Polarographic studies of α-substituted cystines

1967 ◽  
Vol 45 (7) ◽  
pp. 713-717 ◽  
Author(s):  
R. J. Thibert ◽  
R. J. Walton
Keyword(s):  
Hydrochloric Acid ◽  
Linear Relationship ◽  
Diffusion Current ◽  
Polarographic Determination ◽  
Wave Potential ◽  
Titration Curves ◽  
Half Wave Potential ◽  
Half Wave ◽  
Relationship Of

The polarographic determination of some α-substituted cystines in 0.1 N hydrochloric acid, with thymol as a maximum suppressor, was investigated. A linear relationship of the diffusion current to the concentration of the compound was observed. The influence of substituent, thymol concentration, and pH on the apparent half-wave potential and shape of the polarograms was determined. The systems were not reversible.Potentiometric titration curves were obtained for the α-substituted cystines.

Polarography of some coordination compounds of platinum. I. Hexammineplatinum (IV) and Tris(ethylenediamine)platinum(IV) ions

1955 ◽  
Vol 8 (2) ◽  
pp. 158 ◽  
Author(s):  
JR Hall ◽  
RA Plowman
Keyword(s):  
Potassium Chloride ◽  
Supporting Electrolyte ◽  
Platinum Metal ◽  
Potassium Nitrate ◽  
Diffusion Current ◽  
Polarographic Reduction ◽  
Wave Potential ◽  
Half Wave Potential ◽  
Half Wave ◽  
Continuous Discharge

The polarographic reduction of tris(ethylenediamine)platinum(IV) and the hexammineplatinum(IV) ions has been studied in potassium chloride, potassium nitrate, and potassium nitrate plus ammonia solutions. Both ions were reduced irreversibly producing similarly shaped waves, showing well-defined diffusion current regions corresponding to two-electron reductions of the complexes. A linear relationship existed between diffusion current and concentration within the range examined. In aqueous potassium chloride and potassium nitrate media, the waves contained slight inflexions at positions corresponding to one-electron additions. The phenomenon suggested the transient presence of platinum(III) ions, and indicated that the half-wave potential of the reduction of the complexes to the trivalent state was very close to the half-wave potential of the reduction from platinum(IV) to platinum(II). The values were so close together as to indicate the improbability of isolating the trivalent complexes. Gelatin enhanced the inflexion in the wave but shifted the wave in a more negative direction. An increased concentration of supporting electrolyte also shifted the wave to a more negative position. In all cases a continuous discharge began at about -1.3 V (v. S.C.E.). This discharge was so far removed from that of the potassium ions of the supporting electrolyte that it was attributed to the discharge of hydrogen. Since the initial reduction of the platinum complexes corresponded to a two-electron change, it can be represented by reduction to a tetrammine ion. It is postulated that at higher applied potentials (namely, -1.3 V v. S.C.E.) the reduction proceeded further, producing platinum metal. This platinum metal would be in an active state, insoluble in mercury, and being on the surface, would lower the overvoltage of hydrogen leading to its discharge at a more positive potential than on a pure mercury surface. This view was supported by the fact that gas bubbles were observed at the dropping electrode when a voltage greater than -1.3 V was applied to the electrode for some time. When ammonia was added to the supporting electrolyte, a wave, without an inflexion, and corresponding to an irreversible two-electron reduction, was obtained at more negative potentials. The bivalent tetrammineplatinum(II) and bis(ethylenediamine)platinum(II) ions also gave polarograms showing the continuous discharge of hydrogen.

Determination of the half-wave potential of nobelium

1976 ◽  
Vol 38 (6) ◽  
pp. 1171-1173 ◽  
Author(s):  
R.E. Meyer ◽  
W.J. McDowell ◽  
P.F. Dittner ◽  
R.J. Silva ◽  
J.R. Tarrant
Keyword(s):  
Wave Potential ◽  
Half Wave Potential ◽  
Half Wave

A New Method of Analysis of Polarographic Waves

2003 ◽  
Vol 68 (6) ◽  
pp. 1055-1064 ◽  
Author(s):  
Juan Carlos Ruiz-Morales ◽  
Jesús César Rodríguez Placeres ◽  
Manuel Barrera Niebla ◽  
Mariana Cuesta Sánchez
Keyword(s):  
Computer Program ◽  
Kinetic Parameters ◽  
New Method ◽  
Great Precision ◽  
Electrode Processes ◽  
Wave Potential ◽  
Half Wave Potential ◽  
Half Wave ◽  
Thermodynamic And Kinetic Parameters

A method of analysis of polarographic waves of simple electrode processes is proposed. The quasi-reversible half-wave potential, Ec1/2, is involved in the determination of thermodynamic and kinetic parameters of electrode processes. This potential is determined very easily and with great precision. In order to facilitate the use of the method proposed, we have developed a computer program for Windows.

THE POLAROGRAPHIC REDUCTION OF AMARANTH

1954 ◽  
Vol 32 (11) ◽  
pp. 1025-1032 ◽  
Author(s):  
G. G. McKeown ◽  
J. L. Thomson
Keyword(s):  
Direct Relationship ◽  
Polarographic Reduction ◽  
Wave Potential ◽  
Half Wave Potential ◽  
Diffusion Controlled ◽  
Half Wave ◽  
Azo Group ◽  
Ph Range ◽  
Relationship Of ◽  
Coefficient Of Diffusion

Amaranth, a food color, has been studied polarographically over a pH range of 2.0 to 10.0 in aqueous solution and was found to give a well-defined wave, diffusion controlled and suitable for quantitative work. Irreversibility was indicated by the behavior of the half-wave potential to changes in pH and concentration. With pH, a direct relationship of −0.080 v. per pH unit held between pH 2.0 and 7.0, while with concentration, the half-wave potential was found to apparently vary directly with the logarithm of concentration. Using a coefficient of diffusion value obtained by conductance measurements the value of n for the reaction was calculated to be 4, which corresponds to a rupture of the azo group to yield the corresponding amines.

The recording of D.C. Polarographic waves and the measurement of the instantaneous current at the end of the life of the mercury drop

1958 ◽  
Vol 11 (3) ◽  
pp. 260
Author(s):  
HA McKenzie ◽  
MC Taylor
Keyword(s):  
Good Accuracy ◽  
Automatic Recording ◽  
Diffusion Current ◽  
Current Time ◽  
Wave Potential ◽  
Half Wave Potential ◽  
Half Wave ◽  
Current Voltage ◽  
Instantaneous Current ◽  
Average Current

Because of the slowness of response of the current detectors used in the infancy of polarography, it has become the custom to measure the average current rather than the instantaneous current at some given time near the end of the life of the mercury drop. McKenzie (1958a) has pointed out that there are a number of theoretical advantages to be gained by measurement of instantaneous diffusion current. The work reported in the present paper shows that this measurement can be made accurately with conventional electronic equipment. Owing to the inherent lag in automatic recording polarographs which measure average current, it is not possible to obtain from the records the half-wave potential and slope with good accuracy. It is shown that the advantages of automatic recording and accuracy in determining the half-wave potential and slope may be realized by recording instantaneous current-voltage curves. Also abnormalities in current-time curves may be readily detected. Apparatus using a conventional recorder and a preamplifier which is a modification of that of Kelley and Miller (1952) is described. A device which can be used to control pen drive is also described.

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