Selective determination of paracetamol and acetylsalicylic acid on electrode modified with a mixed-valent film of ruthenium oxide-ruthenium cyanide

Article abstract of DOI:10.1134/S1070427211040112

Catalytic activity exhibited by a mixed-valent film of ruthenium oxideruthenium cyanide deposited on the surface of a glassy-carbon electrode in electrooxidation of paracetamol and acetylsalicylic acid was used to develop a high-sensitivity selective method for determination of these compounds in the case of their joint presence under flow-injection conditions.

Full text of DOI:10.1134/S1070427211040112

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 4, pp. 620−627. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © L.G. Shaidarova, A.V. Gedmina, I.A. Chelnokova, G.K. Budnikov, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84,
No. 4, pp. 582−590.
PHYSICOCHEMICAL STUDIES
OF SYSTEMS AND PROCESSES
Selective Determination of Paracetamol and Acetylsalicylic Acid
on Electrode Modified with a Mixed-Valent Film
of Ruthenium Oxide–Ruthenium Cyanide
L. G. Shaidarova, A. V. Gedmina, I. A. Chelnokova,
and G. K. Budnikov
Kazan State University, Kazan, Tatarstan, Russia
Received April 16, 2010
Abstract—Catalytic activity exhibited by a mixed-valent film of ruthenium oxide– ruthenium cyanide deposited
on the surface of a glassy-carbon electrode in electrooxidation of paracetamol and acetylsalicylic acid was used
to develop a high-sensitivity selective method for determination of these compounds in the case of their joint
presence under flow-injection conditions.
DOI: 10.1134/S1070427211040112
Because of the increased amount of pharmaceutical
preparations containing paracetamol (PC, N-(4-
hydrophenyl)acetamide and acetylsalicylic acid (AC,
modified electrodes (CMEs), including those operating
on electrocatalysis principles, makes it possible to
overcome these difficulties. As immobilized catalysts
for determination of PC and AC are commonly used
boron-doped diamond [6], nanoparticles of gold [7] and
nickel oxide [8], metal-polymeric films [9], and carbon
nanotubes [10]. However, use of CMEs fails to always
improve the reproducibility of the analytical signal.
Combination of voltammetry on CMEs and flow-
through methods of analysis frequently improves the
metrological characteristics of determination of organic
compounds [11].
2
-acetyloxybenzoic acid) and threat of their falsification,
development and implementation of new, more perfect
and rapid methods for determination of these organic
compounds is an important and topical task.
PC and AC are commonly determined by various
methods, such as titrimetry, spectrophotometry,
voltammetry, and high-performance liquid chromato-
graphy [1–5]. Most of these techniques are complicate
by the necessary sample preparation and include
extraction or a preceding chemical reaction. The results
obtained when determining PC by the titrimetric and
spectrophotometric methods are affected by presence
of ascorbic or acetylsalicylic acid in a medicinal
preparation, which impairs the metrological
characteristics of determination in their joint presence.
Use of direct voltammetric methods for determination
of PC and AC on metallic and graphite electrodes is
hindered by the lacking reproducibility of their results.
In addition, determination of simultaneously present PC
and AC by voltammetry is hindered by the fact that their
electrooxidation potentials are close. Use of chemically
We studied the electrooxidation of PC and AC on
a glassy carbon (GC) electrode covered with an inorganic
film of a mixed-valent ruthenium oxide–ruthenium
cyanide (RuO–RuCN) and developed a selective method
for determination of PC and AC on a modified electrode
of this kind under conditions of a flow-injection analysis
(FIA).
EXPERIMENTAL
We recorded cyclic voltammograms using a PI-50-
1.1 potentiostat with a PU-1 programming unit in a three-
6
20

SELECTIVE DETERMINATION OF PARACETAMOL AND ACETYLSALICYLIC ACID
621
electrode cell. A GC electrode with a surface area of
(a)
(b)
2
0
.096 cm and a GC electrode coated with a RuO–RuCN
5 μA
film as working electrodes. A silver chloride electrode
served as reference, and a platinum wire as auxiliary
electrode. The cyclic voltammograms were recorded at
E, V
–
1
a potential application rate of 20 mV s . The inorganic
film was formed on the GC surface by potentiodynamic
deposition from an aqueous solution containing 1 mM
RuCl and K [Ru(CN) ] (Aldrich), with a 0.1 M H SO
3
4
6
2
4
1
4
0 μA (1)
0 μA (2)
solution as supporting electrolyte. The electrode surface
was refreshed mechanically.
Solutions of PC andAC were prepared by dissolution
of their precisely weighed portions in an aqueous
solution. Sets of solutions with lower concentrations
were prepared by successive dissolution of the
starting solution immediately before measurements.
Measurements under FIA conditions were made on an
installation including a peristaltic pump of the DLV
type, injector, flow-through electrochemical cell, and
a recording device [12]. Solutions were delivered and
discharged via flow-through lines fabricated from
silicone pipe with an inner diameter of 2.0 mm. The
injection was performed with a microsyringe through
a sealing membrane.
E, V
Fig. 1. Cyclic voltammograms for oxidation of paracetamol
on (a) GC and (b, curve 2) CME with a RuO–RuCN film
on the background of a 0.1 M H SO solution. Paracetamol
concentration 5 × 10–3 M; the same for Figs. 3 and 4. Dashed
line 1 is the background curve obtained on CME; the same for
Fig. 2. (E) Potential; the same for Fig. 2.
2
4
hydrolysis was performed by the method described in
5]. SimilarlytoPC, salicylicacidisoxidizedirreversibly
with a peak formed in a more remote range of potentials,
at E = 1.15 V (Fig. 2a). The oxidation scheme of this
compound is complex [14] and includes formation of
a cation radical, with its subsequent dimerization to give
an oligomeric product:
[
Paracetamol is irreversibly oxidized on GC on the
background of a 0.1 M H SO solution, with a peak
2
4
p
formed at a potential E = 0.90 V (Fig. 1a). By analogy
a
with published data on electrooxidation of aminophenols
[13], it can be assumed that a compound with a quinoid
fragment is formed as a product of a chemical reaction.
The electrode reaction is the following:
COOH
OH
COOH
_e
+
.
O
O
_H+
HO
NH
C
CH3
O
C
COOH
O
COOH
O
_2
e
O
N
CH3.
(1)
_2
H+
.
O
n
(
2)
It should be noted that it is impossible to obtain a well-
reproducible voltammogram. This is due to adsorption
of substrate oxidation products on the graphite surface.
Thus, a graphite electrode cannot be used to determine
PC by direct voltammetry.
The voltammogram of oxidation of PC and AC
in their joint presence shows a single broad peak
Table 1), which hinders use of unmodified graphite
electrodes for selective voltammetric determination of
these compounds. Use of CMEs with electrocatalytic
properties makes it possible to diminish the overvoltage
of the reaction and make higher the determination
(
Acetyl salicylic acid is oxidized in a complicated way,
with a preliminary stage of AC hydrolysis to salicylic
acid, which is oxidized on the electrode. Preliminary
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 4 2011

622
SHAIDAROVA et al.
heterovalent ruthenium oxide– ruthenium cyanide has
(a)
(b)
been studied [15]. A cyclic voltammogram obtained
on the CME is presented in Fig. 1b (curve 1). The
voltammetric curve shows three well-pronounced
anodic and reverse cathodic peaks. The electrochemical
reactions occurring at a potential of 0.05 V are
commonly related to the Ru(III/II) redox pair, and peaks
at potentials of 0.80 and 1.10 V, to oxidation of mixed-
valence ruthenium species bound to oxo and cyano
groups to higher degrees of oxidation. The difficulty
in determining the precise degree of oxidation is due
to the formation of numerous redox centers and to the
polymeric nature of the immobilized metal-complex.
Spectral methods, including X-ray photoelectron
spectroscopy, fail to reliably identify the degree of
ruthenium oxidation, which is due to overlapping of
the energy levels of carbon in the cyano group with the
electron levels Ru(d ) and Ru(d ) [16]. Taking into
5
μA
E, V
3
0 μA
E, V
Fig. 2. Cyclic voltammograms for oxidation of acetylsalicylic
acid on (a) GC and (b, curve 2) CME with a RuO–RuCN film
on the background of a 0.1 M H SO solution. Acetyl salicylic
3
/2
5/2
account the similarity of the voltammograms obtained
on electrodes modified with a ruthenium deposit [17]
and a RuO–RuCN film [18] and comparing the results
of a study of these films in [19], we can attribute the
anodic-cathodic peaks to the following redox pairs:
Ru(III)/Ru(II) (E = 0.05 V), Ru(IV)/Ru(III) (E =
2
4
acid concentration 5 × 10–3 M; the same for Figs. 3 and 4.
sensitivity of PC and AC, and the presence of several
mediator centers in the composition of the inorganic
film improves the selectivity of their determination. The
electrochemical behavior of PC and AC on a CME with
a RuO–RuCN film was studied.
0
.80 V), and Ru(VI)/Ru(IV) (E = 1.05 V).
The RuO–RuCN film has a high chemical and
electrochemical stability, which is indicated by the
Previously, the electrochemical behavior of a film of
a
Table 1. Voltammetric characteristics of oxidation of paracetamol and acetylsalicylic acid on GC and CME with a RuO–RuCN
film on the background of a 0.1 M H SO solution
2
4
Electrode
Еs, V
is, μA
Еmed, V
imed, μA
Е , V
i , μA
i /i
cat
cat
cat med
Paracetamol
GC
0.90
–
21
–
–
–
–
–
–
CME
0.80
11
20
0.80
–
172
–
15.6
–
1
.05
Acetyl salicylic acid
GC
1.15
–
9
–
–
–
–
–
–
CME
0.80
11
20
–
–
–
1
.05
1.10
150
7.5
Mixture of paracetamol and acetylsalicylic acid
GC
1.00
–
32
–
–
–
–
–
–
CME
0.80
11
20
0.80
1.10
172
150
15.6
7.5
1
.05
a
E and i are the potential and current of the peak of substrate oxidation on GC; E and imed, potential and current of the peak of mediator
s
s
med
oxidation; Ecat and i , potential and current of the peak of catalytic oxidation of the substrate on CME.
cat
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SELECTIVE DETERMINATION OF PARACETAMOL AND ACETYLSALICYLIC ACID
623
good reproducibility of voltammograms obtained upon
a cyclic variation of the potential during a month, with
a 0.1 M H SO solution as a background. Raising the pH
of the supporting electrolyte makes the voltammograms
worse. In alkaline solutions, the film disintegrates and
voltammograms take the form of a background curve
characteristic of GC without a film.
peak current i on the potential application rate ν, we
p
—
—
observed a linear dependence of i /√ ν on √ ν, with
p
a negative slope (Fig. 3a, curve 1). According to the
Reynolds–Shevchik equation, this dependence indicates
that the substrate electrooxidation is complicated by
a chemical reaction [20, 21]. By changing the initial
2
4
potential E from which voltammograms were recorded
in
and the delay time t of this potential (Figs. 3b and
We compared the electrochemical behaviors of
PC and AC on a CME with a RuO–RuCN film. In
electrooxidation of PC and AC, voltammograms show
well-pronounced peaks (Figs. 1b and 2b, curves 2). The
current of the oxidation peak of the mediator increases
at E = 0.80 V in oxidation of PC (Fig. 1b, curve 2)
and at E = 1.05 V in oxidation of AC (Fig. 2b, curve
d
3
c, curves 1), we found that the height of the peak
remains unchanged as E decreases and t increases.
p
d
This indicates that there is no adsorption component in
the oxidation of PC [20, 21]. The scheme of catalytic
electrooxidation of PC on CME can be represented as
_Ru(III)O
_Ru(IV)O + e,
2
). The background curve shows at the same potentials
0.80 and 1.05 V) current peaks corresponding to the
transitions –Ru(III)O → –Ru(IV)O and –Ru(IV)O →
Ru(VI)O, respectively, i.e., the substrates are oxidized
(3)
(
O
–
2Ru(IV)O
+
HO
NH
C
CH3
in the oxidation range of various forms of the modifier.
The many-times increase in the height of these peaks
and the linear dependence of the recorded currents on
the concentration of PC and AC enable us to identify
this process as a catalytic process. The catalytic effect
is manifested in that the oxidation potentials of the
substrates on CMEs are lower, compared with the
unmodified electrode, by 100 and 150 mV for PC and
AC, respectively, and the mediator oxidation current
is many times higher. The ratios between the catalytic
oxidation current icat of the substrates to the oxidation
current imed of the mediator are icat/imed = 15.6 and 7.5
for PC and AC, respectively.
O
+
2
Ru(III)O + O
N
C
CH3 + 2H .
(4)
—
—
The plot of the dependence of i /√ ν on √ ν in
p
oxidation of AC has a positive slope (Fig. 3a, curve 2),
and the current of the peak grows with increasing td
and decreasing E (Figs. 3b and 3c, curves 2), which is
indicative of the adsorption contribution to the process
of AC electrooxidation on this CME by the scheme
in
_Ru(IV)O
_Ru(VI)O + 2e,
When studying the dependence of the PC oxidation
(5)
ip, μA
(b)
(c)
(a)
–
√
ν, mV1/2 s–1/2
–
Ep, V
td, s
Fig. 3. Catalytic current i of the oxidation peak for (1) paracetamol and (2) acetylsalicylic acid on CME vs. (a) potential application
p
rate ν, (b) initial potential from which a voltammogram is recorded, and (c) the delay time t of the initial potential from which
d
a voltammogram is recorded.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 4 2011

624
SHAIDAROVA et al.
COOH
OH
current results in that the reproducibility of the currents
measured is unsatisfactory. Amperometric detection
of PC and AC under FIA condition eliminates this
disadvantage. A chemically modified electrode based
on a RuO–RuCN film was used to determine PC and
AC under the FIA conditions, with FIA signals recorded
in the potentiostatic mode. Preliminarily, the effect of
hydrodynamic parameters of the system on the intensity
of the analytical signal was considered. We studied the
dependence of the current on the volume V of a sample
being injected and flow rate u. The strongest FIA signal
is observed for PC and AC for a 0.15-ml injected sample
Ru(VI)O + 2
Ru(IV)O + 2
COOH
+
.
O
+ 2H+.
(6)
The cyclic voltammogram for electrooxidation of
jointly present PC andAC on a CME with a RuO–RuCN
film shows in its anodic branch two well-pronounced
peaks at E = 0.80 and 1.05 V, which correspond to the
catalytic oxidation of PC andAC, respectively (Table 1).
(
Fig. 4a). The dependence of i on u for PC and AC
–1
passes through a maximum at u = 16 ml min (Fig. 4b).
With these hydrodynamic parameters, we studied the
dependence of the current on potential. The maximum
current is observed in detection on CME at E = 0.75 V
for PC and E = 1.05 V for AC (Fig. 4c). Based on the
dependences obtained, we chose the working conditions
for recording the FIAsignal: V = 0.5 ml, u = 17 ml min ,
and E = 0.75 V for PC; and V = 0.5 ml, u = 17 ml min ,
and E = 1.05 V for AC.
The magnitude of the electrocatalytic response of
CMEs depends on the method by which a RuO–RuCN
film is deposited onto the GC surface. The film was
produced electrochemically. We varied the electrolysis
duration and potential in the case of a potentiostatic
deposition, and the range and rate of a cyclic variation
of the potential, in potentiodynamic deposition.
A pronounced catalytic effect is observed in oxidation
of PC and AC when the film is deposited by cyclic
variation of the potential in the range from –0.10 to
–1
–1
The method of flow-injection determination of PC
and AC on a CME with a RuO–RuCN film consists in
that the FIA signal is recorded at E = 0.75 V for PC
and E = 1.05 V for AC after a sample with a volume
of 0.5 ml is injected into a carrier (0.01 M solution of
–
1
+
1.10 V at a potential application rate of 100 mV s in
the course of 15 min.
Thus, the electrocatalytic oxidation of PC and AC
occurs on a CME with a RuO–RuCN film at different
potentials (the potential differenceΔE is 300 mV), which
makes it possible to develop a method for selective
voltammetric determination of these compounds.
However, the adsorption nature of the AC oxidation
–
1
H2SO4) at its flow rate of 17 ml min . The dependence
of the FIA signal on the PC and AC concentrations is
linear in logarithmic coordinates in the range from 5 ×
–
3
–8
10 to 5 × 10 M and is described by Eqs. (7) and (8),
respectively:
(b)
(c)
(a)
V, μl
E, V
u, ml min–1
Fig. 4. Catalytic response of CME under FIA conditions to (1) paracetamol and (2) acetylsalicylic acid vs. (a) volume V of an injected
sample, (b) flow rate u, and (c) applied potential E on the background of an H SO solution with pH 2.0. (i ) Current.
2
4
p
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SELECTIVE DETERMINATION OF PARACETAMOL AND ACETYLSALICYLIC ACID
625
Table 2. Metrological characteristics of the flow-through–
injection determination of paracetamol and acetylsalicylic
acid on a CME with a RuO–RuCN film; n = 6, P = 0.95
verified by the introduced–found method (Table 2).
An assessment of the metrological characteristics
revealed a good accuracy of the results of voltammetric
determination of PC and AC in a flow-through system.
The improved reproducibility of the analytical signal in
a low is due to the absence of sorption of the substrate
and its oxidation production the CME surface. The
suggested method for amperometric detection of PC
and AC with a CME based on a RuO–RuCN film under
FIA conditions is distinguished by simplicity, high
sensitivity, selectivity, and fast determination.
Content of an analyte, μM
Analyte
PC
Sr
introduced
0.5
found х ± Δх
0.51 ± 0.02
4.9 ± 0.2
0.05
0.04
0.03
5
.0
0.0
00
0.5
.0
0.0
00
1
10.2 ± 0.3
1
1
99 ± 1
0.49 ± 0.02
0.01
0.05
AC
We used a chemically modified electrode with
a RuO–RuCN film to determine PC and AC in
pharmaceutical preparations. It was found that there is
no mutual influence of PC and AC on the results of their
determination (Table 3). In addition, we examined the
influence of various components present in medicinal
materials on the determination of the analytes. Table 3
lists results we obtained when determining PC and
AC in the presence of a number of compounds, such
as caffeine, phenobarbital, cacao, codeine, citric
acid, and codeine phosphate, which are contained
in the corresponding preparations, but do not hinder
determination of PC and AC. It was found that, in the
presence of their compounds, a good reproducibility of
5
4.8 ± 0.2
9.9 ± 0.4
101 ± 2
0.05
0.04
0.02
1
log i = (2.44 ± 0.09) + (0.46 ± 0.01)log c, R = 0.997
p
(
ip, μA; с, M);
(7)
(8)
Log i = (2.72 ± 0.04) + (0.57 ± 0.03)l0g c, R = 0.999
p
(
ip, μA; с, M);
The detection limit calculated using the 3s criterion
–8
[
21] is 2 × 10 M. The adequacy of the procedure was
Table 3. Determination of paracetamol and acetylsalicylic acid on a CME with a RuO–RuCN film in the presence of matrix
components of pharmaceutical preparations; n = 6, P = 0.95, ttab = 2.57
Introduced
Found
Preparation
Ascofen
Analyte
PC
Matrix component
AC
Ratio
Sr
g
1 : 1
1 : 5
1 : 1
1 : 5
1 : 6
1 : 8
0.20
0.15
0.20
0.30
0.3
0.22 ± 0.01
0.140 ± 0.007
0.190 ± 0.006
0.28 ± 0.01
0.04
0.05
0.03
0.04
0.04
0.05
Caffeine
PC
AC
PC
Caffeine
Caffeine
Cacao
Citropar
0.29 ± 0.01
0.4
0.398 ± 0.008
Citric acid
Caffeine
1 : 4
1 : 8
0.25
0.500
0.242 ± 0.008
0.470 ± 0.005
0.03
0.01
AC
PC
AC
Cacao
1 : 10
0.15
0.146 ± 0.005
0.03
Citric acid
Phenobarbital
1 : 5
1 : 8
0.2
0.180
0.19 ± 0.01
0.176 ± 0.009
0.05
0.05
Sedalgin-N
Caffeine
1 : 4
0.250
0.255 ± 0.008
0.42 ± 0.01
0.0747 ± 0.0008
0.297 ± 0.006
0.242 ± 0.003
0.03
Codeine phosphate
Phenobarbital
1 : 20
1 : 8
0.4
0.0750
0.03
0.01
Caffeine
1 : 4
0.300
0.240
0.02
0.01
Codeine phosphate
1 : 20
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 4 2011

626
SHAIDAROVA et al.
Table 4. Results of determination of paracetamol and acetylsalicylic acid on a CME with a RuO–RuCN film in pharmaceutical
preparations; n = 6, P = 0.95, ttab = 2.57
Preparation (in pellets)
Analyte
PC
Certified value of m, g
Found m, g
S
tcal
Paracetamol
Ascofen
Sedalgin-N
Citropar
0.500
0.200
0.300
0.180
0.495 ± 0.006
0.196 ± 0.007
0.306 ± 0.007
0.173 ± 0.008
0.006
0.007
0.007
0.008
2.04
1.40
2.10
2.14
Ascofen
Sedalgin-N
Citropar
AC
0.20
0.200
0.240
0.204 ± 0.005
0.194 ± 0.007
0.242 ± 0.003
0.005
0.007
0.003
1.96
2.10
1.63
measurement results is observed (S < 0.05).
good reproducibility of the determination results (S <
r
r
5
%).
Results of analyses for PC and AC in selected
pharmaceutical preparations are listed in Table 4.
As certified values serve the contents of PC and AC,
specified in the medicine instruction sheets. A statistical
assessment of the results by the value of the t-criterion
demonstrated that there is no statistically significant
systematic error: tcal < ttab.
ACKNOWLEDGMENTS
The study was supported by the Russian Foundation
for Basic Research (grant no. 08-03-00749).
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