Sine-wave polarographic determination of zirconium or niobium in aqueous media

The sine-wave polarographic determination of zirconium in aqueous media was investigated using solutions which were 0.55 – 5.5·10^-3M in zirconyl chloride and 1 M in potassium chloride and had been adjusted to pH 2.0 with hydrochloric acid. It was possible to determine zirconium in the concentration range of 0.05 to 0.4 mg per ml. The sine-wave polarographic behavior of zirconium in aqueous solutions in the pH range 2–3 is discussed. The sine-wave polarographic determination of niobium in aqueous media was investigated using concentrated sulfuric acid containing 5 to 0.1 mg of niobium per ml in a supporting electrolyte of citric acid; the determination of niobium was possible down to 0.1 mg of niobium per ml of concentrated sulfuric acid although the D.C. polarographic method was impractical for the determination of less than 0.5 mg of niobium per ml.     

Indirect polarographic microdetermination of sulphur in organic compounds

A polarographic method for the microdetermination of sulphur in organic compounds is described; it is based on oxygen-flask combustion to yield sulphate, which is then reacted with excess of barium dichromate solution in hydrochloric acid, followed by adjustment to pH 12, collection of the combined barium chromate and sulphate precipitate, and polarographic determination of the free chromate (equivalent to the sulphate originally present).     

m-Nitrophenylarsonic acid as a polarographic reagent for titanium

A sensitive polarographic method for titanium, based on its selective and quantitative precipitation with polarographically reducible m-mtrophenylarsonic acid is described, factors affecting the quantitative precipitation — pH, concentration, of titanium and reagent, nature and concentration of anions, and digestion — have been studied.After precipitation of the titanium under controlled conditions, the precipitate is dissolved and the polarographic diffusion current of the organic reagent is related, by a calibration, to the original titanium concentration.The method has been applied successfully to the determination of titanium in complex high temperature alloys, after the removal of iron by a mercury cathode electrolysis.     

Polarographic determination of phenylalanine,tyrosine, methionine,glutamic acid and histidine with a dropping copper amalgam electrode

The anions of the phenylalanine, tyrosine, methionine and glutamic acid give an anodic wave when a dropping copper amalgam electrode is oxidized in their presence, approximately at the same half-wave potential of that of the glycine anion (?0.28 V vs. SCE). The height of these waves depends on pH and amino acid concentration and can be utilized for the polarographic determination of these substances using the same procedure as that described previously for the determination of glycine. The polarographic behaviour of histidine is somewhat different because the zwitterion of this amino acid reacts with the Cu²⁺ and the anion forms a more stable complex. The polarographic determination of histidine can be also carried out with the same procedure.     

Polarographic (DCP & DPP) Determination of Ellagic Acid in Strawberries & Pharmaceutical Formulations

Direct Current (DC) and Differential Pulse (DP) Polarographic methods have been developed for the qualitative as well as quantitative analysis of ellagic acid in plant products (i.e. strawberries) and pharmaceutical formulations (Ellagic insurance formula). Ellagic acid produces a well‐defined polarographic wave/peak in pyridine hydrochloride at pH 6.8 ± 0.1 with E_1/2 /Ep = ?1.298 V vs. SCE. The wave/peak height is found to be proportional to the concentration of ellagic acid. The developed procedure was used for the analysis of ellagic acid in an extract of strawberries (Fragaria × ananassa) and pharmaceutical formulations. Statistical treatment of the observed polarographic data revealed high accuracy and good precision of determination. The work has been supplemented by FTIR screening of the sample. The percentage of ellagic acid in pharmaceutical formulations was determined by the developed method, which is in close agreement with the labeled amount.     

AC polarographic reduction of biguanides

Biguanides present ac polarographic activity in buffered media. At acid pH the reduction process is controlled by diffusion. The equation of waves and measurement criteria are discussed.     

Simultaneous polarographic determination of cadmium and tellurium in electro-deposited cadmium telluride thin films

A polarographic method has been developed for the simultaneous determination of cadmium and tellurium in thin-film cadmium telluride. The procedure involves dissolution of the film with concentrated nitric acid, which is subsequently removed by evaporation. The Cd(II) and Te(IV) waves are well separated at pH 10, but sufficient ammonia must be present to prevent the precipitation of cadmium hydroxide.     

Polarographic and voltammetric behaviour of 2-hydroxy-3-tert-butyl-5-methylazobenzene

The polarographic and voltammetric behaviour of 2-hydroxy-3-tert-butyl-5-methylazobenzene has been studied in aqueous-ethanol mixtures of different pH using DCP and DPP polarographic and CV and SWV voltammetric methods. The reduction of the azo linkage takes place via two electrons at pH > 7, but four electrons at pH < 7 in aqueous-ethanol mixtures. It has been determined that there is a linear relationship between the current and concentration and the lowest detection limit has been found as 1 × 10^–7 M (for SWV).     

Application of differential pulse polarography for trace determination of polycytidylic acid in absence and presence of some metal ions

Summary A differential pulse polarographic method has been applied to the determination of trace concentrations of polycytidylic acid (Poly-C) in absence and presence of metal ions. The applicability of differential pulse polarography for the trace determination of the investigated biological compound was examined with regard to the dependence of differential pulse current on various parameters such as pH, pulse amplitude, scan rate and drop time. The selectivity of this technique for the determination of binary and a ternary mixtures of poly-C and some metal ions has been also reported. Limits of detection and quantitation have been calculated for the differential pulse polarographic determination of the poly-C and various metal ions. The validity of this method is supported by the constancy of the i_p/C values and a statistical analysis is included on calibration curve parameters and observed concentration.     

Polarographic studies of iron complexes as potential contrast as agents in magnetic resonance imaging

Iron(III) complexes of polyaminocarboxylic acids of potential use as contrast agents in magnetic resonance imaging wre investigated by differential pulse polarography. The complexes with diethylenetrinitrilopentaacetic acid, trans-1,2-cyclohexylenedinitrilotetraacetic acid and triethylenetetranitrilohexaacetic acid (TTHA) wre found to decompose slowly at pH 7.2. With TTHA, a mixture of 1:1 and 2:1 complexes was obtained, and the transformation between the two complexes was slow. Ethylenediimonobis[(2-hydroxyphenyl)acetic acid] (EHPG) was found to be the most suitable ligand. The complex formation is kinetically slow, and a special procedure for the preparation of the complex is required; the complex is then stable for one week at pH 7.2. The polarographic measuremeents are preferably made at pH 9.2, where a well-defined reduction peak is obtained. The complex is stable for 2 days at pH 9.2. At pH values below 9, a double peak is obtained, except for low concentrations of the complex. Both Fe(III)EHPG and Fe(II)EHPG adsorb at the mercury electrode. The polarographic determination can be done in the presence of 10% of urine or serum without interference. The detection limit is in the low μM range.     

Voltammetric determination of agriculturally-significant benzenearsonic acids

Direct current and differential pulse polarographic measurements are reported on a series of substituted benzenearsonic acid compounds that are important in agricultural applications. Compounds studied were o-aminobenzenearsonic acid, p-aminobenzene-arsonic acid, p-nitrobenzenearsonic acid, p-ureidobenzenearsonic acid, and 3-nitro-4-hydroxybenzenearsonic acid. Polarographic reduction potentials varied with pH for all compounds, shifting to more negative values as the pH was increased. Although diffusion-controlled reduction waves were observed in all cases, some compounds exhibited a dependence of E$\text{1}\text{2}$ on concentration, especially at relatively high concentrations. Differential pulse polarographic peak currents were proportional to concentration from 10^-4 M to 10^-6 M.     

Polarographische Uranbestimmung in Anwesenheit großer Phosphatmengen

The method developed by ?u?ic and Gy?rbiró makes possible the polarographic determination of uranium even under a high phosphate content (e.g. the analysis of superphosphate), provided that following the reduction of the contaminating ions by ascorbic acid the solution is reneutralized to pH 0.10. 20–100 μg of U/ml have been determined with an accuracy of ±5%.     

Resacetophenone isonicotinic acid hydrazone as a reagent for the catalytic polarographic determination of nanogram quantities of vanadium(V)

The polarographic method proposed for 1–12 ng of vanadium(V) is based on the reduction of bromate, catalysed by the metal ion, with resacetophenone isonicotinic acid hydrazone at pH 5.0. Only iron interferes seriously.     

Polarographic Determination of Aztreonam

Abstract

The polarographic behaviour of Aztreonam is studied. In acid media, at pH values lower than 6, in differential pulse polarography a peak is observed at a potential close to ? 0.6 volts. The optimum conditions for the polarographic signal are established and the different parameters affecting the electrochemical process are studied. The relationship between peak intensity and the concentration of Aztreonam is linear for concentrations lower than 1.0 ? 10^?5 M, the detection limit being 1.4 × 10^?8 M It was observed that the presence of 1-arginine does not affect the polarographic signal of Aztreonam to any significant extent.     

Electrochemical reduction of 5,5′-dichlorohydurilic acid. mechanism and analytical applications

The electrochemical reduction of 5,5′-dichlorohydurilic acid has been studied at the dropping mercury electrode (DME) and the pyrolytic graphite electrode (PGE). At the DME the single polarographic reduction wave observed at pH 6–11 involves a direct 4e—2H⁺ reduction of the carbon-halogen bond to give hydurilic acid and chloride. The state of hydration or ionization of the 5,5′-dichlorohydurilic acid has no effect on the electrochemical reaction. At the PGE, 5,5′-dichlorohydurilic acid shows two voltammetric peaks. Peak I_c, observed between pH 5 and 7, arises from an overall 4e—2H⁺ reduction of 5,5′-dichlorohydurilic acid via a mechanism that involves initial electron attack at a carbonyl group alpha to a carbon-halogen bond with simultaneous elimination of chloride ion. The peak II_c process involves an initial 2e—1H⁺ reduction of a partially hydrated form of 5,5′-dichlorohydurilic acid with only one unhydrated halocarbonyl moiety available for reaction. Attack is again via the carbonyl group with simultaneous elimination of chloride and formation of 5-chlorohydurilic acid. A chemical dehydration step then occurs with a rate constant of ca. 0.24 s^?1 at pH 8.2, with formation of a further reducible halocarbonyl group. This is again reduced in an overall 2e—2H⁺ reaction to give hydurilic acid and chloride ion. The peak II_c process hence proceeds via an ECE mechanism. The different mechanisms observed for reduction of 5,5′-dichlorohydurilic acid at mercury and pyrolytic graphite electrodes are unusual. Analytical methods have been developed for the polarographic determination of 5,5′-dichlorohydurilic acid via its reduction wave at the DME, and for the voltammetric determination of hydurilic acid via its first oxidation peak at the PGE.     

Contribution a l'electrochimie des thiols et disulfures : Partie III. Polarographie d.c., a.c., et polarographie differentielle a impulsions de l'acide thiobarbiturique et du pentothal sodique

D.c., a.c. and differential pulse polarography were used to elucidate the electrochemical behaviour of thiobarbituric acid and sodium pentothal.Important adsorption phenomena were shown, particularly for thiobarbituric acid. Considerable differences were found in the polarographic curves of the two compounds. The number of waves obtained depends on the concentration and the pH for both compounds.     

Indirekte polarographische Bestimmung der o-Phthals?ure neben ihren Estern

Zusammenfassung Eine indirekte polarographische Methode zur Bestimmung von Phthalsäure in Gegenwart ihrer Ester wird vorgeschlagen. Hierbei wird Blei(II)-phthalat aus einer alkoholischen Lösung der Phthalsäure abgeschieden, abfiltriert und in Ammoniumacetatlösung gelöst. Die polarographische Stufe wird bei Galvonometerempfindlichkeit 1/70, Potential -0,6 V und pH 5,6 gemessen. Der Fehler beträgt maximal 5%.

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Summary An indirect polarographic method is proposed for the determination of phthalic acid in presence of its esters. Lead(II) phthalate is precipitated from an alcoholic phthalic acid solution, is filtered off, and is dissolved in ammonium acetate solution. The polarographic wave is measured at galvanometer sensitivity 1/70, a potential of -0.6 V and pH 5.6. The maximum error is 5%.

     

Solution Equilibria. A Unified Mathematical Treatment of Experimental Polarographic and Potentiometric Data from Acid?Base and Ligand Titrations. A Polarographic and Ion Selective Electrode Study of CdII?(N‐(2‐hydroxyethyl)iminodiacetic acid)?OH System

It has been demonstrated that potentiometric and polarographic data coming from either acid? base or ligand titrations can be evaluated by the same set of equations and mathematical procedures involving mass‐balance equations written for any metal? ligand model, including polynuclear species. It is shown that the concept of the complex formation curves, used previously in modeling and refinement of stability constants in acid‐base titration, is of general nature and can be successfully used in polarographic and potentiometric experiments conducted as a function of pH or an excess of a ligand. It appears that the linear relationship ΔE vs. log [M], typical for potentiometric studies with ISE, holds also in the case of the study of kinetically mixed metal‐ligand system studied by polarography when the corrected shift in the polarographic signal is used. The relationship ΔE vs. log [M] applies equally to the acid‐base and ligand titration for both experimental techniques employed (potentiometry and polarography). The significance of the corrected shift is discussed and its meaning in the study of kinetically fast or slow metal? ligand systems is elaborated. Advantages of the acid‐base titration over the ligand titration are discussed. The generalized mathematical data treatment was successfully employed in the study of the Cd^II? (N‐(2‐hydroxyethyl)iminodiacetic acid) system. Results obtained from both analytical techniques (potentiometry with the use of an ion selective electrode, and two polarographic techniques) and analytical procedures (acid? base and ligand titrations) compare well with each other and with the literature data (the formation and stability constants of ML and ML₂). In addition, a new complex M(HL) was identified and its stability constant is reported.     

Polarography of thiodiglycolic acid and thiodipropionic acid at the dropping mercury electrode

The polarographic behaviour of thiodiglycolic acid (R?S?R) and thiodipropionic acid (R?CH₂?S?CH₂R) at the DME, has been investigated in presence of 0.1 M KCl and 0.01% thymol with respect to the effects of changes in pH, concentration, drop time, and temperature on the wave characteristics. Well-defined irreversible cathodic waves were obtained in the pH range 2.40 to 4.76 for R?S?R and 2.3 to 4.98 for R?CH₂?S?CH₂R. At lower (<2.0) and higher (>5) pH values, ill-defined waves were obtained. The mechanism of the electrode process in aqueous solutions has also been elucidated.     

Contribution à l'étude Électrochimique de Dérivés de l'Acide Mercapto-2 Pyridinecarboxylique-5. II

Abstract

Electrochemical caracteristics of 2-mercaptopyridine-5-carboxylic acid and its methylic ester have been determined using recent polarographic techniques. Measurements have been carried out as a function of parameters such as frequency, others surimposed signals and as a function of concentration and pH. Results are compared to those obtained for selectively methylated on sulfur or nitrogen atoms derivatives. Interpretations of the data are given. The optimal conditions for a quantitative determination by D.C. and differential pulse polarography are fixed.