 3.65 μg L^?1 and 3.92 μg L^?1, respectively. The results obtained in the simultaneous determination of sulfamethoxazole and trimethoprim in three different commercial formulations were similar to those obtained using a standard HPLC method at 95% confidence level.     

Differential Pulse Voltammetric Simultaneous Determination of Four Anti‐Inflammatory Drugs by Using Soft Modelling

An application of a partial least squares calibration method for the simultaneous voltammetric determination of indomethacin, acemethacin, piroxicam and tenoxicam is suggested. It was shown that it is possible to resolve complex mixtures of analytes even when they have strongly overlapped signals. In order to check the proposed method, statistical analysis of the results was performed by mean of hypothesis tests. The method developed was applied to the electrochemical reduction region of four anti‐inflammatory drugs and allowed the drugs to be quantified at concentrations between 0.52 and 4.09 μg mL^?1 for acemethacin, 0.44 and 3.50 μg mL^?1 for indomethacin, 0.43 and 3.40 μg mL^?1 for piroxicam, and 0.42 and 3.30 μg mL^?1 for tenoxicam with good results. The average absolute value of relative errors was 2.25%, 4.31%, 1.68% and 2.49%, respectively.     

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.