Prior to the deposition of the film, the glassy carbon electrode
was polished with water slurry of 0.30 and 0.05 lm alumina powder
on a polishing kit to a mirror-like appearance, rinsed and then
ultrasonicated with 1:1 (v/v) HNO3 aqueous solution, absolute ethanol
(99.7%) and water, respectively. Then the well-polished glassy
carbon electrode was voltammetrically cycled between 0.5 and
1.4 V (vs. Ag/AgCl) at a scan rate of 200 mV s1 in 0.50 M H2SO4
for 10 cycles, the activated electrode was placed in 2.00 mM
p-ABSA and 0.10 M phosphate buffer solution (pH 7.6) and then
it was modified by 15 cycles of potential sweep between 1.0
and 2.0 V (vs. Ag/AgCl) at a scan rate of 200 mV s1
. Subsequently,
the modified glassy carbon electrode was voltammetrically cycled
and characterized in 0.10 M acetate buffer solution (pH 4.0) until a
stable cyclic voltammogram was obtained. After that, the electrode
was rinsed with ethanol and doubly distilled water successively,
and used for the following experiments.
Stripping voltammetric measurements were performed in a
10 mL electrochemical cell, if not stated otherwise, containing
appropriate amounts of Cd(II), 3.0 mg L1 Bi(III), 2.0 mg L1 Sn(II)
and 3.0 mL of 0.10 M acetate buffer solution (pH 4.0). The preconcentration
was carried out at 1.1 V for 150 s under stirring
and after a 10 s equilibration period, the voltammogram was
recorded by applying a positive-going square-wave stripping voltammetric
potential scan from 1.2 to 0.2 V with a frequency of
35 Hz, pulse amplitude of 75 mV and scan increment of 2 mV.
Prior to the next measurement, a 30 s clean step at 0.3 V under
stirring was used to remove the residual metals and the
stannum/bismuth film. All potentials were referred to the Ag/
AgCl reference electrode.
3. Res