Development of an optode for detection of trace amounts of Hg2+ in different real samples based on immobilization of novel tetradentate schiff bases bearing two thiol groups in PVC membrane

Article abstract of DOI:10.1007/s10895-014-1364-5

A very sensitive and reversible optical chemical sensor based on a novel tetradentate Schiff base namely N.N^/bis(2-aminothiophenol)benzene-1, 2-dicarboxaldehyde (ATBD) immobilized within a plasticized PVC film for Hg ²⁺ determination is described. At optimum conditions (i.e. pH 6.0), the proposed sensor displayed a linear response to Hg²⁺ over 1.0×10^-10 - 1.0×10^-2 mol L^-1 with a limit of detection of 7.23×10^-11 mol L^-1 (0.0145 μgL^-1). Moreover, the results revealed that, under batch condition, the sensor is fully reversible within a response time~35 s. In addition to its high stability and reproducibility, the sensor showed good selectivity towards Hg²⁺ ion with respect to common metal cations. The sensor was successfully applied for determination of Hg²⁺ ion in some real samples, including hair, urine and well water samples. The results were in good correlation with the data obtained using cold vapor atomic absorption spectrometry.

Full text of DOI:10.1007/s10895-014-1364-5

J Fluoresc
DOI 10.1007/s10895-014-1364-5
ORIGINAL PAPER
Development of an Optode for Detection of Trace Amounts
of Hg2+ in Different Real Samples Based on Immobilization
of Novel Tetradentate Schiff Bases Bearing Two Thiol Groups
in PVC Membrane
Ay ma n A . A bd el Az iz & Soha F. Mohammed &
Magdy M. El Gamel
Received: 28 December 2013 /Accepted: 3 February 2014
#
Springer Science+Business Media New York 2014
.
.
Abstract A very sensitive and reversible optical chemical
sensor based on a novel tetradentate Schiff base namely
N.N/bis(2-aminothiophenol)benzene-1,2-dicarboxaldehyde
(ATBD) immobilized within a plasticized PVC film for Hg2+
determination is described. At optimum conditions (i.e.
pH 6.0), the proposed sensor displayed a linear response to
Hg2+ over 1.0×10−10 − 1.0×10−2 mol L−1 with a limit of
detection of 7.23×10−11 mol L−1 (0.0145 μgL−1). Moreover,
the results revealed that, under batch condition, the sensor is
fully reversible within a response time~35 s. In addition to its
high stability and reproducibility, the sensor showed good
selectivity towards Hg2+ ion with respect to common metal
cations. The sensor was successfully applied for determination
of Hg2+ ion in some real samples, including hair, urine and well
water samples. The results were in good correlation with the
data obtained using cold vapor atomic absorption spectrometry.
Keywords NSSN Schiff base PVC membrane Fluorescent
sensor Hg2+ ion
.
Introduction
Development of sensitive chemosensors have been receiving
much attention in recent years because of their potential
applications in clinical biochemistry and environment.
Metal-selective fluorescent chemosensors are served as useful
tools for detection of metal ions due to their intrinsic sensitiv-
ity and selectivity [1, 2].
Chemical optical sensors (optodes) offer several advan-
tages such as simple preparation procedure, relatively fast
response, wide response range, reasonable selectivity and high
sensitivity [3, 4]. The immobilization of various sensing re-
agents of optode membranes have been developed for many
analytically relevant ions, especially heavy metal ions. Immo-
bilization of dyes into or onto a solid support is a key issue for
their application in optical sensing [5]. The reagent is normal-
ly physically entrapped by adsorption, electrostatic attraction
or chemical bonding to the solid support. Generally, sol–gel
glasses [6, 7] or polymer matrices [8, 9] are used for the
preparation of the optodes. Poly(vinyl chloride) (PVC) has
been used for the preparation of membrane optodes due to its
relatively low cost, good mechanical properties and amena-
bility to plasticization [10].
A. A. A. Aziz (*)
Department of Chemistry, Faculty of Science, Ain Shams University,
11566 Cairo, Egypt
e-mail: aymanaziz31@gmail.com
A. A. A. Aziz
e-mail: aabdelaziz@ut.edu.sa
A. A. A. Aziz
Department of Chemistry, Faculty of Science, University of Tabuk,
Tabuk 71421, Saudi Arabia
Mercury ion is one of the most prevalent toxic heavy metal
ions causing environmental and health problems because of its
wide distribution and severe immunotoxic, genotoxic, and
neurotoxic effects [11–13]. Hg2+ is a highly stable inorganic
form of mercury, which, according EPA and WHO guidelines,
must be in concentrations<0.002 mgL−1 in well water [14].
:
S. F. Mohammed M. M. El Gamel
Department of Chemistry, Faculty of Science, Zagazig University,
44519 Zagazig, Egypt
M. M. El Gamel
Department of Chemistry, College of Sciences and Humanities,
Shaqra University, Aldawadmi 11911, Saudi Arabia

J Fluoresc
HS
SH
HS
EtOH/CH3COOH
Reflux / 5 h
N
N
+
2
H2N
O
O
N.N/bis(2-aminothiophenol)benzene-1,2-dicarboxaldehyde
1,2-benzenedialdehyde
2-aminothiophenol
ATBD
Scheme 1 Synthetic route of ATBD
Many current techniques for mercury screenings were
assigned such as atomic absorption spectrometry [15–18],
inductively coupled plasma-mass spectroscopy [19–21],
X-ray fluorescence spectrometry [22, 23], neutron activation
analysis [24, 25], cold vapor atomic absorption spectrometry
[26], electrothermal atomic absorption spectrometry [27–29],
anodic stripping voltammetry [30–33], high-performance liq-
uid chromatography [34–36], atomic fluorescence spectrom-
etry [37], potentiometric ion-selective electrodes [38–40] and
spectrophotometry [41–50].
Most of these methods suffer from some problems such as
poor reproducibility, limited sample adaptability, high cost,
well-controlled experimental conditions, multi-step sample
pre-treatments, some inherent interference, time consuming
procedures and too expensive involving the use of sophisti-
cated instrumentation, the wide utilization of these methods is
largely limited. So, for simplicity, convenience, no necessity
of the reference solution, low cost, and fieldwork applicability
the easily prepared optical sensors are highly demanding.
Recently, some selective fluorescent chemosensors for
Hg2+ based on fluorescence enhancement or fluorescence
quenching has been reported [51–67]. However, most of them
have disadvantage in practical use, such as low water solubil-
ity, interference from other metal ions, strict reaction condition
or complicated synthetic route. Therefore, development of
simple fluorescent chemosensor that can selectively sense
Hg2+ in aqueous media is significant. In construction of opti-
cal sensors Schiff’s base ligands have been frequently used as
ionophores in construction of membrane sensors because of
their ability to form stable complexes with transition metal
ions. They produce remarkable selectivity, sensitivity and
stability for a specific ion [68–71].
Keeping these facts in mind, in this work, we develop an
optode for sensitive and selective determination of Hg2+. This
optode is prepared by immobilizing a novel tetradentate Schiff
base bearing two thiol groups as the sensing reagent in PVC
membrane according to a simple method. The membrane sen-
sitivity, selectivity, reproducibility, short-term stability, lifetime
and regeneration under optimum conditions were fully studied.
Moreover, the response mechanism and binding mode were
investigated by 1H NMR and TOF-MS. Finally, the novel sensor
was applied for determination of Hg2+ ion in some different real
samples, including hair, urine and well water samples.
Experimental
Instruments
All fluorescence measurements were carried out on a Jenway
6270 Fluorimeter. The excitation source was a Pulsed Xenon
Lamp. The UV–Vis spectra were recorded on a Shimadzu UV
1800 Spectrophotometer. pH measurements were performed
by Jenway pH meter model 3510 equipped with Glass bodied
combination pH electrode (924005) and calibrated with Meck
pH standards of pH 4.00, 7.00, and 10.00. All of the experi-
ments were carried out at room temperature 25 1 °C. FT-IR
spectrum of the ionophore was obtained in KBr discs on a
1
Unicam-Mattson 1000 FT-IR. H NMR spectra were per-
formed on a 300 MHz NMR spectrometer in DMSO-d6
solvent and TMS was used as an internal reference. Mass
spectra (TOF-MS) were recorded on Waters (USA) KC-455
model with ES+ mode in DMSO.
Materials and Reagents
2-aminothiophenol, benzene-1,2-dicarboxaldehyde (o-
phthaldhyde) and the lipophilic anionic additive reagent potas-
sium tetrakis-(4-chlorophenyl) borate (KTpClPB) were supplied
from Aldrich. The polymer membrane components, polyvinyl
Fig. 1 Optimal structure of the chemosensor (ATBD)

J Fluoresc
Fig. 2 UV–Vis absorption
1.2
1.0
0.8
0.6
0.4
0.2
0.0
spectra of ATBD (2.0 μM) with 1
equivalent metal ions (K+, Na+,
Mg2+, Ca2+, Ba2+, Sr2+, Al3+
,
,
ATBD
Co2+, Ni2+, Cu2+, Zn2+, Pb2+
Ag+, Cd2+, Mn2+, Fe3+, Cr3+ and
Hg2+
+
+
2+
2+
2+
2+
2+
3+
2+
2+
2+
K , Na , Mg , Ca , Ba , Sr , Al , Co , Ni
,
)
2+
2+
2+
+
3+
3+
Cu , Zn , Pb , Ag , Cd , Mn , Fe and Cr
.
2+
Hg
250
300
350
400
450
500
550
600
650
Wavelength (nm)
chloride (PVC) (high molecular weight) and the plasticizers,
bis-(2-ethylhexyl) phtalate (DOP), bis(2-ethylhexyl)sebecate
(DOS), bis-(2-ethylhexyl) adipate (DAO) and 2-nitrophenyl
octyl ether (NPOE) were obtained from Fluka. Absolute ethanol
(EtOH), tetrahydrofuran (THF), and dicholormethane (DCM)
were purchased from Merck. All solvents were of analytical
grade and they were used as received. A stock solution of 1.0×
10−2 M was prepared by dissolving 0.3606 g of Hg(NO3)2·
2H2O in exactly 100 ml of deionized water and standardized
with the EDTA solution [72]. The stock solution was serially
diluted to achieve the desired concentrations.
aromatic). TOF-MS (m/z): 348 (M+). The optimal structure
of the chemosensor (ATBD) is shown in Fig. 1 by using
Avogadro program Version 1.0.1.
Preparation of the Optode Membrane
Membrane solutions were prepared by dissolving 30 mg of
PVC, 65 mg of plasticizer (DOS), 2.0 mg of KTpClPB and
3.0 mg ATBD in 2.0 ml THF. The solution was stirred with a
magnetic stirrer to obtain a homogeneous mixture. Glass slides
for bulk measurements were cut from microscope slides into
12 mm×16 mm dimensions to fit precisely into its diagonal
width of standard quartz cell. To improve the adhesion of the
membrane, the glass slides were cleaned with THF, sulfuric
acid and sodium hydroxide solutions, respectively, then thor-
oughly rinsed with deionized water and finally dried in an oven
Synthesis of N.N/bis(2-aminothiophenol)
benzene-1,2-dicarboxaldehyde (ATBD)
An ethanolic solution of 2-amiothiophenol (10 mmol) was
mixed with an ethanolic solution of o-phaldehyde (5 mmol), 2
drops of acetic acid and magnetically stirred in a round bottom
flask. The reaction mixture was then refluxed for~5 h at 60 °C
in water bath and kept overnight. The resulting solution was
then poured into crushed ice water. The precipitate formed
was filtered and recrystallized from hot methanol and dried in
a desiccator over anhydrous CaCl2 under vacuum to get
chromatographically (TLC) pure compound. Synthetic route
of ATBD is shown in Scheme 1.
Characteristics of ATBD were as follows (C20H16N2S2):
M.Wt: 348.494 Yield: 87 %. Color: Orange. Elemental anal-
ysis Calc. (%): C, 68.93; H, 4.62; N, 8.03 Found: C, 68.40; H,
4.39; N, 8.00. IR (KBr pellet. cm−1): 2543 (νSH); 1612
(νC=N); 798 (νC−S). 1H NMR (DMSO-d6, 300 MHz): δ 3.64
(s, 2H; SH); 8.23 (s, 2H; HC=N); 6.74−7.57 (m, 14H;
Fig. 3 The color change of the sensor upon complexation with Hg2+ ions
(1 ATBD; 2 ATBD + Hg2+
)

J Fluoresc
30
25
20
15
10
5
Fig. 4 Emission and excitation
spectra of ATBD in (a) DCM, (b)
THF, (c) EtOH and (d) PVC
(d)
(d)
(c)
(c)
(b)
(b)
(a)
(a)
0
300
400
500
600
700
Wavelength (nm)
at 110 °C. Membranes were cast by placing 35 μl of the
membrane solution onto the glass slide of ~10 μm thickness
and spread evenly using a capillary glass tube [73, 74]. The
thickness of the films was in the order of 3–4 μm (as evaluated
from the volume employed for spreading). After 2 min. the
coated slides were transferred to a Petri dish with a filter paper
cover and then stored away from light for 12 h before use.
Blank (reference) membranes were prepared in a similar way
excluding ATBD from the membrane solution. Absorption and
fluorescence emission spectra of PVC membranes were record-
ed in quartz cells which were filled with sample solution. The
polymer films were placed in diagonal position in the quartz
cell. All of the experiments were operated at room temperature
(25 1 °C). The membranes were not conditioned before use.
sample was first soaked in deionized water for 10 min. This
was followed by soaking in 1 % triton X-100 solution for
20 min [75]. The hair sample was then rinsed five times with
deionized water and air-dried. 0.250 g of dried hair sample
was digested with 5.0 ml 0.1 M HNO3 for 2 h at ~120 ◦C.
Finally 3.0 ml of H2O2 was added to the sample and digested.
The residue was diluted with deionized water to 50.0 ml
volumetric flask.
Urine Samples
Most mercury present in the urine is in the form of inorganic
mercury. The mercury concentration in the urine increases in
relation to the level of inorganic mercury accumulated in the
kidneys [76]. Accordingly, the total mercury value in the urine
is an important biomarker for evaluating inorganic mercury/
mercury vapor exposure. Dental clinics are known to be one of
the largest users of inorganic and metalic mercury [77]. Mer-
cury, which vaporizes at room temperature and easily enters
the environment, is used in the preparation of amalgam alloy
Measurement Procedure
The membranes were diagonally placed inside the sample
cuvette of the instrument containing 2 ml buffer solution of
pH 6.0 and a blank membrane (without ionophore) was put in
the reference cuvett containing the buffer solution. The fluo-
rescence intensity at an excitation wavelength of 403 nm was
measured at 544 nm. The sample was then titrated with a
standard Hg2+ ion solution using a pre-calibrated micropipette
and the fluorescence intensity of the system was measured
after ~35 s (required to reach equilibrium).
Table 1 Emission and excitation spectral data of ATBD in various
solvents and PVC membrane
Solvent Polarity
Wavelength
Stokes shift Refractive index
index (P) (nm)
λex
λem
ΔλST (nm)
η
Preparation of Real Samples
DCM
THF
3.1
4
406
400
408
403
502
498
510
544
96
98
1.42
1.40
1.36
1.52
Hair Samples
EtOH
PVC
5.2
–
102
141
Scalp hair samples as a suitable specimen for monitoring
human exposure to mercury, were used in this study. The hair

J Fluoresc
Fig. 5 Emission spectra of
400
350
300
250
200
150
100
50
ATBD sensing membrane after
exposure to 1.0 μM different
metal ions (K+, Na+, Mg2+, Ca2+
,
Ba2+, Sr2+, Al3+, Co2+, Ni2+
,
,
Cu2+, Zn2+, Pb2+, Ag+, Cd2+
Mn2+, Fe3+, Cr3+,Al3+and Hg2+
)
2+
Hg
+
+
2+
ATBD, K , Na , Mg
,
2+
2+
2+
3+
Ca
,
Ba , Sr , Al
,
2+
2+ 2+
2+
Co , Ni , Cu , Zn
,
2+
+
2+
2+
Pb , Ag , Cd , Mn
,
3+
3+
Fe and Cr
.
0
400
450
500
550
600
650
700
750
Wavelength (nm)
that consists chiefly of silver mixed with mercury and variable
amounts of other metals and is used as a dental filling. It is well
documented that dentists who work with amalgam are chroni-
cally exposed to mercury vapors, which can accumulate in their
bodies to much more higher levels than for most non-
occupationally exposed individuals. 24-h urine samples were
obtained from dentists who had several months of steady
exposure, at the end of a working week in 2.5 l polypropylene
sampling vessels followed by the addition of concentrated
HNO3 to yield a final acid concentration of 1–3 % v/v and
the samples were stored at −20 °C prior to analysis.
samples were oxidized in the presence of 1 % H2O2 followed
by addition of concentrated nitric acid, then the pH of water
samples was adjusted to 6.0.
Results and Discussion
UV–Vis Spectral Responses of ATBD
It has been anticipated that, due to the presence of various
donor sites in the form of N and S atoms, ATBD would behave
as a potential ligand for complexation reaction with metal
ions. To explore the properties of ATBD as an optically
sensing material, various metal ions were tested in a prelimi-
nary experiment. The binding affinity of ATBD was moni-
tored through absorption spectra of ATBD (2.0 μM) in
Preparation of Well Water Samples
Before the analysis, water samples were filtered through a
Whatman No. 41 filter paper. The organic content of the water
Ta b l e 2 The effect of membrane ingredients on the response behavior of optodes (n=5)
Optode No.
PVC (mg)
Plasticizer (mg)
KTpClPB (mg)
ATBD (mg)
Working concentration range (mol L−1
)
Response time (sec)
1
30
30
30
30
30
30
30
30
30
NPOE (67)
DOA (67)
DOP (67)
DOS (67)
DOS (66)
DOS (65)
DOS (64)
DOS(64)
DOS (64)
0
0
0
0
1
2
3
4
5
3
3
3
3
3
3
3
2
1
6.4×10−7 to 2.0×10−5
2.6×10−6 to 1.0×10−5
5.0×10−7 to 3.0×10−4
1.0×10−8 to 3.0×10−4
1.3×10−9 to 2.0×10−3
1.0×10−10 to 1.0×10−2
6.4×10−7 to 4.0×10−5
8.0×10−7 to 3.0×10−3
2.0×10−6 to 3.0×10−3
120
150
200
80
2
3
4
6
60
7
35
8
80
9
100
130
10

J Fluoresc
Fig. 6 Effect of pH on the
response of the ATBD optode in
the presence of 1.0 μM Hg2+ at
544 nm (λex 403 nm)
600
500
400
300
200
100
0
0
1
2
3
4
5
6
7
8
9
10
11
pH
absence and presence of 1 equivalent tested metal ions of K+,
Na+, Mg2+, Ca2+, Ba2+, Sr2+, Al3+, Co2+, Ni2+, Cu2+, Zn2+,
Pb2+, Ag+, Cd2+, Mn2+, Fe3+ Cr3+ and Hg2+ (Fig. 2). As
shown in Fig. 2, ATBD shows two absorption bands, the first
at 293 which can be assigned to π-π* transitions from the
benzene ring and the double bond of the azomethine group
and the second at 356 nm due to n-π* transition of non-
bonding electrons present on the nitrogen of the azomethine
group. Upon addition of addition of Hg2+, the color of ATBD
solution concomitantly, changes from yellow-orange to a pink
(Fig. 3), inducing a bathochromic shift of ATBD bands and a
new band was originated at 428 nm, which may assigned to
charge transfer. In contrast, addition of other metal ions
showed insignificant changes. The results demonstrated that
ATBD is characteristic of high selectivity toward Hg2+ over
other competitive metal ions.
the ATBD was observed in EtOH. Moreover, ATBD exhibited
higher fluorescence intensity in PVC matrix compared to that
in the solvents. The immobilization of ATBD molecules in
solid matrix may reduce intramolecular motions and rear-
rangements, thus leading to enhanced fluorescence capability.
In order to explore the selective sensing of ATBD towards
Hg2+, fluorescence spectra of ATBD immobilized on PVC
membrane were measured in EtOH with respective metal
ions including K+, Na+, Mg2+, Ca2+, Ba2+, Sr2+, Al3+, Co2+,
Ni2+, Cu2+, Zn2+, Pb2+, Ag+, Cd2+, Mn2+, Fe3+ Cr3+ and
Hg2+ (Fig. 5). As in shown in Fig. 5, ATBD exhibit weak
fluorescence emission when excited at 403 nm and when
Hg2+ (1.0 μM) was added, a prominent fluorescent en-
hancement was observed at 544 nm and it was found that
the other studied ions didn’t induce any apparent fluores-
cent enhancement.
Fluorescence Spectral Responses of ATBD
Optimization of Composition of the Membrane Components
In order to perform the fluorescence characterization of the
ATBD, the emission and excitation spectra of ATBD were
recorded in solvents of different polarities and PVC matrix.
The gathered excitation-emission spectra are shown in Fig. 4.
The Stokes shift values, ΔλST (the difference between
excitation and emission maxima) were extracted from spectral
data which are given in Table 1. Since larger Stokes shifts
are obtained in polar solvents [78], the highest Stokes shift for
The response characteristics and working concentration range
of optical membrane sensors are known to be largely affected
by changes in the membrane composition [9, 79]. A compar-
ative study on the effect of different plasticizers and matrix
materials on the performance of sensor has been made. Sev-
eral optode membranes were prepared using different plasti-
cizers such as DOP, DOS, DAO, NPOE and the fluorescence
measurements were made for different concentrations of
L(org) + K+ + TpClPB- + Hg2+
LHg(org) + TpClPB-(org) + K+
(aq)
(aq)
Scheme 2 Response mechanism of immobilized ATBD on PVC membrane towards Hg2+

J Fluoresc
Fig. 7 1H NMR spectra of sensor
ATBD (1.0 μM) with Hg2+ in d6-
DMSO: (a) ATBD and (b) ATBD
+ Hg2+ (1.0 eq.)
Hg2+. The results are shown in Table 2. The widest working
concentration range was obtained with DOS; therefore, this
plasticizer was used for further studies. Lipophilic borate salts
are frequently used as anionic additives in potentiometric and
optical cation-selective sensors based on solvent polymeric
membranes [80]. The amount of anionic sites in the mem-
branes has effects on the linear range and selectivity of
optodes [8]. The composition of the optode membrane with
respect to KTpClPB was optimized by preparing several
membranes with different amounts of KTpClPB. The re-
sponse behavior of these optode membranes are shown in
Table 2. From the results it can be seen that the response
concentration range of the optode membrane becomes wider
with shorter response time as the amount of KTpClPB in the
optode membrane increases from 1 % to 2 %, which might be
attributed to the increasing of hydrophilicity upon addition of
KTpClPB. However, the response concentration range of the
optode membrane becomes narrower when the content of
KTpClPB is larger than 2 %. Therefore, 2 % KTpClPB
provided the best response for Hg2+ and was chosen for
further studies.
Effects of pH
The effect of the pH of the solution, in which the sensor is
applied is a critical factor that must be considered definitely.
To study the effect of pH on the optode response to Hg2+, the
fluorescence intensity versus pH plot was obtained by chang-
ing the solution pH with different buffer solutions and fixing
the Hg2+ concentration at 1.0 μM (Fig. 6). The pH of solution
was adjusted by buffers of CH3COOH/NaCH3COONa Tris–
HCl buffer and NH4Cl/NH3. As it is seen, the response of the
sensor increased with increasing pH value of solution and
reached a plateau between pH 5.0 and 7.0. At pH<5.0 the
fluorescence response of the sensor membrane decreased with
decreasing pH value due to proton binding by imine nitrogen
[81] and on the other hand, the diminished fluorescence
response at pH>7.0 could be attributed to the formation of
Hg2+ ion hydroxides [82], as well as a possible slight swelling
of the polymeric film under alkaline conditions. Hence, in the
subsequent experiments, the pH values of all solutions were
adjusted to 6.0 for further studies.
The data given in Table 2 give an indcation of the pro-
nounced influence of the amount of the ionophore on the
working range of the proposed optical sensor. As it can be
seen, an increase in the amount of ATBD from 1 % to 3 %
resulted in an improved lower limit of the working range,
emphasizing the expected increase in the sensitivity of the
optical sensor in the presence of increased amount of the
ionophore in the membrane phase.
Response Mechanism, Binding Mode and Measuring Range
Among the various detection systems used in mercury
optodes, those based on sulfur-containing ligands. Generally,
these systems have shown better selectivity and sensitivity
[82]. Hg2+ displays great affinity for soft coordination centers
like sulfur [83, 84], therefore, ligand ATBD with sulfur-
containing sites was investigated as an active ionophore for

J Fluoresc
Fig. 8 TOF-MS spectra of sensor
ATBD (1.0 μM) with Hg2+ in d6-
DMSO: (a) ATBD and (b) ATBD
+ Hg2+ (1.0 eq.)
highly selective and sensitive determination of mercury ion.
Hg2+ bonding takes place with NSSN donor sites of the
azomethine –N and thiophenolate -S [85]. When ATBD
(LH2) was doped in plasticized PVC together with the anionic
additive KTpClPB at pH 6.0, the system becomes a selective
Hg2+ sensor. Furthermore, the fluorescence intensities of the
optode membrane gradually increased with increasing Hg2+
concentrations, which constitutes the basis for the determina-
tion of Hg2+ with the proposed sensor proposed in this work.
The lipophilic anionic sites, i.e. TpClPB- provide the optode
membrane with the necessary ion-exchange properties be-
cause the flouroionophore acts as a neutral ligand, and hence
can’t function as an ion exchanger. The overall equilibrium
between the aqueous sample solution (aq) and the organic
membrane phase (org) is represented in Scheme 2.
The enhancement of the fluorescence of Hg2+ complex
compared to the parent ligand may be due to CHEF (chelation
enhancement of fluorescence emission) [86]. Factors like a
simple binding of the ligand to the metal ions [87], an increase
in rigidity in structure [88], a restriction in the photo induced
electron transfer (PFT) [89, 90] etc. are assigned to the ap-
pearance and enhancement of the photoluminescence (PL). In
the present case, the first two factors seem to be responsible
for the enhancement PL.
1
For elucidation the binding mode, the H NMR-titration
1
experiments were carried out. As shown in Fig. 7, the H

J Fluoresc
with Hg2+. Taken together, the above results indicated a
plausible interaction mode of ATBD/Hg2+ as proposed in
Scheme 3, in which Hg2+ ion was coordinated with two “N”
and two “S” atoms of ATBD.
Figure 9 shows the fluorescence emission spectra of the
sensing membrane exposed to the solutions containing differ-
ent concentrations of Hg2+ (λex 403 nm). The linearity was
determined by plotting the fluorescence enhancement value
ΔF (ΔF=F - F0, where F0 and F were the fluorescence emis-
sion intensities before and after addition of Hg2+) against the
negative logarithm of Hg2+ concentration, obtaining a linear
equation of ΔF=995.99+84.689 log [Hg2+] (R=0.9948) in
the concentration range of 1.0×10−10 to 1.0×10−2 mol L−1
(Fig. 10). The limit of detection (LOD) based on 3σ of the
N
N
Hg
S
S
Scheme 3 Plausible interaction mode of ATBD/Hg2+
blank was 7.23×10−11
.
Response Time, Reproducibility, Short-Term Stability,
Lifetime and Regeneration
NMR spectrum of ATBD showed a singlet signal at δ
3.64 ppm which was attributed to thiol -SH protons. Upon
addition of Hg2+, the SH signal disappeared, which suggested
that a Hg2+ bound to the two sulphur atoms of the ATBD
backbone via deprotonation of SH groups. The singlet signal
at δ 8.23 ppm in the parent ATBD which was attributed to the
azomethine (-CH=N-) protons displayed an upper filed shift
(δ 7.94) upon the addition of Hg2+ which originated from the
coordination of the azomethine nitrogen to Hg2+. Moreover,
the binding mode of ATBD (LH2) with Hg2+ was also exam-
ined by TOF-MS spectra (Fig. 8). The positive-ion mass
spectrum of ATBD upon addition of Hg2+ (1 equiv) exhibited
one intense peak at m/z=547, corresponding to the ion [HgL],
corroborating the 1:1 binding stoichiometry of LH2 (ATBD)
The dynamic response time, is an important analytical feature
of any optode. The response time was tested by recording the
fluorescence intensity change from a buffered solution at pH=
6 to a buffered Hg2+ solution over a wide concentration range
(1.0×10−10 to 1.0×10−2 mol L−1). The resulting intensity–
time curve (Fig. 11) revealed that, the fluorescence intensity of
the corresponding signal reached its equilibrium response in a
relatively short time of less than 35 s. It was obvious that the
response time is lower in concentrated solutions than dilute
solutions.
The repeatability and reproducibility of optical sensors are
two of their important characteristic features both of which
Fig. 9 Emission spectra of
ATBD sensing membrane after
exposure to different Hg2+
900
800
700
600
500
400
300
200
100
0
concentrations (1.0×10−10−1.0×
10−2 mol L−1) at pH=6.0. Dashed
curve represent blank solution
and arrows show the changes in
fluorescence intensity with
2+
Hg
respect to an increase of Hg2+
concentration (λex 403 nm and
λem 544 nm)
400
450
500
550
600
650
700
750
Wavelength (nm)

J Fluoresc
Fig. 10 Calibration plot of the
sensor in the concentration range
of 1.0×10−10 − 1.0×10−2 mol L−1
at pH=6.0 in EtOH (λex=403 nm)
1000
900
800
700
600
500
400
300
200
100
0
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
2+
-Log [Hg ]
were studied in this work. The reproducibility was examined by
preparing 8 different membranes from the same mixture and
measuring the fluorescence of each membrane at 544 nm using
1.0 μM Hg2+ (three repeated determinations) in the buffer
solutions at pH 6.0. The resulting coefficient of variation was
found to be 1.7 %. The short-term stability of the optical
sensor was studied by measuring its fluorescence intensity in
contact with 1.0 μM Hg2+ at pH 6.0 over a period of 10 h. From
the fluorescence measurements, after every 60 min (n=10), it
was found that the response was almost complete with only
2.5 % change in the fluorescence after 10 h monitoring. In
addition, it was found that the membrane sensor could be stored
in wet conditions without any measurable changes in its fluo-
rescence for at least 15 weeks, which implies that the ionophore
is quite stable in the membrane. Thus, the membrane sensor
was immersed in the buffer solution of pH 6.0 when not in use.
The reversibility of the optode was checked by washing the
used optodes with 0.2 mol L−1 thiocyanate and/or iodate
Fig. 11 Dynamic response of the
proposed fluorescence membrane
sensor for step change in
900
800
700
600
500
400
300
200
100
0
(a)
concentration of Hg2+ ion at pH=
(b)
6.0): (a) 1.0×10−2, (b) 1.0×10−3
(c) 1.0×10−4, (d) 1.0×10−5, (e)
,
(c)
1.0×10−6, (f) 1.0×10−7, (g) 1.0×
10−8, (h) 1.0×10−9, (i) 1.0×−10
(d)
(e)
(f)
(g)
(h)
(i)
0
50
100
150
200
250
300
350
400
450
Time (s)

J Fluoresc
Fig. 12 Interferences of different
5
4
metal ions (1.0×10−2 mol L−1
onto the fluorescence
)
2+
Cu
3+
Al
2+
determination of Hg2+ ion (1.0×
10−10 mol L−1) using the
proposed membrane sensor at
pH 6.0
Co
2+
2+
Mg
Sr
2+
Zn
3
2+
Ca
2+
+
Ba
Na
2+
2+
Cd
2
Pb
3+
2+
Fe
2+
Ni
Mn
1
0
+
-1
-2
-3
3+
K
Cr
+
Ag
solutions. The results showed that the optodes were not re-
generated to use one more time for Hg2+ determination. In
addition, HCl and/or HNO3 were also checked for the regen-
eration of the used optode by immersion of the used optode to
the acids solution (0.01, 0.05, and 0.10 mol L−1) for 180 s. The
results showed that the optodes could be regenerated in
0.10 mol L−1 HNO3 solution. Therefore, each optode can be
used several times for Hg2+ analysis.
human hair samples, urine samples, collected from dentists
and well water samples. The water samples were collected
from three different places in Tabuk (Saudi Arabia). For
evaluating the accuracy of the method, a comparison between
results obtained by proposed method and cold vapor atomic
absorption spectrometry (CVAAS) was performed. As can be
seen in Table 3, the results obtained for both methods have
good agreements.
Selectivity
Ta b l e 3 Determination of Hg2+ in real samples of six replicate
measurements
The selectivity behavior which is the relative optode response
for the primary ion over other ions present in solution, is one
of the most important characteristics of any ion-selective
optical sensor. To investigate the selectivity of the proposed
membrane sensor, the fluorescence intensity of a fixed con-
centration of Hg2+ (1.0×10−10 mol L−1) in a solution of
pH 6.0 was measured before (F0) and after addition (F) of
some potentially interfering ions such as K+, Na+, Mg2+, Ca2+,
Ba2+, Sr2+, Al3+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Ag+, Cd2+,
Mn2+, Fe3+ and Cr3+ at concentrations up to 1.0×10−2
mol L−1. The resulting relative error is defined as RE
(%)=[(F−Fo)/Fo]×100. The experimental results (Fig. 12) re-
vealed that most alkali, alkaline earth, and many transition
metal cations don’t show significant interference on the Hg2+
assay, where the observed relative error was less than 5 %
relative error, which is considered as tolerable.
Sample
Amount of mercurya
CVAAS
Relative error (%)
Proposed sensor
Hair samplesc
1
2
3
172.90a 0.90b
279.50a 4.40b
197.50a 2.40b
173.64 a 0.80b
277.43 1.40b
1.96.43 1.25b
−0.43
0.74
0.56
Urine samplesd
1
2
3
3.47a 0.05b
3.80a 0.08b
3.65a 0.02b
3.45a 0.05b
3.83a 0.08b
3.62a 0.02b
0.58
−0.78
0.82
Well water samplesd
1
2
3
1.72a 0.03b
1.10a 0.07b
1.45a 0.05b
1.71a 0.02b
1.12a 0.06b
1.43a 0.07b
0.58
−1.82
1.38
a
b
c
c
Mean values of three determinations
Standard deviation
Reported value: μgKg−1
Analytical Applications
To assess the applicability of the proposed chemosensor to
real samples, we further conducted Hg2+ detection in different
Reported value: μgL−1

J Fluoresc

J Fluoresc
8. Bakker E, Buhlmann P, Pretsch E (1997) Carrier-based ion-selective
electrodes and bulk optodes. 1. General characteristics. Chem Rev
97(8):3083–3132
Comparison of the Proposed Optode with Previously
Reported Methods
9. Bühlmann P, Pretsch E, Bakker E (1998) Carrier based ion-selective
electrodes and bulk optodes. 2. Ionophores for potentiometric and
optical sensors. Chem Rev 98(4):1593–1687
10. Brook TE, Narayanaswamy R (1998) Polymeric films in optical gas
sensors. Sens Actuat B 51(1–3):77–83
The present proposed sensor was compared to recently
Hg2+ sensing methods based on S-containing, Schiff bases
or immobilized ionphore (Table 4) [45, 54, 63, 68, 73, 82,
91–105]. Each of the reported method has its own merits,
but each method also offers some problems such as poor
reproducibility, limited sample adaptability, high cost, well-
controlled experimental conditions, complicated sample-
pretreatment, some inherent interference and time consum-
ing procedures. As can be seen, the proposed sensor
shows better selectivity, better LOD (7.23×10−11 mol L−1)
and short response time (35 s) relative to other reported
methods.
11. Boening DW (2000) Ecological effects, transport, and fate of mer-
cury: a general review. Chemosphere 40(12):1335–1351
12. Ha-Thi M, Penhoat M, Mochelet V, Leray I (2007) Highly selective
and sensitive phosphane sulfide derivative for the detection of Hg2+
in an organoaqueous medium. Org Lett 9(6):1133–1136
13. Wang Q, Kim D, Dionysiou DD, Sorial GA, Timberlake D (2004)
Sources and remediation for mercury contamination in aquatic
systems–a literature review. Environ Pollut 131(2):323–336
14. Drinking water standards and health advisories, EPA 822-R-04-005,
U.S. Environmental Protection Agency, Washington, DC, 2004
(U.S. Environmental Protection Agency Site at http://www.epa.
gov/safewater/dwh/c-ioc/nickel.html) and WHO’s Drinking Water
Standards 2006(http://www.who.int/water_sanitation health/dwq/
gdwq0506.pdf)
15. Anselmi A, Tittarelli P, Katskov DA (2002) Determination of trace
elements in automotive fuels by filter furnace atomic absorption
spectrometry. Spectrochim Acta B 57(3):403–411
16. Baralkiewicz D, Gramowska H, Kózka M, Kanecka A (2005)
Determination of mercury in sewage sludge by direct slurry sam-
pling graphite furnace atomic absorption spectrometry. Spectrochim
Acta B 60(3):409–413
17. Madden JT, Fitzgerald N (2009) Investigation of ultraviolet photol-
ysis vapor generation with in-atomizer trapping graphite furnace
atomic absorption spectrometry for the determination of mercury.
Spectrochim Acta B 64(9):925–927
18. Araujo RGO, Rennan GO, Vignola F, Castilho INB, Borges DLG,
Welz B, Vale MGR, Smichowski P, Ferreira SLC, Becker-Ross H
(2011) Determination of mercury in airborne particulate matter
collected on glass fiber filters using high-resolution continuum
source graphite furnace atomic absorption spectrometry and direct
solid sampling. Spectrochim Acta B 66(5):378–382
Conclusion
In conclusion, an efficient, easy, low-cost and high selective
fluoroionophore is developed and potentially utilized for selec-
tive and sensitive determination of Hg2+ based on a novel dithiol
Schiff base namely: N.N/bis(2-aminothiophenol)benzene-1,2-
dicarboxaldehyde (ATBD) immobilized within a plasticized
PVC membrane, with good optical and mechanical proper-
ties. The sensor showed short response time (35 s), appropri-
ate linear dynamic range (1.0×10−10 − 1.0×10−2 mol L−1)
and low detection limit (7.23×10−11 mol L−1). The proposed
fluorescence optode was successfully applied to the deter-
mination of Hg2+ ions in hair, urine and well water samples.
19. Harrington CF, Merson SA, D’ Silva TMD (2004) Method to
reduce the mem-ory effect of mercury in the analysis of fish tissue
using inductively coupled plasma mass spectrometry. Anal Chim
Acta 505(2):247–254
20. Anthemidis AN, Zachariadis GA, Michos CE, Stratis JA (2004)
Time-based on-line preconcentration cold vapour generation proce-
dure for ultra-trace mercury determination with inductively coupled
plasma atomic emission spectrometry. Anal Bioanal Chem 379(5–
6):764–769
21. Krata A, Bulska E (2005) Critical evaluation of analytical perfor-
mance of atomic absorption spectrometry and inductively coupled
plasma mass spectrometry for mercury determination. Spectrochim
Acta B 60(3):345–350
22. Martinez T, Lartigue J, Zarazua G, Avila-Perez P, Navarrete M,
Tejeda S (2008) Application of the Total Reflection X-ray
Fluorescence technique to trace elements determination in tobacco.
Spectrochim Acta B 63(12):1469–1472
References
1. de Silva AP, Gunaratne HQN, Gunnlaugsson T, Huxley AJM,
McCoy CP, Rademacher JT, Rice TE (1997) ChemInform abstract:
signaling recognition events with fluorescent sensors and switches.
Chem Rev 97(5):1515–1566
2. Valeur B, Leray I (2000) Design principles of fluorescent molecular
sensors for cation recognition. Coord Chem Rev 205(1):3–40
3. Oehme I, Wolfbeis OS (1997) Optical sensors for determination of
heavy metal ions. Microchim Acta 126(3–4):177–192
4. Hisamoto H, Suzuki K (1999) Ion-selective optodes: current devel-
opments and future prospects. Trac-Trend Anal Chem 18(8):513–
524
5. Oehme I, Praltes S, Wolfbeis OS, Mohr GJ (1998) The effect of
polymeric supports and methods of immobilization on the perfor-
mance of an optical copper(II)-sensitive membrane based on the
colourimetric reagent Zincon. Talanta 47(3):595–604
6. Zevin M, Reisfeld R, Oehme I, Wolfbeis OS (1997) Sol–gel derived
optical coatings for determination of chromate. Sens Actuat B 39(1–
3):235–238
7. Cabello-Carramolino G, Petit-Dominguez M (2008) Application of
new sol–gel electrochemical sensors to the determination of trace
mercury. Anal Chim Acta 614(1):103–111
23. Bennun L, Gomez J (1997) Determination of mercury by total-
reflection X-ray fluorescence using amalgamation with gold.
Spectrochim Acta B 52(8):1195–1200
24. Osawa T, Hatsukawa Y, Appel PWU, Matsue H (2011) Mercury
and gold concentrations of highly polluted environmental samples
determined using prompt gamma-ray analysis and instrument neu-
tron activation analysis. Nucl Instrum Meth B 269(8):17–720
25. Sysalová J, Kučera J, Fikrle M, Drtinová B (2013) Determination of
the total mercury in contaminated soils by direct solid sampling
atomic absorption spectrometry using an AMA-254 device and

J Fluoresc
radiochemical neutron activation analysis. Microchem J 110:691–
694
44. Ebdelli R, Rouis A, Mlika R, Bonnamour I, Jaffrezic N, Ouada J,
Davenas HB (2012) Ion sensing film optodes based on chromogenic
calix[4]arene: application to the detection of Hg2+, Ni2+ and Eu3+
ions. J Incl Phenom Macrocycl Chem 73(1–4):109–117
45. Firooza AR, Movahedia M, Ensafi AA (2012) Selective and sensi-
tive optical chemical sensor for the determination of Hg(II) ions
based on tetrathia-12-crown-4 and chromoionophore I. Sens Actuat
B 171–172:492–498
46. Martínez R, Espinosa A, Tárraga A, Molina P (2010) A new
bis(pyrenyl)azadiene-based probe for the colorimetric and fluores-
cent sensing of Cu(II) and Hg(II). Tetrahedron 66(21):3662–3667
47. Kaura P, Kaura S, Kasettic Y, Bharatam PV, Singh K (2010)
A new colorimetric chemodosimeter for Hg2+ based on
chargetransfer compound of Nmethylpyrrole with TCNQ. Talanta
83(2):644–650
26. Romero V, Costas-Mora I, Lavilla I, Bendicho C (2011) Cold vapor-
solid phase microextraction using amalgamation in different Pd-
based substrates combined with direct thermal desorption in a
modified absorption cell for the determination of Hg by atomic
absorption spectrometry. Spectrochim Acta B 66(2):156–162
27. Gil S, Lavilla I, Bendicho C (2007) Green method for ultrasen-
sitive determination of Hg in natural waters by electrothermal-
atomic absorption spectrometry following sono-induced cold
vapor generation and ‘in-atomizer trapping. Spectrochim Acta
B 62(1):69–75
28. Sardans J, Montes F, Peñuelas J (2010) Determination of As, Cd,
Cu, Hg and Pb in biological samples by modern electrothermal
atomic absorption spectrometry. Spectrochim Acta B 65(2):97–112
29. Jiang X, Gan W, Wan L, Zhang H, He Y (2010) Determination of
mercury by electrochemical cold vapor generation atomic fluores-
cence spectrometry using polyaniline modified graphite electrode as
cathode. Spectrochim Acta B 65(2):171–175
48. Bao WT, Jian LJ, Bing BC, Qi L, Hong Y, Qiang XY, Ming ZY
(2013) A highly selective colorimetric sensor for Hg2+ based on a
copper (II) complex of thiosemicarbazone in aqueous solutions. Sci
China Chem 56(7):923–927
30. Shahar T, Tal N, Mandler D (2013) The synthesis and characteriza-
tion of thiol-based aryl diazonium modified glassy carbon electrode
for the voltammetric determination of low levels of Hg(II). J Solid
State Electrochem 17(6):1543–1552
31. Filho NLD, do Carmo DR, Rosa AH (2006) An electroanalytical
application of 2-aminothiazole-modified silica gel after adsorption
and separation of Hg(II) from heavy metals in aqueous solution.
Electrochim Acta 52(3):965–972
49. Hamzeh AY, Abdoli A (2010) Sol–gel derived highly selective
optical sensor for sensitive determination of the mercury(II) ion in
solution. J Hazard Mater 178(1–3):713–717
50. Al-Kady AS, Abdelmonem FI (2013) Highly sensitive and selective
spectrophotometric detection of trace amounts of Hg2+ in environ-
mental and biological samples based on 2,4,7-triamino-6-
phenylpteridine. Sens Actuat B 182:87–94
51. Lu F, Yamamura M, Nabeshima T (2013) A highly selective and
sensitive ratiometric chemodosimeter for Hg2+ ions based on an
iridium(III) complex via thioacetal deprotection reaction. Dalton
Trans 42(34):12093–12100
32. do Nascimento FH, Masini JC (2012) Complexation of Hg(II) by
humic acid studied by square wave stripping voltammetry at screen-
printed gold electrodes. Talanta 100:57–63
33. Chaiyo S, Chailapakul O, Sakai T, Teshima N, Siangproh W (2013)
Highly sensitive determination of trace copper in food by adsorptive
stripping voltammetry in the presence of 1,10-phenanthroline.
Talanta 108:1–6
34. Harrington CF (2000) The speciation of mercury and
organomercury compounds by using high-performance liquid
chromatography. TrAC 19(2–3):167–179
52. Udhayakumari D, Velmathi S (2013) Colorimetric and fluorescent
sensor for selective sensing of Hg2+ ions in semi aqueous medium. J
Lumin 136:117–121
53. Dong Z, Tian X, Chen Y, Hou J, Guo Y, Sun J, Ma J (2013) A highly
selective fluorescent chemosensor for Hg2+ based on rhodamine B
and its application as a molecular logic gate. Dyes Pigments 97(2):
324–329
35. Bramanti E, Lomonte C, Onor M, Zamboni R, D’Ulivo A, Raspi G
(2005) Mercury speciation by liquid chromatography coupled with
on-line chemical vapour generation and atomic fluorescence spec-
trometric detection (LC–CVGAFS). Talanta 66(3):762–768
36. Wang M, Feng WY, Shi JW, Zhang F, Wang B, Zhu MT, Li B, Zhao
YL, Chai ZF (2007) Development of a mild mercaptoethanol ex-
traction method for determination of mercury species in biological
samples by HPLC–ICP-MS. Talanta 71(5):2034–2039
37. Liu Q (2010) Direct determination of mercury in white vinegar by
matrix assisted photochemical vapor generation atomic fluores-
cence spectrometry detection. Spectrochim Acta B 65(7):587–590
38. Fakhari AR, Ganjali MR, Shamsipur M (1997) PVC-based
hexathia-18-crown-6-tetraone sensor for mercury(II) ions. Anal
Chem 69(18):3693–3696
39. Perez-Marin L, Lopez-Valdivia H, Avila-Perez P, Chamaro JA,
Lopez-Valdivia H (2000) Mercury(II) ion-selective electrode.
Study of 1,3- diphenylthiourea as ionophore. Analyst 125(10):
1787–1790
40. Ugo P, Mortto L, Bertoneell P, Wang J (1998) Determination of
trace mercury in saltwaters at screen-printed electrodes modified
with sumichelate Q10R. Electroanal 10(15):1017–1021
41. Mandal AK, Suresh M, Suresh E, Mishra SK, Mishra S, Das A
(2010) A chemosensor for heavytransition metal ions in mixed
aqueous-organic media. Sens Actuat B 145(1):32–38
54. Firooz AR, Ensafi AA, Hajyani Z (2013) A highly sensitive and
selective bulk optode based on dithiacyclooctadecane derivative
incorporating chromoionophore V for determination of ultra trace
amount of Hg(II). Sens Actuat B 177:710–716
55. Mandal S, Banerjee A, Lohar S, Chattopadhyay A, Sarkar B,
Mukhopadhyay SK, Sahana A, Das D (2013) Selective sensing of
Hg2+ using rhodamine–thiophene conjugate: red light emission and
visual detection of intracellular Hg2+ at nanomolar level. J Hazard
Mater 261:198–205
56. Zhang N, Li G, Cheng Z, Zuo X (2012) Rhodamine B immobilized
on hollow Au–HMS material for naked-eye detection of Hg2+ in
aqueous media. J Hazard Mater 229–230:404–410
57. Vasimalai N, Sheeba G, John SA (2012) Ultrasensitive
fluorescence-quenched chemosensor for Hg(II) in aqueous solution
based on mercaptothiadiazole capped silver nanoparticles. J Hazard
Mater 213–214:193–199
58. Wang F, Nam S, Guo Z, Park S, Yoon J (2012) A new rhodamine
derivative bearing benzothiazole and thiocarbonyl moieties as a
highly selective fluorescent and colorimetric chemodosimeter for
Hg2+. Sens Actuat B 161(1):948–953
59. García-Beltrán O, Mena N, Berríos TA, Castro EA, Cassels BK,
Núñez MT, Aliaga ME (2012) A selective fluorescent probe for the
detection of mercury (II) in aqueous media and its applications in
living cells. Tetrahedron Lett 53(48):6598–6601
42. Zou Q, Tian H (2010) Chemodosimeters for mercury(II) and
methylmercury(I) based on 2,1,3benzothiadiazole. Sens Actuat B
149(1):20–27
60. Tharmaraj V, Pitchumani K (2012) An acyclic, dansyl based color-
imetric and fluorescent chemosensor for Hg(II) via twisted intramo-
lecular charge transfer (TICT). Anal Chim Acta 751:171–175
61. Wang F, Nam S, Guo Z, Park S, Yoon J (2012) A new rhodamine
derivative bearing benzothiazole and thiocarbonyl moieties as a
43. Zou Q, Jin J, Xu B, Ding L, Tian H (2011) New photochromic
chemosensors for Hg2+ and F-. Tetrahedron 67(5):915–921

J Fluoresc
highly selective fluorescent and colorimetric chemodosimeter for
81. Abdel Aziz AA (2013) A novel highly sensitive and selective
optical sensor based on a symmetric tetradentate Schiff-base em-
bedded in PVC polymeric film for determination of Zn2+ ion in real
samples. J Lumin 143:663–669
82. Shamsipur M, Hosseini M, Alizadeh K, Alizadeh N, Yari A,
Caltagirone C, Lippolis V (2005) Novel fluorimetric bulk optode
membrane based on a dansylamidopropyl pendantarmderivative of
1aza4,10dithia7oxacyclododecane ([12]aneNS2O) for selective
subnanomolar detection of Hg(II) ions. Anal Chim Acta 533(1):
17–24
Hg2+. Sen. Actuators B 161:948–953
62. Liu W, Chen J, Xu L, Wu J, Xu H, Zhang H, Wang P (2012)
Reversible “off-on” fluorescent chemosensor for Hg2+ based on
rhodamine derivative. Spectrochim Acta A 85(1):38–42
63. Aksuner N, Basaran B, Henden E, Yilmaz I, Cukurovali A (2011) A
sensitive and selective fluorescent sensor for the determination of
mercury(II) based on a novel triazine-thione derivative. Dyes
Pigments 88(2):143–148
64. Li J, Meng J, Huang X, Cheng Y, Zhu C (2010) Highly selective
fluorescent sensor for Hg2+ based on the water-soluble poly(p-
phenyleneethynylene). Polymer 51:3425–3430
83. Blake AJ, Schröder M (1990) Chemistry of thioether macrocyclic
complexes. Adv Inorg Chem 35:1–80
65. Kim HJ, Park JE, Choi MG, Ahn S, Chang S (2010) Selective
chromogenic and fluorogenic signalling of Hg2+ ions using a
fluorescein-coumarin conjugate. Dyes Pigments 84(1):54–58
66. Wang J, Huang L, Xue M, Liu L, Wang Y, Gao L, Zhu J, Zou Z
(2008) Developing a novel fluorescence chemosensor by self-
assembly of Bis-Schiff base within the channel of mesoporous
SBA-15 for sensitive detecting of Hg2+ ions. Appl Surf Sci
254(17):5329–5335
67. Bozkurt SS, Cavas L (2009) Can Hg(II) be determined via quenching
of the emission of green fluorescent protein from anemonia sulcata var.
smaragdina. Appl Biochem Biotechnol 158(1):51–58
68. Alizadeh K, Parooi R, Hashemi P, Rezaei B, Ganjali MR (2011) A
new Schiff’s base ligand immobilized agarose membrane optical
sensor for selective monitoring of mercury ion. J Hazard Mater
186(2–3):1794–1800
69. Ganjali MR, Poursaberi T, Hajiagha-Babaei L, Rouhani S, Yousefi
M, Kargar-Razi M, Moghimi A, Aghabozorg H, Shamsipur M
(2001) Highly selective and sensitive copper(II) membrane coated
graphite electrode based on a recently synthesized Schiff’s base.
Anal Chim Acta 440(2):81–87
70. Gholivand MB, Ahmadi F, Rafiee E (2006) A novel Al(III)-selec-
tive electrochemical sensor based on N, N–bis(salicylidene)-1,2-
phenylenediamine complexes. Electroanal 18(16):1620–1626
71. Ganjali MR, Rezapour M, Norouzi P, Salavati‐Niasari M (2005) A
new pentadentate S-N Schiffs-base as a novel ionophore in con-
struction of a novel Gd(III) membrane sensor. Electroanal 1:2032–
2036
72. Schwarzenbach G, Flaselika H, Irving H (1969) Complexometric
titrations, 2nd edn. Methuen, London
73. Khezri B, Amini MK, Firooz AR (2008) An optical chemical sensor
for mercury ion based on 2-mercaptopyrimidine in PVC membrane.
Anal Bioanal Chem 390(7):1943–1950
74. Amini MK, Momeni-Isfahani T, Khorasani JH, Pourhossein M
(2004) Development of an optical chemical sensor based on 2-(5-
bromo-2-pyridylazo)-5-(diethylamino)phenol in Nafion for deter-
mination of nickel ion. Talanta 63(3):713–720
75. Pournaghi-Azar MH, Dastangoo H (2000) Differential pulse
anodic stripping voltammetry of copper in dichloromethane:
application to the analysis of human hair. Anal Chim Acta
405(1–2):135–144
76. Suzuki T, Akagi H, Arimura K, Ando T, Sakamoto M, Satoh H,
Naganuma A, Futatsuka M, Matsuyama A (2004) Mercury analysis
manual. Ministry of the Environment, Japan
77. Mantyla DG, Wright OD (1976) Mercury toxicity in the dental
office: a neglected problem. JADA 92(6):1189–1194
78. Lakowicz JR (1999) Principles of fluorescence spectroscopy, 2nd
edn. Kluwer Academic/Plenum Publishers, New York
79. Morales-Bahnik A, Czolk R, Reichert J, Ache HJ (1993) An
optochemical sensor for Cd(II) and Hg(II) based on a porphyrin
immobilized on Nafion@ membranes. Sens Actuat B 13(1–3):424–
426
80. Rosatzin T, Bakker E, Suzuki K, Simon W (1993) Lipophilic and
immobilized anionic additives in solvent polymeric membranes of
cation-selective chemical sensors. Anal Chim Acta 280(2):197–208
84. Housecroft CE (1992) Silver. Coord Chem Rev 115:141–161
85. Yilmaz I, Temel H, Alp H (2008) Synthesis, electrochemistry and in
situ spectroelectrochemistry of a new Co(III) thio Schiff-base com-
plex with N, N/-bis(2-aminothiophenol)-1,4-bis(carboxylidene
phenoxy)butane. Polyhedron 27(1):125–132
86. Vicente M, Bastida R, Lodeiro C, Macias A, Parola AJ, Valencia L,
Spey SE (2003) Metal complexes with a new N4O3 amine pendant-
armed macrocyclic ligand: synthesis, characterization, crystal struc-
tures, and fluorescence studies. Inorg Chem 42(21):6768–6779
87. Zengin H, Dolaz M, Golcu A (2009) Preparation,
photoluminescence and antimicrobial activity of loracarbef and
its various complexes. Curr Anal Chem 5(4):358–362
88. Cai LZ, Chen WT, Wang MS, Guo GC, Huang JS (2004) Syntheses,
structures and luminescent properties of four new 1D lanthanide
complexes with 2-thiopheneacetic acid ligand. Inorg Chem
Commun 7(5):611–614
89. Chan WH, Yang RH, Mo T, Wang KM (2002) Lead-selective
fluorescent optode membrane based on 3,3′,5,5′-tetramethyl-N-(9-
anthrylmethyl)benzidine. Anal Chim Acta 460(1):123–132
90. Cao YD, Zheng QY, Chen CF, Huang ZT (2003) A new fluorescent
chemosensor for transition metal cations and on/off molecular
switch controlled by pH. Tetrahedron Lett 44(25):4751–4755
91. Flamini A, Panusa A (1997) Development of optochemical
sensors for Hg(II), based on immobilized 2-(5-amino-3,4-
dicyano-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide. Sens
Actuat B 42(1):39–46
92. Sanchez-Pedreno C, Ortuno JA, Albero MI, Garcia MS,
Valero MV (2000) Development of a new bulk optode mem-
brane for the determination of mercury(II). Anal Chim Acta
414(1–2):195–203
93. Safavi A, Bagheri M (2004) Design and characteristics of a mercury
(II) optode based on immobilization of dithizone on a
triacetylcellulose membrane. Sens Actuat B 99(2–3):608–612
94. Nuriman BK, Dam HH, Reinhoudt DN, Verboom W (2007)
Development of a disposable mercury ion-selective optode based
on trityl-picolinamide as ionophore. Anal Chim Acta 591(2):208–
213
95. Ensafi AA, Fooladgar M (2006) Development of a mercury optical
sensor based on immobilization of 4-(2-pyridylazo)-resorcinol on a
triacetylcellulose mem-brane. Sens Actuat B 113(1):88–93
96. Ensafi AA, Far AK, Meghdadi S (2008) Highly selective optical
sensor for mercury assay based on covalent immobilization of 4-
hydroxy salophen on a triacetylcellulose membrane. Sens Actuat B
133(1):84–90
97. Amini MK, Khezri B, Firooz AR (2008) Development of a highly
sensitive and selective optical chemical sensor for batch and flow-
through determination of mercury ion. Sens Actuat B 131(2):470–
478
98. Kalyan Y, Pandey AK, Bhagat PR, Acharya R, Natarajan V, Naidu
GRK, Reddy AVR (2009) Membrane optode for mercury(II) deter-
mination in aqueous samples. J Hazard Mater 166(1):377–382
99. Ensafi AA, Fouladgar M (2009) A sensitive and selective bulk optode
for determi-nation of Hg(II) based on hexathiacyclooctadecane and
chromoionophore V. Sens Actuat B 136(2):326–331

J Fluoresc
100. Yari A, Papi F (2009) A of mercury (II) by development and
characterization of a PVC-based optical sensor. Sens Actuat B
138(2):467–473
101. Yang Y, Jiang J, Shen G, Yu R (2009) An optical sensor for mercury
ion based on the fluorescence quenching of tetra(p-
dimethylaminophenyl)porphyrin. Anal Chim Acta 636(2–3):83–88
102. Yari A, Abdoli HA (2010) Sol–gel derived highly selective optical
sensor for sensitive determination of the mercury(II) ion in solution.
J Hazard Mater 178(1–3):713–717
103. Yari A, Papi F (2011) Ultra trace mercury(II) detection by a highly
selective new optical sensor. Sens Actuat B 160(1):698–704
104. Tavallali H, Shaabanpur E, Vahdati P (2012) A highly selective
optode for deter-mination of Hg (II) by a modified immobilization
of indigo carmine on a triacetylcellulose membrane. Spectrochim
Acta A 89:216–221
105. Ling L, Zhao Y, Du J, Xiao D (2012) An optical sensor for mercuric
ion based on immobilization of Rhodamine B derivative in PVC
membrane. Talanta 91:65–71