2. Experimental2.1. ApparatusThe vo

2. Experimental
2.1. Apparatus
The voltammetric measurements were performed using a
Metrohm 693 VA Processor in combination with a 694 VA
Stand (all fromMetrohm, Herisau, Switzerland). The three-electrode configuration was consisted of MFE, BiFE or
HMDE as working electrodes, an Ag/AgCl reference
electrode (3 mol L

1
KCl) and a glassy carbon tip as
auxiliary electrodes. MFE and BiFE were produced by the
deposition of Hg(II) and Bi(III) ions at the graphite
electrode (Ultra-Trace Graphite) and the glassy carbon
(GC) as supporting electrodes (both from Metrohm).
Before use, the electrodes were polishedwith a water slurry
of 0.3mmAl2O3 on a microcloth polishing pad and rinsed
with ethanol and water.
2.2. Reagents and Solutions
All chemicals were of analytical grade purity. Water was
purified by a Milli-Q Ultra Pure Water System (Millipore,
Bedford, USA). All chemicals were of analytical-reagent
grade. All aqueous solutions were prepared with distilled
anddeionizedwater,whichwas further purifiedbyaMilli-Q
high purity water device (Millipore, Bedford, USA). The
metal stock solutions containing 1000 mgL
1
wereprepared
from Cd(SO
4)2, Pb(NO
3)2, Cu(SO
4)2
(Merck, Darmstadt,
Germany), andTlNO3(Sigma-Aldrich, St. Louis, USA) and
working standard solutions by suitable dilutions of the stock
solutions. Hydrochloric acid (37%), Hg(NO3)2, Bi(NO
3)3
·
5H2O and aluminum oxide (0.3mm) were obtained from
Merck (Darmstadt, Germany), Sigma-Aldrich (St. Louis,
USA), ACROS (New Jersey, USA), and Metrohm (Her-isau, Switzerland), respectively. Standard solutions of
1000 mg L

1
Hg(II) and 400 mg L

1
Bi(III) were prepared
by dissolving appropriate amounts of the salts in 1 mol L

1
HCl.