Electronic Supplementary Material
Determination of nimesulide in human serum using a glassy carbon electrode
modified with SiC nanoparticles
Raouf Ghavami*, Aso Navaee
Department of Chemistry, Faculty of Science, University of Kurdistan, P. O. Box 416,
*Corresponding author, Tel.: +98 871 6624133; fax: +98 871 6624133. Sanandaj, Iran; E-mail
addresses:rghavami2000@yahoo.con; rghavami@uok.ac.ir
Properties of SiC nanoparticles
Silicon carbide is a wide band gap semiconductor with a range of excellent physical, chemical,
mechanical and electronic properties [1]. Due to various technological applications,
nanoparticles of silicon carbide have attracted the interest of scientists and engineers [2]. Silicon
carbide nanoparticles are promising raw materials for high temperature engineering ceramic
devices and polymers [3-5]. SiC-NPs are expected to have the ability to exhibit
photoluminescence (PL) at shorter wavelengths than silicon nanoparticles, making them a
promising material for optoelectronic devices [6].
The application of SiC slurry for the electrolyte matrix of phosphoric acid fuel cell and metal
oxide gas sensors have been reported [7,8]. SiC–C composite film has been used for sensing of
dopamine and ascorbic acid [9]. Furthermore, SiC electrode has been used as an ordinary
oxidation-reduction indicator electrode in potentiometric titrations [10]. In addition, GC
electrode modified with SiC nanoparticles has been used for electrocatalytic and flow injection
analysis of insulin [11]. The stability and optical properties of SiC quantum dots, luminescence
behavior of amorphous silicon-carbide film and electrochemical properties of SiC nanoparticles
have been investigated [12-14].
Electrochemical behavior of nimesulide on the SiC-NPs/GC electrode
The relationship between the peak current and the potential scan rate of nimesulide in the 0.1 M
PBS was studied and CVs of 8.0 μM nimesulide in different potential scan rates from the range
of 0.01-0.17 V.s-1 was recorded (Fig. S1). The experimental results indicate a good linear
dependence of the catalytic reduction peak current with the square root of scan rate (v1/2) by
regression coefficient R2=0.9921 (Fig. S1, inset A). This result also indicated the reaction
involves mass transport and depends on concentration of nimesulide, which was ideal case for
quantitative applications.
-10
-8
A
Ip (mA)
-6
-8
-4
-2
y = -16.433x + 0.8387
R2 = 0.9921
-6
I (mA)
0
0.1
0.2
0.3
V1/2
0.4
-13.8
Ln Ip (mA)
-4
-2
0.5
B
-13.2
y = -20.296x - 14.713
R2 = 0.9942
-12.6
-0.04
0
-0.06
-0.08
-0.10
E-Eo'
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
E (V) vs . Ag/AgCl
Fig. S1. CVs of 8 µM nimesulide in different scan rate (0.01-0.17 V·s-1) and plot of Ip versus
square root of scan rate (inset A) and LnIp versus Ep-Eº (inset B).
-1.0
-8.E-07
Ip = -5 x 10-7t-1/2 - 5 x 10-7
I (A)
R2 = 0.9929
-0.8
I (mA)
-7.E-07
0.25
0.29
t
-0.6
0.33
-1/2
-1/2
(s)
-0.4
0
100
200
t (s)
Fig. S2. Chronoamperogram of 2.47 × 10 -3 µmol.cm-3 nimesulide and plot of current versus
inverse square root of time in 0.1 M pH 2.0 PBS.
According to the peak current equation for a totally irreversible diffusion process [15]:
1
I p  (3.01 10 5 )nAC  (n D ) 2
(2)
That αnα was determined by the following equation [15]:
Ep  E p 
2
1.857 RT 47.7

mV
n F
n
(3)
where α is the electron-transfer coefficient, nα is the number of electrons involved in the rate
determining step and Ep/2 is the potential corresponding to Ip/2. The value for αnα was found to be
0.548 (T = 298 K) for the reduction of nitro group at the surface of the modified electrode. Also,
A (effective area, cm2) was determined by recording CVs of a standard concentration of
K4[Fe(CN)6] in different scan rate and according to the Randles-Sevcik equation [16]:
2
3
1
2
I p  (2.69  10 )n AC D 
5

1
2
(4)
where C* and D are the bulk concentration (47 × 10-3 µmol.cm-3) and diffusion coefficient (7.5 ×
10-6 cm2.s-1) of K4[Fe(CN)6], respectively. Plot of Ip vs. v1/2 gives a straight line that from the
slope of this line, the value of A can be estimated which equals to 0.144 cm2. Then inserting the
obtained values of αnα and A in equation 1 the value of D can be estimated equal to 6.08 × 10-5
cm2.s-1.
Moreover, by plotting of LnIp vs. Ep-Eº in different scan rate (Fig. S1, inset B) (Eº can be
determined by the extrapolating of Ep vs. v, the value is equal to -0.39 V vs. Ag/AgCl), gives a
straight line LnIp = -14.713 – 20.296 (Ep-Eº), R2 = 0.9942; that from slop and intercept based on
following equation [17]:
I p  0.227nFAC  K s exp[ n
F
( E p  E  )]
RT
(5)
the value of αnα and Ks (standard heterogeneous rate constant of the electrochemical reaction)
can be determined equal to 0.535 and 4.4×10-3 cm.s-1 respectively. Simultaneous
chronoamperometric detection of 2.47×10-3 mol.cm-3 of nimesulide in 0.1 M PBS, pH 2.0, using
modified electrode based on Cottrell equation [16]:
1
I (t ) 
nFAC * D 2
1 1
2 2
(6)
 t
(C*=2.47 × 10-3 μmol.cm-3 is concentration of nimesulide in bulk solution, and A=0.144 cm2 is
the effective area of modified electrode calculated from equation 4) and plot of I(t) vs. t−1/2 for
each chronoamperograms were give a straight lines (Fig. S2); the slopes of those lines can be
used to estimate the diffusion coefficient (D) of nimesulide. The value of D was found equal to
4.97×10−5 cm2.s-1, that this value has a little difference to the value of D received from equation
1 (6.08 × 10-5 cm2.s-1), so the mean value of diffusion coefficient for nimesulide from equations
2 and 6 can be 5.52 × 10-5 cm2.s-1.
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