Electronic Supplementary Material
Simultaneous determination of ascorbic acid, dopamine and uric acid using a glassy carbon
electrode modified with the nickel(II)-bis(1,10-phenanthroline) complex and single-walled
carbon nanotubes
Songling Yan a, Xi Lia*, Yan Xionga, Mengmeng Wanga, Linlin Yang a, Xin Liua, Xiaoyu Lia,
Lina Abdullah M Alshahrania, Peng Liua, Chaocan Zhangb*
a
Department of Chemistry, School of Science, Wuhan University of Technology, Wuhan 430070,
PR China
b
School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070,
PR China
* Corresponding author, Tel.: +86 27 87863157; fax: +86 27 87863157, E-mail address:
chemlixi@whut.edu.cn (Li X); polymers@whut.edu.cn (Zhang C)
Figure S1 FTIR spectra of (a) SWCNTs; (b) poly [Ni(phen)2]2+; (c) poly [Ni(phen)2]2+
/SWCNTs/GCE;(d) [Ni(phen)2]2+ power.
FT-IR measurements were carried out to investigation the structure of the prepared [Ni(phen) 2]2+
complex and the formation of [Ni(phen)2]2+ complex film on the electrode. For the IR
experiments, the [Ni(phen)2]2+ was electropolymerized on the surface of ITO substrate. The IR
results are shown in Fig. S1.
In the FT-IR spectrum of SWCNTs (line a), 1723 cm-1 was attributed to the C=O stretching
in carboxylic acid groups. 1540 cm-1 was due to C=C bonds, and 1363-1021 cm-1 was O-H
bending or C-O stretching.
In the FT-IR spectrum of [Ni(phen)2]2+, the broad peak around 3346 cm-1 can be attributed to
O-H vibration of H2O in the samples ( line b, c and d). While, comparing with [Ni(phen)2]2+
power (line d), these bands become smaller in the spectrum of poly [Ni(phen)2]2+ (line b)and poly
[Ni(phen)2]2+/ SWCNTs (line c) on ITO because the loss of H2O during the electropolymerization.
In the FT-IR spectrum of [Ni(phen)2]2+ power , the absorption peaks at 1626, 1605 cm-1 were
ascribed to the C=N groups of phen. The bonding of the [Ni(II)] ion to phenanthroline through
the nitrogen atoms was supported by the presence of bands in 643 cm-1 due to the M-N stretching.
The spectrum of poly [Ni(phen)2]2+ (line b) imilar the spectrum of [Ni(phen)2]2+ power,
indicated that the process of electropolymerization was carried out without any decomposition of
[Ni(phen)2]2+. While the absorption peaks of C=N shows a red shift slightly with the close
packing of [Ni(phen)2]2+, superposition of electron cloud and raising of electron density.
The influence of pH
Figure S2 The dependence of the oxidation peak potential (a) and peak current (b) of 500 µmol
L-1 AA, 60 µmol L-1 DA and 60 µmol L-1 UA on the solution pH at [Ni(phen)2]2+ / SWCNTs /
GCE in 0.2 mol L-1 phosphate buffer containing 0.1 mol L-1 KCl．
The influence of electrolyte pH on the peak potentials and the currents for AA, DA and UA
at the [Ni(phen)2]2+/SWCNTs/GCE were studied by differential pulse voltammetry (DPV) in 0.2
mol L-1 phosphate buffer in the pH range of 2.0–7.0. Fig. 4(a) showed that the oxidation peak
potentials for AA, DA and UA shifted negatively as the pH increased from 2.0 to 7.0. The slope
of − 0.053 V/pH units for AA, − 0.058 V/pH units for DA and −0.064 V/pH units for UA were
obtained, which was close to the theoretical value of 0.059 V·pH-1 ，suggesting that the protons
were involved in the electrode redox processes for AA, DA and UA. Meanwhile, the oxidation
peak currents of AA, DA and UA also depended on the solution pH as shown in Fig. 4(b). The
oxidation peak current of AA attained the maximum at pH 4.0. In consideration of the lowest
sensitivity of the [Ni(phen)2]2+/SWCNTs/GCE to AA among these three substances, pH 4.0 was
chosen as the optimum pH value in the electrochemical detection of AA, DA and UA.
The influence of amount of SWCNTs and [Ni(II)] complex modified on GCE
Figure S3 The dependence of the peak current of 1 mmol L-1 AA in 0.2 molL-1 phosphate
buffer containing 0.1 molL-1 KCl at [Ni(Phen)2]2+/SWCNTs-modified electrode on the amount of
SWNCTs(a) and scanning number of polymerization (b);
The amount of SWCNTs and [Ni(II)] complex also influenced the electrocatalytic activity of
the modified electrode. For the lowest sensitivity of the modified electrode to AA among these
three substances, AA was chose to characterize the effect of the [Ni(phen)2]2+/SWCNTs/GCE by
DPV.
The amount of SWCNTs on the electrode surface was controlled by the additon time of
SWCNTs suspension with specified concentration. The relationship between the oxidation peak
current of AA and dropping times was shown in Fig. 5(a). With the increase of the dropping time,
the peak current of AA also increased. When the dropping times came to 4, the peak current
reached the maximal value 11.3 μA. So dropping four times was chosen in subsequent
experiments.
The amount of complex can be controlled by changing the number of scan cycles during the
electrochemical polymerization. As shown in Fig. 5(b), with the number of scan cycles changing
from 5 to 15 cycles, the peak current of AA increased gradually until it attained the maximum at
15 cycles. After 15 cycles, the peak current became lower. Thus the suitable number of scan
cycles was 15 in the electrochemical polymerization of [Ni(phen)2]2+.