Pulse polarography: VIII. A new digital to analog pulse polarograph

A new pulse polarograph for normal mode instantaneous current sampling with digital control of timing and of potential generation, is described. Pulse times and delay times are independently variable over a wide range. Pulse times can be varied in 10 ms intervals. The performance of the instrument has been tested in the determination of pulse-polarographic diffusion coefficients of Tl⁺, Cd²⁺, Co(III)(en)₃³⁺ and Co(NH₃)₆³⁺. The reproducibility was found to be excellent.     

Pulse polarography: IX. Proton diffusion in aqueous sulphate solution

Average diffusion currents, , of the ions H₃O⁺ and HSO₄^? in the system 0.1 M K₂SO₄+H₂SO₄ (pH=3.1?3.8) have been measured at 25°C both with a dropping mercury and a rotating disk electrode, using pulse techniques. The separate diffusion coefficients D_HSO4 and D_H have been estimated fromand it was found that D_H≤61×10^?6 cm²s^?1, which is definitely less than the value calculated when relaxation and (bulk) viscosity effects are taken into account. This is at variance with all the literature D_H values for non-sulphate systems and also with our experimental result D_H=(84.6±0.2)10^?6 cm²s^?1 for the system 0.1 M KCl+HCl, which is about 7% above the value from Onsager's theory. The peculiar behaviour of D_H in a K₂SO₄ solution is attributed to a strong decrease in rotational freedom of water molecules in such a medium.This paper also gives a critical evaluation of the principle of “independent diffusion” in excess neutral electrolyte if more than one species participates in the diffusion process.     

Pulse polarography: Part X. Formaldehyde hydration in aqueous acetate and phosphate buffer solutions

Formaldehyde hydration has been studied with pulse polarography in acetate and phosphate buffers, at 25°C. It could be shown that in both buffer systems extrapolation to zero buffer concentration produces the equilibrium constant K_d=[CH₂O]/[CH₂(OH)₂]=(6.31±0.05) 10^?4 in pure water, a value of as yet unmatched precision. In the buffers mentioned two novel features appear in the hydration mechanism: (a) buffer acids form addition compounds with CH₂O where the, corresponding equilibria are rapidly established. The equilibrium constants have been derived. (b) H₂PO₄^?/HPO₄^2? buffers are exceptional in that the polarographic specific rate of hydration as a function of the concentration of this buffer is less than expected on the basis of a normal linear dependence. This is explained, as in the case of free-aldehyde glucose [23], on the basis of a solvent (water)-shared associate of (presumably) H₂PO₄^? with CH₂O which decreases the rate of diffusion of the latter, the more so as the buffer concentration increases. It is pointed out, that the occurrence of such associates can explain the excess activity of H₂PO₄^? as an acid catalyst in aldehyde hydration [16].