Polarographic current-time curves and the Ilkovic Equation.

1958 ◽  
Vol 11 (3) ◽  
pp. 271 ◽  
Author(s):  
HA McKenzie
Keyword(s):  
Mercury Electrode ◽  
Potassium Nitrate ◽  
Current Time ◽  
Current Voltage ◽  
Modified Equations ◽  
Dropping Mercury Electrode ◽  
Instantaneous Current ◽  
Average Current ◽  
The One ◽  
Oxygen Measurements

The Ilkovic equation for the limiting diffusion current obtained with a dropping mercury electrode predicts that the instantaneous current grows during the life of the mercury drop as the one-sixth power of the time, and that the ratio of the instantaneous current at the end of the drop life (the maximum current) to the average current is 1.17. McKenzie (1948) showed in a preliminary study that these relations are not obeyed. The present paper is concerned with a more detailed study of current-time curves for cadmium(II), lead(II), and thallium(I) ions and oxygen. Measurements are made both in the presence and absence of maximum suppressor (gelatin) in two supporting electrolytes (potassium chloride and potassium nitrate). It is found that the rate of growth of the instantaneous current is not in accordance with the Ilkovic equation. Also, it does not accurately follow the modified equations, such as the Lingane-Loveridge equation, particularly during the early stages of drop life. The ratio of maximum to average current varies for the different electroactive substances, but in all cases examined 1.23<imax./iav.<1.30. An interesting observation is also made on the current-time curves for cadmium(II) in potassium nitrate in the presence of gelatin. At pH values appreciably below the isoelectric point (?pH 5) the current-time curves and the current-voltage curves are distorted. The implications of these results in the measurement of polarographic waves, both in theoretical and analytical applications, are discussed.

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.

Current-time characteristics of the rapidly dropping mercury electrode

1960 ◽  
Vol 23 ◽  
pp. 585-591 ◽  
Author(s):  
Reita Tamamushi ◽  
Sunao Momiyama ◽  
Nobuyuki Tanaka
Keyword(s):  
Mercury Electrode ◽  
Current Time ◽  
Dropping Mercury Electrode

Polarography of azobenzene and its p-sulphonic acids

1964 ◽  
Vol 17 (10) ◽  
pp. 1085 ◽  
Author(s):  
TM Florence ◽  
YJ Farrar
Keyword(s):  
Ph Effect ◽  
Aqueous Media ◽  
Mercury Electrode ◽  
Electrode Reaction ◽  
Ammonium Ions ◽  
Current Time ◽  
Electrode Processes ◽  
Ph Values ◽  
Strong Adsorption ◽  
Dropping Mercury Electrode

The behaviour at the dropping mercury electrode of trans-azobenzene and its p-sulphonic acids has been studied by several techniques including d.c., a.c., single sweep, and Kalousek polarography. Current-potential curves recorded at the streaming mercury electrode provided information on the reversibility of the electrode processes, while current-time and electrocapillary curves aided in elucidating the effects of adsorption. The results show that the rate of the electrode reaction of the azo-hydrazo couple is dependent on pH, the minimum rate occurring near pH 9 for azobenzene-4-sulphonic acid in aqueous media. At very low and high pH values, the couple approaches full reversibility at the dropping mercury electrode. This pH effect is apparently due to strong adsorption of both the azo and hydrazo derivatives near the potential of the electrocapillary maximum. Ammonium ions associate with azobenzene-4-sulphonate, and improve the reversibility in intermediate pH regions.

Polarography of some coordination compounds of Platinum. III. Ions of the tetrammineplatinum(II) type

1956 ◽  
Vol 9 (1) ◽  
pp. 14 ◽  
Author(s):  
JR Hall ◽  
RA Plowman
Keyword(s):  
Trans Isomer ◽  
Coordination Compounds ◽  
Supporting Electrolyte ◽  
Mercury Electrode ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Current Voltage ◽  
Dropping Mercury Electrode ◽  
Divalent Platinum ◽  
Cis And Trans

A number of tetrammine ions of divalent platinum, in which the ligands were ammonia, methylamine, dimethylamine, ethylenediamine, pyridine, aniline, and combinations of some of these, were studied at the dropping mercury electrode. Some of the ions showed maxima in their current-voltage curves (c-v curves). The formation of hydrogen interfered with the c-v curves of other ions, so that limiting currents were not obtainable. A method was devised for the measurement of a voltage by means of which the ease of reduction of the ions could be compared. Using a supporting electrolyte of 0.1M KCl and 0.01% gelatin, the order of increasing ease of reduction was found to be [Pt{(CH3)2NH)4]2+ = [Pt(NH3)4]2+ = [Pt(NH3)3(C5H5N)]2+ = [Pt{C2H4(NH2)2}2]2+ < cis-[Pt(NH3)2(C5H5N)2]2+ < trans-[Pt(NH3)2C5H5N)2]2+ < [Pt(CH3NH2)4]2+ = [Pt(NH3)(C5H5N)3]2+ <[Pt(C6H5N)4]2+ < cis-[Pt(NH3)2(C6H5NH2)2]2+ < trans-[Pt(NH3)2(C6H5NH2)2]2+. When the ammonia groups of [Pt(NHS),l2+ were successively replaced by pyridine groups, the resulting e-v curves shifted progressively to more positive voltages. It was also found that cis- and trans-isomers of [PtA,B,I2+ reduced at different voltages. The trans-isomer reduced more readily.

An interface reaction of Hexavalent chromium: The polarographic behaviour of HCrO4- and CrO42-

1955 ◽  
Vol 8 (1) ◽  
pp. 51 ◽  
Author(s):  
JH Green ◽  
A Walkey
Keyword(s):  
Ph Value ◽  
Mercury Electrode ◽  
Interface Reaction ◽  
Proton Donor ◽  
Interface Reactions ◽  
Inorganic Systems ◽  
Trivalent State ◽  
Current Voltage ◽  
Dropping Mercury Electrode ◽  
Adsorption Desorption

Current-voltage relationships have been determined for the electroreduction of dilute chromate solutions in a range of bicarbonate-carbonate buffers at the dropping mercury electrode. Double waves are obtained whose relative heights are a function of the pH value. By analogy with the behaviour of pyruvic acid an interface reaction with some proton donor prior to the reduction to the trivalent state is suggested (CrO42- +HB- → HCrO4- + B-). The rate constants for the interface reaction are computed for different donors by the method of Koutecky and Brdicka (1947). Adsorption-desorption processes in the region of the electrocapillary zero may account for the shape of the current-voltage curves, and, if so, the explanation based simply on an interface reaction will require modification. The occurrence of interface reactions and of adsorption-desorption processes in other inorganic systems is discussed.

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