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Sensors and Actuators B 166–167 (2012) 269–274
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Sensors and Actuators B: Chemical
journal homepage: www.elsevier.com/locate/snb
A novel optical chemical sensor for the determination of nickel(II) based on
ﬂuorescence quenching of newly synthesized thiazolo-triazol derivative
and application to real samples
Nur Aksuner a,∗ , Emur Henden a , Ibrahim Yilmaz b , Alaaddin Cukurovali c
Department of Chemistry, Faculty of Science, University of Ege, 35100 Bornova, I˙ zmir, Turkey
Department of Chemistry, Faculty of Science, University of Karamano˘glu Mehmet Bey, 70200 Karaman, Turkey
c
Department of Chemistry, Faculty of Arts and Sciences, University of Fırat, 23169 Elazı˘g, Turkey
a
b
a r t i c l e
i n f o
Article history:
Received 16 November 2011
Received in revised form 14 February 2012
Accepted 20 February 2012
Available online 27 February 2012
Keywords:
Thiazolo-triazol
PVC matrix
Optical sensor
Fluorescence spectroscopy
Nickel(II)
a b s t r a c t
The characterization of a new optical sensor membrane is described for the determination of Ni(II) based
on the immobilization of the ﬂuorescent thiazolo-triazol derivative in PVC matrix. This optode has a wide
linear range of 1.0 × 10−9 –4.4 × 10−3 M at pH 6.0 for Ni(II) ions with the detection limit of 8.5 × 10−10 M.
The response of the optode membrane to Ni(II) is fully reversible and reveals a very good selectivity
towards Ni(II) ion over a wide variety of other metal ions in solution. The membrane showed a good
durability and short response time with no evidence of reagent leaching. The proposed optical sensor
gives good results for applications in direct determination of Ni(II) in real samples that are satisfactorily
comparable with corresponding data from ﬂame atomic absorption spectrometry.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Nickel is a moderately toxic element compared to other transition metals. However, it is known that inhalation of nickel and
its compounds can lead to serious problems, including respiratory
system cancer [1,2]. Moreover, nickel can cause a disorder known
as nickel-eczema [3]. Its determination is thus important in view of
toxic nature and widespread presence in environment. The determination of trace nickel in water and environmental samples is
difﬁcult due to various factors, particularly low concentration and
matrix effects. To overcome these problems, several preconcentration and separation techniques are needed before measuring
[4–6]. Many of these pretreatment techniques are, however, time
consuming or require complicated and expensive instruments.
Therefore, development of accurate and rapid detection method
for monitoring the level of nickel in environmental and biological
samples is necessary and indispensable.
Chemical optical sensors (optode) offer advantages such as simple preparation procedure, relatively fast response, wide response
range, reasonable selectivity and high sensitivity [7–9]. The immobilization of various sensing reagents of optode membranes have
been developed for many analytically relevant ions, especially
∗ Corresponding author. Tel.: +90 232 388 82 64; fax: +90 232 388 82 64.
E-mail address: [email protected] (N. Aksuner).
0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.snb.2012.02.059
heavy metal ions. Immobilization of dyes into or onto a solid support is a key issue for their application in optical sensing [10].
The reagent is normally physically entrapped by adsorption, electrostatically attracted or chemically bonded to the solid support.
Generally, sol–gel glasses [11,12] or polymer matrices [13,14] 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 amenability to
plasticization [15]. Recently, our group has been involved in optical
sensors for heavy metal ions embedded in PVC ﬁlms [16–18].
Up to now, there are only a few reports on determination of
nickel based on chemical optical sensor. A Ni(II) optode based on
immobilizing of 2-amino-1-cyclopentene-1-dithiocarboxylic acid
to transparent acetyl cellulose ﬁlm was developed by Ensaﬁ and
Bakhsi [19]. The detectable concentration of nickel in a sample
solution was in the range of 5.0 × 10−6 –1.0 × 10−3 M with the
detection limit of 5.2 × 10−7 M (0.03 ␮g/ml) Ni(II). Shamsipur et al.
[20] have designed a new ﬂuorimetric bulk optode membrane for
the determination of Ni2+ ions. The plasticized PVC-membrane
incorporating 2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole), as
a highly ﬂuorescent chromoionophore, displays a calibration
response for Ni2+ ions with a linear range covering from 1.0 × 10−3
to 1.0 × 10−8 M. An optical sensor for nickel ion based on immobilization of 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol in
Naﬁon membrane was offered by Amini et al. [21]. Hashemi et al.
[22] recently reported a photometric senor based on the covalently
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N. Aksuner et al. / Sensors and Actuators B 166–167 (2012) 269–274
Table 1
General performance characteristics of some Ni2+ optodes.
Reagent/support matrix
Working range (M)
Limit of
detection (M)
Response
time
Measured
signal
Reference
2-amino-1-cyclopentene-1-dithiocarboxylic acid/acetyl
cellulose membrane
2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole)/PVC membrane
2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol/Naﬁon
membrane
thionine/agarose membrane
2-amino-1-cyclopentene-dithiocarboxylic acid/PVC membane
2-{6-(3-methyl-3-mesitylcyclobutyl)-thiazolo[3,2b][1,2,4]triazol-2-yl}-phenol/PVC
membane
5.0 × 10−6 –1.0 × 10−3
5.2 × 10−7
10 min
Absorbance
[19]
1.0 × 10−8 –1.0 × 10−3
8.5 × 10−6 –3.4 × 10−4
8.0 × 10−9
5.1 × 10−6
<40 s
3 min
Fluorescence
Absorbance
[20]
[21]
1.0 × 10−10 –1.0 × 10−7
3.1 × 10−8 –8.0 × 10−3
1.0 × 10−9 –4.4 × 10−3
9.3 × 10−11
NRa
8.5 × 10−10
3 min
3 min
2 min
Absorbance
Absorbance
Fluorescence
[22]
[23]
This work
a
NR: not reported.
immobilized thionine in agarose membrane. The detection limit
of the sensor for Ni2+ was 9.30 × 10−11 M. Yari et al. [23] developed an optical sensor for determination of nickel, which was based
on the incorporation of 2-amino-1-cyclopentene-dithiocarboxylic
acid in a plasticized PVC membrane. The sensor displays a calibration response for Ni2+ ion over a wide concentration range of
3.1 × 10−8 –8.0 × 10−3 M. In Table 1 the recently published optical sensors for Ni (II) determination were compared in terms of
their working ranges, limit of detections (LOD), sensing agents and
matrix materials with the offered work.
Here we present a new optical thin-ﬁlm sensor based on the
ﬂuorescent thiazolo-triazol derivative entrapped in PVC matrix.
The proposed optical sensor shows a signiﬁcant ﬂuorescence signal change on exposure to an aqueous solution containing Ni(II)
ion. Based on this, a highly sensitive, selective and rapid method
for the determination of nickel was developed. The sensor was
applied to determine the concentrations of Ni(II) in real samples,
with satisfactory results.
2. Experimental
was used as reference (Фst = 0.54) for ﬂuorescence quantum yield
calculations of the dye. Schematic structure of the employed
dye molecule 2-{6-(3-methyl-3-mesitylcyclobutyl)-thiazolo[3,2b][1,2,4]triazol-2-yl}-phenol (MMT) is shown in Fig. 1.
2.2. Instrumentation
UV–vis absorption spectra were recorded using Varian Cary 100
bio UV–visible spectrophotometer. All ﬂuorescence measurements
were carried out on a Shimadzu RF-5301 PC spectroﬂuorimeter
with a Xenon short arc lamp as the light source. GBC 904 PBT atomic
absorption spectrophotometer with an air-acetylene ﬂame (FAAS)
was also used for nickel measurements. A CEM MARS 5 (CEM,
Matthews, NC, USA) microwave apparatus equipped with PTFE vessels was used for microwave digestion. The ﬁlm thicknesses of the
sensing slides were measured with Ambios Technology XP-1 HGH
Resolution surface proﬁler.
2.3. Synthesis and the characterization of the 2-{6-(3-methyl-3mesitylcyclobutyl)-thiazolo[3,2-b][1,2,4]triazol-2-yl}-phenol
(MMT)
2.1. Reagents
The polymer membrane components, polyvinylchloride
(PVC) (high molecular weight) and the plasticizers, bis-(2ethylhexyl) phtalate (DOP), bis(2-ethylhexyl)sebecate (DOS),
bis-(2-ethylhexyl)adipate (DAO) and 2-nitrophenyl octyl ether
(NPOE) were obtained from Fluka. The lipophilic anionic additive
reagent potassium tetrakis-(4-chlorophenyl) borate (PTCPB) was
supplied by Aldrich. Absolute ethanol (EtOH), tetrahydrofuran
(THF) and dimethylformamide (DMF) were of analytical grade.
Solvents for the spectroscopic studies were used without further
puriﬁcation. EDTA was obtained from BDH. Sheets of Mylar-type
polyester (Dupont, Switzerland) were used as support. All solutions
were prepared with glass-distilled water.
The pH values of the solutions were checked using a digital pH meter (WTW) calibrated with standard buffer solutions
of Merck. Buffer components and metal salts were of analytical
grade (Merck and Fluka). All of the experiments were operated at room temperature, 25 ± 1 ◦ C. Quinine sulphate (Sigma)
The compound was synthesized as in Fig. 1 by the following
procedure. To a stirred solution of 5-(2-hydroxy-phenyl)-2,4dihydro-[1,2,4]triazole-3-thione (1.9323 g, 10 mmol) in 30 mL
of ethanol, 2-chloro-1-(3-methyl-3-mesityl-cyclobutyl)-ethanone
(2.6479 g, 10 mmol) was added in portions. After the addition of
the ␣-haloketone, the temperature was kept at 50–55 ◦ C for 2 h.
After cooling to the room temperature, the solution pH was brought
about 6.8 with an aqueous solution of NH3 (5%). The precipitate was ﬁltered off, washed with aqueous NH3 solution several
times and dried in air. Yellow crystals of the compound were
obtained by slow evaporation of its ethanol solution. Yield: 93%,
melting point: 152 ◦ C. Characteristic IR bands: 3445 cm−1 (O H),
2951–2867 cm−1 (aliphatics), 1624 cm−1 (C N), 1586 cm−1
(C N), 754 cm−1 (C S C). Characteristic 1 H NMR shifts (CDCl3 ,
ı, ppm): 1.73 (s, 3H, CH3 ), 2.24 (s, 6H, o-CH3 ), 2.26 (s, 3H, p-CH3 ),
2.69–2.74 (m, 2H, CH2 cyclobutane), 2.86–2.92 (m, 2H, CH2
cyclobutane), 3.88 (quint, j = 8.92 Hz, 1H, CH cyclobutane), 6.56
(d, j = 1.2 Hz, 1H, aromatic on thiazole ring), 6.80 (s, 2H, aromatics
Fig. 1. Synthetic route for the synthesis of the 2-{6-(3-methyl-3-mesitylcyclobutyl)-thiazolo[3,2-b][1,2,4]triazol-2-yl}-phenol (MMT).
N. Aksuner et al. / Sensors and Actuators B 166–167 (2012) 269–274
271
on mesityl), 6.94–6.98 (m, 1H, aromatic), 7.04–7.06 (m, 1H, aromatic), 7.26–7.35 (m, 1H, aromatic), 8.11 (dd, j1 = 7.8 Hz, j2 = 1.8 Hz,
1H, aromatic), 10.74 (s, 1H, OH, D2 O exchangeable). Characteristic 13 C NMR shifts (CDCl3 , ı, ppm): 166.14, 157.13, 143.74, 137.55,
135.33, 135.32, 131.60, 130.74, 130.72, 127.40, 119.60, 117.50,
114.77, 106.30, 42.14, 41.86, 27.47, 24.78, 21.69, 20.69.
2.4. Preparation of polymer ﬁlm
The membrane cocktail was prepared using a mixture of 120 mg
of PVC, 240 mg of plasticizer (DOA), 2.0 mg of PTCPB and 1.5 mg of
MMT dye. The membrane components were dissolved in 1.5 mL
dried THF in a glass vial. The solution was immediately shaken
vigorously to achieve complete homogeneity. The prepared mixtures contained 33% PVC and 66% plasticizer by weight which is
in accordance with literature [24,25]. The resulting cocktails were
spread onto a 125 ␮m polyester support (Mylar TM type) by knife
coating located in a THF-saturated desiccator. The polymer support
is optically fully transparent, ion impermeable and exhibits good
adhesion to PVC. The ﬁlms were kept in a desiccator in the dark.
This way the photostability of the membrane was ensured and the
damage from the ambient air of the laboratory was avoided. Each
sensor ﬁlm was cut to a size of 13 × 50 mm. The ﬁlm thicknesses of
the sensing slides were measured with the high resolution surface
proﬁler and found to be 4.78 ± 0.024 ␮m for PVC matrices (n = 8).
Absorption and ﬂuorescence emission spectra of PVC membranes were recorded in quartz cells which were ﬁlled with sample
solution. The polymer ﬁlms were placed in diagonal position in the
quartz cell. The advantage of this kind of placement was to improve
the reproducibility of the measurements. All of the experiments
were operated at room temperature, 25 ± 1 ◦ C. The membranes
were not conditioned before use.
2.5. Sample preparation
Sample solutions of tea leave and wild edible mushroom samples were prepared by microwave digestion method. For the
digestion of samples, 0.5 g of each sample was accurately weighed
and transferred into the Teﬂon vessels. Samples were digested with
3 ml of HNO3 and 1 ml of H2 O2 in a microwave digestion system
and diluted to 10 ml with pure water. Digestion program for the
microwave system were applied sequentially as 3 min for 180 W,
5 min for 360 W and 3 min for 180 W. Certiﬁed reference material
and the blank digestions were also carried out in the same way. All
the solutions were stored in tightly capped polythene bottles.
Fig. 2. Excitation and emission spectra of MMT dye in different solvents and PVC.
(a) THF (ex = 380 nm, em = 493 nm), (b) DMF (ex = 379 nm, em = 495 nm), (c) EtOH
(ex = 378 nm, em = 487 nm), (d) PVC (ex = 384 nm, em = 502 nm).
Stokes’ shifts of MMT exhibited an enhancement with respect to the
solution phase. Therefore, when immobilized, the MMT dye could
be excited at longer wavelengths with respect to the solution phase.
This result can be attributed to the restricted vibrational rotational
motions in solid states.
3.2. Fluorescence quantum yield calculations
Fluorescence quantum yield values (ФF ) of the MMT compound
were calculated employing the comparative William’s method
which involves the use of well-characterized standards with known
(ФF ) values [26]. For this purpose, the UV–vis absorbtion and emission spectra of six different concentrations of reference standard
(quinine sulphate in 0.1 M H2 SO4 ) and MMT were recorded. The
integrated ﬂuorescence intensities were plotted versus absorbance
for the reference standard and the dye. The gradients of the plots
are proportional to the quantity of the quantum yield of the
studied molecules. The equations of the plots are y = 1,578,160 x;
R2 = 0.9988 for reference standard, y = 36,341 x; R2 = 0.9954 for
MMT dye in PVC, and y = 17,845 x; R2 = 0.9742 for MMT dye in
EtOH. The data obtained and quantum yield (ФF ) values calculated
according to Eq. (1) are shown in Table 2.
x = ST
3. Results and discussion
3.1. Spectral characterization studies
In order to perform the spectral characterization of the MMT
dye, excitation and emission spectra were recorded in the solvents
of different polarities and PVC ﬁlm (Fig. 2). In all the employed
solvents and PVC ﬁlm the Stokes’ shift values, ST (the difference between excitation and emission maximum), calculated from
the spectral data were quite high and was found to spread in the
wavelength range of 109–118 nm (Table 2). When doped in PVC the
Grad n2 x
x
GradST
n2ST
(1)
where ST and x denote standard and sample, respectively, Grad
is the gradient from the plot and n is the refractive index of the
solvent or polymer matrix material. According to the data obtained,
the MMT dye exhibited higher quantum yield in plasticized PVC
compared to that obtained in the solvents used.
3.3. Fluorescence quenching of optode by Ni2+
To investigate the optical response of MMT embedded PVC ﬁlm
toward Ni2+ , a ﬂuorescence determination was carried out in the
Table 2
The excitation-emission spectra related characteristics of MMT in diluted solutions of THF, DMF, and EtOH and in solid matrices of PVC.
Matrix
Excitation wavelength ex (nm)
Emission wavelength em (nm)
Stokes’ shift ST (nm)
Refractive index n
Quantum yield ФF
THF
DMF
EtOH
PVC
380
379
378
384
493
495
487
502
113
116
109
118
1.4070
1.4305
1.3614
1.5247
0.025
0.016
0.028
0.035
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N. Aksuner et al. / Sensors and Actuators B 166–167 (2012) 269–274
Fig. 3. Fluorescence response of the MMT dye doped PVC ﬁlm to Ni2+ ions at pH 6.0.
(a) Ni-free buffer, (b) 1.0 × 10−9 M, (c) 5.0 × 10−9 M, (d) 2.5 × 10−8 M, (e) 1.3 × 10−7 M,
(f) 6.5 × 10−7 M, (g) 3.3 × 10−6 M, (h) 1.7 × 10−5 M, (i) 8.5 × 10−5 M, (k) 4.3 × 10−4 M,
(m) 2.2 × 10−3 M, (n) 4.4 × 10−3 M (ex = 384 nm).
Ni2+ concentration range from 1.0 × 10−9 to 4.4 × 10−3 M. A signiﬁcant decrease in ﬂuorescence intensity of the optode was observed
upon increasing Ni2+ concentration in this range (Fig. 3). A calibration curve was obtained from the plot of ﬂuorescence intensity
with the added Ni2+ concentration. The curve equation as shown in
the inset of Fig. 3 was y = −0.1023 x + 0.932, R2 = 0.9928. The limit of
detection based on 3 of the blank was 8.5 × 10−10 M. The detection
limit obtained for Ni2+ in the present study was compared with the
reported methods is given in Table 1. It can be seen from Table 1
that the limit of detection obtained in the present method is one of
the lowest for Ni2+ .
Quenching can occur by different mechanisms. In dynamic
quenching, charge transfer occurs and ﬂuorescence is quenched
when the quenher collides with the excited ﬂuorophore. Because
the collision between the quencher and ﬂuorophore affects only
the excited state of the ﬂuorophore, no changes in the absorption
or excitation spectrum are expected. On the contrary, the formation of ground-state complex in static quenching will perturb the
absorption spectra of the ﬂuorophore [27]. Thus, by examination of
the absorption spectrum, static and dynamic quenching can be distinguished. Fig. 4 shows the absorption spectra of the MMT in the
absence and presence of the quencher. By considering the changes
in the absorption spectrum the quenching type is assumed to be
static.
The stoichiometry of Ni2+ –MMT complex was determined by
means of Job’s method (Fig. 5). The ﬂuorescence quenching of MMT
by Ni2+ was attributed to the 1:1 complex formation between
Ni2+ and MMT and its association constant was calculated as
2.24 × 106 M−1 .
Fig. 4. Absorption spectra of MMT (a) in the absence and (b) in the presence of the
quencher; Ni(II).
For a homogeneous membrane phase, the membrane solvent
(plasticizer) must be physically compatible with polymer. The
nature of the plasticizer is also well known to affect the dynamic
concentration range and selectivity behavior of the sensing membrane and facilitate the transport of target ions. In order to study
the nature of the plasticizer, several solvent mediators such as DOP,
DOS, DAO and NPOE were tested. Due to its linear dynamic range
toward Ni(II) ions, which is the longest, and its superior physical
properties, the DAO containing membrane was selected as the optimum composition for preparation of the membranes to be used in
subsequent experiments.
The amount of PTCPB as anionic sites in the membrane is another
parameter that affects the optode response. In the design of the
proposed optical sensor, the optode membrane working range
becomes wider and response time shorter as the amount of PTCPB
in the optode membrane increases from 1 mg to 2 mg. Thus, 2 mg
PTCPB was selected for further studies.
The other parameter of the membrane composition, which has
to be investigated, is the concentration of the ligand. Optimum
response was found when the amount of MMT was 1.5 mg. From
the data shown in Table 3, the membrane number 8 with optimized
PVC:DOA:MMP:PTCPB weight percentage ratio of 33:66:0.4:0.6
was selected for further studies.
3.4. Optimization of membrane composition
The response characteristics of optodes such as dynamic range
and response time depend on membrane composition [25]. Different aspects of the composition of membranes-based on MMT
for Ni2+ ions were optimized, and the results are summarized in
Table 3. In all cases, the membranes were prepared according to
recommended procedures.
Fig. 5. Job’s plot of MMT and Ni(II) in water (pH 6.0). The total concentration of MMT
and Ni(II) was 1.0 × 10−6 M.
N. Aksuner et al. / Sensors and Actuators B 166–167 (2012) 269–274
273
Table 3
Optimization of the membrane composition.
Composition
Response
No.
Plasticizer
MMT (mg)
PTCPB (mg)
Response time (min)
Working concentration range (M)
1
2
3
4
5
6
7
8a
DOP
DOS
DOA
NPOE
DOA
DOA
DOA
DOA
1
1
1
1
0.5
1
1.5
1.5
1
1
1
1
1
1
1
2
3
3
3
4
3
3
3
2
5.0 × 10−7 –5.0 × 10−3
1.0 × 10−7 –1.0 × 10−4
5.0 × 10−8 –4.4 × 10−3
1.0 × 10−6 –1.0 × 10−4
1.0 × 10−7 –1.0 × 10−4
5.0 × 10−8 –1.0 × 10−4
5.0 × 10−8 –4.4 × 10−3
1.0 × 10−9 –4.4 × 10−3
a
Optimum membrane composition.
3.5. Effect of pH
The response characteristics of the optode such as sensitivity,
response range and detection limit depend on pH. The response
curve data were obtained by measuring the ﬂuorescence values for
3.3 × 10−6 M Ni2+ at different pH values and the results are shown
in Fig. 6. From this ﬁgure, we see that the pH of the solution has no
considerable effect on the response of the ﬁlm in pH range 5.0–8.0.
On the other hand, the decreased optical response of the sensor
at pH > 8.0 could be due to the hydroxide formation of nickel ions
as well as a possible slight swelling of the polymeric ﬁlm under
alkaline conditions of solution. Therefore, a pH of 6.0 adjusted by a
0.01 M acetate buffer was considered as optimum and used for Ni2+
determinations.
3.6. Reversibility, reproducibility and short-term stability
The regeneration of the proposed membrane sensor was studied by using different reagents including HCl, HNO3 and EDTA in
different concentrations. The results indicated that a 0.1 M EDTA
solution can efﬁciently remove any adsorbed Ni2+ from the membrane and return its ﬂuorescence to its initial value in about 3 min.
The reproducibility of the optical membrane was evaluated by performing eight determinations with the same standard solution of
nickel ions using a single membrane sensor. The results are shown
in Fig. 7. As can be seen from this ﬁgure, the system is highly
reversible. The relative standard deviation (RSD) for the determination of 3.3 × 10−6 M Ni(II) standard solution was 3.1%.
The short-term stability of the optode membrane was deﬁned
in term of the stability of ﬂuorescence of the optode membrane.
To study the short-term stability of the optode membrane, its ﬂuorescence intensity in contact with a 3.3 × 10−6 M solution of Ni2+
buffered at pH 6.0 was measured over a period of 6 h. From the
ﬂuorescence intensities taken every 30 min (n = 12), it was found
that the response is almost constant with only a 1.6% increase in
Fig. 6. The effect of pH on the sensor response in solutions containing 3.3 × 10−6 M
Ni2+ .
Fig. 7. Reproducibility and reversibility of the response of the optode membrane to
3.3 × 10−6 M Ni2+ and to the regeneration solution, 0.1 M EDTA.
intensity after 6 h monitoring. This indicated a satisﬁed short-term
stability.
3.7. Selectivity
Obviously, the selectivity is one of the most important properties of the response of a sensor. This property represents the
preference of a sensor response to the primary ion with respect
to the potentially interfering ions. For the evaluation of the selectivity of the proposed ﬁlm, the resulting tolerated relative error in
the presence of an interfering ion was deﬁned as, Relative error
(%) = [(F − F0 )/F0 ] × 100, in which F and F0 denote the ﬂuorescence
of the ﬁlm in the presence and absence of the interfering ion,
respectively. The selectivity of the optode was tested for the determination of Ni2+ in the presence of other interfering cations namely
Ag(I), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mg(II), Na(I), Pb(II) and
Zn(II). The concentration of the interfering ion was 100 times as
much the primary ion (Ni2+ , 3.3 × 10−6 M). The results of selectivity studies are summarized in Fig. 8. As can be seen in this ﬁgure,
Fig. 8. Effect of some cations on the optode response to the Ni(II) ion.
274
N. Aksuner et al. / Sensors and Actuators B 166–167 (2012) 269–274
Table 4
Determination of Ni(II) in tea leave and wild edible mushroom samples of three
replicate measurements with the proposed sensor and FAAS.
Sample
Ni2+ (␮g g−1 )
Optode
Tea leave 1
Tea leave 2
Mushroom 1
Mushroom 2
5.20
4.22
5.14
3.75
Relative error (%)
FAAS
±
±
±
±
0.21
0.12
0.15
0.23
5.09
4.17
5.28
3.61
±
±
±
±
0.16
0.15
0.21
0.18
2.16
1.19
−2.65
3.88
in the presence of all the interfering ions studied, the relative error
is less than 5.0%, which is recognized as tolerable.
3.8. Analytical application
To test the practical application of the present sensor, applications for direct determination of Ni(II) in tea leave and wild edible
mushroom samples were carried out. Three parallel analyses were
done for each sample. The samples were prepared as described in
Section 2.5. To check the validity of the proposed method, the concentrations of Ni(II) in the samples were also determined by ﬂame
atomic absorption spectrometry (FAAS). The relative error obtained
with the sensor varied in the range, 1.19–3.88% compared to the
results obtained by FAAS (Table 4).
In order to validate the accuracy of the developed method, certiﬁed reference material (NIST-SRM 1547 Peach leaves) was analyzed
for nickel(II). The measured value (0.67 ± 0.06 ␮g g−1 ) was in good
agreement with the certiﬁed value (0.69 ± 0.09 ␮g g−1 ).
4. Conclusion
The proposed sensor is a precise, low cost, sensitive and highly
selective metod for determination of Ni(II), based on the ﬂuorescent thiazolo-triazol derivative entrapped in PVC matrix. The
sensor produced a linear response for Ni(II) concentration range of
1.0 × 10−9 –4.4 × 10−3 M with the detection limit of 8.5 × 10−10 M.
The optical sensor has a good selectivity toward Ni(II) versus other
metal ions. The sensing membrane also exhibited good photostability and reproducibility. The optode was found to be stable and
reliable for use in real samples. Moreover, a comparison of the
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Biographies
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Nur Aksuner has B.Sc. degree in chemistry, M.Sc. and Ph.D. degree in analytical chemistry from Ege University, Izmir, Turkey. Her current research interests
include ﬂuorescence spectroscopy, photo-characterization of newly synthesized
ﬂuoroionophores, developing optical chemical sensors for metal ions.
Emur Henden has B.Sc. degree in chemistry from Ege University, Izmir, Turkey. He
received his M.Sc. degree and Ph.D. degree in 1976 in chemistry at the University of
Birmingham, UK. He is currently a professor of analytical chemistry at Ege University. His current research interests include the development of atomic spectrometric
methods and optical sensors.
Ibrahim Yilmaz has B.Sc. degree in chemistry from Inonu University, M.Sc. and Ph.D.
degree in chemistry from Fırat University, Elazı˘g Turkey. He works as a professor in
Karamano˘glu Mehmet Bey University. His current research interests include synthesis of new thiazole and thiazole ring containing compounds, and substituted Schiff
base ligands.
Alaaddin Cukurovali has B.Sc. degree in chemistry from Ankara University, M.Sc.
and Ph.D. degree in chemistry from Fırat University, Elazı˘g Turkey. He is currently
a professor of chemistry at Fırat University. His current research interests include
synthesis and design of new heterocycles (thiazole and thiazole ring containing
compounds, cyclobutane derivatives, azomethine and hydrazone compounds).