Selective optical detection of HSO4 ? via hydrolysis of a simple Schiff Base

Article abstract of DOI:10.1007/s11164-018-3351-y

A very simple Schiff Base derived from 1-Naphthylamine and 4-(Trifluoromethy) benzaldehyde (L) was prepared as a selective colorimetric and turn-on fluorescent sensor for hydrogen sulfate. In the CH₃CN:H₂O (3:2, v/v) solvent system, L shows a highly selective colorimetric response to HSO₄ ^? ions by changing its color from yellow to colorless immediately. In addition, the weakly fluorescent receptor L shows a highly selective enhancement of fluorescence intensity at 425?nm for HSO₄ ^? upon excitation at 320?nm. The recognition process is proven to be hardly influenced by the other tested competitive anions. The sensing is suggested to involve a hydrolysis process promoted by HSO₄ ^? which has been further supported by UV–Vis, ¹H NMR and HRMS spectroscopic studies. Applicability of L to detect HSO₄ ^? in tap water has been demonstrated. An easy-to-prepare test strip of L has also been made for the naked-eye detection of HSO₄ ^? in real samples.

Full text of DOI:10.1007/s11164-018-3351-y

Res Chem Intermed
https://doi.org/10.1007/s11164-018-3351-y
2
Selective optical detection of HSO4 via hydrolysis
of a simple Schiff Base
Zhen Ming Dong1 Jia Na Wang1 Wei Wang1 Jian Bin Chao1
Yu Wang1
•
•
•
•
Received: 2 August 2017 / Accepted: 24 February 2018
Ó Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract A very simple Schiff Base derived from 1-Naphthylamine and 4-(Tri-
fluoromethy) benzaldehyde (L) was prepared as a selective colorimetric and turn-on
fluorescent sensor for hydrogen sulfate. In the CH3CN:H2O (3:2, v/v) solvent sys-
-
tem, L shows a highly selective colorimetric response to HSO4 ions by changing
its color from yellow to colorless immediately. In addition, the weakly fluorescent
receptor L shows a highly selective enhancement of fluorescence intensity at
425 nm for HSO4- upon excitation at 320 nm. The recognition process is proven to
be hardly influenced by the other tested competitive anions. The sensing is sug-
-
gested to involve a hydrolysis process promoted by HSO4 which has been further
1
supported by UV–Vis, H NMR and HRM
-
S spectroscopic studies. Applicability of L to detect HSO4 in tap water has been
demonstrated. An easy-to-prepare test strip of L has also been made for the naked-
-
eye detection of HSO4 in real samples.
-
Keywords Optical Á Detection Á HSO4 Á Schiff Base Á Hydrolysis
Introduction
In recent years, the development of optical chemosensors for anions has attracted
considerable attention as these anions play various crucial roles in biological,
clinical, environmental, and industrial fields [1–3]. Among the anions, hydrogen
sulfate (HSO4-) is one of the most abundant ones in human plasma and is required
&
Yu Wang
wangyu1168@sxu.edu.cn
1
School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, People’s
Republic of China
123

Z. M. Dong et al.
for the proper cell growth and development of the organism [4]. On the other hand,
hydrogen sulfate is a toxic pollutant of great concern for the environment. This
amphiphilic oxoanion, which can be found in many industrial raw materials,
agricultural fertilizers and nuclear fuel waste, dissociates at high pH to generate
toxic sulfate (SO42-) and can result in diseases related to the skin, eyes and
respiratory system [5]. Recognition and sensing of hydrogen sulfate (HSO4-) is thus
of considerable importance and highly desirable. In comparison to other widely
investigated anions such as fluoride, cyanide, phosphate and acetate, however, the
detection of hydrogen sulfate has been much less studied so far. Although, research
in recent years has yielded some progress in developing hydrogen sulfate sensors
based on different strategies like metal–ligand coordinative interaction and
hydrogen bonding [6–27], these available sensors suffer from limitations like water
intolerance, poor application in the ‘‘naked-eye’’ detection and insufficient
selectivity and/or sensitivity. Owing to its very high standard Gibbs energy of
hydration (- 1080 kJ mol-1), developing new and practical sensor systems for
-
HSO4 which functions in aqueous media remains a great challenge for a chemist
[28].
It was previously reported that Schiff Bases are prone to hydrolysis in acidic
medium [29] and HSO4- (relatively strong acid with pKa 1.99 in aqueous solution)
as a proton donor in aqueous/semi-aqueous medium may induce the hydrolysis of a
-
Schiff Base [30]. To date, only a few chemodosimeters for HSO4 based on
hydrolysis of Schiff Base have been developed [31–36]. And some limitations still
exist, e.g., involving a complicated multistep synthesis process and slow response,
as well as using tetrabutylammonium as a counter cation, although potassium
hydrogen sulfate is more widespread in the environmental and biological samples.
Thus, there is still a critical need for easily synthesizable receptors that can rapidly
and selectively detect KHSO4 in aqueous media. In the current study, an easy-to-
prepare naphthalene-based Schiff Base (L) was synthesized and utilized for the
detection of HSO4- through highly selective and differential color change and Turn-
On fluorescence responses. The presence of an electron withdrawing trifluoromethyl
-
group increases the electrophilicity of the imine carbon, thereby enhancing HSO4
-
mediated hydrolysis of probe L. Applicability of L to detect HSO4- in tap water has
been demonstrated. Also, paper strips were fabricated for the naked-eye sensing of
-
HSO4
.
Experimental
Materials and instrumentation
The 1-Naphthylamine (98%) was purchased from Energy Chemical (Shanghai,
China). The 4-(Trifluoromethy) benzaldehyde (97%) was obtained from Aladdin
Reagent Co. (Shanghai, China). All the other chemical reagents of analytical grade
were purchased commercially and used as such. The anions were added in the form
of sodium or potassium salts. Double distilled water was used throughout the
analytical experiments.
123

-
Selective optical detection of HSO4 via hydrolysis of a…
The UV–Vis and fluorescence spectra were recorded respectively on a UV-2450
spectrophotometer (Shimadzu, Japan) and LS-55 spectrofluorimeter (PerkinElmer,
USA). The samples were excited at 320 nm. The excitation and emission slits were
set at 12 and 4 nm, respectively. Fluorescence lifetimes were measured using a
PicoMaster 1000-TCSPC fluorescence spectrofluorometer (PTI, USA). IR spectra
were taken on a SHIMADZU 8400S infrared spectrometer (Nicolet, Waltham,
Japan) in pellet mode. NMR spectra were recorded on a DRX-600 spectrometer
¨
(Fallenden, Switzerland). High resolution mass spectra were obtained on a Bruker
micrOTOF-Q III mass spectrometer.
Synthesis of L
Probe L is readily prepared by the procedure outlined in Scheme 1 with 67% yield.
The 4-(trifluoromethy) benzaldehyde (0.17 g, 1.0 mmol) was dissolved in 14 mL
isopropanol and two drops of acetic acid was added. After stirring for 10 min at
room temperature, the isopropanol solution of 1-Naphthylamine (0.14 g, 1.0 mmol
in 8 mL) was added, and the resulting mixture was stirred at room temperature for
48 h. The precipitation was filtered to give a pale yellow solid, which was further
washed with cold isopropanol and dried in vacuum. IR mmax (KBr), 3067 (C–H),
1623 (C=N), 1576, 1504, 1413 (C=C), 1328 (C–F). 1H NMR (DMSO-d6) d: 8.87 (s,
1H, HC=N), 8.31 (d, J = 3.00 Hz, 1H, ArH), 8.29 (d, J = 3.00 Hz, 2H, ArH), 7.98
(d, J = 6.00 Hz, 1H, ArH), 7.95 (d, J = 3.00 Hz, 2H, ArH), 7.85 (d, J = 3.00 Hz,
1H, ArH), 7. 60 (m, 1H, ArH), 7.58 (m, 1H, ArH), 7.55 (m, 1H, ArH), 7.31 (d,
J = 3.00 Hz, 1H, ArH); 13C NMR (DMSO-d6): 160.22, 148.14, 140.14, 134.00,
131.48, 129.94, 128.84, 128.20, 127.03, 126.79, 126.71, 126.53, 126.30, 126.27,
123.82, 113.67. HRMS (ESI ?) [L ? H]?, calculated for C18H12NF3 299.09218,
found 300.09964.
General method for UV–Vis and fluorescence studies
The stock solutions of L (1 9 10-3 M) and anions (1.0 9 10-2 M) were prepared in
CH3CN and deionized water, respectively. For the UV–Vis titration experiments, to
a comparison tube containing 0.1 mL of L stock solution, an appropriate aliquot of
-
HSO4 was added and the mixture was diluted to 5 mL with CH3CN–H2O (3:2,
v/v). The mixed solution was shaken well before the absorption spectra were
measured. The fluorescence titrations were performed by varying equivalents of
Scheme 1 Synthesis of probe L
123

Z. M. Dong et al.
-
HSO4 ions from 0.1 to 5 and fixing the concentration of L at 4.0 lM. The
fluorescence quantum yields of L in solutions and in the presence of HSO4 were
-
measured by the steady-state comparative method using quinine sulfate as the
standard (UF = 0.54).
For competition experimental purposes, to a comparison tube containing
-
0.02 mL of L stock solution, aliquots of HSO4 (0.01 mL) and all other tested
competitive anion (0.01 mL) salt solutions were added. The respective spectra were
recorded.
Colorimetric test kit
Receptor L (0.030 g, 0.01 mol) was dissolved in a mixture of CH3CN–H2O (3:2,
v/v) to get a 0.01 M solution. Test strips made of Whatman filter papers
(2 9 1 cm2) were dipped into this receptor L solution for 5 min, and then dried in
air. The yellow dried strips were then investigated against different concentrations
of HSO24 by immersing the strip in the aqueous solution containing different
concentrations of HSO24 individually for few seconds, and then the strip was dried
in air.
Results and discussion
2
Colorimetric sensing of HSO4 by L
The anions sensing ability of L was investigated by UV–Vis spectroscopy in a
CH3CN–H2O (3:2, v/v) solution. As shown in Fig. 1a, L exhibited two main
absorptions at 286 nm (e = 8.50 9 103 M-1cm-1) and 354 nm (e = 7.46 9 103
M-1cm-1). Upon addition of various anions (F-, Cl-, Br-, I-, CN-, AcO-, SO3
HSO4-, HSO3-, NO3-, HCO3-, SO42-, H2PO4-, PO43-, CO32-, P2O74-, HPO4
,
2-
2-
and H2PO4-), only HSO4- induces a noticeable change in the absorption spectra of
Fig. 1 a UV–Vis spectra of L (20 lM) in the presence of various anions (100 lM) in CH3CN–H2O (3:2,
v/v). Inset: visual changes of the solution of L (20 lM) in the presence of HSO4-. b Absorption spectra of
-
L (20 lM) in the presence of different concentrations of HSO4 (up to 5 equiv.) in CH3CN–H2O (3:2,
v/v). Inset: the absorbance of L as a function of HSO4 ion concentration
-
123

-
Selective optical detection of HSO4 via hydrolysis of a…
L and no other anion does it, manifesting a good chromogenic selectivity of the
-
probe toward HSO4 ions in aqueous media. The yellow L solution turns to
colorless immediately (inset in Fig. 1a), which rendered naked-eye detection of
-
HSO4 in aqueous solution.
Figure 1b shows that on addition of increasing amounts of KHSO4, the
absorbance of L at 286 and 354 nm gradually decreased, accompanied by the
formation of a new absorption peak at 320 nm. The presence of two clear isosbestic
points at 308 and 326 nm indicated the formation of a new species. The
-
spectrophotometric titration of L with HSO4 shows a linear dependence of the
-
absorbance at 354 nm as a function of HSO4 concentration, which enables
quantification of HSO4-. Good linearity was observed in the range of 0–90 lM
(R2 = 0.9941). The limit of detection was measured to be 2.33 9 10-6 M (signal to
noise ratio of 3:1).
Fluorescence spectral response
Next, the fluorescence sensing ability of the probe L toward various anions was
investigated. Changes in the emission spectra of L upon addition of hydrogen
sulfate are presented in Fig. 2. Upon excitation at 320 nm, L displays a very weak
fluorescence emission at 425 nm with a low quantum yield value of 0.004, probably
due to rotation of the C=N bond in the excited state. With the gradual addition of
hydrogen sulfate (0–5 equiv.), the emission of L at 425 nm shows a 15-fold
fluorescence enhancement. (UF = 0.41)This Turn-On fluorescence response was
also noticeable by the naked eye as the solution of L showed a vivid color change
from dark to fluorescent blue under a UV lamp (Inset, Fig. 2a). Figure 3 shows the
time-resolved luminescence spectra of both L and L upon addition of hydrogen
sulfate in CH3CN–H2O (3:2, v/v) using 297 nm excitation. The average fluores-
cence lifetime of L was estimated to be 7.78 ns. Upon the addition of HSO4- to the
solution of L, the average lifetime is increased to 10.49 ns. According to the
equations s-1 = kr ? knr and kr = /F/s, the radiative decay rate constant kr and the
total nonradiative decay rate constant knr of L were calculated to be 5.14 9 105 and
Fig. 2 a Fluorescent emission spectra of probe L (4 lM) in the presence of different concentrations of
HSO4-(0–20 lM) in CH3CN–H2O (3:2, v/v). Inset: visual changes observed for L in the presence of
HSO4 under UV light. b The fluorescence intensity of L as a function of HSO4 ion concentration
-
-
123

Z. M. Dong et al.
Fig. 3 Fluorescence decay
fitting curves of L (4 lM) and L
-
(4 lM) ? HSO4 (20 lM) in
CH3CN–H2O (3:2, v/v) obtained
at 297 nm for a Nano LED
Lamp
1.28 9 108 s-1, respectively. In the presence of HSO4-, the kr and knr of L changed
to 3.91 9 107 and 5.62 9 107 s-1, respectively. The data show that the kr/knr ratio
was reasonably enhanced resulting in a strong fluorescence in the presence of
HSO4-. Here we presume that the observed fluorescence enhancement could be due
-
to the hydrolysis of Schiff base L induced by HSO4 (pKa = * 1.9) [30], which
will be discussed later.
Consistent with the UV–Vis results, only hydrogen sulfate induced dramatic
fluorescence enhancement while the rest of the anions tested failed to alter the
-
emission behavior of L, making it easier to distinguish HSO4 ions from other
anions (Fig. 4a). The specificity of L for the detection of HSO4- was next examined
in the presence of other interfering anions. Again, the observed fluorescence
-
enhancement induced by HSO4 was not affected by other coexistent anions,
-
suggesting these ions do not interfere with the detection of HSO4 by L (Fig. 4b).
-
Thus, L shows a good selectivity and specificity toward HSO4 over other
competitive anions.
Optimization of pH on the efficiency of the sensor was essential. The pH
-
dependency of probe L toward the detection of HSO4 was thus investigated in
Fig. 4 a Fluorescent emission spectra of L (4 lM) in the presence of various anions (20 lM) in
CH3CN–H2O (3:2, v/v). b Results of the interference experiments in the presence of 5 eq. of different
anions
123

-
Selective optical detection of HSO4 via hydrolysis of a…
CH3CN-H2O (3/2, v/v) solution. Figure 5 shows the fluorescence intensity of probe
-
L with HSO4 (5 equiv.) remained almost unchanged in the pH range 6.0–8.0,
which makes it suitable for application under physiological conditions.
The response time is an important practical parameter. The response of L for
HSO4- as a function of time was monitored in aqueous acetonitrile solution at room
temperature by recording the fluorescence intensities at 425 nm at various time
intervals. The time-dependence changes in the fluorescence spectra of L upon the
-
addition of HSO4 were almost complete within 15 s and thereafter no change in
the fluorescence intensity was observed (Fig. 6), indicating that the Turn-On
-
fluorescence response of L toward HSO4 in solution is very fast.
Using the emission titration data and the slope of the calibration curve (Fig. 2b),
the detection limit was determined by following the 3r method [37] and was found
to be 1.44 9 10-7 M, which is comparable or superior to most of the other reported
sensors for HSO4- based on the hydrolysis of Schiff Bases (Table 1). The important
features of our probe highlight its very easy single step process, high selectivity and
rapid response time.
Sensing mechanism
-
The spectroscopic responses of L toward HSO4 indicate an efficient interaction
-
between L and HSO4-. To gain insight into the sensing mechanism of L to HSO4
UV–Vis studies were performed. As shown in Fig. 7, the absorption spectrum of L
,
-
in the presence of 5 equiv. HSO4 aqueous solution exhibited a similar pattern as
that of the corresponding 1-Naphthylamine, suggesting that the Schiff Base-
derivative L was subjected to HSO4--promoted hydrolysis.
The HSO4--promoted hydrolysis was further ascertained by a combination of 1H
NMR spectroscopy and high-resolution mass spectrometry studies. A solution of L
in DMSO-d6 was monitored by 1H NMR spectroscopy with the gradual addition of
KHSO4 dissolved in D2O. As shown in Fig. 8, free L has a singlet peak at d
8.75 ppm corresponding to imine proton (N=CH). After addition of HSO4-, the
imine proton peak disappeared whereas a new singlet at d10.09 ppm assigned to
aldehyde protons (-CHO) appeared, confirming that L was hydrolyzed in the
Fig. 5 Effect of pH on the
fluorescence intensity of L and L
toward HSO4-. [L] = 4 lM,
[HSO4-] = 20 lM
123

Z. M. Dong et al.
Fig. 6 The fluorescence
intensity of L (4 lM) at 425 nm
as a function of time after
adding KHSO4 (20 lM)
Table 1 Comparison of chemosensors for hydrogen sulfate based on hydrolysis of a Schiff Base
Structure of
sensors
Synthesis Reaction
yield
Media
Detection limit Response References
time
H3CO
Two
steps
51% (total
reaction
yield)
CH3CN/
H2O,
4/1, v/v
0.24 lM
1 min
[31]
[32]
OCH3
N
NO2
N
H
N
N
O
THF/H2O, 6.45 9 10-9
8/1, v/v
M
No data
C8H17
N
Five
steps
80.5% (the
last step)
O
N
O
C8H17
N
N
H3CO
OCH3
Five
steps
86% (the
last step)
THF
0.35 lM
20 s
[33]
[34]
THF/H2O, 6.45 9 10-8
8/1, v/v
M
2 min
Br
Three
steps
12% (total
reaction
yield)
H
C
N
N
N
B
F
F
Calix[4]arene
containing
benzothiazole
Six steps 80% (the
last step)
CH3CN/
H2O,
4/1, v/v.
9.79 9 10-7
7.79 9 10-7
M
M
20 s
[35]
[36]
O
Four
steps
44% (total
reaction
yield)
DMSO-
H2O,
1/1, v/v
3.5 min
N
N
N
O
HO
HN
1.44 9 10-7
M
15 s
This work
N
One step 67%
CH3CN/
H2O,
3/2, v/v
CF3
123

-
Selective optical detection of HSO4 via hydrolysis of a…
Fig. 7 Absorption spectra of
1-Naphthylamine,
4-Trifluoromethylbenzaldehyde,
L (20 lM) and L upon addition
of HSO4- (5 equiv.) in CH3CN–
H2O (3:2, v/v)
Fig. 8 1H NMR spectra of L in CD3CN–D2O (10:1, v/v) in the absence (a) and in the presence (b) of 5.0
equiv of KHSO4
presence of HSO4-. In addition, the hydrolysis of L was further supported by the
appearance of a peak at m/z 192.13823, assignable to [2-hydroxy-1-naphthalde-
hyde ? H2O] as well as a peak at m/z 144.0808, assignable to [1-Naphthy-
lamine ? H] in the ESI/MS (Fig. 9).
The unique high reactivity of the probe can be explained based on the acid
catalyzed hydrolysis mechanism of a Schiff Base as shown in Scheme 2. The
reaction involves the protonation of imino nitrogen and followed by the attack of a
water molecule on the imine carbon [34], which is facilitated in the case of L,
because the presence of an electron withdrawing trifluoromethyl group increases the
electrophilicity of the imine carbon.
Real sample analysis
To investigate its practical application, receptor L was preliminarily applied in the
-
determination of HSO4 in tap water samples. The water sample was prepared by
adding known amounts of hydrogen sulfate to samples. As shown in Table 2, L was
able to measure the concentrations of spiked HSO4- with satisfactory recovery and
123

Z. M. Dong et al.
Fig. 9 ESI-mass spectrum of L (1.0 9 10-5 M) upon addition of 5 equiv of KHSO4 in CH3CN
analytical precision (R.S.D \ 3%), indicating that the probe could potentially be
used for the determination of HSO4 in real samples.
For convenient use in an on-site analysis, the test kits coated with L were
-
-
fabricated and utilized to sense HSO4 in aqueous medium. As shown in Fig. 10,
-
obvious color changes from yellow to colorless were observed with HSO4
solution. In addition, a vivid color change from dark to fluorescent blue can be
observed by the ‘naked eye’ under the 365 nm UV lamp. Therefore, such a ‘‘dip
-
stick’’ approach could be conveniently used to detect HSO4 in natural water
without resorting to instrumental analysis. Hence, L can be used for determination
of cyanide in aqueous samples using UV–Visible, fluorescence and naked eye
determination. These results showed that L could be a valuable practical sensor for
-
environmental analyses of HSO4 easily and rapidly.
123

-
Selective optical detection of HSO4 via hydrolysis of a…
-
Scheme 2 The possible hydrolysis mechanism of L in the presence of HSO4
-
Table 2 Determination of HSO4 by the fluorometric method in tap water samples
HSO4 added (10-6 M)
HSO4 found (10-6 M)
Recovery (%)
R.S.D.a (%)
-
-
Samples
1
2
3
4.00
8.00
12.0
3.80
7.99
12.9
95.04
99.89
107.7
2.17
1.95
2.94
aRSD relative standard deviation, n = 5
Fig. 10 Color of L-based test strips before and after addition of HSO4-: naked eye (a); under UV lamp
(b)
123

Z. M. Dong et al.
Conclusion
In summary, a facile, low-cost, and efficient Schiff Base probe as a highly selective
chemosensor for HSO4- was developed. The Schiff Base probe L demonstrated the
presence of HSO4- by an instantaneous change of color from yellow to colorless as
well as a ‘turn-On’ fluorescence response. The various studies (fluorescence, UV–
Vis, HNMR and HRMS) support the hydrolysis of probe L promoted by HSO4-. L
-
could be used as a practical, visible colorimetric test kit for HSO4 in an aqueous
environment. The important features of our probe highlight its one-step synthesis,
-
its applicability for naked eye detection as well as its fast response toward HSO4
-
ions, which makes L a promising candidate as a chemosensor for HSO4 ions.
Acknowledgements This work was financially supported by the Natural Science Foundation of Shanxi
Province (No. 2013011040-6) and the Project Sponsored by the Scientific Research Foundation for the
Returned Overseas Chinese Scholars, State Education Ministry.
References
1. T. Gunnlaugsson, M. Glynn, G.M. Tocci, P.E. Kruger, F.M. Pfeffer, Coord. Chem. Rev. 250, 3094
(2006)
2. R.M. Duke, E.B. Veale, F.M. Pfeffer, P.E. Kruger, T. Gunnlaugsson, Chem. Soc. Rev. 39, 3936
(2010)
3. P.A. Gale, C. Caltagirone, Chem. Soc. Rev. 44, 4212 (2015)
4. B. Sen, M. Mukherjee, S. Pal, S. Sen, P. Chattopadhyay, RSC Adv. 5, 50532 (2015)
5. P.I. Jalava, R.O. Salonen, A.S. Pennanen, M.S. Happo, P. Penttinen, A.I. Halinen, M. Sillanpaa, R.
Hillamo, M.R. Hirvonen, Toxicol. Appl. Pharmacol. 229, 146 (2008)
´
6. M. Alfonso, A. Tarraga, P. Molina, Org. Lett. 13, 6432 (2011)
7. Q. Li, Y. Guo, S.J. Shao, Analyst 137, 4497 (2012)
8. W.J. Xue, L. Li, Q. Li, A.X. Wu, Talanta 88, 734 (2012)
9. P. Kaur, H. Kaur, K. Singh, Analyst 138, 425 (2013)
10. J.J. Chang, Y. Lu, S. He, C. Liu, L.C. Zhao, X.S. Zeng, Chem. Commun. 49, 6259 (2013)
11. U. Fegade, H. Sharma, K. Tayade, S. Attarde, N. Singh, A. Kuwar, Org. Biomol. Chem. 11, 6824
(2013)
12. D.W. Zhang, X.Z. Jiang, Z.Y. Dong, H.Q. Yang, A. Martinez, G.H. Gao, Tetrahedron 69, 10457
(2013)
13. U. Fegade, S.K. Sahoo, A. Singh, P. Mahulikar, S. Attarde, N. Singh, A. Kuwar, RSC Adv. 4, 15288
(2014)
14. T. Chatterjee, A. Ghosh, S. Madhu, M. Ravikanth, Dalton Trans. 43, 6050 (2014)
15. B. Sen, M. Mukherjee, S. Pal, S.K. Mandal, M.S. Hundal, A.R. Khuda-Bukhsh, P. Chattopadhyay,
RSC Adv. 4, 15356 (2014)
16. S. Chopra, J. Singh, N. Singh, N. Kaur, Anal. Methods 6, 9030 (2014)
17. D. Sarkar, A.K. Pramanik, T.K. Mondal, RSC Adv. 4, 25341 (2014)
18. H.J. Jia, S.Z. Pu, C.B. Fan, G. Liu, C.H. Zheng, Dyes Pigments 121, 211 (2015)
19. B.Y. Kim, H.S. Kim, A. Helal, Sens. Actuators B Chem. 206, 430 (2015)
20. Q. Wan, J.B. Zhuo, X.X. Wang, C.X. Lin, Y.F. Yuan, Dalton Trans. 44, 5790 (2015)
21. M. Mukherjee, B. Sen, S. Pal, S. Banerjee, S. Lohar, E. Zangrando, P. Chattopadhyay, RSC Adv. 5,
4468 (2015)
22. D. Sain, C. Kumari, A. Kumar, S. Dey, Sen. Actuators B Chem. 221, 849 (2015)
23. K. Tayade, B. Bondhopadhyay, K. Keshav, S.K. Sahoo, A. Basu, J. Singh, N. Singh, D.T. Nehete, A.
Kuwar, Analyst 141, 1814 (2016)
24. J. Rull-Barrull, M. d’Halluin, E.L. Grognec, F.X. Felpin, Chem. Commun. 52, 2525 (2016)
25. S.D. Padghan, R.S. Bhosale, N.V. Ghule, A.L. Puyad, S.V. Bhosale, S.V. Bhosale, RSC Adv. 6,
34376 (2016)
123

-
Selective optical detection of HSO4 via hydrolysis of a…
26. S. Samanta, P. Dey, A. Ramesh, G. Das, Chem. Commun. 52, 10381 (2016)
27. Y. Upadhyay, S. Bothra, R. Kumar, H.J. Choi, S.K. Sahoo, Spectrochim. Acta A Mol. Biomol.
Spectrosc. 180, 44 (2017)
28. F.P. Schmidtchen, Top. Curr. Chem. 132, 101 (1986)
29. H. Khanmohammadi, K. Rezaeian, RSC Adv. 4, 1032 (2014)
30. V. Kumar, A. Kumar, U. Diwan, K.K. Upadhyay, Chem. Commun. 48, 9540 (2012)
31. C.Y. Lin, K.F. Huang, Y.P. Yen, Spectrochim. Acta A Mol. Biomol. Spectrosc. 115, 552 (2013)
32. L.Y. Wang, L.L. Yang, D.R. Cao, J. Fluoresc. 24, 1347 (2014)
33. L.Y. Wang, L.L. Yang, L.B. Huang, D.R. Cao, Sens. Actuators B Chem. 209, 536 (2015)
34. L.Y. Wang, J.J. Ou, G.P. Fang, D.R. Cao, Sens. Actuators B Chem. 222, 1184 (2015)
35. S. Erdemir, B. Tabakci, M. Tabakci, Sens. Actuators B Chem. 228, 109 (2016)
36. Z.L. Luo, K. Yin, Z. Yu, M.X. Chen, Y. Li, J. Ren, Spectrochim. Acta A Mol. Biomol. Spectrosc.
169, 38 (2016)
37. A. Ono, H. Togashi, Angew. Chem. Int. Ed. 43, 4300 (2004)
123