Utilizing the chemiluminescence of 2-substituted-4,5-di(2-furyl)-1H- imidazole-H2O2-Cu2+ system for the determination of Cu2+

Article abstract of DOI:10.1016/j.jphotochem.2010.11.009

In the paper, 2,4,5-tri(2-furyl)-1H-imidazole (TFI) and 2-phenyl-4,5-di(2-furyl)-1H-imidazole (PDFI), were chosen to investigate chemiluminescence (CL) properties of 2-substituted-4,5-di(2-furyl)-1H- imidazoles. The directly oxidized CL of analytes by H

Full text of DOI:10.1016/j.jphotochem.2010.11.009

Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 376–382
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Utilizing the chemiluminescence of
2
+
2
-substituted-4,5-di(2-furyl)-1H-imidazole–H O –Cu system for the
2 2
2+
determination of Cu
∗
Jing Kang, Yumin Zhang, Lu Han, Jieli Tang, Shuaijun Wang, Yihua Zhang
College of Chemistry, Jilin University, Changchun 130012, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 August 2010
Received in revised form 29 October 2010
Accepted 16 November 2010
Available online 21 November 2010
In the paper, 2,4,5-tri(2-furyl)-1H-imidazole (TFI) and 2-phenyl-4,5-di(2-furyl)-1H-imidazole (PDFI),
were chosen to investigate chemiluminescence (CL) properties of 2-substituted-4,5-di(2-furyl)-1H-
imidazoles. The directly oxidized CL of analytes by H2O2 was in detail studied. The H2O2 could directly
oxidize TFI/PDFI to produce strong CL emission in basic solution. The addition of Cu into the sys-
tem could induce significant enhancement of CL signal. Based on this study, it was found that the
2+
2
+
2+
TFI/PDFI–H2O2–Cu CL system could be successfully applied to the determination of Cu . The pro-
Keywords:
Chemiluminescence
2
+
posed method has been used to determine trace amount of Cu with a limit of detection (3ꢀ) of
−11
6
.5 × 10
mol/L, which enables minimal amount of sample for analysis. A satisfactory result has been
2
2
,4,5-Tri(2-furyl)-1H-imidazole
-phenyl-4,5-di(2-furyl)-1H-imidazole
2
+
obtained for the determination of Cu in the reference material samples. The possible oxidized CL
mechanism was also discussed briefly based on the photoluminescence (PL) and CL spectra.
Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
H2O2
2+
Cu
1
. Introduction
a means for preparing functionalized materials [11]. Imidazole
nucleus forms the main structure of some well-known compo-
Chemiluminescence (CL) can be defined as emission of light
ultraviolet, visible or infrared) from a molecule or atom in an
nents of human organisms, i.e. the amino acid histidine, vitamin
B12, a component of DNA base structure, purines, histamine and
biotin. It is also present in structures of many natural or synthetic
drug molecules, i.e. azomycin, cimetidine and metronidazole [12].
Phenylimidazoles have been studied because of their important
laser properties [13,14]. Further substitution by phenyl groups
results in other significant optical properties. An important imida-
zole derivative is lophine (2,4,5-triphenylimidazole). Recently, a
number of lophine derivatives were synthesized based on lophine
skeleton substituted at the ortho-, meta- and para-substituted in
the 2-phenyl ring and para-substituted in the 4- and 5-aryl rings
according to slightly modified procedure of the Debus method
[15–20]. A variety of lophine analogues having 2-pyridyl or 2-
furyl group at both 4- and 5-positions of heterocyclic imidazole
derivatives have been reported [19,20]. Among the derivatives,
compounds carrying a 2-furyl group showed strong photolumi-
nescence (PL) intensities, while those having a 2-pyridyl group
gave very weak intensities [11]. Hitherto, many heterocyclic
imidazole derivatives have been synthesized and studied with
regard to their ultraviolet (UV), PL and CL properties [18,19].
Lophine is a well-known potential CL compound synthesized by
Radziszewski (1877). It has been used for analysis of some metal
ions [21–24] and chlorinated compounds [23]. However, applica-
tion of 2-substituted-4,5-di(2-furyl)-1H-imidazoles in CL was quite
rare.
(
electronically excited state produced by a chemical reaction at
ordinary temperature without any associated generation of heat.
There are two types of CL reactions, direct or indirect CL (also
described as sensitized or energy transfer CL). Eliminating external
light source and employing minimal instrumentation for chem-
ical excitation, CL detection efficiently avoids the factors that
limit the sensitivity of classical detections and avoids expensive
instrumentation. Owing to its low detection limit, wide dynamic
range, rapid response, simple instrumentation and no background
scattering light interference, the CL detection method is growing
important in analytical chemistry [1–3], particularly in pharma-
ceutical and biomedical analysis [4–7]. The increase in CL reagents,
CL labeling reagents and derivatization methods as well as spe-
cific interface designs has widened the application areas of the CL
detector.
Over the years, heterocyclic imidazole derivatives have
attracted considerable attention because of their unique optical
properties [8–10]. These compounds play a very important role
in chemistry as mediators for synthetic reactions, primarily as
∗ Corresponding author. Tel.: +86 431 85168352 6.
E-mail address: yihuazh47@yahoo.com.cn (Y. Zhang).
1
010-6030/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.11.009

J. Kang et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 376–382
377
a
a
W
Black box
R
air
W
O
O
O
BPCL
O
O
SL1
N
NH
P1
CH3COONH4 (10equiv)
SL2
CH COOH
3
S
V
W
W
reflux
PMT
O
air
O
O
PC
P2
TFI
O
b
CHO
b
O
W
Black box
R
O
O
air
air
CH3COONH4 (IL)
Hbim]BF4 100oC
N
N H
+
BPCL
[
P1
SL1
W
SL2
W
O
S
V
W
PMT
PC
PDFI
P2
Fig. 1. Synthesis of TFI and PDFI.
Fig. 2. Schematic diagram of the steady-injection CL system. A: H2O2 solution; B:
NaOH solution; P1, P2: peristaltic pump; SL: sample loop; V: eight-way valve; R:
chemifold; S: sample cell; PMT: photomultiplier tube; PC: computer; W: waste. (a)
Loading position and (b) injection position.
In the present work, two 2-substituted-4,5-di(2-furyl)-1H-
imidazoles, 2,4,5-tri(2-furyl)-1H-imidazole (TFI) and 2-phenyl-4,5-
di(2-furyl)-1H-imidazole (PDFI), were synthesized according to the
reported methods [20,25]. The H O could directly oxidize TFI and
mixture of petroleum ether and ethyl acetate (3:1) as eluents. Then
TFI was recrystallized from methanol. Yellow single crystals were
obtained by slow evaporation of the solvent at ambient tempera-
ture.
2
2
PDFI to produce strong CL emission in basic solution. The addition
of Cu2+ into the TFI/PDFI–H O CL systems could induce significant
2
2
enhancement of CL signal. The possible enhancement mechanism
of the CL systems was also further investigated. The proposed
method offers the advantages of sensitivity, selectivity, simplicity
PDFI was synthesized according to the literature [20]. The study
was conducted using the ionic liquid (IL), 1-butyl imidazolium
tetrafluoroborate ([Hbim]BF4) as the reaction medium and pro-
moter to generate PDFI by the reaction of furil with benzaldehyde,
2
+
and rapidity for Cu determination. It was successfully applied to
the determination of trace amount of Cu2+ in the reference mate-
◦
and ammonium acetate, respectively, at 100 C. The reaction in the
rials, such as silicate rock, soil and stream sediments. This may
intrigue researchers into gaining a new interest in investigating
the CL property of heterocyclic imidazole derivatives.
◦
IL was carried out at 100 C for 24 h. The PDFI was prepared.
2.3. Characterization of TFI and PDFI
2
. Experimental
The TFI and PDFI were characterized by melting point, IR, MS
and NMR. The results obtained by elemental analysis were in con-
formity with the theoretical results. The results are described as
follows.
2
.1. Reagents and chemicals
All the reagents were of analytical reagent grade and all solu-
tions were prepared with double-distilled water. Ammonium
acetate, acetic acid, ethyl acetate, methanol, H O , NaOH, HNO ,
2
.3.1. 2,4,5-Tri(2-furyl)-1H-imidazole (TFI)
2
2
3
◦
−1
M.p. 196–197 C. IR (KBr) ꢁ (cm ): 3417, 3114, 2926, 1627,
KCl, NaCl, MgCl , CaCl , ZnCl , Al (SO ) ·18H O, Ni(NO ) ·6H O,
2
2
2
2
4
3
2
3
2
2
1
538, 1477, 1430, 1380, 1201, 1016, 887, 748. 1H NMR (500 MHz,
BCl ·2H O, AgNO , CdCl , MnSO ·H O, Cr(NO ) ·9H O, Pb(NO ) ,
2
2
3
2
4
2
3
3
2
3 2
CDCl ), ı (ppm): 10.48 (s, 1H), 7.42 (s, 2H), 7.36 (s, 1H), 6.92 (d,
J = 3.3 Hz, 3H), 6.46 (dd, J = 3.0, 1.7 Hz, 2H), 6.41 (dd, J = 3.1, 1.6 Hz,
1
C, 67.65; H, 3.79; N, 10.53. The elemental analysis gave the molec-
ular formula C15H10N O (Found: C, 67.53; H, 3.71; N, 10.45).
FeCl ·4H O and CuSO ·5H O were purchased from Beijing Chem-
3
2
2
4
2
ical Plant in China. Furfural, petroleum ether and benzaldehyde
were purchased from Tianjin Guangfu Fine Chemical Research
Institute in China. The certified reference materials such as GSS-4
+
H). MS (m/z): (M+H) 267.3 (Calcd. 266.25). Calcd. for C15H N O :
10
2
3
(
limestone soil), GSR-3 (basalt), GSD-2 and GSD-8 (stream sedi-
2
3
ments) produced by Bulletin of the Institute of Geophysical and
Geochemical Exploration (IGGE) in China.
2.3.2. 2-Phenyl-4,5-di(2-furyl)-1H-imidazole (PDFI)
◦
−1
M.p. 197–198 C. IR (KBr) ꢁ (cm ): 3118, 3054, 1599, 1551,
1
2.2. Synthesis of TFI and PDFI
1481, 1404, 1233, 1090, 886, 732, 590. H NMR (300 MHz, CDCl3),
ı (ppm): 7.92 (dd, J = 8.2, 1.5 Hz, 2H), 7.57–7.33 (m, 5H), 6.99 (d,
+
The synthesis of TFI and PDFI is shown in Fig. 1. TFI was synthe-
J = 3.3 Hz, 2H), 6.53 (dd, J = 3.4, 1.8 Hz, 2H). MS (m/z): (M+H) 277.9
sized according to the literature [25]. A mixture of 1 g furil and
.05 g ammonium acetate in 20 mL acetic acid was heated and
(Calcd. 276.29). Calcd. for C17H12N2O2: C, 73.80; H, 4.38; N, 10.14.
The elemental analysis gave the molecular formula C17H12N2O2
(Found: C, 73.55; H, 4.34; N, 9.95).
4
refluxed. After completion of the reaction, the mixture was cooled
to room temperature, diluted with 100 mL of water, and then neu-
tralized with a 20% NaOH aqueous solution to pH 9. The mixture
was extracted with ethyl acetate, and the solvent was removed.
The ethyl acetate was evaporated by rotary evaporation. The crude
product was further purified by column chromatography using a
2.4. Apparatus
The CL analysis was conducted on a laboratory-built steady
injection CL system. The schematic diagram of the system is shown

3
78
J. Kang et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 376–382
180
(
A) 1.00
(B)
a
a
1
1
50
20
0
0
0
0
.75
.50
.25
.00
b
b
90
60
30
0
b
a
-0.25
2
50 300 350 400 450 500 550 600
Wavelength (nm)
250 300 350 400 450 500 550 600 650
Wavelength (nm)
Fig. 3. Absorption spectra (A) and PL spectra (B) of TFI and PDFI. Concentration: TFI (curve a), 2 × 10− mol/L; PDFI (curve b), 2 × 10−6 mol/L.
6
in Fig. 2. The steady injection Analysis Processor FIA-3100 (Beijing
Wantuo Instruments Co., Ltd.) consists of two peristaltic pumps, a
were synchronously injected into the sample cell using the steady
injection system.
1
6-hole eight-way valve and a digital-system to control the time
In sequence 1 (Fig. 2a), pumps P1 and P2 were activated, and
and pump pressure. PTFE tube (0.8 mm i.d.) was used as connec-
tion material in the steady system. The CL emission was detected
by an ultra-weak luminescence analyzer (type BPCL manufactured
at the Institute of Biophysics, Chinese Academy of Sciences, Beijing,
China). The acquisition and treatment of data were performed with
BPCL software running under Windows XP.
valve V was in the loading position. The pump P was used to deliver
1
H O solution into the sample loop1 (SL ) and the pump P2 was
2
2
1
used to introduce NaOH solution into the sample loop2 (SL ). In
2
sequence 2 (Fig. 2b), pumps P and P were activated, and valve V
1
2
was in the injection position. The pumps P1 and P2 were used to
deliver the air current. The H O solution and NaOH solution were
2
2
PL spectra were recorded on a RF-5301 spectrofluorimeter
Shimadzu, Japan). The absorption spectra were recorded on an
simultaneously pumped at the same rate separately into chemi-
fold R where they were mixed. The mixed solution was carried
into sample cell S and mixed with TFI/PDFI (or solution contain-
ing TFI/PDFI and Cu2+) in the sample cell S. CL signal was measured
and recorded. After determination, the mixed solution in the sam-
ple cell S was emptied. The sample cell S was washed and dried. All
experiments were performed in triplicate.
(
Australian GBC Cintra 10e UV–vis Spectrometer within the wave-
length range from 200 to 800 nm. The CL spectrum was obtained
with a series of interference filters. The interference filters were
inserted between the sample cell and the PMT. The spectral range
detected with the PMT is from 400 to 640 nm.
The concentration of analyte was quantified by measuring the
change of CL intensity. ꢂI = Is − I0, where I0 and Is are CL signals in
the absence and presence of Cu2+, respectively.
2.5. Procedure
Experimental results were obtained using the following oper-
ation parameters: pump rate, 60 rpm/min; sample loop volume,
00 ␮L; flow rate, 2.4 mL/min; sampling time, 12 s; sample injec-
2.6. Preparation of sample
3
tion time, 20 s; the PMT negative voltage, −100 V; the integral time
of the CL signal, 60 s. 200 ␮L of TFI/PDFI solution (or solution con-
taining TFI/PDFI and Cu2 ) was first added into the sample cell
0.5000 g of sample was weighed and added to 50 mL beaker.
5 mL of 65% HNO3 solution was added cautiously into the beaker
when the solution was stirred continuously, and slowly heated on
the electric hot plate. When there was about 2 mL solution left,
+
(
colorless glass tube 1 cm i.d.), and then H O2 and NaOH solution
2
8
6
4
2
00
00
00
00
0
2500
TFI
PDFI
2
1
1
000
500
000
a
b
500
c
0
0
10
20
30
40
50
60
a
b
Time (S)
2
+
Fig. 5. The catalysis effect of Cu on CL intensity. Concentration: (a) TFI/PDFI,
Fig. 4. CL kinetic curves of TFI and PDFI. Concentration: (a) TFI, 0.1 mmol/L; NaOH,
.1 mol/L; H2O2, 1 mol/L, (b) PDFI, 0.1 mmol/L; NaOH, 0.1 mol/L; H2O2, 1 mol/L and
c) NaOH, 0.1 mol/L; H2O2, 1 mol/L.
0.1 mmol/L; NaOH, 0.1 mol/L; H O , 1 mol/L and (b) Cu2+, 0.1 mmol/L; TFI/PDFI,
2
2
0
(
2 2
0.1 mmol/L; NaOH, 0.1 mol/L; H O , 1 mol/L. The error bars denote the standard
deviation of the values with the three same determinations.

J. Kang et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 376–382
379
1
1
1
400
200
000
5000
4000
3000
2000
1000
0
a
a
b
8
00
00
00
00
0
b
6
4
2
0
.0
0.2
0.4
0.6
0.8
1.0
Concentration of NaOH (mol/L)
0
100
200
300
400
500
Fig. 6. Influence of NaOH concentration on the CL intensity. Concentration: (a)
Concentration of TFI/PDFI (µmol/L)
2+
TFI, 0.1 mmol/L; H2O2, 1 mol/L; Cu , 0.01 mmol/L and (b) PDFI, 0.1 mmol/L; H2O2,
+
1
mol/L; Cu2 , 0.01 mmol/L. The error bars denote the standard deviation of the
Fig. 8. Influence of TFI/PDFI concentration on the CL intensity. Concentration: (a)
values with the three same determinations.
2+
H2O2, 0.01 mmol/L; 0.25 mol/L; Cu , 0.01 mmol/L and (b) H2O2, 0.005 mmol/L;
2
+
NaOH, NaOH, 0.25 mol/L; Cu , 0.01 mmol/L. The error bars denote the standard
deviation of the values with the three same determinations.
6000
5000
4000
3000
2000
1000
0
liquid was cooled and proper content of water was added into the
beaker. The solution was filtered into the beaker, and the resulting
solution was adjusted by NaOH solution to ensure pH value of about
6
.5. Then the obtained solution was filtered. The filter liquor was
quantitatively transferred into a 250 mL volumetric flask, diluted
to the mark at room temperature and mixed thoroughly.
a
b
3. Results and discussion
3.1. Absorption spectra, PL spectra and CL kinetic curves of TFI
and PDFI
0.0
0.2
0.4
0.6
0.8
1.0
Concentration of H O (mol/L)
Fig. 3 shows the absorption spectra (Fig. 3A) and PL spectra
Fig. 3B) of TFI and PDFI. It can be seen from Fig. 3A that the first
excitonic absorption peaks of the TFI and PDFI appear at 316 and
14 nm, respectively. The PL spectra show that the excitation peaks
of TFI and PDFI are at around 319 and 317 nm, respectively, corre-
sponding with the emission peaks of 422 and 435 nm.
2
2
(
Fig. 7. Influence of H2O2 concentration on the CL intensity. Concentration: (a) TFI,
2+
0
0
.1 mmol/L; NaOH, 0.25 mol/L; Cu , 0.01 mmol/L and (b) PDFI, 0.1 mmol/L; NaOH,
3
.25 mol/L; Cu2 , 0.01 mmol/L. The error bars denote the standard deviation of the
+
values with the three same determinations.
The CL reaction between H O and TFI/PDFI was further investi-
2
2
HNO was cautiously added drop-wise for continuous digestion till
gated. The H O can, in the available concentration range, directly
3
2 2
the HNO are excess. The evaporation was continued until copious
reddish brown fumes of nitrogen dioxide are evolved. The residual
oxidize TFI and PDFI to generate strong CL emission. The dynamic
CL intensity-time profiles of the TFI/PDFI–H O systems are shown
3
2
2
(
A) 120
(
B) 90
a
8
7
6
0
0
0
a
1
00
8
0
0
0
0
b
b
6
4
2
50
4
3
2
0
0
0
4
00
450
500
550
600
650
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
Fig. 9. The CL spectra of different systems. (A) The CL spectra of TFI–H2O2–Cu2+system (curve a) and TFI–H2O2 system (curve b). Concentration: TFI, 0.1 mmol/L;
2
+
−7
2+
2+
Cu , 5 × 10 mol/L; H2O2, 0.01 mol/L. (B) The CL spectra of PDFI–H2O2–Cu system (curve a) and PDFI–H2O2 system (curve b). Concentration: PDFI, 0.1 mmol/L; Cu
,
−
7
5
× 10 mol/L; H2O2, 0.005 mol/L. The error bars denote the standard deviation of the values with the three same determinations.

3
80
J. Kang et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 376–382
Cu2+ + H2O2
H+ + Cu+ O2H*
sity increases with the increase of the concentration of H O .
2 2
The CL intensity reach a maximum when the concentrations
Cu+ O2H + H2O2
*
Cu+ + OH* + O2 + H2O
2+
of H O2 are 0.01 mol/L and 0.005 mol/L for TFI–H O –Cu and
2
2
2
Cu+ + H+ + H O2
OH* + Cu2+ + H O
2+
PDFI–H2O2–Cu system, respectively. When the concentrations
2
2
2+
of H O2 are higher than 0.01 and 0.005 mol/L for TFI–H O –Cu
2
2
2
O2 + OH- + H O2
OH* + O - + H O
2
2
2
2+
and PDFI–H O –Cu system, respectively, the CL intensity of the
TFI/PDFI–H2O2–Cu system decreases with the increase of H2O2
concentration. So 0.01 and 0.005 mol/L H O were chosen for fur-
2
2
2+
O2- + H2O2
OH* + 1O2
-*
2
2
OH* + H2O2
+
H+ + H O
2
ther research, respectively.
.4. Effect of the concentration of TFI/PDFI
The effect of TFI/PDFI concentration on the CL intensity of
O2
3
O
O
N
N
N
O2-
*
R
the studied system was tested. From Fig. 8, it can be seen that
the concentration of the TFI/PDFI has great influence on the CL
intensity. With the increase of concentration of TFI/PDFI, the CL
intensity increases when the concentration of TFI/PDFI is lower
than 0.1 mmol/L, and the intensity decreases when the concentra-
tion of TFI/PDFI is higher than 0.1 mmol/L. Therefore, the optimum
concentration of TFI/PDFI was chosen to be 0.1 mmol/L.
R
+
HOO
N
H
O
O
O
O
3.5. Determination of Cu2+
-
-
N
N
O
O
R
O*
N
R
O
N
hv
Under the optimal conditions, the relationship between
2+
enhanced CL intensity and the concentration of Cu was obtained.
The analytical parameters are given in Table 1. It demonstrated that
there was a good linear relationship between enhanced CL inten-
sity and the concentration of Cu2+ over a wide range. The results
demonstrate that the analytical figures of merits for the proposed
method are satisfactory.
O
O
R:
TFI
O
3.6. Selectivity
PDFI
The interference of some metal ions was tested when the con-
centration of Cu2+ was 5.0 × 10 mol/L. The results are listed in
−7
Fig. 10. The mechanism of the CL.
Table 2. From the results, it was found that most ions, which gener-
ally accompany Cu2+, did not interfere with the detection of Cu
2+
.
in Fig. 4. It has been found experimentally that the addition of Cu2+
into the system could induce significant enhancement of CL signal.
The results are shown in Fig. 5. So Cu2+ was chosen to enhance the
CL intensity of the TFI/PDFI–H O system in the experiment.
The proposed method is quite selective for determination of Cu2+.
This fact was further attested by applying the present method to the
determination of Cu in some samples, including geo-standards of
2+
2
2
diverse matrices.
3.2. Effect of the concentration of NaOH
3.7. Analytical application
The effect of the concentration of NaOH on the CL intensity
The method finds an excellent application for the determination
of Cu in the reference materials, such as silicate rock, soil and
2
+
2+
of TFI/PDFI–H O –Cu
system was examined in the range of
2
2
0
.001–1 mol/L, and the results are shown in Fig. 6. The CL inten-
stream sediments. The results are shown in Table 3. The reference
material samples, which were diluted 100-fold, were analyzed. The
results obtained were found to be in agreement with the certified
values. The relative errors for the analytical results were from −4.0%
to 3.1%.
sity increases when the NaOH concentration increases from 0.001
to 0.25 mol/L, and the intensity starts to decrease when the con-
centration is higher than 0.25 mol/L. Therefore, the optimum NaOH
2+
concentration was chosen to be 0.25 mol/L for TFI/PDFI–H O –Cu
2
2
system.
3.8. Study of the mechanism of the system
3
.3. Effect of the concentration of H O2
2
To explain the CL reaction mechanism and confirm the emission
The effect of the H O2 concentration on the CL intensity was
species, the following experiments were performed. The H O -
2
2 2
studied, and the plot of CL intensity versus H O2 concentration
is shown in Fig. 7. From Fig. 7, it can be seen that the CL inten-
oxidized CL spectra of TFI/PDFI were measured using a series of
high-energy cutoff interference filters, as shown in Fig. 9. It could
2
Table 1
Linear calibration equation for Cu2+
.
System
Linear range (mol/L)
Calibration curve (C, ␮mol/L)
R
Detection limit (mol/L)
RSD (%)
TFI–H2O2–Cu2
+
5.0 × 10 –1.0 × 10
−10
−5
−6
ꢃI = 119.7C + 10.92
ꢃI = 99.45C + 6.292
0.9972
0.9975
2.7 × 10
−10
1.8
2.3
PDFI–H2O2–Cu2
+
1.0 × 10 –5.0 × 10
−10
6.5 × 10
−11
The RSD was estimated at 5.0 × 10−7 mol/L for Cu2+ (n = 11).

J. Kang et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 376–382
381
Table 2
Tolerance of foreign substances.
Substance
Concentration (␮mol/L)
TFI–H2O2–Cu2+ system
Concentration (␮mol/L)
PDFI–H2O2–Cu2+
change of ꢃI (%)
system change of ꢃI
(
%)
+
−
K , Cl
500
500
10
500
500
100
50
500
25
10
500
500
10
250
250
100
5
500
25
5
1.0
+
−
Na , Cl
Mg , Cl
Ca , Cl
−0.7
−2.0
3.1
2.0
3.7
−0.2
−2.0
1.2
4.5
3.1
2+
−
2+
−
−
2+
Zn , Cl
3
+
2−
Al , SO
4
2+
−
Ni , NO
Ba , Cl
Ag , NO
Cd , Cl
3.5
1.6
3
2+
−
−0.9
−1.7
+
−
0.3
0.6
3
2+
−
−2.9
3.0
−1.8
−2.5
2.8
3.9
2+
2−
Mn , SO
500
2.5
10
25
250
10
25
−1.7
−1.4
−3.4
2.7
4
3
+
−
Cr , NO
3
2+
−
Pb , NO
Fe , Cl
3
2+
−
25
Concentration of Cu2+ is 5.0 × 10−7 mol/L.
Table 3
Determination of Cu2 in diverse samples.
+
Sample
Certified value (␮g/g)
Proposed method (␮g/g) (n = 5)
Relative error (%)
GSD-2
GSD-8
GSR-3
GSS-4
4.90
4.10
48.60
40.00
4.75 ± 0.08
3.95 ± 0.07
50.11 ± 1.00
38.40 ± 0.88
−3.1
−3.7
3.1
−4.0
be clearly seen from Fig. 9 that there was only one emission band
conditions were investigated. The increase of CL intensity of the
2+
around 460–640 nm for TFI/PDFI–H O2 CL reaction. The CL peaks
TFI/PDFI–H O –Cu system is proportional to the concentration of
2
2 2
2
+
were at around 535 nm and 540 nm for the TFI–H O2 and the
Cu in the range of certain concentration. Significantly, the method
had been used to determine trace amount of Cu with a limit of
2
2
+
PDFI–H O CL reactions, and the corresponding CL spectra are
2
2
−
11
shown in Fig. 9A (curve b) and Fig. 9B (curve b), respectively. The
difference of CL peaks for the TFI–H O and the PDFI–H O system
detection (3ꢀ) of 6.5 × 10
mol/L. Under the condition of low con-
2+
3+
centration, the other metal ions (such as Pb and Cr ) do not
2
2
2
2
is due to the difference of 2-substituents on the imidazole ring. The
PL spectra (Fig. 3B) of the stable emitting species were not identi-
cal with the CL spectra. Therefore, it is proposed that the TFI/PDFI
can be oxidized to new substance by oxidant. The relaxation of this
excited state of the substance induces the transitions, which pro-
duces CL signals. The possible oxidized CL mechanism was similar
to that of lophine [11,23], and it was clarified that a hydroperoxide
as a reaction intermediate is intramolecularly decomposed to yield
an excited singlet state of diaroylamidine followed by the emission
of light. Fig. 9 also shows significant difference of the CL spectra in
the absence and presence of Cu2 for TFI/PDFI–H O systems. The
interfere with the determination of Cu2+. The proposed method is
2+
highly selective for determination of Cu . The reason may be that
Cu can catalyze the decomposition of H O , which can enhance
2+
2
2
the CL of the TFI/PDFI–H O2 system, and the catalysis reaction is
2
highly selective. The proposed method enables minimal amount of
sample for analysis. The lophine CL has been utilized for determi-
nation of Cu2+ [23], and its major weakness is lack of selectivity.
The proposed method has the advantages, such as high sensitivity
and selectivity, and wide linear response range. These new phe-
nomena would further enable people to exploit more CL analytical
applications of the heterocyclic imidazole derivatives.
+
2
2
CL emission peaks of TFI–H O and PDFI–H O systems are at about
2
2
2
2
2
+
5
35 and 540 nm, respectively. When the Cu was added into the
systems, there was not significant influence on the shapes of the CL
emission peaks, but the CL intensity was enhanced. It is suggested
that the emission species is excited singlet state of diaroylamidine.
On the basis of many experimental results, the mechanism of
the TFI/PDFI CL is proposed to be as follows: (1) Cu2 catalyzes
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