Spectral properties of 4-(4-hydroxy-1-naphthylazo)benzenesulfonic acid and its application for colorimetric determination of trace Fe3+

Article abstract of DOI:10.1039/c4ra00512k

A multifunctional dye, 4-(4-hydroxy-1-naphthylazo)benzenesulfonic acid (HNABA) was identified and synthesized. The dye, combining hydroxyl, azo and carboxyl groups, possessed excellent optical absorption properties changing with pH, solvent and coexisting metal ions. In particular, its spectral properties remained extremely stable under acid or neutral conditions and it was effectively applied for colorimetric determination of Fe³⁺ from brick-red to light red in aqueous solution under physiological pH conditions (pH 7.0). Under the optimum conditions, the detection possessed a linear range of 9.5-400 × 10^-8 mol L^-1 with a correlation coefficient (R) of 0.9938 and a limit detection (3σ, n = 20) of 4.2 × 10^-9 mol L^-1. The relative standard deviation (R.S.D.) was lower than 3.5% (n = 5). The proposed method was successfully used to determine trace Fe³⁺ in three real environmental water samples. The mechanism of action between HNABA and Fe³⁺ ion is discussed in detail. the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra00512k

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Spectral properties of 4-(4-hydroxy-1-
naphthylazo)benzenesulfonic acid and its
application for colorimetric determination of
trace Fe
Cite this: RSC Adv., 2014, 4, 19370
3
+
Lei Hu, Li Nie, Guangnian Xu, Han Shi, Xiaoqing Xu, Xiangzhong Zhang
and Zhengquan Yan*
A multifunctional dye, 4-(4-hydroxy-1-naphthylazo)benzenesulfonic acid (HNABA) was identified and
synthesized. The dye, combining hydroxyl, azo and carboxyl groups, possessed excellent optical
absorption properties changing with pH, solvent and coexisting metal ions. In particular, its spectral
properties remained extremely stable under acid or neutral conditions and it was effectively applied for
3+
colorimetric determination of Fe from brick-red to light red in aqueous solution under physiological
pH conditions (pH 7.0). Under the optimum conditions, the detection possessed a linear range of 9.5–
Received 24th January 2014
Accepted 6th March 2014
ꢁ8
ꢁ1
4
4
00 ꢀ 10 mol L with a correlation coefficient (R) of 0.9938 and a limit detection (3s, n ¼ 20) of
ꢁ
9
ꢁ1
.2 ꢀ 10 mol L . The relative standard deviation (R.S.D.) was lower than 3.5% (n ¼ 5). The proposed
DOI: 10.1039/c4ra00512k
3+
method was successfully used to determine trace Fe in three real environmental water samples. The
3+
www.rsc.org/advances
mechanism of action between HNABA and Fe ion is discussed in detail.
2
4–29
than complex instruments,
can be used to observe change,
1
. Introduction
3
+
colorimetric sensors for Fe
have attracted considerable
3
0–33
31
Detection of metal ions has continued to attract tremendous attention in recent years.
Typically, Yun et al. presented an
3
+
attention in recent years due to its importance in environ- easy naked-eye detection method for Fe with a detection limit
mental, biology and chemistry domains. Iron, the third most of 0.024 mg mL , based on 1-nitroso-2-naphthol, an excellent
abundant element in the earth's crust, is not only a very color-forming chelating agent. Adebayo et al. found a novel
ꢁ1
34
important macro-element in the environment, but also an 8-hydroxyquinoline-based colorimetric sensor for the simple
3
+
3+
1,2
essential mineral nutrient for human health. People who lack and rapid determination of Fe using the reaction of Fe with
iron will suffer from iron deciency anemia and other serious the sensor to form a metaloxine complex in chloroform solu-
30
effects on human health, while excess iron would cause an tion. Wallace et al. developed a system that was able to detect
3
+
increased risk of cancer, heart disease and other illnesses such low levels of Fe using a squaraine dye to model on side-
3
–8
as haemochromatosis. Therefore, there is an urgent need to rophores. All these conrm that organic colorimetric sensors
3
+
develop chemical sensors that are capable of detecting and are a promising, easy and practical strategy for detecting Fe .
monitoring iron levels in environmental samples. Considerable However, the sensitivity of common colorimetric sensors is still
efforts have been made to develop various detection methods, lower than that of the instrumentally intensive methods
9
–14
such as uorescent spectrometry,
electro-chromic tech- mentioned above. To develop novel and efficient colorimetric
15,16
17,18
niques
ow injection spectro-photometry,
mass spectrometry, nuclear magnetic resonance,
and inductively coupled plasma mass spectrometry. However,
chromatog- sensing materials will remain a big challenge for a long time in
1
9,20
21
22
raphy,
the future.
3
+
23
Herein, to improve the sensitivity and selectivity of Fe
these instrumentally intensive methods oen require utilizing detection in aqueous systems, a multifunctional dye, 4-(4-
sophisticated instrumentation or complicated pretreatment hydroxy-1-naphthylazo)benzenesulfonic acid (HNABA), was
3
+
procedures, and are not suitable for on-line or in-eld moni- identied and applied for Fe detection aer its optical prop-
toring. By virtue of its simplicity, rapidity, non-destructive erties were studied in detail. The multifunctional dye was
3
+
characteristics and especially the fact that the naked eye, rather expected to possess high selectivity and sensitivity to Fe using
31
35,36
both a hydroxyquinoline group and an –N]N– group
as
chelating groups and to further increase the solubility in
Anhui Provincial Laboratory of Biomimetic Sensor and Detecting Technology & Solar aqueous solution combining –SO
Photovoltaic Materials Research Center, West Anhui University, Lu'an 237012,
China. E-mail: yanzhq2008@163.com; Tel: +86 5643305801
H, –OH and –N]N– groups.
3
19370 | RSC Adv., 2014, 4, 19370–19374
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
3
+
The action mechanism between HNABSC and Fe was dis- 10 mL with doubly deionized water. Aer 20 min, the absorp-
cussed by means of Job's plots and theoretical calculation.
tion spectra were measured from 200 nm to 600 nm and the
band-slit was set as 2.0 nm. The absorption intensity difference
at 478 nm was used for quantitative analysis. The decreased
2. Experiments
absorption intensity of HNABA was represented as DA ¼ A
0
ꢁ A,
2.1 Reagents and apparatus
where A and A were the absorption intensities of the systems in
0
3
+
All the chemicals in the experiment were of AR grade and used the absence and presence of Fe , respectively.
as received from Sinopharm Chemical Reagent Co. Ltd. Water
used throughout was doubly deionized.
ꢁ
1
3+
3
. Results and discussion
A 1.0 mmol L
Fe standard solution for testing was
prepared in doubly deionized water at room temperature and
diluted to the appropriate concentration daily. HNABA was
3.1 The UV-vis absorption spectrum of HNABA
It is well known that HNABA is a strong polar compound, whose
solubility is quite low in nonpolar solvents. To illustrate the
effect of solvents on the absorption spectrum of HNABA, the UV-
vis spectra in different polar solvents, i.e., N,N-dimethyl form-
amide (DMF), tetrahydrofuran (THF), acetone, ethanol and
water were recorded as shown in Fig. 1.
In Fig. 1, we can nd that HNABA has a strong and sharp
absorption peak at ca. 478 nm in polar protic water and ethanol,
attributed to the whole molecular p-conjugated system, with
37,38
synthesized according to our previous work
and a 5.0 ꢀ
ꢁ3
ꢁ1
10
mol L HNABA stock solution was prepared in doubly
ꢂ
deionized water at room temperature and stored at 4 C.
ꢁ1
Phosphate buffers (PB) were prepared by mixing a 0.01 mol L
ꢁ
1
ꢁ1
H PO solution, a 0.01 mol L K HPO solution, a 0.01 mol L
3
4
2
ꢁ
4
1
KH PO solution or a 0.01 mol L KOH solution in the proper
2
4
ratio to achieve the desired pH (pH ¼ 3.0, 4.0, 5.0, 6.0, 7.0, 7.5,
8.0, 9.0, 10.0).
FTIR spectra of HNABA using a KBr disc were acquired using
4
ꢁ1
ꢁ1
molar absorptivity (3) of 2.54 ꢀ 10 L mol cm and 1.95 ꢀ
a Nicolet NEXUS 870 FTIR spectrophotometer at room
4
ꢁ1
ꢁ1
10 L mol cm , respectively, meaning that HNABA exists in
ꢁ
1
1
temperature from 4000–500 cm
recorded using a Bruker AMX-500 spectrometer operating at
00 MHz, with tetramethyl-silane (TMS) used as the reference
.
H NMR spectra were
the form of a monomolecule, i.e., polar protic water and ethanol
are both good solvents for HNABA. However in polar aprotic
acetone, THF and DMF, the absorption intensity at ca. 478 nm
decreases and a new blue-shied absorption peak emerges at
ca. 420 nm. The widening and blue-shi of the absorption
might be attributed to the H-aggregation of HNABA in poor
4
and D O as solvent. Elemental analysis was conducted using an
2
Elemental Vario EL-III apparatus. UV-vis spectra were recorded
on a Lambda 35 UV/vis spectrometer using a 1 cm square quartz
cell. pH was measured by a PHS-25 pH meter.
39,40
solvents such as acetone, THF and DMF.
The conclusion
could be further conrmed by the fact that the absorptions at
ca. 240, 266, 290, 330 nm appear clearly in polar protic water
p-amino benzenesulfonic acid and ethanol while they decrease or disappear almost in polar
2
.2 Preparations of HNABA
37,38
According to the literature,
(
0.87 g, 5 mmol) was dissolved in an ice–water solution of 15% aprotic acetone, THF and DMF, attributed to the p/p*, n/p*
ꢂ
sodium nitrite (0.38 g, 5.5 mmol). Aer cooling to 0 C, the transitions of the C]C, N]N and O]C bonds in the non-
solution was added to concentrated hydrochloric acid (1.2 mL) conjugated benzenesulfonic acid and naphthol moieties.
and stirred for 30 min. The excess nitrous acid was destroyed
with about 5 mg urea. The mixture was then added dropwise to have a more signicant inuence on the form in which it exists
0 mL buffered aqueous solution (KH PO /Na HPO
For an acidic HNABA molecule, the pH of the system will
1
2
4
2
4
, pH ¼ 6) and so will make its absorption spectrum change. Here the
containing naphthol (0.73 g, 5 mmol) and stirred for another 2 h effect of pH on the absorption spectrum was investigated in
at 0–5 C. The resultant precipitate was ltered and puried by polar protic water with a pH range of 3.0–10.0. As shown in
ꢂ
recrystallizing three times from ethanol to provide dark red
crystals of HNABA in a yield of 92.1%.
ꢁ
1
IR (KBr), n (cm ): 3433–2500 (OH, SO
3
H), 1594, 1518 (Ar),
O, 400 Hz) d (ppm):
.74 (d, J ¼ 8.5 Hz, 1H, Ar–H), 8.61 (d, J ¼ 8.4 Hz, 1H, Ar–H), 8.40
1
1
8
(
1 2
376 (Ar–N (R R)), 1169 (S–O). H-NMR (D
d, J ¼ 8.4 Hz, 1H, Ar–H), 8.12 (d, J ¼ 7.8 Hz, 1H, Ar–H), 8.06 (d,
J ¼ 7.8 Hz, 1H, Ar–H), 7.48 (t, J ¼ 6.4 Hz, 1H, Ar–H), 7.51 (t, J ¼
6
–
.7 Hz, 1H, Ar–H), 7.15 (t, J ¼ 6.5 Hz, 1H, Ar–H), 5.15 (s, 1H,
OH). Anal. calcd for C16 SO : H, 3.68; C, 58.53; N, 8.51; S,
.77%. Found: H, 3.73; C, 58.49; N, 8.50; S, 9.79%.
H
12
N
2
4
9
3
+
2
.3 Fe detection procedure
3
+
For the Fe determination, 1.0 mL PB (pH 7.0), 1.0 mL 5.0 ꢀ
ꢁ4
ꢁ1
3+
10
mol L of HNABA and 1.0 mL of the appropriate Fe
solution or sample were transferred into a 10 mL volumetric
Fig. 1 The UV-vis spectra of HNABA in polar solvents, DMF, THF,
ask. The mixture was stirred thoroughly and nally diluted to acetone, water and ethanol.

This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 19370–19374 | 19371

View Article Online
RSC Advances
Paper
Fig. 2 Effect of pH on the UV-vis spectra of HNABA (From up to down:
3
.0, 4.0, 5.0, 6.0, 7.0, 7.5, 8.0, 9.0, 10.0).
Fig. 3 Effect of different metal ions on the UV-vis spectra of HNABA.
Fig. 4 The colour change (4a) and the absorption spectra (4b) of
3+
Fig. 2, it is interesting to nd that the absorption at 478 nm HNABA in different Fe concentrations (from up to down: 0, 9.5, 20,
ꢁ
8
ꢁ1
6
0, 100, 150, 200, 250, 300, 350, 400 ꢀ 10 mol L ); and the linear
keeps quite stable as long as the pH is less than 7.0. When pH is
more than 8.0, the absorption intensity at 478 nm decreases
3+
relationship between the DA of HNABA at 478 nm and cFe (4c).
gradually and red shis. The reason may be that the SO
3
H and
ꢁ
ꢁ
OH groups in HNABA molecules are all ionized to SO
3
and O
+
3+
2+
2+
3+
2+
2+
system in the presence of Ag , Al , Ba , Cd , Co , Cu , Zn ,
ions under basic conditions, which would enlarge the whole
molecular p-conjugated system, but decrease the molecular
dipole moment. The same phenomenon is also found in the
absorbance at ca. 240, 266, 290, 330 nm as shown in Fig. 2,
meaning that HNABA could possess good optical absorption
properties under a wide pH range, i.e., physiological conditions
2
+
+
2+
+
2+
2+
2+
3+
2+
Mn , K , Mg , Na , Ni , Pb , Hg , Cr and Fe show
negligible change even with 100-fold higher concentrations
3
+
than that of Fe and the alterations in DA are all less than 5%
detection error). The results indicate that HNABA possesses
(
3
+
excellent selectivity for Fe even in the presence of other
coexisting metal ions under very high concentrations.
(
pH ca. 7.0) will be selected in the next experiments.
3
+
To illustrate the response speed of HNABA to Fe and the
stability of the proposed system, the effect of incubation time
on the absorption intensity was also investigated. The results
show that a maximum and constant DA is reached aer all
reagents are added and incubated for ca. 20 min at room
temperature. DA remains constant for more than 1 h, implying
3
+
3
.2 Special response to Fe
3
+
To demonstrate the selectivity of HNABA sensing for Fe , we
investigated its colorimetric response to some other environ-
mentally relevant metal ions, i.e., Ag , Al , Ba , Cd , Co ,
Cu , Zn , Mn , K , Mg , Na , Ni , Pb , Hg , Cr and Fe
+
3+
2+
2+
3+
3
+
2
+
2+
2+
+
2+
+
2+
2+
2+
3+
2+ that the HNABA sensor for Fe is stable and reliable.
The inuence of ionic strength on DA of the system at
478 nm was also investigated by varying NaCl concentration
at high concentrations in aqueous solutions at pH 7.0. Aer the
ꢁ
4
ꢁ1
addition of 100 equiv. (4.0 ꢀ 10 mol L ) of the different
ꢁ2
ꢁ1
ꢁ6
ꢁ1
3
+
ꢁ6
ꢁ1
from 1.0 ꢀ 10 mol L to 1.0 ꢀ 10 mol L . It is worth
noting that all the ion strengths tested have no obvious effect on
DA, hinting that the target sensing system is quite stable and
may be applied in various kinds of surroundings.
metal ions above and Fe (4.0 ꢀ 10 mol L ), the relative
changes in absorption intensities of the sensing system were
recorded as shown in Fig. 3, respectively. It can be seen from
Fig. 3 that the absorption intensities of the HNABA sensing
19372 | RSC Adv., 2014, 4, 19370–19374
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
a
Table 1 Determination results for environmental water samples (n ¼ 5)
b
3+
b
Samples
C
Fe in sample (nM)
Spiked (nM)
Found (nM)
Recovery (%)
R.S.D. (%)
1
2
3
(The Pi river)
(Underground)
(Pure water)
788.5
985.2
0.00
500.0
500.0
500.0
1277.7
1496.0
492.8
97.8
102.2
98.6
2.2
3.5
1.3
a
b
3+
PB, pH 7.0. The environmental water Fe concentration determined using HNABA with the proposed method. The real values are the table
ꢁ
2
ꢁ1
values ꢀ 10 nmol L for the detected water samples were concentrated 100 times.
the Pi River, underground water and tap water on campus,
respectively (Table 1). All the samples were obtained by ltering
several times and concentrated by a factor of 100 before testing.
3
+
For recovery studies, some known concentrations of Fe were
3
+
added to the environmental water samples and the total Fe
concentrations were determined following the method
proposed above. The recoveries of different known amounts of
3
+
Fe spiked solution were obtained from 97.8% to 102.2% with a
satisfying analytical precision (R.S.D. #3.5%).
3
+
3.4 Action mechanism between HNABA and Fe
To investigate the nature of the bonding between HNABA and
Fe , the binding stoichiometry of HNABA with Fe was
3
+
3+
Fig. 5 Job plot of HNABA–Fe system. [HNABA] + [Fe ] ¼ 8.0 ꢀ
3+
3+
ꢁ5
ꢁ1
1
0
mol L in aqueous at pH 7.0.
determined by using a Job plot. For the Job plot analyses, a
3
+
series of solutions with varying mole fractions of Fe were
3
+
prepared by maintaining the total HNABA and Fe concentra-
ꢁ
5
ꢁ1
tion constant (6.0 ꢀ 10 mol L ). The absorption intensity at
4
1
78 nm was measured for each solution. As shown in Fig. 5a
: 1 stoichiometry for the complex between HNABA and Fe
can be drawn from the Job plots, which conrms that Fe
3
+
41
3+
might coordinate with the nitrogen atoms in the –N]N bonds
or with oxygen atoms on the naphthol rings.
Fig. 6 Optimized geometries of HNABA before and after reaction with
Fe ion. O, N, C, H, S and Fe atom are represented as red, blue, gray,
white-gray, yellow and blue-purple, respectively.
3+
Theoretical calculations have been carried out to further
understand the nature of the bonding between HNABA and
3
+
Fe . The structures of HNABA before and aer coordinating
3
+
with Fe are shown in Fig. 6, and were optimized using the
B3LYP/6-31G level of theory and method implemented in the
3.3 Analytical parameters and samples detection
42
Gaussian 03 suite of programs. From the results, we can nd
Fig. 4 shows the colour change and the absorption spectra of
3
+
easily that the terminal phenyl rings were greatly distorted,
HNABA at different concentrations of Fe between 9.5–400 ꢀ
3
+
ꢁ8
ꢁ1
because of the binding of Fe with the nitrogen atoms in the
N]N bonds in HNABA, which resulted in the original conju-
10
mol L . From Fig. 4a, it is easy to nd that the colour of
–
the sensing system changes from brick-red to light red, which
can be detected by the naked eye. Also, the calibration graph,
gated system being destroyed and so the absorbance at 478 nm
was reduced and even quenched.
3
+
the detection limit and precision for Fe detection are obtained
under the optimal conditions from Fig. 4b and c. A linear
3
+
relationship between DA and Fe concentration is exhibited in
4. Conclusions
ꢁ
8
ꢁ1
the range of 9.5–400 ꢀ 10 mol L with a correlation coeffi-
ꢁ4
cient of 0.9938. The regression equation is A ¼ ꢁ0.04834 ꢀ 10
In conclusion, a multifunctional dye, 4-(4-hydroxy-1-naph-
ꢁ
3
+
1.37 ꢀ 10 c. Based on the denition of detection limit, three thylazo)benzenesulfonic acid (HNABA) possessed a strong
4
ꢁ1
ꢁ1
times the average deviation of UV absorption at 478 nm in 20 absorption (3 ¼ 2.54 ꢀ 10 L mol cm ) at ca. 478 nm in polar
3
+
blank samples without Fe divided by the slope absolute value protic water and remained tremendously stable under acid or
of the standard curve in Fig. 4c here, the limit of detection neutral conditions. Based on the results, the dye was success-
3
+
ꢁ9
ꢁ1
3+
(
LOD) for Fe is up to 4.2 ꢀ 10 mol L
.
fully developed for trace Fe detection with high selectivity and
To conrm its feasibility, the proposed method was applied sensitivity under physiological pH conditions (pH 7.0). The
3
+
to determine Fe in three environmental water samples from optimal test conditions were obtained (aer 20 min incubation
time at room temperature under pH ¼ 7.0, cHNABA 5.0 ꢀ
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 19370–19374 | 19373

View Article Online
RSC Advances
Paper
ꢁ5
ꢁ1
10
mol L in water) by investigating the inuences of solvent, 17 B. Haghighi and A. Safavi, Anal. Chim. Acta, 1997, 354, 43–50.
pH, ion intensity and incubation time on detection sensitivity. 18 W. Ruengsitagoon, Talanta, 2008, 74, 1236–1241.
3
+
The linear range for detection of Fe in aqueous environments 19 M. Sugiyama, Y. Naraki and T. Hori, J. Liq. Chromatogr. Relat.
ꢁ
8
ꢁ1
ꢁ9
was 9.5–400 ꢀ 10 mol L with a detection limit of 4.2 ꢀ 10
Technol., 2009, 32, 788–800.
ꢁ
1
mol L and a correlation coefficient of 0.9938. The mechanism 20 H. Matsumiya, N. Iki and S. Miyano, Talanta, 2004, 62, 337–
of action of HNABA and Fe ion was conrmed by means of Job
3
+
342.
plots, as well as experimental and theoretical deduction.
21 I. A. Korobeinikova, G. B. Pronchev and A. N. Ermakov,
J. Anal. Chem., 2011, 66, 740–744.
2
2
2 H. Fujii, J. Am. Chem. Soc., 2002, 124, 5936–5937.
3 S. B. Khan, M. M. Rahman, H. M. Marwani, A. M. Asiri,
Acknowledgements
The authors gratefully acknowledge nancial support from the
K. A. Alamry and M. A. Rub, Appl. Surf. Sci., 2013, 282, 46–51.
National Natural Science Fund of China (no. 21277103) and 24 L. Hu, Z. Q. Yan and H. Y. Xu, RSC Adv., 2013, 3, 7667–7676.
Anhui Provincial Natural Science Fund (no. 1308085ME57).
25 L. Hu, Y. F. Zhang, L. Nie, C. G. Xie and Z. Q. Yan,
Spectrochim. Acta, Part A, 2013, 104, 87–91.
2
6 Z. Q. Yan, S. Y. Guang, H. Y. Xu and X. Y. Liu, Analyst, 2011,
36, 1916–1921.
7 Z. Q. Yan, L. Hu, L. Nie and H. Lv, Spectrochim. Acta, Part A,
011, 79, 661–665.
Notes and references
1
1
R. K. Shervedani, A. Hate-Mehrjardi and A. Asadi-Farsani,
Anal. Chim. Acta, 2007, 601, 164–171.
2
2
2
M. Shamsipur, M. Sadeghi, A. Garau and V. Lippolis, Anal.
Chim. Acta, 2013, 761, 169–177.
J. Mao, Q. He and W. S. Liu, Talanta, 2010, 80, 2093–2098.
P. Blatny, F. Kvasnicka and E. Kenndler, J. Chromatogr. A,
28 E. W. Baumann, Analyst, 1992, 117, 913–916.
29 M. A. Kabil and S. E. Ghazy, Anal. Sci., 1995, 11, 817–822.
30 K. J. Wallace, M. Gray, Z. L. Zhong, V. M. Lynch and
E. V. Anslyn, Dalton Trans., 2005, 2436–2441.
3
4
1
997, 757, 297–302.
3
3
1 J. Yun and H. Choi, Talanta, 2000, 52, 893–902.
2 S. Kawakubo, K. Shimada, Y. Suzuki and K. Hattori, Anal.
Sci., 2011, 27, 341–344.
5
6
M. J. C. Marenco, C. Fowley, B. W. Hyland, D. Galindo-Riano,
S. K. Sahoo and J. F. Callan, J. Fluoresc., 2012, 22, 795–798.
T. A. Ali, G. G. Mohamed, M. M. I. El-Dessouky, S. M. Abou El
Ella and R. T. F. Mohamed, Int. J. Electrochem. Sci., 2013, 8,
3
3
3
3
3
3
3
4
4
4
3 S. P. Wu, Y. P. Chen and Y. M. Sung, Analyst, 2011, 136, 1887–
1891.
1469–1486.
4 B. K. Adebayo, S. Ayejuyo, H. K. Okoro and B. J. Ximba, Afr.
J. Biotechnol., 2011, 10, 16051–16057.
5 S. Zareba and H. Hopkala, J. Pharm. Biomed. Anal., 1996, 14,
351–1354.
6 A. K. Sharma and I. Singh, Food Anal. Methods, 2009, 2, 221–
25.
7 Z. Q. Yan, Y. F. Chen, S. Y. Guang, H. Y. Xu and L. F. Li,
Polym. Sci., Ser. B, 2011, 53, 535–539.
7
8
9
N. R. Chereddy, S. Thennarasu and A. B. Mandal, Dalton
Trans., 2012, 41, 11753–11759.
B. D. Wang, J. Hai, Z. C. Liu, Q. Wang, Z. Y. Yang and
S. H. Sun, Angew. Chem., Int. Ed., 2010, 49, 4576–4579.
Y. Y. Du, M. Chen, Y. X. Zhang, F. Luo, C. Y. He, M. J. Li and
X. Chen, Talanta, 2013, 106, 261–265.
0 C. H. Ma, L. P. Lin, Y. Y. Du, L. B. Chen, F. Luo and X. Chen,
Anal. Methods, 2013, 5, 1843–1847.
1 K. G. Qu, J. S. Wang, J. S. Ren and X. G. Qu, Chem.–Eur. J.,
1
2
1
1
1
1
8 Z. Q. Yan, S. Y. Guang, H. Y. Xu and X. Y. Liu, Dyes Pigm.,
2013, 99, 720–726.
2
013, 19, 7243–7249.
2 S. H. Wang, L. Y. Du, A. M. Zhang and B. Li, Anal. Lett., 1997,
0, 2099–2107.
3 X. F. Wu, B. W. Xu, H. Tong and L. X. Wang, Macromolecules,
010, 43, 8917–8923.
9 Z. Q. Yan, H. Y. Xu, S. Y. Guang, X. Zhao, W. L. Fan and
X. Y. Liu, Adv. Funct. Mater., 2012, 22, 345–352.
0 Z. Q. Yan, S. Y. Guang, H. Y. Xu, X. Y. Su, X. L. Ji and X. Y. Liu,
RSC Adv., 2013, 3, 8021–8027.
3
2
1 H. J. Kim, J. E. Park, M. G. Choi, S. Ahn and S. K. Chang, Dyes
Pigm., 2010, 84, 54–58.
2 M. J. T. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr,
T. Vreven, K. N. Kudin and J. C. Burant, Gaussian 03,
revision A.1, Gaussian, Inc., Pittsburgh, PA, 2004.
1
1
4 X. S. Zhu and R. R. Jiang, J. Fluoresc., 2011, 21, 385–391.
5 M. Becuwe, P. Rouge, C. Gervais, M. Courty, A. Dassonville-
Klimpt, P. Sonnet and E. Baudrin, J. Colloid Interface Sci.,
2
012, 388, 130–136.
1
6 M. M. Zareh, I. F. A. Ismail and M. H. Abd El-Aziz,
Electroanalysis, 2010, 22, 1369–1375.
19374 | RSC Adv., 2014, 4, 19370–19374
This journal is © The Royal Society of Chemistry 2014