The present study elucidates the electrochemical behavior of cadmium in the presence of
S-methylisothiosemicarbazone of 5-tert-butyl-2-(tert-butyl-thio)-benzene-1,3-dialdehyde, which
can serve as a cadmium accumulation agent on the mercury drop surface. In the presence of Smethylisothiosemicarbazone
of 5-tert-butyl-2-(tert-butyl-thio)-benzene-1,3-dialdehyde cadmium
(II) forms a reduction peak. The allure of reduction peak in different support solutions, such as
0.1M KCl, 0.2M NaClO4 and 0.5M potassium hydrogenophtalate remains unchanged. The
reduction peak is recorded at –0.71V, -0.75V and -0.72V, respectively. The observed value of
reduction current does not differ significantly in the above-mentioned support solutions at the
same concentrations of cadmium (II) and ligand.
The slope of line in coordinates lgIp - lg V, which is determined from the study of the
peak current (Ip) dependence on voltage scanning speed (V), represents the speed coefficient “X”
that has been found equal to 0.85. The experimentally obtained value of speed coefficient
characterizes the electrochemical electrode processes, which are accompanied by the adsorption
of depolarizing agent on the mercury electrode surface by diffusion. This is reflected also in
curves presenting current variation as a function of applied to electrode potential (fig.2). In pH
range of 4–6 the variation of reduction potential and reduction current practically become
constant, which permits to consider the 5.5 pH value as an optimal for further investigations.
From the dependence peak size of the accumulation time on stationary mercury drop it
has been established that after 180 s the surface of mercury drop is totally covered by the
adsorbed particles of depolarizing agent.
The adsorptive accumulation demonstrates that depending on the mercury drop size and
accumulation time, the detectable cadmium concentration diminishes by one order, in
comparison with cadmium determination without accumulation (2.510-8 M, accumulation time
180 s. versus 2·10-7 M, respectively). The optimal accumulation potential is of –0.35  - 0.40V.
The deviation from this value of potential leads to a reduction current decrease.
The molar ratio of the adsorbed on the mercury electrode surface complex Cd(II) - L has
been estimated by amperometric titration as Cd(II) : L = 1 : 1. The Cu(II), Co(II), Fe(III), Cd(II),
Pb(II) and Ni(II) ions in a molar ration Cd : Me = 1 : 10 do not present interference in the
experiment conditions.
The presence in solution of ions CH3COO-, I-, Br- and SCN- in a ratio An : Cd = 10:1
does not influence on the peak intensity. A linear dependence between the value of peak
maximal current and cadmium concentration is maintained in the 1.0·10-8-2.0·10-6 M range
(hanging mercury drop electrode, accumulation time 10 s, stationary diffusion).
Acknowledgment:
The author is grateful to her colleagues Dr. Lozan Vasile and Dr. Cocu Maria, researchers of the
Institute of Chemistry, for their synthesis of ligand.