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The adsorption of berberine and canadine was measured by a.c. polarography. For berberine three different superficial structures were observed: the ions lying flat, the mixed layer of flat and perpendicular ions and the condensed film of perpendicular ions which incorporates anions of the supporting electrolyte. The boundaries between these structures are diffuse. The condensation is an instantaneous nucleation and two-dimensional film growth process. The adsorption of canadine is similar, but its condensed film is very stable and the exchange rate between the adsorbed canadine and the dissolved berberinium ions is very low. Different structures of the adsorbed berberine result in different faradaic square-wave responses.

A model of the anion-induced adsorptive accumulation combined with a square-wave voltammetric stripping is developed. The dependence of peak currents and peak potentials on the reversibility of redox reactions and on the reaction mechanism is demonstrated. The sensitivity of the method is estimated.

The basic model for the E↓E mechanism, in which the intermediate is attached to the surface of the electrode in a form of an electroactive monolayer film, is developed. Splitting of the currents corresponding to the individual charge transfers is predicted. The splitting depends on the stability of the intermediate and on the difference between the standard rate constants of the individual charge transfers. It is, also, inversely proportional to the drop lifetime or the potential-pulse duration. The maximum on the second wave at the DME is predicted. The differences between the logarithmic analyses of the total redox currents for E↓E and simple EE mechanisms are shown and discussed.

The absorption spectra of berberrubine in the visible and uv spectral range were recorded. The measurements were made in four different solvents (water, absolute methanol, absolute ethanol, and absolute propanol) changing the acidity and the alkalinity of the solutions in the wide range from pH 2 to pH 13 by the addition of HCl and KOH. The experimental and theoretical results, derived by simple Hückel MO calculations, were compared and discussed.

Etude theorique de l'adsorption liquide-liquide a une electrode en mercure en fonction de l'electrolyte

The theory for the EE mechanism influenced by adsorption of the intermediate (E↓E) has been developed. For an adsorption process following Henry's isotherm the analytical expression is reported, while for an adsorption process following Langmuir's isotherm the working curves for pulse polarography and differential pulse polarography, obtained by numerical integration, were given. The parameters of adsorption βΓ s and A * /Γ s , the thermodynamic stability of the intermediate and the parameters of the polarographic techniques were varied. The resulting variation of pulse polarographic total current of the E↓E mechanism has been described and discussed. Two main features of the E↓E mechanism are the splitting of the single, two-electron main wave into two separate one-electron waves, if the adsorption follows Henry's isotherm, and the simultaneous appearance of both the prewave and the postwave at the bottom and near the top of the main wave if the adsorption follows Langmuir's isotherm.

The pseudo-polarographic properties of Zn 2+ are described. It has been shown that the pseudo-polarograms of a quasi-reversible redox reaction can be recorded. The results were compared with square-wave polarographic measurements and with the theoretical predictions. The main reason for recording pesudo-polarograms is the possibility of measuring the dependence of their half-wave potentials on the concentration of a certain complex-forming ligand at vrey low metal concentration. The stability constants of zinc chloride complexes, at a zinc concentration of 1 × 10 −8 mol/dm 3 , were calculated and compared with literature data. Pseudo-polarography improves the possibility of verifying experimentally the chemical models of trace metal speciation in natural waters.

The enhancement of square-wave (SW) voltammetric peak currents caused by adsorption depends on the reversibility of the redox reaction from the adsorbed state. The phenomenon is analysed by a simple mathematical model. The SW characteristics of ten metal ions, Tl(I), Cd(II), Pb(II), Zn(II), UO2+2 Cu(II), In(III), Bi(III), Ni(II) and Co(II), in different electrolytes containing ClO−4, Cl−, NO−3 and SO2−4 ions are reported. A very high ratio between the SW peak currents of reversible and totally irreversible redox reactions is noticed. An extremely high ratio was observed between the SW responses of Bi(III) in chloride and in perchlorate. These high ratios are attributed to the adsorption of metal ionic species on the DME surface.

The maxima on pulse polarograms influenced by the reversible, linear adsorption of a reactant of a quasi-reversible redox reaction on a stationary, planar electrode have been analysed theoretically. Some criteria for the estimation of the reversibility of the redox reaction from the adsorbed state are proposed. In the second part, the experimentally obtained maxima on pulse polarograms of berberine are described and analysed. The reduction of berberine is quasi-reversible in the pulse polarographic sense.

The phenomenon of maxima on pulse polarograms of tottally irreversible redox reactions has been investigated. Only the linear adsorption isothern has been considered. Some analyses of the possible influcence of the adsorption induced capactive current on the total pulse polarographic current response are presented. It was assumed that the electrode surface area is constant. The model could be applied to the description of pulse polarographic experiments on a static mercury drop electrode.

The influence of the adsorption of electractive species on DPP responses of non-reversible redox reactions is described. A linear isotherm and stationary planar diffusion were assumed. The DPP resposes influenced by the adsorption of both the reactant and product are enhanced if the redox reaction is quasi-reversible or totally irreversible. The dependence of the degree of enhancement on the various parameters of the redox reaction, the adsorption process and the excitation signal is analysed.

The influence of reactant adsorption on square-wave voltammograms of totally irreversible redox reactions is analyzed theoretically. Characteristics of the response ip, Ep and ΔEp/2 are expressed by the equations 6, 7 and 8, respectively. SW voltammograms of berberine are compared with theoretical predictions and the transfer coefficient α = 0.32 and the maximum surface concentration Γs = (8.2 ±0.4)·10−11 mol cm−2 are determined.

The vibrating dropping mercury ele·ctrode (VDME) is applied to the characterization of ionic species and to electroanalytical measurements of metal ion concentrations in water samples strongly polluted with different kinds of surface active substances (SAS). The Cd2+ /CdNTA- system in citrate buffer solution at pH = 6 was chosen as a model for the effect of a preceeddng homogeneous chemical reaction on the reveraible charge transfer of »free« metal ions. The influence· of Triton- X-100 on the Cd2+ poiarographic wave is a good example of nonionic SAS interference with metal ion charge transfer. The possibilities of the VDME for electrochemical measurements of methylene-blue and iatrorubine in NaCl and KN03 supporting electrolytes are discussed. The VDME with its short drop li.fe time of up to 200 drops/s is more convenient and reliable than other kinds of electrodes for kinetic measurements and for the analysis of samples which are highly polluted by organics.