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deposition conditions. It was also found that the concentration of
Pb in the plating solution strongly affects the microstructure of
the formed lead films. For Pb concentrations that do not exceed
5 × 10−5 M Pb, the film was not uniform and crystallites 1.3 m high
and up to 5 m in diameter were observed, whereas for the higher
Pb concentration (1 × 10−4 M Pb), a more homogenous and com-
pact film was formed, with smaller crystallites. The microscopic
observations correlated well with the results of the electrochemical
studies.
It was also confirmed that metal film electrodes, even those
produced from a non-noble metal such as lead, might be useful
in electroanalytical determination in which sufficiently negative
potentials are applied during measurements. One of the reasons
why new electrode materials are being developed is the toxicity of
mercury. Bismuth, on the other hand, has been one of the most
popular environmentally friendly materials for some time now.
Lead as an electrode material utilized for film generation on the
surface of glassy carbon supports, is also characterized by higher
toxicity in comparison to bismuth. However, it is a less toxic sub-
stitute for mercury, and has been shown to be more useful than
bismuth-based and mercury-based electrodes in adsorptive strip-
ping voltammetry. Furthermore, lead and inorganic lead salts are
much less volatile than mercury and its salts. Lead film electrodes
may be effectively employed for the determination of cobalt and
nickel by catalytic adsorptive stripping voltammetry with nioxime
and nitrite in ammonia buffer solutions, yielding better signals and
resolutions than other types of film electrodes, such as bismuth film
electrodes or mercury film electrodes. High hydrogen overvoltage
combined with a favorable signal-to-background ratio, excellent
resolution and good reproducibility were obtained using the lead
film electrode. These characteristics are comparable to those of
hanging mercury drop electrodes. The PbFE can be easily regener-
ated by stripping the lead film after a preceding measurement and
formation of a new film prior to each measurement. Furthermore,
the application of the cyclic scan procedure improves the repro-
ducibility of the deposited metal film. Contrary to the BiFE, the PbFE
can be easily deposited in situ in ammoniacal solutions, provid-
ing good reproducibility. This is undoubtedly a very advantageous
analytical feature of the investigated sensor.
Fig. 7. Comparison of the differential pulse voltammograms obtained at the PbFE
(solid line), BiFE (dotted line), MFE (dash dot dot line), GCE (dashed line) in the solu-
tion containing 0.1 ammonia buffer, 2.5 × 10−5 M nioxime, 5 × 10−9 M Co, 5 × 10−8
M
Ni and 0.25 M NaNO2. In the case of the PbFE the solution contained an additional
5 × 10−5 M Pb. Instrumental parameters: Enuc = −1.45 V; Eacc = −0.75 V for BiFE, MFE
and GCE or Eacc = −0.65 V for PbFE, tacc = 120 s, ꢀE = 20 mV, ES = 2 mV.
tion of Co–nioxime and Ni–nioxime complexes. It is also possible
to obtain exploitable signals with chronopotentiometric stripping
analysis, if a stripping current of 5 A or less is applied. Higher
currents yielded smaller, poorly shaped signals and low sensitivity.
The working potential ranges of the PbFE in different support-
ing electrolytes, both neutral and basic, were also investigated. The
accessible potential window is restricted by the decomposition of
the supporting electrolytes at the negative potential region, and
by the oxidation of lead at the positive potential region, which are
strongly dependent on the pH of the solution (Fig. 6).
3.3.3. Comparison with other film electrodes
Four types of electrodes were compared: the investigated lead
film electrode (PbFE), the bismuth film electrode (BiFE), the mer-
cury film electrode (MFE) and the bare glassy carbon electrode
(GCE). The above electrodes were tested in the solution contain-
ing 0.1 M ammonia buffer, 2.5 × 10−5 M nioxime, 0.25 M NaNO2,
5 × 10−9 M Co and 5 × 10−8 M Ni and the adsorptive stripping
voltammetric responses were recorded and compared (Fig. 7). As
can be seen in Fig. 7, the analytical signal of Co recorded at the
PbFE has the best shape, as it is the most narrow and symmetri-
cal. Moreover, the separation of the adsorptive stripping peaks of
Ni and Co is the best at the PbFE. Another advantage of the PbFE
is the largest signal-to-noise ratio of all the four electrodes under
consideration. For the determination of Ni or of Ni and Co, accu-
mulation at a potential of −0.65 V is recommended. Application of
even more positive accumulation potentials can cause the oxida-
tion of the lead film. Higher but also more asymmetrical signals for
nickel are obtained with a BiFE. Fig. 7 also show that the baseline of
BiFE is not flat, but raises at negative potentials. This phenomenon
is caused by the GC surface being incompletely covered by the
metal film. Hence, the observed signals are the superimpositions
of the currents for glassy carbon and metal surfaces [1,45,46]. For
the tested system the described effect is much smaller for the MFE
and PbFE resulting in more symmetrical signals. In case of use GCE
as the working electrode no signals could be observed, either for Co
or for Ni.
Acknowledgements
Financial support from the Polish Ministry of Science and Higher
Education (Project No. N507063 32/1767) is gratefully acknowl-
edged. The authors would also like to thank Dr Elz˙ bieta Pamuła
for performing the AFM experiments and for the constructive com-
ments.
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The specific surface microstructure and topography of the lead
film deposited on GC from mild, alkaline solutions was viewed
by SEM and AFM for the first time, revealing the heterogeneous
character of the obtained film, strongly dependent on the applied