The fabrication and characterization of an ex situ plated lead film electrode prepared with the use of a reversibly deposited mediator metal

Article abstract of DOI:10.1016/j.electacta.2011.02.015

In this paper an ex situ plated lead film electrode prepared with use of the mediator metal (Zn) was elaborated. The electrochemical method for lead film formation is based on a co-deposition of a metal of interest (Pb) with a reversibly deposited mediator metal (Zn) and then on an oxidation of zinc and further deposition of lead by the appropriate potential. This serves to increase the density of islands of lead atoms, promoting lead film growth. The lead-based sensors were characterized by optical method (atomic force microscopy (AFM)) and as well as cyclic, linear sweep and square wave voltammetry. The adsorptive system of folic acid was employed to investigate the electrochemical characteristics a novel type of lead film electrode. Well-formed stripping peaks and a linear dependence of the stripping current on the folic acid concentration were observed on the lead film electrode prepared with use of the mediator metal while comparative measurements attempted with the lead film electrode prepared without use of the mediator metal were unsuccessful.

Full text of DOI:10.1016/j.electacta.2011.02.015

Electrochimica Acta 56 (2011) 3975–3980
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
The fabrication and characterization of an ex situ plated lead film electrode
prepared with the use of a reversibly deposited mediator metal
∗
Katarzyna Tyszczuk
Faculty of Chemistry, Maria Curie-Sklodowska University, Maria Curie Sklodowska Sq. 3, 20-031 Lublin, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
In this paper an ex situ plated lead film electrode prepared with use of the mediator metal (Zn) was
elaborated. The electrochemical method for lead film formation is based on a co-deposition of a metal of
interest (Pb) with a reversibly deposited mediator metal (Zn) and then on an oxidation of zinc and further
deposition of lead by the appropriate potential. This serves to increase the density of islands of lead atoms,
promoting lead film growth. The lead-based sensors were characterized by optical method (atomic force
microscopy (AFM)) and as well as cyclic, linear sweep and square wave voltammetry. The adsorptive
system of folic acid was employed to investigate the electrochemical characteristics a novel type of lead
film electrode. Well-formed stripping peaks and a linear dependence of the stripping current on the folic
acid concentration were observed on the lead film electrode prepared with use of the mediator metal
while comparative measurements attempted with the lead film electrode prepared without use of the
mediator metal were unsuccessful.
Received 6 December 2010
Received in revised form 4 February 2011
Accepted 4 February 2011
Available online 1 March 2011
Keywords:
Lead film electrode
Mediator metal
Stripping analysis
Microscopic study
©
2011 Elsevier Ltd. All rights reserved.
1
. Introduction
trodes (carbon paste electrodes or screen printed electrodes) with
a metal precursor, such as Bi O3 [24].
2
Metal film electrodes have become widespread in electrochem-
In this paper the lead film electrode was prepared using an elec-
trochemical, defect-mediated, thin-film growth method [25,26].
In this approach, the metal of interest (Pb) is co-deposited with
a reversibly deposited mediator metal. A necessary character-
istic of the mediator is that it must be less noble than the
metal of interest, so for further study zinc was used as medi-
ator. Such an electrode was tested using solutions containing
acetate buffer and folic acid by adsorptive stripping voltamme-
try. The results were compared to those already reported for
in situ lead film electrode [18] and to those obtained at ex situ
plated lead film electrode prepared without use of the mediator
metal. The main aims of this paper were to obtain a mechanically
stable sensor useful in electroanalytical applications and present
some fundamental facts concerning the surface properties of this
sensor.
ical stripping analysis due to their relatively simple fabrication
and surface regeneration [1]. The most commonly used examples
are mercury film electrodes [2–4], and recently, also film elec-
trodes from non-noble metals, such as bismuth [5–10] or antimony
[
11–15]. In 2005, a new type of electrode, a lead film electrode, was
proposed as an alternative to mercury electrodes [16–23]. The lead
film electrode exhibited interesting characteristics, such as lower
toxicity compared to the mercury electrodes, a wide potential win-
dow and the ability to operate in a wide range of pH media, simple
preparation, good reproducibility and a simple way of electrochem-
ical surface renewal.
The method of coating the substrate with film is critical for a sat-
isfactory performance of the resulting metal film electrodes. There
are three general methods of electrochemical coating the substrate
surface with a metal deposit. In the first method, in situ plating,
metal ions are added directly into the sample solution and the
film is deposited on the electrode surface during the analysis. The
second method, ex situ plating, involves electroplating film before
transferring the electrode to the sample solution for analysis. The
third plating method is based on modifying the heterogeneous elec-
2. Experimental
2.1. Reagents
An acetate buffer, used as a supporting electrolyte, was prepared
−
1
from CH COOH and NaOH obtained from Merck. 0.01 mol L solu-
3
tions of Pb(NO3)2 and ZnCl2 were prepared from reagent obtained
from POCh, Poland. Folic acid was obtained from Fluka. A stock
standard solution of folic acid (10 mol L ) was prepared in
∗ Corresponding author. Tel.: +48 81 5375592; fax: +48 81 5333348.
E-mail address: ktyszczuk@poczta.umcs.lublin.pl
− −1
2
0
013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2011.02.015

3
976
K. Tyszczuk / Electrochimica Acta 56 (2011) 3975–3980
−
1
0
.02 mol L NaOH and stored in a refrigerator until used. Work-
ing solutions were prepared daily by dilution of the stock solution.
All solutions were prepared in deionized water of resistivity not
−1
less than 18.2 Mꢀ cm at 298 K (Millipore, UK).
2.2. Apparatus
All voltammetric measurements were performed using
a
␮
Autolab analyser made by Eco Chemie, The Netherlands. A
classical three-electrode quartz cell of volume 10 mL was used
throughout, consisting of a glassy carbon working electrode, with
an Ag/AgCl reference electrode and a platinum wire as an auxiliary
electrode. The homemade working electrode included an easy-
to-take-out disk (diameter 10 mm, thickness 5 mm) with a glassy
carbon surface (diameter 1 mm). The PEEK housing was equipped
with a stainless steel piston to make electrical contact with the disk.
Atomic force microscopy (AFM) measurements were performed
using a Digital Instruments NanoScope III (USA, 2001). Contact
mode topographic images were recorded using Si N probes with
3
4
−1
a spring constant of 0.05 N m
and a nominal radius of curva-
TM
ture 20 nm (NANOPROBE SPM Tips, type NP-1). The images were
recorded at a scan area of 5 ␮m × 5 ␮m for three randomly chosen
places (512 × 512) and with the scan rate of 1 Hz. The software used
in data acquisition and analysis was the NanoScope version 5.12
−
1
Fig. 1. Cyclic voltammograms obtained from the solution containing 0.1 mol L
−
4
−1
−5
−1
acetate buffer (pH 4.6), 1 × 10 mol L of Zn(II) and 5 × 10 mol L of Pb(II). The
lead and zinc were deposited at −1.4 V for 60 s. Instrumental parameters: start
(
Digital Instruments, Veeco Metrology Group, CA) and the Scanning
potential of −1.4 V; first vertex potential of −1.7 V; second vertex potential of 0.25 V;
Probe Microscopy Software (WSxM 4.0 Develop 8.0 June 2005, Nan-
otec Electronica S.L.). The square root of average surface roughness
−1
and scan rate of 50 mV s
.
(
RRMS) was calculated from the following formula:
2.4. Electroanalysis
ꢀ
ꢁ
ꢁ
ꢂ
N
ꢃ ꢄ
ꢄ
ꢄ
1
N
The prepared lead film electrode was tested by adsorptive strip-
ꢄ
RRMS
=
Zi − Z
ping voltammetry of folic acid according to the procedure earlier
described in literature [18]. All voltammetric measurements of folic
i=1
−
1
acid were carried out in 0.1 mol L acetate buffer (pH 5.6) con-
taining variable concentration determined organic compound. A
preconcentration potential of −0.88 V (vs. Ag/AgCl) was applied for
where N is tfhe number of measured points (in this case:
5
12 × 512 = 262,144); Z is the height of the topographic element
i
in point ‘i’; and Z is the arithmetic mean of the heights of all topo-
1
20 s to the working electrode under stirring, to effect adsorption of
graphic elements.
folic acid on the lead film surface. Then the stirring was stopped and
after 5 s equilibration time, the square wave voltammograms were
recorded between −0.88 and −1.2 V with a frequency of 200 Hz and
amplitude of 50 mV. The potential step was 4 mV. All voltammetric
measurements were carried out in undeaerated solutions.
2
.3. Preparation of the lead film with the use of a reversibly
deposited mediator metal
The lead film electrode was prepared by an electrochemical
method with the use of a reversibly deposited mediator metal.
As a substrate for plating, a glassy carbon electrode was cho-
sen based on the published experiments with the use of such
an electrode support for the preparation of the lead film elec-
trode [16–23]. The glassy carbon surface was polished daily using
3
. Results and discussion
The most notable advantages of an ideal working electrode used
in stripping analysis are a high hydrogen overpotential, a well-
defined electrochemical behaviour in a wide potential range, with
a low background and noise, and the possibility of obtaining low
detection limits. Although reports on metal ions and organic com-
pounds determinations at an in situ plated lead film electrode can
be found in literature [16–23], it is obvious that the elaboration of
an electrode with properties similar to those possessed by an ideal
working electrode is the crucial point for successful research work
in applied electroanalysis. Due to this fact, the aim of this paper
was the application of an electrochemical method with use of the
mediator metal, in order to improve some properties of the lead
film electrode already described in literature.
Preliminary electrochemical measurements were carried out in
the plating solutions after electrodeposition of lead and zinc on a
glassy carbon surface, in order to identify the oxidation potentials
of those metals. Fig. 1 displays the cyclic voltammogram obtained
from the solution containing 0.1 mol L
0.3 ␮m alumina slurry on a Buehler polishing pad and then was
washed and sonicated for 2 min. After mechanical cleaning the
electrode was transferred into the plating solution containing
−
1
−5
−1
0
7
.1 mol L
acetate buffer (pH 3.5), 5 × 10 mol L
Pb(II) and
−5
−1
.5 × 10 mol L
Zn(II). Before each deposition experiment the
electrode was cleaned electrochemically at 0.5 V for 30 s. In the
course of electrodeposition the potential of the electrode was
changed in the following sequence: −1.4 V for 45 s and −0.7 V
for 45 s. In the first step Pb (metal of interest) and Zn (reversibly
mediator metal) were deposited simultaneously on a glassy car-
bon surface. During the second step Zn atoms were stripped from
surface as Pb continued to deposit resulting in islands of lead atoms
growth. During both steps the solution was stirred using a magnetic
stirring bar. After preparation the electrode was carefully rinsed
with water and immersed in the tested solutions. In the case of
microscopic measurements the disk with a lead-coated surface was
taken out from the housing and the sample was carefully placed in
the detection chamber of the microscope.
−1
acetate buffer (pH 4.6),
−4
−1
−5
1
× 10 mol L ZnCl2 and 5 × 10 Pb(NO ) . The lead and zinc
3
2
were deposited at −1.4 V for 60 s. It was found that the oxida-
tion lead and zinc start at the potentials around −0.6 and −1.1 V,

K. Tyszczuk / Electrochimica Acta 56 (2011) 3975–3980
3977
Fig. 3. Linear sweep voltammograms obtained at electrode after: (a) deposition of
lead and zinc at a potential of −1.4 V for 45 s (solid line); (b) deposition of lead
and zinc at a potential of −1.4 V for 45 s and then at a potential of −0.7 V for 45 s
oxidation of zinc and further deposition of lead (dash line); and (c) deposition of lead
at a potential of −1.4 V for 45 s and then at a potential of −0.7 V for 45 s (solid line).
−
1
−5
−1
The solution contained 0.1 mol L acetate buffer (pH 3.5), 5 × 10 mol L Pb(II)
−
5
−1
and 7.5 × 10 mol L Zn(II). In the case of a lead film electrode prepared without
−
1
use the mediator metal the solution contained 0.1 mol L acetate buffer (pH 3.5)
−
5
−1
−1
.
and 5 × 10 mol L Pb(II) (c). Scan rate of 50 mV s
fixed at 60 s and −1.4 V, respectively. In these experiments zinc
was stripped and lead was further deposited at −0.7 V for 60 s.
−
7
−1
was accumu-
The folic acid at concentration of 1 × 10 mol L
−
1
lated at −0.88 V for 120 s. The influence of the pH of 0.1 mol L
acetate buffer added to the plating solution on the peak current
of folic acid was studied. The concentrations of Zn(II) and Pb(II)
−
4
−1
−5
−1
were 1 × 10 mol L
and 5 × 10 mol L , respectively. It was
observed that the change of the pH of the solution from 3.5 to 6.1
did not influence significantly the peak current of folic acid. How-
ever, the lowest background current at a pH of 3.5 was obtained,
so for further study this value of the pH of the solution was chosen.
Then the concentration of Pb(II) added to the plating solution was
Fig. 2. (A) The dependence of folic acid peak current on the deposition potential
of lead and zinc. (B) The influence of the time of the oxidation zinc and further
deposition of lead on: (a) the folic acid peak current and (b) the oxidation peak
−
4
−1
changed in the range from 0 to 2 × 10 mol L and its influence
on the folic acid peak was studied. The measurements were done
−
1
−4
−1
current of zinc. The plating solution contained 0.1 mol L acetate buffer (pH 3.5),
at a constant concentration of Zn(II) equal to 1 × 10 mol L . It
−
5
−1
−5
−1
7
.5 × 10 mol L Zn(II) and 5 × 10 mol L Pb(II). The folic acid at concentration
was found that the folic acid peak current increases as the concen-
−7 −1
of 1 × 10 mol L was accumulated at −0.88 V for 120 s. The deposition potential
−
5
−1
tration of Pb(II) increases to 4 × 10 mol L and then is stable. In
the absence of Pb(II) the peak of folic acid was not observed on
the voltammogram because it was not adsorbed on the glassy car-
bon electrode. The increase of the folic acid peak current with the
increase of Pb(II) concentration added to the plating solution prob-
ably is connected with the increase of the lead film area accessible
for adsorption of folic acid. It must be noted that the lead was fur-
ther deposited in the course of the second step of film plating. For
of lead and zinc in (B) was −1.4 V. The deposition time of lead and zinc in (A) and
(
B) was 45 s. The potential of the zinc oxidation and further deposition of lead in (A)
was −0.7 V. The time of the zinc oxidation and further deposition of lead in (A) was
6
0 s.
respectively. On the basis of the above experimental result it can
be stated that at a potential in the range from −0.6 to −0.75 V zinc
will be stripped from the surface as lead will continued the depo-
sition. Additionally, lead and zinc can be deposited simultaneously
at potential more negative than −1.1. In further measurements
a potential of −1.4 V and time of 60 s were used for plating zinc
and lead, and a potential of −0.7 V and time of 60 s were used for
stripping zinc and further plating of lead.
−
5
−1
further measurements a concentration of Pb(II) 5 × 10 mol L
was chosen. The results show also that prolongation of the depo-
sition time of lead and zinc from 45 to 240 s did not influence the
peak current of folic acid, so in further measurements the depo-
sition time of 45 s was used. Then the influence of concentration
of Zn(II) added to the plating solution on the folic acid signal was
studied. The measurements for this optimisation were done at a
3.1. Conditions of lead film formation and electrode regeneration
−
5
−1
4
constant concentration of Pb(II) equal to 5 × 10 mol L , while
−
−1
.
The influence of the conditions of lead film formation was opti-
mised. The time and the potential of lead and zinc deposition were
the concentration of Zn(II) was changed from 0 to 2 × 10 mol L
It was found that the folic acid peak current increases as the con-

3
978
K. Tyszczuk / Electrochimica Acta 56 (2011) 3975–3980
Fig. 4. AFM images of the electrode surface after: (a) the deposition of lead and zinc at a potential of −1.4 V for 45 s; (b) the deposition of lead and zinc at a potential of −1.4 V
for 45 s and then at a potential of −0.7 V for 45 s oxidation of zinc and further deposition of lead; and (c) the deposition of a lead at potential of −1.4 V for 45 and then at
potential −0.7 V for 45 s. The plating solution contained 0.1 mol L− acetate buffer (pH 3.5), 0 or 7.5 × 10 mol L Zn(II) and 5 × 10 mol L Pb(II).
1
−5
−1
−5
−1
centration of Zn(II) increases to 5 × 10−5 mol L . On the basis of the
−1
obtained results are presented in Fig. 2A. The potential of the zinc
experimental results for further study the concentration of Zn(II)
oxidation and further deposition of lead was equal to −0.7 V. The
folic acid peak attained the maximal value as the deposition poten-
tial of the lead film was −1.4 V, so for further study this potential
was chosen. The results show also that the changes of the poten-
−5
−1
7
.5 × 10 mol L was chosen. Next, the potential of the deposition
of zinc and lead was changed in the range from −1.1 to −1.45 V and
its influence on the peak currents of folic acid was studied. The

K. Tyszczuk / Electrochimica Acta 56 (2011) 3975–3980
3979
tial of the oxidation zinc and further deposition of lead in the range
from −0.6 to −0.75 V did not influence the peak current of folic acid,
so in further measurements the potential of −0.7 V was used. Next,
the time of the oxidation of zinc and further deposition of lead film
was studied. The time was changed in the range from 0 to 120 s and
its influence on the oxidation peak of zinc and the reduction peak
of folic acid was studied (Fig. 2B). It was observed that the folic acid
peak current increases with the prolongation of the time to 30 s and
then is nearly stable. However, all zinc is stripped from the surface
of the electrode, while the time of the oxidation is equal to 45 s. As
a compromise between the value of the peak current of folic acid
and the complete oxidation of zinc the time of 45 s was chosen for
further study.
In the previous articles about the application of an in situ plated
lead film electrode to the determination of folic acid the poten-
tial of +0.5 V for 10 s was applied to clean the electrode surface
[
18]. The reproducibility of the ex situ plated lead film electrode
−
7
−1
was evaluated measuring the peak current of 1 × 10 mol L folic
acid twenty times. Before each measurement the electrode was
cleaned electrochemically at the potential +0.5 V for 10 s and the
lead film was deposited with use of the mediator metal on a
glassy carbon surface. The relative standard deviation was 5.9%.
Prolongation of the cleaning time to 30 s caused a better repro-
ducibility of the electrode. The relative standard deviation was 4.3%
Fig. 5. Square wave voltammograms obtained at a lead film electrode: (a) prepared
without use of the mediator metal; (b) prepared with use of the mediator metal;
−
1
and (c) in situ plated, in a 0.1 mol L acetate buffer (pH = 5.6) in the presence of
5
(
(
n = 20), so for further study the cleaning potential of +0.5 V and the
−
8
−1
−1
× 10 mol L folic acid. The plating solution contained 0.1 mol L acetate buffer
cleaning time of 30 s were chosen.
−5 −1 −5 −1
pH 3.5), 0 or 7.5 × 10 mol L Zn(II) and 5 × 10 mol L Pb(II). The lead and zinc
were deposited for 45 s at −1.4 V and then. at −0.7 V for 45 s zinc was stripped from
the surface and lead was deposited. Stripping parameters: frequency 200 Hz; step
height 4 mV; and amplitude 50 mV.
3
.2. Characterisation of deposits on a glassy carbon surface
In order to present evidence of the role of the mediator metal in
the increase of the lead film mass linear sweep voltammetric mea-
respectively. The microscopic images showed considerable vari-
ability in the morphology of the deposited layer depending on the
way of the preparation of the lead film (Fig. 4b and c). On the basis
of the results it can be stated that the application of the mediator
metal to the preparation of the lead film causes an increase of the
surface coverage and roughness of the deposit.
−
−5
1
surements from a solution containing 0.1 mol L acetate buffer (pH
−5
−1
−1
3
.5), 5 × 10 mol L Pb(II) and 0 or 7.5 × 10 mol L Zn(II) were
performed (Fig. 3). Using the peak areas under Zn and Pb strip-
ping peaks, and Faraday’s law, it was calculated that approximately
0
.026 ␮g of Zn and 0.183 ␮g of Pb (for the time of zinc oxidation and
further deposition of lead equal to 0 s) (Fig. 3a), and 0 ␮g of Zn and
.361 ␮g of Pb (for the time of zinc oxidation and further deposi-
tion of lead equal to 45 s) (Fig. 3b), and 0.229 ␮g of Pb (the lead
film electrode prepared without use of the mediator metal) were
stripped from the glassy carbon surface. The results showed that
the application of the mediator metal (Zn) increases the mass of Pb
plated on the surface to 60% of its value obtained when no zinc was
present in the plating solution.
The surface morphology of the electrode surface was charac-
terized by atomic force microscopy (Fig. 4). AFM images show the
electrode surface prepared with and without use of the mediator
metal. As was mentioned in Section 2.4, the process of the depo-
sition of the lead film occurs in two steps. In the first step, at a
potential of −1.4 V Pb and Zn grow in the active areas of the sur-
face forming a random particle array (Fig. 4a). The whole substrate
surface is covered with rather uniform particles of 0.1–0.25 ␮m
diameter and an average height of 50 nm (bright areas in the left
picture). In the second step of lead film formation, at a potential
of −0.7 V the zinc particles are oxidised and stripped from the
surface. During this step, also the growth of the earlier formed
nuclei of Pb takes place (Fig. 4b). The microstructure of the lead
film changes from the nuclei to crystallites with the size found in
the range of 70–180 nm in height. The surface coverage and rough-
ness (Ra) are about 100 ± 5% and 12.5 ± 2.1, respectively. Fig. 4c
shows that the lead deposit obtained without use of the media-
tor metal in the same conditions than those formed with use of
the mediator zinc, consists of smaller grains with the size found in
the range of 35–50 nm in height, and approximately 0.1–0.4 ␮m in
diameter and separated by a small number of bigger ones. The sur-
face coverage and roughness (Ra) were about 50 ± 8% and 7.2 ± 3.3,
0
3.3. Comparison of the lead film electrodes prepared with use of
different plating methods
The investigated lead film electrode prepared with use of the
mediator metal was compared to an ex situ plated lead film elec-
trode prepared without use of the mediator metal and an in situ
plated lead film electrode. The adsorptive stripping voltammetric
responses were recorded and compared (Fig. 5). As can be seen in
Fig. 5, well-defined and sharp peak with relatively low background
was obtained using a lead film electrode prepared with use of the
mediator metal in contrast to the broader and lower analytical sig-
nal recorded at an in situ plated lead film electrode. In the case
of use an ex situ plated lead film electrode prepared without use
−8
−1
of the mediator metal no signal of 5 × 10 mol L folic acid was
observed.
Calibration curves for determination of folic acid at in situ plated
lead film electrodes prepared with and without use of the media-
tor metal and an in situ plated lead film electrode were carried out
under optimal condition. Calibration curves comparing an in situ
plated lead film electrode and an ex situ plated lead film elec-
trode prepared with use of mediator zinc for the accumulation
time of 120 s are shown in Fig. 6a and b. The stripping currents
of the lead film electrode prepared with use of the mediator metal
−
9
were linear in the concentration range of folic acid from 2 × 10 to
−
7
−1
1.5 × 10 mol L (Fig. 6b). The calibration plot is expressed by the
first-order equation y = 12.17x + 4.33, where y is the peak current
(nA) and x is a folic acid concentration (nmol L ). The linear cor-
−
1
2
relation coefficient (r ) was equal to 0.999. The relative standard
deviation from five determinations of folic acid at a concentration

3
980
K. Tyszczuk / Electrochimica Acta 56 (2011) 3975–3980
The microscopic observation correlated well with the results of
the electrochemical study. The complete coverage of the surface
by Pb crystallites causes that the background current recorded for
the investigated system of folic acid is more flat and lower, in
contrast to the baselines recorded at the in situ plated lead film
electrode (Fig. 5). Additionally, as can be seen in Fig. 5, the analyt-
ical signal of folic acid is a higher and has a better shape than that
recorded at the in situ plated lead film electrode. It is obvious that
the higher surface coverage and roughness are advantageous the
investigated lead film electrode prepared with use of the medi-
ator metal because they lead to an increase in the active areas
of the surface of the electrode and improve its electrochemical
properties.
Under the optimized conditions of lead film formation, the
proposed procedure of determination of folic acid by adsorptive
stripping voltammetry offers a lower detection limit than that
obtained at an in situ plated lead film electrode.
In spite of the prolongation of the time of the preparation of
an ex situ lead film compared to an in situ lead film, this electrode
exhibits notable advantages, so it can be a very promising analytical
tool.
Acknowledgements
Fig. 6. Calibration curves for folic acid obtained at an in situ plated lead film
electrode (a) and an ex situ plated lead film electrode prepared with use of
mediator zinc (b). The plating solution contained 0.1 mol L acetate buffer (pH
−
1
The author acknowledges the financial support of the Founda-
tion for Polish Science (START Program, 2010).
−
5
−1
−5
−1
3
.5), 7.5 × 10 mol L Zn(II) and 5 × 10 mol L Pb(II). The lead and zinc were
deposited for 45 s at −1.4 V and then at −0.7 V for 45 s zinc was stripped from the
surface and lead was deposited. In the case of an in situ plated lead film electrode the
References
−1
−5
−1
solution contained 0.1 mol L acetate buffer (pH 5.6) and 7.5 × 10 mol L Pb(II).
Folic acid was accumulated at −0.88 V for 120 s.
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8
−1
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10
−9
−1
folic acid were about 5 × 10
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The favorable performance of the lead film electrode prepared with
use of the mediator metal is supported by the calculated detection
(
2003) 765.
−10
−1
limit valueof 5 × 10
mol L , eight timelowerthan that foundfor
[9] A. Krolicka, A. Bobrowski, K. Kalcher, J. Mocak, I. Svancara, K. Vytras, Electro-
analysis 15 (2003) 1859.
−
9
−1
an in situ plated lead film electrode (4 × 10 mol L ) [18]. In the
case of use an ex situ plated lead film electrode prepared without
use of the mediator metal no signal of folic acid in the concentra-
tion range from 2 × 10 to 2 × 10 mol L was observed. On the
basis of the obtained results it can be speculated that this struc-
ture of metal film (Fig. 4c) possesses inferior adsorptive properties
than the uniform lead film formed with use of the mediator metal
[
10] L. Baldrianova, I. Svancara, A. Economou, S. Sotiropoulos, Anal. Chim. Acta 580
(
2006) 24.
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Electrochim. Acta 54 (2009) 1506.
−9
−7
−1
[
13] V. Jovanovski, S.B. Hocevar, B. Ogorevc, Electroanalysis 21 (2009) 2321.
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113.
1
[
[
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(
Fig. 4b).
1185.
[
[
[
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4
. Conclusions
In this paper an electrochemical method was used for the prepa-
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[
[
[
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ration of an ex situ plated lead film electrode with use of the
mediator metal (Zn). The microscopic images showed considerable
variability in structure and compactness of the deposited lead layer
depending on the way of the preparation of the film. The applica-
tion of the mediator metal to the preparation of a lead film caused
an increase of the surface coverage and roughness of the deposit.
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Norkus, K. Kalcher, Anal. Bioanal. Chem. 374 (2002) 1155.
[
[
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