Direct current and differential pulse polarographic behaviour of benzylpenicilloic acid

The differential pulse and direct current polarographic behaviour of benzylpenicilloic acid (BPA) is discussed. In pH 9.2 borate buffer, the single anodic wave (E_{$\text{1}\text{2}$} = -0.25 V) obtained is diffusion-controlled at concentrations less than 2 × 10^-5 M but adsorptioncontrolled in 10^-4 M solution. Cyclic voltammetry at a hanging mercury drop electrode shows that the electrode reaction is reversible at pH 9.2. The differential pulse peak current is linearly related to concentration in the range 10^-6—2 × 10^-5 M. Penicillamine yields an anodic peak well separated from the BPA peak. Both substances may be determined in each other's presence. Intact penicillin decreases the BPA peak but the linearity between i_p and BPA concentration is maintained.     

Electrochemical study and polarographic determination of ranitidine

In the polarographic reduction of ranitidine, an H₂-antagonist of histamine, three waves are observed; their half-wave potentials and limiting currents depend strongly on the pH of the solution. The first and second waves are due to reduction of teh protonated, CHNO₂H⁺, and unprotonated, CHNO₂, nitroethene group of ranitidine, respectively; the origin of the third wave is unknown. The characteristics of the second and third waves are studied in acetic acid/acetate buffer at pH 5.5; the first wave does not appear at this pH. The second wave (E_{$\text{1}\text{2}$} = ?0.90 V, vs. Ag/AgCl) is useful for determining ranitidine in the range 2.4–4.9 × 10^?4 M by direct current polarography and in the range 2.5 × 10^?7?2.05 × 10^?5 M by differential pulse polarography.     

Polarographic investigations of some copper chelates of 3-arylazopentane-2,4-diones

The polarographic curves of the copper chelates of twelve substituted 3-arylazopentane-2, 4-diones exhibit single 4e diffusion-controlled irreversible waves between pH 2 and 11. The two azo groups in the compound are equivalent so that only a single 4e wave is obtained; no copper reduction wave is observed. The polarographic behaviour differs from that of p-bisazobenzene. There is a linear correlation between the E$\text{1}\text{2}$ values and the Hammett substituent constants.     

Acid—base equilibria of some benzhydryl piperazine derivatives

The ultraviolet spectral and polarographic behaviour of several benzhydryl piperazine derivatives is described. Attempts have been made to associate the pK data obtained with protonations at various nitrogen atoms in the molecules. Analysis of the plots of E_{$\text{1}\text{2}$} vs. pH have yielded direct polarographic methods for determining some of these compounds in the presence of possible metabolic products.     

Analytical application of triethylenetetraaminehexa- acetic acid: Part 2. Polarographic Investigation of the reactions of TTHA at the dropping mercury electrode

TTHA gives an anodic d.c. wave and s.w. peak corresponding to oxidation of mercury at the d.m.e. surface with formation of a Hg(II)—TTHA complex. Similar processes are known for other ligands, e.g. EDTA and DCTA, but the greater stability of the Hg(II)—TTHA complex gives a significant improvement in the shapes of the anodic wave and s.w. peak. An increase in pH shifts the E_{$\text{1}\text{2}$} and E_p values towards more negative values because the conditional stability constant of the Hg(II)—TTHA complex is increased. Although the half–wave potentials of the reduction wave of Hg(II)—TTHA and of the anodic wave of TTHA, are the same, other criteria for the reversibility of polarographic reactions suggest that the anodic TTHA process at the d.m.e. is not completely reversible. The temperature coefficient of the wave and s.w. peak as well as the dependence of the wave height on the square root of the mercury head prove that the process is diffusion–controlled. Supporting electrolytes are given for which the d.c. wave and the s.w. peak of TTHA are well-shaped, with linear dependence between the wave or peak height and the concentration of TTHA in the ranges 5 × 10^-5–5 × 10^-4 M (d.c.) and 1 0^-5–1 × 10^-4 M (s.w.).     

Dosage de l'histidine: Étude polarographique et dosage du dinitrofluorobenzene

After polarographic study and determination of dinitrofluorobenzene at varying pH and determination of a number of electron exchanges (n), standardization curves have been constructed at pH 5 and 10. They allow the estimation of DNFB to a concentration of 1γ/ml with a precision of 4–7%. The curve shows 2 or 3 leaps, according to pH.. The E_{$\text{1}\text{2}$} of the first two are less than 1 volt.     

Electrochemical studies of organometallic compounds : III. The polarographic determination of the CH acidity of metallocenes

The polarographic reduction of the tree sets of compounds, i.e. organomercury salts, symmetrical organomercury compounds and σ-derivatives of π-cyclopentadienyliron dicarbonyl, have been investigated. The polarographic parameters obtained have been correlated with the pK_a values of RH. A least squares treatment of the results and a comparison of the accuracy of the determination for the new pK_a values of RH obtained for the three sets of reactions investigated show that the best correlation is obtained for a plot of the half-wave reduction potentials E_{$\text{1}\text{2}$} of π-C₅H₅Fe(CO)₂-σ-R and the pK_a values of RH. The pK_a values for ferrocene, cyclopentadienylmanganese and rhenium tricarbonyls as CH acids have been determined.     

Pulse polarographic determination of nitrosamines: Part 2. Methods for the Determination of N-Nitrosodiphenylamine and N-Nitrosodibutylamine

Differential pulse polarographic methods are reported for the determination of N-nitrosodiphenylamine and N-nitrosodibutylamine in aqueous media. Optimum conditions for analysis were obtained with acetate buffer (pH 3.74) and 0.01 M H₂SO₄, where reduction peak separations were of the order of 300 mV and 200 mV, respectively. Detection limits were approximately 3×10^-8 M for each compound. Methods for the extraction of these nitrosamines from iso-octane to aqueous solutions were quantitatively examined.     

Studies on organophosphorus compounds—XXXVI: Simple new routes to phosphorins from 2-hydroxy-, 2-mercapto-, and 2-aminobenzoic acids and their derivatives

2-Hydroxybenzoic acid heated with 2,4 - bis(4 - methoxyphenyl) - 1,3,2,4 - dithiadiphosphetane - 2,4 -disulfide, 1, gave 2 - (p - methoxyphenyl) - 4$\text{H}$ - 1,3,2 - benzoxathiaphosphorin - 4 - one 2 - sulfide, 3, and its thio-analogue, 4, while its ethyl or phenyl esters gave 4 as the sole product. 2 - Mercaptobenzoic acid and its ethyl ester when heated with 1 produced 3$\text{H}$ - 1,2 - benzodithiole - 3 - one, 8, 3$\text{H}$ -1,2 - benzodithiole - 3 - thione, 9, and 2- (p - methoxyphenyl) - 4$\text{H}$ - 1,3,2 - benzodithia - phosphorin - 4 - one 2 - sulfide, 10. The reaction of 2 -aminobenzoic acid with 1 gave 1,2 - dihydro - 2 - (p - methoxyphenyl) - 4$\text{H}$ - 3,1,2 - benzoxaphosphorin - 4 - one 2 - sulfide, 12. Reactions of 1 with methyl 2 - aminobenzoate and 2 - aminobenzamides are described. Mechanistic considerations for the formation of the heterocyclic phosphorus compounds are presented.     

Heterodiene syntheses—XIX: Correlation of the kinetic data with lumo energies in the reaction between 1-aryl-4-benzylidene-5-pyrazolones and isopropyl vinyl ether

The kinetics of the reaction between 1-p-substituted phenyl-4-benzylidene-5-pyrazolones and isopropyl vinyl ether have been studied by quantitative spectroscopic analysis and liquid chromatography. The rate increases with the electron attracting character of the substituents and a correlation is obtained with σ- constants. The polarographic one-electron half-wave reduction potentials E^red_{$\text{1}\text{2}$}, which represent an experimental measure for the relative energy of the lowest unoccupied molecular orbital (LUMO), were measured. Good correlations were obtained between these and the kinetic data, thus demonstrating the frontier-controlled character of the cycloaddition and the dominant interaction between the LUMO of the pyrazolone and the highest occupied molecular orbital (HOMO) of the vinyl ether.     

Analytical applications of triethylenetetraminehexaacetic acid : Part I. the influence of TTHA on the polarographic reduction of some metal ions

The influence of triethylenetetraminehexaacetic acid (TTHA) on the d.c. and square-wave polarographic curves of Cu(II), Pb(II), Cd(II), Ni(II), Co(II), Zn(II), Fe(III), Bi(III), Sb(III), As(III) and In(III) has been investigated in several supporting electrolytes over the pH range 1–13. The E_{$\text{1}\text{2}$} and E_p values with and without a 10-fold excess of TTHA are compared. Some analytical applications are suggested.     

Differential-pulse polarography of amino acids in acetaldehyde-borax medium

A differential-pulse polarographic method for the determination of amino acids is reported, based on the formation of Schiff's base compounds in borax buffer solution (pH 10.10) containing acetaldehyde. The compounds are reduced at a mercury electrode with peak potentials of about ?1.5 V (vs. SCE) and well defined polarographic waves are obtained which can be used to determine amino acids in borax medium. The differential-pulse polarographic method was found to be the most sensitive and suitable for the determination of amino acids in the concentration range 1 × 10^?6–8 × 10^?4 M (lysine) and 2.8 × 10^?6–1 × 10^?3 M (arginine). The polarographic characteristics of these waves were studied by differential-pulse polarographic and cyclic voltammetric methods. The waves are ascribed to the reduction of the imido group in the Schiff's base compounds. The procedure was applied to the determination of lysine and arginine in foodstuffs and the total proteins in serum samples.     

A kinetic study of the permanganate—oxalate reaction and kinetic determination of manganese(II) and oxalic acid by the stopped-flow technique

The reduction of permanganate by oxalate in the presence of manganese(II) ion in acidic media is described. All reactions were run at 525 nm and constant ionic strength 1.0 M. The reaction was found to obey the rate expression —$\text{d[MnO}{}_4{}^{\mathrm{-}}\text{]}\text{d}\text{t}$ = k [Mn²⁺] [C₂O₄^2-]² [MnO₄^-] [H⁺]^-2 = k' [MnC₂O₄] [MnO₄^-]. The values of k and k' were shown to be 5.4 × 10⁴ M^-1 s^-1 and 8.2 × 10⁴ M^-1 s^-1, respectively. Reaction rate methods for the determination of manganese(II) and oxalic acid are reported. The rate of disappearance of permanganate was monitored automatically and related directly to manganese-(II) and oxalic acid concentrations. Manganese(II) in the ranges 1–10 × 10^-4 M and 1–10 × 10^-3 M and oxalic acid in the range 0–20 μg ml^-1 can be determined very rapidly with a precision of 1–2%.     

A study on sorbitol-ceric ion initiated polymerization of acrylonitrile

The polymerization of acrylonitrile (M) initiated by the sorbitol (R)-Ce(IV) redox system has been studied in sulphuric acid in the range 30–40° under nitrogen. At moderately high concentrations of Ce(IV) (0.00015-0.02 M), the rate of polymerization (R_p) is proportional to $\text{[}\text{M}\text{]}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{[}\text{R}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and the rate of Ce(IV) disappearance is proportional to [R] and [Ce(IV)]. At lower concentration of Ce(IV) (0.00005–0.00015 M) R_p is proportional to [M], [R]^1/2 and [Ce(IV)]^1/2 and rate of Ce(IV) disappearance is proportional to [R] and [Ce(IV)]. The effects of certain salts, acid, solvent and temperature on both rates have been investigated. A kinetic scheme involving mutual termination has been proposed and various rate and energy parameters evaluated. At still higher concentration of Ce(IV) (0.02 M), a linear mode of termination seems to operate.     

Studies in polarographic analysis : Determination of manganese after oxidation to the manganic state stabilized by triethanolamine

The manganic complex with triethanolamine, prepared by the oxidation of manganous solution in presence of 0.5M NaOH and 4% by volume triethanolamine with atmospheric oxygen, is found suitable for the polarographic determination of manganese. Under these conditions, the diffusion current is proportional to the Mn⁺² concentration from 2.10^-4·7.10^-3ME$\text{1}\text{2}$,for the Mn⁺³/Mn⁺² wave = — 0.5 V vs S.C.E. The temperature coefficient for the diffusion current 1.2% per degree I and D° decrease by increasing the alkali or triethanolamino concentration. They amount in presence of NaOH = 0.5M and 4% triethanolamine to I = 1.27 and D° = 4.18·10^-6 cm²/sec.     

The application of 2,4,6-trinitrobenzene-1-sulphonic acid in the differential pulse polarographic determination of amines

The differential pulse polarographic behaviour of 2,4,6-trinitrophenyl (TNP) derivatives of several primary amines and amino acids was investigated in the presence of sulphite ion. All the derivatives produced a polarographic peak for their complexes with sulphite (1 × 10^?2 M) in pH 8.0 phosphate buffer (0.05 M)/0.1 M potassium chloride. The derivatives of proteins and peptides did not give such a peak. A 5-min reaction time at room temperature (or 50°C for lysine) and pH 10.5 using 1 × 10^?4 M 2,4,6-trinitrobenzene-1-sulphonic acid provides the optimal conditions for the determination of 5 × 10^?6?2.5 × 10^?5 M amines. The relative standard deviation for determining 1 × 10^?5 M glycine (n = 5) was 1%.     

Some electroanalytical aspects of using pulse polarography for determination of Ge(IV)

Summary Presented data give some informations of analytical importance as a result of pulse polarographic investigations of Ge(IV) in KCl solutions within pH range 3–12 at Ge concentration from 1×10^–4 to 2.5×10^–6 M. It was shown that Ge(IV) can be polarographically active in acidic solution but its reduction interferes with hydrogen gas development. The addition ofp-quinone enables the determination of Ge(IV) without this interfering effect.Suggested explanation of the observed changes in polarographic curves dependent on pH and Ge concentration based on the existence of several polarographically active forms.

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Elektroanalytische Bemerkungen zur pulspolarographischen Bestimmung von Ge(IV)

Zusammenfassung Unsere Ergebnisse bieten einige Informationen über die pulspolarographische Bestimmung von Ge(IV) in KCl-Lösungen innerhalb pH 3–12 und bei Ge-Konzentrationen zwischen 10^–4 und 2,5×10^–6 M. Es wurde gezeigt, daß Ge(IV) in saurer Lösung polarographisch aktiv ist, seine Reduktion aber durch Wasserstoff-Entwicklung gestört wird. Der Zusatz vonp-Chinon beseitigt diese Störung. Die Änderung der polarographischen Kurven je nach Ge-Konzentration und pH beruht vermutlich auf der Existenz verschiedener polarographisch aktiver Formen.

     

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.     

Étude du comportement polarographique de Ge(IV)

A reduction wave of Ge(IV) is observed at pH valvest greater than 7. The study of the wave has shown that the reduction is irreversible and occurs from Ge⁺⁴ to Ge° and that its height is strongly dependend on the pH. We have shown that the second wave observed by Das Gupta and Nair in the medium NH₄CI-NH₄OH cannot be ascribed to Ge. From an analytical point of view, it should be operated in the pH-regiXXXn. from 8 to 9, wliere the height of the wave can be considered as constant ; the diffusion current constant equals 6.82. In the KCl 0.05M medium, we have measured D = 0.79.1O^-5 cm²/sec and E$\text{1}\text{2}$ = —1.50 volt v/SCE; where as NH₄Cl-NH₄OH, medium. D = 0.89–10^-5 cm²/sec and E$\text{1}\text{2}$ = —1.56 volt v/SCE,     

The effect of pH on some outer-sphere electrode reactions at carbon electrodes

The apparent heterogeneous rate constant, k°_app, for three couples known to undergo outer-sphere electron transfer reactions has been investigated at carbon, gold, and platinum electrodes as a function of solution pH. The rates are found to be pH dependent at two different types of glassy carbon and at carbon paste but not at metallic electrodes. The rate is found to decrease with increasing pH for Fe(CN)^{$\text{3?}\text{4?}$}₆ and IrCl^{$\text{2?}\text{3?}$}₆, and the opposite effect is observed for the Ru(NH₃)^{$\text{3+}\text{2+}$}₆ couple. For the three compounds examined, the magnitude of the pH dependent rate changes can be associated with a change in the magnitude of the potential of the reaction layer induced by a change in surface charge of ～ 2 × 10^?7 C cm^?2. The pH dependence of the observed rate constant at glassy carbon can be attenuated by heat treatment, chemical reduction, or esterification of the surface. This behaviour is consistent with the theory that the pH dependence of k°_app arises from the presence of functional groups on the carbon surface.