be overcome using the glassy carbon electrode (GCe)
and the very sensitive technique Osteryoung squarewave
voltammetry (OSWV). Fig. 1 shows the dependence
of the pH on the OSWS voltammogram of
110
ÿ5 M manganese at three pH values, namely:
4, 6 and 8 in the presence of acetic acid/NH4OH. The
metal ion is accumulated at the three pH values chosen
but the sensitivity of the adsorption process is more
pronounced in slightly acid medium (pH4.0) and in
alkaline medium (pH9.0). Measurements without
ammonium acetate (without the ligand a small manganese
peak is obtained), at a similar potential, the
peak was greatly enhanced upon adding the ammonium
acetate. The optimum ligand concentration for
an effective interfacial accumulation of Mn±ammonium
±acetate complex is found to be 0.05 M acetic
acid and 0.125 M NH4OH, pH 9.0.
A series of optimization studies of the square-wave
stripping voltammetric parameters was made. The
best parameters are summarized in Table 1, they will
be always used unless otherwise it will be stated in the
text.
The reversibility of the complex formed,
Mn(NH4)acetate, was checked applying cyclic voltammetry.
Although as it is well-known, the reduction
of manganese occurs via an irreversible process, its
reduction in the formed complex is found to be
reversible (Fig. 2). The number of electrons consumed
during the electrochemical process is 3 as calculated
according to the equation [26]:
Epa ÿ Epc 0:059
n
: