526
A. Nosal-Wierci´ nska and W. Kaliszczak
3 Experimental Methods
3.1 Adsorption Measurements
The double-layer capacity (C d ) was measured using the electrochemical impedance
spectroscopy (EIS). For the whole polarization range, the capacity dispersion was
tested at different frequencies between 200 and 1000 Hz. To obtain proper equilibrium values of differential capacity, the linear dependence of capacity on the square
element from frequency was extrapolated to the zero frequency [10, 22].
The potential of zero charge (E z ) was measured for each solution by the method
of streaming the mercury electrode [10, 22]. The interfacial tension (γ z ) between
mercury and the electrolyte solutions at E z was measured with a conventional
maximum bubble pressure capillary electrometer described earlier [10, 22].
3.2 Kinetic Studies
Research on the mechanism of the electrode process was associated with the need
to determine kinetic parameters such as formal potential (E
0
f ), reversible half-wave
potential (E
r
1/2 ), transfer coefficients (α), standard rate constants (k s ), or apparent rate
constants (k f ) of Bi(III) ion electroreduction as well as diffusion coefficients (D ox ).
These parameters were determined in the way presented in the paper [23]. In the
DC polarography, square-wave voltammetry (SWV), cyclic voltammetry (CV), and
electrochemical impedance spectroscopy (EIS), the optimal experiment operating
conditions were as given in the papers [24, 25].
4 Results and Discussion
As follows from the studies, 6-mercaptopurine, 6-thioguanine, azathioprine, and
surfactants adsorbed on the mercury surface change the interface area structure.
It was proved that thiopurine derivatives adsorb on the electrode specifically [29]
whereas Tween 80 and Triton X-100 physically [26–29].
The differential capacity curves (Fig. 1) obtained in the studied systems for
6-mercaptopurine [29, 30], 6-thioguanine [31], azathioprine [32] point out to the
changes in the capacity values compared with the supporting electrolyte.
In the region of the “hump” potentials, appearing in 2 mol · dm chlorate(VII)
without the thiopurine derivatives (≈ −200 to −800 mV), after the addition of
6-mercaptopurine and 6-thioguanine to the solution, the height of the “hump”
decreases. In turn after the introduction of azathioprine into the solution, the height
A. Nosal-Wierci´ nska and W. Kaliszczak
3 Experimental Methods
3.1 Adsorption Measurements
The double-layer capacity (C d ) was measured using the electrochemical impedance
spectroscopy (EIS). For the whole polarization range, the capacity dispersion was
tested at different frequencies between 200 and 1000 Hz. To obtain proper equilibrium values of differential capacity, the linear dependence of capacity on the square
element from frequency was extrapolated to the zero frequency [10, 22].
The potential of zero charge (E z ) was measured for each solution by the method
of streaming the mercury electrode [10, 22]. The interfacial tension (γ z ) between
mercury and the electrolyte solutions at E z was measured with a conventional
maximum bubble pressure capillary electrometer described earlier [10, 22].
3.2 Kinetic Studies
Research on the mechanism of the electrode process was associated with the need
to determine kinetic parameters such as formal potential (E
0
f ), reversible half-wave
potential (E
r
1/2 ), transfer coefficients (α), standard rate constants (k s ), or apparent rate
constants (k f ) of Bi(III) ion electroreduction as well as diffusion coefficients (D ox ).
These parameters were determined in the way presented in the paper [23]. In the
DC polarography, square-wave voltammetry (SWV), cyclic voltammetry (CV), and
electrochemical impedance spectroscopy (EIS), the optimal experiment operating
conditions were as given in the papers [24, 25].
4 Results and Discussion
As follows from the studies, 6-mercaptopurine, 6-thioguanine, azathioprine, and
surfactants adsorbed on the mercury surface change the interface area structure.
It was proved that thiopurine derivatives adsorb on the electrode specifically [29]
whereas Tween 80 and Triton X-100 physically [26–29].
The differential capacity curves (Fig. 1) obtained in the studied systems for
6-mercaptopurine [29, 30], 6-thioguanine [31], azathioprine [32] point out to the
changes in the capacity values compared with the supporting electrolyte.
In the region of the “hump” potentials, appearing in 2 mol · dm chlorate(VII)
without the thiopurine derivatives (≈ −200 to −800 mV), after the addition of
6-mercaptopurine and 6-thioguanine to the solution, the height of the “hump”
decreases. In turn after the introduction of azathioprine into the solution, the height