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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
j o u r n a l h o m e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / s a a
Highly sensitive sensing of zinc(II) by development and characterization of a
PVC-based fluorescent chemical sensor
Nur Aksuner
a,∗, Emur Henden
a, Berrin Yenigul
a, Ibrahim Yilmaz
b, Alaaddin Cukurovali
c aDepartment of Chemistry, Faculty of Science, University of Ege, Ankara Caddesi, 35100 Bornova, ˙Izmir, TurkeybDepartment of Chemistry, Faculty of Science, University of Karamano˘glu Mehmet Bey, 70200 Karaman, Turkey cDepartment of Chemistry, Faculty of Arts and Sciences, University of Fırat, 23169 Elazı˘g, Turkey
a r t i c l e i n f o
Article history: Received 21 May 2010 Received in revised form 16 December 2010 Accepted 19 December 2010 Keywords: PVC matrix Fluorescence spectroscopy Optical sensor Zinc(II)
a b s t r a c t
A sensor membrane with excellent performance based on 1-methyl-1-phenyl-3-[1-hydroxyimino-2-(succinimido)ethyl]cyclobutane has been developed for the determination of zinc(II) ions. The sensing membrane is capable of determining zinc(II) with an outstanding high selectivity over a dynamic range between 8.0× 10−8and 1.6× 10−4mol L−1with a limit of detection of 2.5× 10−8mol L−1(1.6g L−1). It can
be easily and completely regenerated by using 0.1 mol L−1EDTA solution. The optical sensor developed
here was found to be stable, cost effective, easy to prepare, and has unique selectivity towards Zn2+ion
with respect to common metal ions. The proposed sensor was then applied for the determination of zinc in tap water and hair samples with satisfactory results.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Zinc is an essential trace element of great importance for humans, plants and animals. It plays an important role in sev-eral biochemical processes[1]. It exerts a crucial influence on the maintenance of cell membrane stability and in the function of immune system[2]. This ion is involved in pathological processes, such as Alzheimer’s disease, epilepsy, ischemic stroke, and infan-tile diarrhea[3,4]. It also constitutes an active ingredient in medical products intended for topical application. Zinc salts are used in oph-thalmic solutions, in lotions intended for treatment of chronic skin diseases and incorporated as astringents in various solutions[5]. Zinc deficiency effects may be severe. They range from impaired neuropsychological functions and wound healing to growth retar-dation, immune disorders and dermatitis. On the other hand, zinc can be toxic when exposures exceed physiological needs. After sin-gle or short term exposure to concentrations of zinc in water and beverages between 1.0 and 2.5 mg L−1, poisoning incidents with symptoms of gastrointestinal distress, nausea and diarrhea were reported[6]. Zinc occurs in hair at relatively high levels of about 100–300 mg kg−1 and its determination can be useful for clinical and forensic purposes[7]. Because of the importance of zinc, sim-ple, sensitive and rapid analytical methods for the determination of trace levels of zinc are in great demand. Flame atomic absorption
∗ Corresponding author. Tel.: +90 232 388 82 64; fax: +90 232 388 82 64. E-mail address:[email protected](N. Aksuner).
spectrometry[8], graphite furnace atomic absorption spectrom-etry[9], inductively coupled plasma emission spectrometry[10], inductively coupled plasma-mass spectrometry[11], spectropho-tometry [12] and voltammetry [13] are widely applied to the determination of zinc at trace level. Although these methods are highly sensitive, the spectroscopic methods require expensive and technically demanding equipment. Chemical sensors, especially optical sensors, are elegant alternatives to the traditional analytical instruments. They have the advantages of size, cost-effectiveness, simplicity, no necessity of the reference solution, and fieldwork applicability[14–16].
A variety of zinc ion selective fluorescent sensors that are based on zinquin[17] fluorescein[18], coumarin[19], and indole[20] have been developed. Other works on the development of the optical sensors for zinc ion sensing have been reported recently [21–23]. Crivat et al.[24]described the characterization of analyt-ical properties of fluorescence based zinc ion sensing glass slides and their application in monitoring zinc ion release from pancre-atic cells. Shiraishi’s group has synthesized a quinoline–polyamine conjugate as a fluorescent chemosensor for quantitative detection of Zn2+in water[25]. Jeronimo et al.[26]reported the development
of a sol–gel optical sensor for zinc analysis based on incorporated 4-(2-pyridylazo)resorcinol (PAR). An optical sensor membrane for the detection of Zn2+was offered by Rastergarzadeh and Rezaei
[27]. The sensing membrane was made by immobilizing zincon as an ion pair with methyltrioctylammonium ion on triacetylcel-lulose membrane. Li et al.[28] have designed a new porphyrin derivative containing 2-(oxymethyl)pyridine units, which shows 1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
Table 1
Some reported optical sensors for the determination of Zn2+.
Reagent Working range (mol L−1) Limit of detection
(mol L−1)
Measured signal Reference
N,N -di(quinoline-2-methylene)-1,2-phenylenediimine NRato 2.0× 10−5 NRa Fluorescence [21] 7-Nitrobenz-2-oxa-1,3-diazole NRato 3.0× 10−5 NRa Fluorescence [23] PAR 7.6× 10−8–3.8× 10−7 3.1× 10−8 Absorbance [26] Zincon 7.6× 10−7–3.1× 10−5 1.6× 10−7 Absorbance [27]
Porphyrin derivative 3.2× 10−7–1.8× 10−4 5.5× 10−8 Fluorescence [28]
Benzoxazole derivative 8.0× 10−5–4.0× 10−3 4.0× 10−5 Fluorescence [29]
Bis(pyrrol-2-yl-methyleneamine NRato 9.6× 10−6 NRa Fluorescence [30]
8-Pyridylmethyloxy-2-methyl-quinoline
7.5× 10−8–2.5× 10−5 1.5× 10−8 Fluorescence [31]
Schiff base 5.0× 10−7–1.0× 10−4 2.2× 10−7 Fluorescence [35]
MCB 8.0× 10−8–1.6× 10−4 2.5× 10−8 Fluorescence Present work
aNR: not reported.
ratiometric change of fluorescence intensity in the presence of Zn2+.
Ma et al.[29]also developed a ratiometric fluorescent sensor for zinc ion based on covalently immobilized derivative of benzox-azole. The sensor showed a linear response towards Zn2+in the
concentration range from 8.0× 10−5mol L−1to 4.0× 10−3mol L−1
and the detection limit is 4.0× 10−5mol L−1. A fluorescent sensor
for zinc ion based on bis(pyrrol-2-yl-methyleneamine) ligands was offered by Wu et al.[30]. Jiang and co-workers recently reported a highly sensitive fluorescent sensor of zinc. The sensor can be applied to the quantification of Zn2+with a linear range covering
from 7.5× 10−8mol L−1to 2.5× 10−5mol L−1[31]. The summarized
data inTable 1shows the reagents, working ranges and/or limits of detection (LOD) of zinc sensors.
For some practical applications the attachment of the fluores-cent units to a solid support has advantages like the possibility of recovering the materials for their repetitive use. Various polymeric membranes have been used as supporting matrices for the prepa-ration of optical chemical sensors in literature. Polyvinyl chloride (PVC) is optically transparent, and has good mechanical proper-ties, homogeneity and preparation simplicity. PVC has a very high molecular weight (>100,000) and forms a cage-like structure for holding reagent within it[32]. Up to now, there are several reports on application of PVC membrane as a sensing material. Our group has recently been involved in the study of optical sensor based on Schiff base ligands embedded in PVC[33–35].
In this work we introduce a novel fluorescent sensor, based on a recently synthesized succinimid and cyclobutane containing oxime derivative, for sensitive determination of trace amounts of zinc in real samples. The method developed requires no pretreatment such as concentrating and extraction process. 1-Methyl-1-phenyl-3-[1-hydroxyimino-2-(succinimido)ethyl]cyclobutane (MCB) dye has been used for the first time as sensing agent in optical sensor design.
2. Experimental
2.1. Reagents
The polymer membrane components, polyvinylchloride (PVC) (high molecular weight) and the plasticizers, bis-(2-ethylhexyl) phtalate (DOP), bis(2-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), chloroform (CHCl3), acetonitrile (ACN),
ethylenediaminete-traacetic acid (EDTA), acetone, nitric acid and hydrogen peroxide were purchased from Merck. Ethyl cellulose (EC) (with an ethoxy content of 46%) was from Aldrich. All chemicals were of analytical
reagent grade and used as received without further purification. All solutions were prepared with glass-distilled water. Sheets of Mylar-type polyester (Dupont, Switzerland) were used as support. A stock standard solution containing 1.50× 10−2mol L−1 Zn2+
was prepared by dissolving 100.0 mg of metallic zinc in 2.0 mL con-centrated hydrochloric acid and then by diluting to 100.0 mL with distilled water.
The synthesis of MCB dye has been performed in our laboratories [36]. The structure of the employed dye molecule is shown inFig. 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), zinc hollow cathode lamp and deuterium background correction was also used for zinc measurements. Measurement of pH was performed using a WTW 82362 Weliheim pH 330i pH-meter cal-ibrated with Merck pH standards of pH 4.00, 7.00 and 10.00. The film thicknesses of the sensing slides were measured with Ambios Technology XP-1 HGH Resolution Surface Profiler.
2.3. Synthesis of the 1-methyl-1-phenyl-3-[1-hydroxyimino-2-(succinimido)ethyl]cyclobutane
(MCB)
The synthesis and characterization of oxime derivative has been published earlier[36]. Synthesis procedure of 1-methyl-1-phenyl-3-[1-hydroxyimino-2-(succinimido)ethyl]cyclobutane (MCB) is as follows.
A mixture of
1-phenyl-1-methyl-3-(2-succinimidoacetyl)cyclobutane (2.853 g, 0.01 mol), hydroxylamine hydrochloride (0.695 g, 0.01 mol) and pyridine (5 ml) in ethanol (100 ml) was refluxed for 3 h. The solvent was removed by dis-tillation and the resulting solid was filtered off, washed with cold water, dried and recrystallized from ethanol to obtain the
Fig. 1. Structure of 1-methyl-1-phenyl-3-[1-hydroxyimino-2-(succinimido)-ethyl]cyclobutane (MCB) dye.
title compound (yield 2.8 g, 85%; m.p. 426 K). Elemental analysis calculated for C17H20N2O3: C 67.98, H 6.71, N 9.33%; found: C
68.02, H 6.84, N 9.45%. IR spectroscopy (KBr pellet, , cm−1):
1620 (C N), 3253 (–OH oxime).1H NMR (CDCl
3, p.p.m.): 7.10–7.30
(m, 5H, aromatic), 4.4 (s, 2H, CH2 cyclobutane), 3.5 (quint, 1H,
J = 8.9 Hz, CH cyclobutane), 1.74–2.75 (m, 8H, CH2cyclobutane plus
succinimide), 1.49 (s, 3H, CH3).
2.4. Preparation of polymer film
The membrane cocktail was prepared using a mixture of 120 mg of PVC, 240 mg of plasticizer (DOS), 2.0 mg of PTCPB and 1.5 mg of MCB 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 mix-tures contained 33% PVC and 66% plasticizer by weight which is in accordance with literature[37,38]. The resulting cocktails were spread onto a polyester support (Mylar TM type) by knife coating and 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 dam-age from the ambient air of the laboratory was avoided. Each sensor film was cut to a size of 13 mm× 50 mm. The film thicknesses of the sensing slides were measured and found to be 5.12± 0.098 m for PVC matrices (n = 8).
Absorption and fluorescence emission spectra of PVC mem-branes 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. Preparation of hair samples
Approximately 0.5 g of hair sample was cut with stainless steel scissors from the nape of the neck in the scalp region. Hair wash-ing prior to analysis is required to provide an accurate assessment of endogenous metal content. The washing procedure carried out in this work was the proposed one by the International Atomic Energy Agency[39], using ultrapure water and acetone as wash-ing solvents. The hair samples were decomposed uswash-ing classic acid digestion method. For this purpose, 0.3 g of washed hair sample was accurately weighed into a 100 mL beaker. Then 5 mL of con-centrated HNO3and 2.5 mL of 30% (v/v) H2O2were added and the
mixture was heated on a hot plate for 1 h at 150◦C for complete digestion of the sample. The digest was brought to near dryness, the residue was dissolved in water and made up to 25 mL.
3. Results and discussion
3.1. Spectral characterization studies in solution phase
The photophysical characteristics of MCB dye in organic sol-vent with different polarity have been investigated. The oxime derivative exhibited good solubility in common organic solvents. Absorption, excitation, and emission spectra were recorded in sep-arate solutions of ACN, EtOH, CHCl3, and THF. The emission spectra
were recorded by exciting the MCB dye at 430, 434, 420, and 438 nm, respectively in these solvents. In order to obtain the exci-tation spectra in these solvents, the emissions were measured at 520, 530, 515, and 522 nm, respectively, while changing the exci-tation wavelength in the range of 380–600 nm (Fig. 2). The Stokes shift values,ST(the difference between excitation and emission
Fig. 2. Excitation and emission spectra of MCB dye in different solvents. (a)
ACN (ex= 430 nm,em= 520 nm), (b) EtOH (ex= 434 nm,em= 530 nm), (c) CHCl3 (ex= 420 nm,em= 515 nm) and (d) THF (ex= 428 nm,em= 522 nm).
Table 2
Emission and excitation spectra related data of MCB. Solvent Excitation wavelength ex(nm) Emission wavelength em(nm) Stokes shift ST Refractive index n Quantum yieldФF Acetone 430 520 90 1.36 EtOH 434 530 96 1.36 0.0035 CHCl3 420 515 95 1.44 THF 428 522 94 1.41 PVC 423 520 97 1.52 0.043 EC 430 515 85 1.48 0.029
maximum) and quantum yields were extracted from spectral data which are given inTable 2.
3.2. Spectral characterization studies in solid phase
For spectral characterization of the PVC and EC doped with MCB, excitation and emission spectra of films were recorded. MCB was excited at 430 and 452 nm in EC and PVC, respectively (Fig. 3). In comparison to EC, the MCB dye exhibited higher fluorescence inten-sity and quantum yield in PVC matrix. In the ensuing experiments, PVC was selected as matrix material for further studies.
Fig. 3. Excitation and emission spectra of MCB dye in solid polymer matrix. (a) EC
Fig. 4. The fluorescence emission spectra of the sensing membrane in the presence
of different concentration of Zn2+(1) blank solution; (2) 8.0× 10−8, (3) 1.6× 10−7, (4) 3.2× 10−7, (5) 6.4× 10−7, (6) 1.3× 10−6, (7) 2.6× 10−6, (8) 5.2× 10−6, (9) 1.0× 10−5, (10) 2.0× 10−5, (11) 4.0× 10−5, (12) 8.0× 10−5 and (13) 1.6× 10−4mol L−1Zn2+ (ex= 420 nm).
3.3. Fluorescence quantum yield calculations
The fluorescence quantum yield of MCB in EtOH, EC and PVC matrix was calculated by William’s method [40]. For this pur-pose, the UV–vis absorption and emission spectra of five different concentrations of reference standard (quinine sulphate in 0.1 M H2SO4) were recorded by exciting at 423 nm and 430 nm. By the
similar way, the UV–vis absorption and emission spectra of five different concentrations of MCB dye were recorded. The integrated fluorescence intensities were plotted versus absorbance for the ref-erence standard and the dye. The ratio of gradients of the plots is important and is proportional to the quantum yield. The equations of the plots are y = 2176980x; R2= 0.9978 for reference standard,
y = 91715x; R2= 0.9915 for MCB dye in PVC, y = 88612x; R2= 0.9924
for MCB dye in EC matrix, and y = 84468x; R2= 0.9947 for MCB dye in
EtOH. x= ST
Grad x GradSTn2 x n2 ST (1) Quantum yield (
ФF
) values calculated according to Eq.(1)are shown inTable 2. Where ST and x denote standard and sample, respectively, Grad is the gradient from the plot and n is the refrac-tive index of the solvent or polymer matrix material. The PVC doped dye displayed 12 times enhancement in quantum yield (0.043) compared to the one in EtOH (0.0035).3.4. Fluorescence quenching of sensor membrane by Zn2+
Preliminary experiments showed that MCB immobilized into PVC membrane has the necessary conditions of a suitable ligand for detection of Zn2+. In the presence of zinc ion, a relatively strong
complex is formed between Zn2+and MCB with a corresponding
decrease in the fluorescence intensity.
Fig. 4shows the fluorescence spectra of MCB based optode membrane exposed to solutions containing different concentra-tions of Zn2+, which have been recorded at
ex= 420 nm and
em= 465–600 nm. The fluorescence intensity was decreased with
the increasing Zn2+concentration, meanwhile the spectral shape
kept unchanged.
A characteristic calibration curve obtained for different concen-trations of Zn2+by plotting log(I
0− I)/I0 vs log[Zn2+] is shown in
Fig. 5. Calibration curve of the sensing membrane for determination of Zn2+.
Table 3
Effect of different type of plasticizer on the response of the sensor for determination of Zn2+.
Plasticizer Working concentration range (mol L−1)
Response time (min) (2.6× 10−6mol L−1Zn2+)
DOS 8.0× 10−8–1.6× 10−4 2
DOP 3.0× 10−7–2.0× 10−4 3
DOA 2.6× 10−6–1.0× 10−5 3
NPOE 6.4× 10−7–2.0× 10−5 5
Fig. 5. In the concentration range of 8.0× 10−8–1.6× 10−4mol L−1
a quite good linear correlation was obtained with R2value of 0.9982
for Zn2+.
3.5. Effect of membrane composition
The response characteristics of the sensor such as its sensitiv-ity, selectivity and its dynamic range depend on the membrane composition. A comparative study on the effect of different plasti-cizers and matrix materials on the performance of sensor has been made. Several optode membranes were prepared using different plasticizers such as DOP, DOS, DAO, NPOE, and the fluorescence measurements were made for different concentrations of Zn2+. The
results are shown inTable 3. The widest working concentration range was obtained with DOS; therefore, this plasticizer was used in the following studies.
Lipophilic borate salts are frequently used as anionic additives in potentiometric and optical cation-selective sensors based on solvent polymeric membranes[41]. The amount of anionic sites in the membranes has effects on the linear range and selectivity of optodes[42]. The composition of the optode membrane with respect to PTCPB was optimized by preparing several membranes with different amounts of PTCPB. The response behavior of these optode membranes are shown inTable 4. From the results one can see that the response concentration range of the optode membrane becomes wider and response time shorter as the amount of PTCPB in the optode membrane increases from 1% to 2%, which might be caused by the increasing hydrophilicity owing to the addition of PTCPB. However, the response concentration range of the optode
Table 4
Effect of PTCPB on the response behavior of the optodes. Content of
PTCPB (%)
Working concentration range (mol L−1)
Response time (min) (2.6× 10−6mol L−1Zn2+)
1 1.3× 10−6–2.0× 10−5 4
2 8.0× 10−8–1.6× 10−4 2
Fig. 6. Effect of pH on the determination of Zn2+with proposed optode (the
con-centration of Zn2+was fixed at 2.6× 10−6mol L−1; error bars were calculated with
n = 5).
membrane becomes narrower when the content of PTCPB is larger than 2%. Therefore, 2% PTCPB provided the best response for Zn2+ and was chosen for further studies.
In addition to the optimization of the type of plasticizer and amount of PTCPB, it is also necessary to optimize the amount of lig-and in the membrane. The effects of MCB concentration was studied in the range 0.5–2.0 wt.%. Optimum response was found when the concentration of MCB was 1.5 wt.%.
3.6. Effect of pH
The fluorescence intensity versus pH plot for the optode mem-brane shown in Fig. 6 was obtained by adjusting the solution pH with phosphate buffer and fixing the Zn2+ concentration at
2.6× 10−6mol L−1. As it is seen fromFig. 6, in the section of lower
pH value, the fluorescence intensity of the optode decreased with decreasing pH value. This occurrence might be caused by the pro-tonation of MCB. On the other hand, the increased optical response of the proposed sensor at pH >8.0 could be due to a possible slight swelling of the polymeric membrane under alkaline conditions and the partial precipitation of Zn(II) as Zn(OH)2. It can be seen that,
in a range of pH from 5.0 to 8.0, pH change does not affect the determination of Zn2+with the proposed optode. This result
sim-plifies the practical application of the sensor in the determination of Hg2+concentration in real samples. Therefore, pH 6.0 sodium
acetate/acetic acid (0.1 mol L−1) buffer solution was selected as an ideal experimental condition.
3.7. Reversibility and reproducibility
The reversibility and reproducibility are two important char-acteristics in evaluating the suitability of an optical sensor for selective determination of the ion of interest. Regeneration experiments were carried out in 0.1 mol L−1 EDTA solution and approximately 100% regeneration performance was succeeded. The sensor was fully reversible within the dynamic working range and the approximate response time90was 2 min. The reproducibility
of the optical responses was assessed by repeatedly introducing a sample of 2.6× 10−6mol L−1Zn2+at pH 6.0 and a 0.1 mol L−1EDTA
solution (seeFig. 7). Between the first and eighth cycles, the level of reproducibility of the upper signal level achieved was quite good with a low standard deviation, 110.48± 2.17. One sensor film could be used for about 20 repetitive cycles and when kept in a THF satu-rated desiccator in dark the same sensor film was found to be stable for six months.
The limit of detection (LOD) of Zn2+, defined as the
concentra-tion equivalent to a signal of blank plus three times the standard deviation of the blank, was calculated to be 2.5× 10−8mol L−1
Fig. 7. Successive responses of the MCB membrane to 2.6× 10−6mol L−1Zn2+at pH = 6.0 (Reg = regeneration).
(1.6g L−1). This value is lower than that of the zinc ion sensors
reported in the literature[26–29]and about nine times lower than we have reported earlier using a Schiff base[35].
3.8. Selectivity
Under optimum conditions, the effects of various foreign ions on the determination of zinc were examined. The experiments were carried out by fixing the concentration of Zn2+at 2.6× 10−6mol L−1
at pH 6.0. The fluorescence intensities before and after adding the interference ions into the Zn2+ions solution were recorded.
Toler-ance limit was taken as the concentration causing an error of±5% in the determination of zinc. The results are shown inTable 5. The results confirmed that the optode membrane exhibited excellent selectivity towards Zn2+with respect to the other coexisting
inter-ference ions. Thus, the proposed procedure can be applied to the determination of zinc in real samples without any prior separations. 3.9. Analytical applications
In order to investigate the potential use of the developed optical sensor for the determination of Zn2+, it was applied to actual
sam-ples of hair and tap water. Tap water samsam-ples were used without a previous treatment, and known amounts of Zn2+were spiked with
standard stock solution and determined by the proposed optical membrane. Results are shown inTable 6. One can see that recovery
Table 5
Effect of different metal ions on the optode response to the zinc(II) ion. Interferent Concentration (mol L−1)a Relative error %
(Fb/F 0c× 100) Na+ 1.0× 10−2 2.2 K+ 1.0× 10−2 2.4 Ca2+ 1.0× 10−2 −1.9 Mg2+ 1.0× 10−2 2.9 Ag+ 1.0× 10−2 −2.5 Al3+ 1.0× 10−2 3.2 Co2+ 1.0× 10−2 5.8 Co2+ 1.0× 10−3 1.9 Ni2+ 1.0× 10−2 6.7 Ni2+ 1.0× 10−4 1.7 Cu2+ 1.0× 10−2 2.9 Cd2+ 1.0× 10−2 2.6 Pb2+ 1.0× 10−2 2.7 Fe3+ 1.0× 10−2 2.5 Cr3+ 1.0× 10−2 3.4 Hg2+ 1.0× 10−2 2.8
aThe concentration of Zn2+is fixed at 2.6× 10−6mol L−1.
bF is the difference of fluorescence intensities before and after exposure to interferent ions.
cF
Table 6
Determination of Zn2+in tap water samples with the proposed sensor (n = 3).
Sample Zn2+spiked
(mol L−1)
Zn2+found (mol L−1) Recovery (%)
Tap water 1 – Not detected –
1.0× 10−5 (1.06± 0.42) × 10−5 106.0
1.0× 10−4 (1.02± 0.39) × 10−4 102.0
Tap water 2 – Not detected
1.0× 10−5 (0.95± 0.18) × 10−5 95.0
1.0× 10−4 (0.97± 0.52) × 10−4 97.0
Table 7
Determination of zinc concentration in hair samples (n = 3). Hair
sample
Amount of zinc (g kg−1) Relative error(%)
Optode FAAS
1 174.8± 0.9 170.5± 0.8 2.52
2 120.4± 1.4 118.4± 1.5 1.69
3 134.7± 1.8 132.4± 1.2 1.74
4 98.4± 1.9 100.7± 1.7 −2.28
study of spiked Zn2+determined by proposed optical sensor shows satisfactory results.
The hair samples were prepared as described in Section2. The sensing membrane was also applied to hair samples and the results were compared to those given by the atomic absorption spectrom-etry reference method. FromTable 7one can see that the content of zinc ions in hair samples as determined by the optical sensor was in good agreement with that obtained by atomic absorption spectrometry with a relative error of less than 5%. Therefore, the present sensor can be well used for the determination of zinc in real samples.
4. Conclusion
This study has shown that the optical sensor based on immo-bilized recently synthesized oxime derivative is rapid, simple and sensitive for the quantitative determination of zinc(II). The oxime derivative was used for the first time as a fluoroionophore in the optical sensor design. The membrane is easily prepared and is fully reversible, as it can be easily regenerated with 0.1 mol L−1 EDTA solution. The sensor shows a high selectivity and quick response for Zn2+ over other common metal ions. The
experi-mental procedures developed in the present work have enabled the determination of zinc(II) in solution over a wide concentra-tion range (8.0× 10−8–1.6× 10−4mol L−1). The low detection limit
(2.5× 10−8mol L−1) for zinc determination is suitable in the
anal-ysis for most real samples.
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![Fig. 1. Structure of 1-methyl-1-phenyl-3-[1-hydroxyimino-2-(succinimido)- 1-methyl-1-phenyl-3-[1-hydroxyimino-2-(succinimido)-ethyl]cyclobutane (MCB) dye.](https://thumb-eu.123doks.com/thumbv2/9libnet/4546474.82461/2.892.518.759.965.1077/structure-methyl-phenyl-hydroxyimino-succinimido-hydroxyimino-succinimido-cyclobutane.webp)
