Experiments were conducted by using a PAR (Princeton Applied
Research) model 394 Polarographic analyzer equipped with a
model 303A electrode system (EG&G). A conventional three electrode
system, comprising a medium-sized hanging mercuric drop
electrode, with a surface area of 1.8 mm2, a platinum wire counter
electrode and an Ag/AgCl (in saturated with KCl) reference electrode
was used in all experiments. The reported potentials were
referred to the Ag/AgCl electrode. Solutions were deoxygenated
with high purity nitrogen for 220 s prior to each exp