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Factors to be considered in quantitative polarography with the rotated dropping mercury electrode

The various factors which affect limiting currents at the rotated dropping mercury electrode (RDME) are reviewed. The current at the RDME in the absence of surface active substances involves maxima of the second kind, even under conditions where these maxima are not observed at the conventional dropping mercury electrode (DME). For most practical purposes, it is necessary to eliminate the maxima completely by adding a suitable surface active compound. The presence of 0.01% polyacrylamide is recommended as a maximum suppressor in all polarographic work. At a suitable speed of rotation (200 to 300 r.p.m.) the sensitivity of the RDME in the presence of a surface active substance is about ten times as great as that of the DME.Equation (3), derived in a previous paper² accounts quantitatively for the relation between limiting current in the presence of a suitable maximum suppressor on the one hand and the concentration and diffusion coefficient of electroactive species, speed of rotation, kinematic viscosity and the characteristics of the electrode (m and t) on the other. The limiting current is practically indepndent of the pressure of mercury, but varies with t^a, where a ? 0 5.For reversible reactions half-wave potentials at the RDME are of the same order of magnitude as observed at the DME. The slight difference observed in the reduction of metal ions to metal amalgams is accounted for quantitatively by the larger rate of transport of electroactive species to the RDME.The RDME is recommended for the analysis of solutions containing one or more electroactive species in concentration of less than about l0^-4N. For markedly higher concentrations the DME ib generally preferred.     

Application of the rotated dropping mercury electrode to the analysis of mixtures of electroactive substances

The use of poylacrylamide is recommended instead of gelatin as an ideal maximum suppressor to be employed with both the rotated dropping mercury electrode (RODE) and conventional dropping electrode (DME). It is retained at the mercury surface over the entire potential range and does not combine with heavy metals. Reproducibility of the measurement of the residual current and that of the limiting current at the RDME were studied, and it was found that accurate determinations of a single constituent (±2%) are possible at concentrations as low as 1 to 2.10^-5M. The variation of the limiting current with potential is much greater at the RDME than at the DME. This effect must be considered in the analysis of a mixture of electroactive species at the RDME. Method have been discussed for making the proper correction for a preceding wave when a limiting current of a mixture of constituents is measured. Because of its high sensitivity and good reproducibility of results, the RDME is recommended for the analysis of solutions containing one or more electroactive species at concentrations less than 10^-4M.     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode : A comparison of the baker and morrison cell with the raie.

In the amperometric determination of fluoride at the RAIE a half cell composed of 5% cadmium amalgam in equilibrum with a solution 1 M in cadmium sulfate and saturated with potassium chloride can be used as a reference electrode in a short-circuited cell instead of applying a potential of -0 75 V versus the saturated calomel electrode The standard addition method can be used in the presence of air, although removal of oxygen is recommended Using the Baker and Morrison electrode versus the above half cell and following their directions (10 ml solution, magnetic stirring) proportionality between current and fluoride concentration in a range between 1 · 10^-5 and 1 · 10^-4M was found in oxygen-free solutions Halides and perchlorates do not interfere. The standard addition technique can be used in the determination of fluoride in an unknown.     

Zur maßanalytischen Bestimmung von lllangan,Chrom und Nickel in legierten Stählen aus einer Einwage

Analytical and Bioanalytical Chemistry -     

Die ma?analytische Bestimmung von Ammoniak mit Hypobromit nach der gew?hnlichen und nach der potentiometrischen Methode

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