Determination of ascorbic acid in asparagus by differential pulse polarography

A useful method for the determination of ascorbic acid in a vegetable product (asparagus) by differential pulse polarography has been set up and evaluated. Extraction and instrumental conditions were optimized. The analytical parameters are: linearity (0–18.18 g/ml); detection limit (0.182 g/ml); instrumental and method precision (2.77% and 4%, respectively); accuracy (96.9–113.4%). These data show that the method is sufficiently sensitive, reliable and accurate. It was also compared with the official fluorometric AOAC method.     

Determination of Gallic acid by differential pulse polarography: Application to fruit juices

Phenolic compounds possess antioxidant, antitumor, antimutagenic, antibacterial and anticarcinogenic properties. Gallic acid (2,3,4-trihydroxybenzoic acid) is a natural phenolic compound; therefore, determination of trace gallic acid is very important. In this work, a novel, sensitive and reliable method was developed using differential pulse polarography. The most suitable buffer system was found to be Britton-Robinson (B-R) buffer, pH 10.0. The gallic acid peak in this medium appeared at about ?160 mV, it responded well to standard additions, and high reproducibility was obtained. The calibration graph was linear in the concentration range of gallic acid from 1.0–50.0 μM with a correlation coefficient of 0.999. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 0.3 and 1.0 μM, respectively. The proposed method was successfully applied to the determination of gallic acid in fruit juices. The influences of some other commonly found inorganic and organic salts on the determination were also examined. Some interferiences were eliminated by using complexing agents, e.g. EDTA.     

Determination of ascorbic acid by differential pulse voltammetry

Summary A new approach to the determination of ascorbic acid has been realized with differential pulse voltammetry (DPV) on the carbon paste electrode (CPE). The problems of the reproducibility of the surface of this electrode have been resolved by using always the same surface after its conditioning. The developed method has been applied to the direct determination of vitamin C in pharmaceutical tablets and in different types of fruit juices. Limits of determination are 1.5 ×10^–7 M, 8×10^–7 M and 1×10^–5 M for tablets, dehydrated and liquid juices, respectively.

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Bestimmung von Ascorbinsäure durch Differential-Puls-Voltammetrie

Zusammenfassung Als neues Verfahren zur Ascorbinsäurebestimmung wird die Differential-Puls-Voltammetrie mit Hilfe der Kohlepasteelektrode vorgestellt. Das Problem der Reproduzierbarkeit der Elektrodenoberfläche wurde dadurch gelöst, daß nach Konditionierung immer dieselbe Oberfläche verwendet wurde. Das Verfahren wurde zur Analyse von pharmazeutischen Tabletten und Fruchtsäften angewendet. Die Bestimmungsgrenzen liegen bei 1,5·10^–7 M, 8·10^–7 M und 1·10^–5 M für Tabletten, dehydratisierte bzw. flüssige Säfte.

     

N-nitrosamines and differential pulse polarography

Differential pulse polarography is a versatile and sensitive technique which yields both qualitative and quantitative information about N-nitrosamines. The ability of the technique to carry out determinations in-situ permits the study of anchimeric, metabolic, and mechanistic properties in addition to phenomena such as kinetics and transnitrosation.     

Simultaneous determination of the isomers of nitrophthalic acid by differential pulse polarography

A differential pulse polarographic method has been developed for simulataneous determination of isomers of nitrophthalic acid. In ammonia buffer (1.0 M), the peak potentials for the reduction of 4-and 3-nitrophthalic acids are ?0.54 and 0.67 V vs. SCE, respectively. Response of peak current vs. concentration of each isomer is linear over three orders of magnitude change in concentration. The detection limit for both 4-and 3-nitrophthalic acid is 0.2 mg l^?1. A typical sample can be analyzed for both isomers of nitrophthalic acid in less than 15 min.     

Application of modified normal pulse polarography and its differential mode to alkaline-earth metal ions in acid solutions

The simultaneous determination of alkaline-earth metal ions in acid solution was studied by modified normal pulse polarography. Well-defined waves were recorded for calcium, strontium and barium, but no limiting current was found for magnesium, because of its very negative reduction potential. The differential mode of this method gives peak-type polarograms and is useful for the simultaneous determination of species for which the half-wave potentials lie close together. The interference of dissolved oxygen was eliminated by the use of tetramethylammonium chloride as a supporting electrolyte.     

Determinations of citric acid by differential pulse polarography with immobilized enzymes

Summary Citrate lyase and oxaloacetate decarboxylase can be rapidly and simply immobilized in polyacrylamide gel to provide a selective and sensitive reactor. Conversion ratio of citric acid to pyruvic acid comes up to 90% under the optimal conditions. Generated pyruvic acid can be determined by differential pulse polarography. The bioreactor can be used for thirty determinations over several weeks. Samples of sports drinks and wine were successfully tested without pretreatment; the relative standard deviation with 1.0×10^-5 mol l^-1 citric acid in polarographic solutions was 1.17% and the detection limit was 6.6×10^-7 mol l^-1 (=2).     

Acidity functions of aqueous fluorinated acid solutions by differential pulse polarography

The acidity functions of aqueous trifluoroacetic and trifluoromethanesulphonic acid mixtures, and aqueous hexafluoropropane-2, 2-diol solutions, have been determined by differential pulse polarography. The apparent shift of the half-wave potential for the ferrocene—ferricinium couple, as the solvent composition is changed, is used to indicate the change in potential of a glass electrode; acidity is measured as the H_GF acidity function. The densities of two of these solvent systems as a function of composition are also reported. Trifluoromethanesulphonic acid—water mixtures represent the strongest aqueous acid solvent system so far studied.     

Contribution to the study of pulse polarography part III. Digital simulation of CE mechanisms in differential pulse polarography

The differential pulse polarographic behaviour of electrode reactions complicated by a first order homogeneous chemical reaction has been elucidated by a digital simulation procedure. The effect of systematic variations of the homogeneous and heterogeneous kinetic parameters on experimentally measurable parameters is described.     

Effects of surfactants in differential pulse polarography

Differential pulse polarograms of surfactants exhibit tensammetric peaks at the adsorption and desorption potentials of the surfactant. In the potential range where adsorption occurs the base current is depressed. The heights of the tensammetric peaks are nonlinear functions of the bulk concentration of the surfactant. Differential pulse polarograms of reducible substances are greatly affected by the presence of surfactants, the effect being similar to that observed in a.c. polarography. Surfactants with the same charge as the depolarizer act as electrochemical masking agents, whereas peak currents may be enhanced by oppositely charged surfactants.     

Determination of cyanuric acid in swimming pool water by differential pulse polarography

A reliable differential pulse polarographic method is described for the determination of cyanuric acid (1,3,5-triazine-2,4,6-triol) in pool water. Cyanuric acid in the range 10^?5–10^?3 M is determined by means of the peak at ca. –60 mV (vs. Ag/AgCl/3 M NAcl). The high sensitivity of the polarographic technique allows ten-fold dilution of samples, thus avoiding matrix effects. It it shown that the peak can be attributed to formation of insoluble mercury(I) cyanurate, Hg₂(HC₃N₃O₃), at the mercury electrode.     

Determination of bacitracin by differential pulse polarography.

Differential pulse polarograms of pharmaceutical-grade bacitracin exhibit a well-defined double wave at the dropping mercury electrode over the entire pH range 1–8. The current is diffusion-controlled and proportional to the concentration as well as to the biological activity of the sample. The concentration of bacitracin and of zinc—bacitracin can be determined by pulse polarography with a standard deviation less than 2%. The biologically inactive oxidation product (bacitracin F) is reduced at less negative potentials and can easily be determined in the presence of the biologically active components of bacitracin.     

Estimation of cephalosporin antibiotics by differential pulse polarography

Differential pulse polarographic (DPP) method of determination of cephalosporins has been developed based on the electrochemistry of the azomethine group in the drugs in universal buffers of pH 2.0-12.0. Quantitative measurements were successful in the concentration range of 1.0 x 10(-5) M-2.5 x 10(-8) M, the lower concentration representing the detection limit by DPP. The described procedure has been applied for the determination of these drugs individually in pharmaceutical formulations and urine samples as well as for simultaneous determination in a single run.     

Direct determination of pentachlorophenol by differential pulse polarography

Differential pulse polarography at the dropping mercury electrode and differential pulse voltammetry at the carbon paste electrode are used for direct determinations of pentachlorophenol at concentrations down to 0.27 ppm. PCP is electrochemically reduced in phosphate buffers of pH 8 to produce a concentration-dependent current peak at —0.8 V vs. Ag/AgCl. The procedure requires only 15 min. Cyclic voltammetry at the hanging mercury drop electrode is used to evaluate the electrochemical reaction and to establish the reversibility of the PCP electrode reaction.     

Speciation of Pu ions by differential pulse polarography

By means of differential pulse polarography, Pu ions of different oxidation states have been investigated in 1M Na₂CO₃ solution. Redox reactions of Pu/III/, Pu/IV/, Pu/V/ and Pu/VI/, which are mostly of irreversible nature, have been observed within the potential range of the dropping mercury electrode /DME/, from 0 to –1.5 V, against a Ag/AgCl/NaCl (3M) reference electrode. Based on the peak potential observed for each reaction, the stability of a given oxidation state in the solution could be ascertained. The redox potential of the Pu/IV/–Pu/III/ pair, which was found to be –1.0 V, indicated that the Pu/IV/ carbonate complex was of high stability. The detection sensitivity of the Pu/IV/ ion was found to be 1×10^–6M.     

Aqueous sulfur species determination using differential pulse polarography

Sulfur species play pivotal roles in biogeochemistry; however, quantification remains difficult because such species are transitory. Our objective was to determine the utility of using differential pulse polarography (DPP) to characterize soluble sulfur species of potential interest in agriculture and environmental quality. Polarographic responses for sulfide, disulfide, pentasulfide, sulfite, thiosulfate, tetrathionate, pentathionate, cysteine, and glutathione were determined. Sulfur in the compounds was categorized as cysteine-S, thiosulfate-S, nonpurgeable or purgeable sulfide-S, or sulfite based on characteristic polarographic responses for each respective category. Nonpurgeable sulfide-S, cysteine-S, and thiosulfate-S were polarographically separated using a pH 8.0 phosphate buffer. Nitrate/bicarbonate (pH 10.0) and acetate (pH 5.0) buffers were used to determine purgeable sulfide-S and sulfite, respectively. Sulfur in water extracts from cysteine-amended soils was quantified using the developed DPP method. Cysteine-, thiosulfate-, and sulfide-S were measured from these extracts without interferences during a 16-d incubation period. The developed DPP method provides qualitative and quantitative information concerning sulfur species in aqueous solutions and is potentially applicable to soil and sediment extracts.     

The applicability of the superposition principle in differential pulse polarography

It is shown theoretically that the superposition principle is applicable to pulse voltammetry if the electrochemical system can be separated into a potential-dependent nonlinear part and a linear part. For systems not complicated by adsorption or electrode kinetics, the applicability of the principle depends on diffusion coefficients, electrode and cell geometry. For plane semi-infinite diffusion, applicability is expected; this is generally not the case for spherical electrodes or bounded regions (film electrode or thinlayer cell). The implications of the theory on differential pulse polarography are discussed and an experimental study on the applicability for iron(III), cadmium(II) and lead(II) is presented.     

Characterisation of the approach to equilibrium of the osazone of dihydroxytartaric acid in aqueous solutions by differential pulse polarography

Differential pulse polarography is used to determine the changes in the enthalpy, entropy and Gibbs function for the forward and reverse conversions of the osazone of dihydroxytartaric acid from one tautomeric form to another at pH 11.4 in aqueous solution. This is done by determining the individual rate constants associated with these conversions at different temperatures through combining kinetic measurements with measurements on the system at equilibrium. The equilibrium constant was found to vary widely with pH and to increase with increase in temperature. The driving force for the endothermic conversion of the osazone from the hydrazone form to the azohydrazine form is shown to be the much greater freedom of movement (greater entropy) available to the latter form.