Voltammetry with cathode stripping is widely used for determination of a number of
heavy metals in various objects of the environment. This paper is focused towards the
application of methods developed within the study of electrochemical behavior of heavy metals
(Cu, Cd, Pb V) on the mercury electrode in the presence of a series of complexing agents. Using
the adsorptive cathodic stripping voltammetry for dosage of V (V), Cu (II), Pb (II) and Cd (II),
2,3-dihydroxy-benzaldehide (2,3-DHBA), thiosemicarbazide diacetic acid (TSCDA), the
reagents semicarbazone 8 - quinolinaldehyde (SCQA) and 4-phenyl-thiosemicarbazide (4-
FTSC) respectively have served as agents of accumulation. Metals form complex compounds
with those reagents that are adsorbed on the dropping and stationary mercury electrodes. In the
case of Cu (II) the simplest concentration process of Mn+ can be expressed by the equations (1)
and (2), for Pb the process according to scheme 3 is assumed, for vanadium and cadmium a
process of stepwise complexation is observed:
pMn+ + qL-   MpLq pn-q
(sol) (1)
Reaction (1) occurs in solution and is considered as a chemical stage (R) of the process. The
formed complex are adsorbed on the electrode:
 MpLq pn-q
(sol)   MpLq pn-q
(ads) (2)
Reaction (2) takes place on the electrode and has an adsorption nature (A). The overall
scheme of the process can be depicted as R → A. The mechanism consists in adsorption of L and
it is an adsorption stage (A):
qL-
(sol)  qL-
(ads) (3).
At the second stage (R), the adsorbed ligand reacts with metal ions Mn+:
pMn+ + qL-
(ads)   MpLq pn-q
(ads) (4).
Contrasting the reaction (1), the process (4) occurs on the electrode surface, but leads to
formation of the complex with the same composition. The general scheme of the process can be
depicted as A → R. The adsorptive nature of the recorded reduction peaks has been proved by
the speed coefficients and the variation of dropping time of capillary in function of the potential
applied to electrodes in solutions with separated and mixed components.
The mixing ratio Me:L in solution as well as the species that is reduced on the electrode
surface, have been determined by amperometric titration. For each metal separately the effect of
pH and the impact of other species Zn(II), Fe(III), Ni(II), Cr(VI), Co(II), CH3COO-, CO3
2-, SO4
2-
, Cl-, Br-, I-, CNS-, CH3COO-, CO3
2-, SO4
2-) on the analytical signal intensity have been
investigated.
The time of accumulation of analyzed species on the suspended mercury drop is dictated
by the interference of other species, is dependent on the metal nature and varies within 10-180 s.
The developed methods have been applied for determination of Cu (II), Pb (II), V (v) and Cd (II)
in waters of the Prut River.