Accepted Manuscript

Title: Poly(luminol) based sensor array for determination ofdissolved chlorine in water

Author: <ce:author id="aut0005" biographyid="vt0005">Monika Szili<ce:author id="aut0010" biographyid="vt0010">Ivan Kasik<ce:author id="aut0015" biographyid="vt0015">Vlastimil Matejec<ce:author id="aut0020"biographyid="vt0020"> Geza Nagy<ce:author id="aut0025"biographyid="vt0025"> Barna Kovacs

PII: S0925-4005(13)01266-5DOI: http://dx.doi.org/doi:10.1016/j.snb.2013.10.080Reference: SNB 16115

To appear in: Sensors and Actuators B

Received date: 1-5-2013Revised date: 30-9-2013Accepted date: 20-10-2013

Please cite this article as: M. Szili, I. Kasik, V. Matejec, G. Nagy,B. Kovacs, Poly(luminol) based sensor array for determination ofdissolved chlorine in water, Sensors and Actuators B: Chemical (2013),http://dx.doi.org/10.1016/j.snb.2013.10.080

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Poly(luminol) based sensor array for determination of dissolved

chlorine in water

Monika Szili1*, Ivan Kasik2, Vlastimil Matejec2, Geza Nagy1,2, Barna Kovacs1,2*

1Department of General and Physical Chemistry, University of Pécs, Ifjúság 6, H-7624 Pécs,

Hungary

2Institute of Photonics and Electronics ASCR, v.v.i., Chaberska 57, 182 51 Prague 8, Czech

Republic

3Szentágothai János Research Center, University of Pécs, Ifjúság 20, H-7624 Pécs, Hungary

*Corresponding authors: Monika Szili

Barna Kovacs

Department of General and Physical Chemistry, University of Pecs, Ifjusag 6, H-7624

Pecs, Hungary

Email: szilim@gamma.ttk.pte.hu

kovacs1@gamma.ttk.pte.hu

Tel: +36 72 503 600 / 4680

Fax: +36 72 503 635

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Abstract

An optical sensor for determination of free chlorine content of drinking water was

prepared and tested. The function of the sensor is based on detecting

chemiluminescence signal provided by thin immobilized poly(luminol) reagent layer.

The poly(luminol) reagent film was prepared by electropolymerization of luminol onto

planar indium-tin-oxide (ITO) electrode. Different methods, like electrode potential

cyclization (cyclic voltammetry, CV), pulsed potential electrolysis (pulsed

amperometry, PA) and potentiostatic electrolysis (constant potential electrolysis, PSE)

were employed for preparation of the poly(luminol) layer. The chemoluminescence

(chemiluminescence) of the differently prepared films was investigated in the

poly(luminol) – hypochlorite - hydrogen peroxide reaction. Highest luminescence

signal was obtained by the films prepared with CV. Poly(luminol) layers deposited

with pulsed potential showed 80% less luminescence while almost no signal was

obtained in case of films made with constant potential technique. The effects of the

buffer composition and pH on the analytical properties of the electro polymerized

sensing layer were investigated. The lower concentration limit of free chlorine detection

was 5·10-7M in phosphate buffer at pH = 8.0. It was found that the chemiluminescence

signal decreased significantly when hypochlorite concentrations over 1 mM were

applied. An array of 24 micro wells was fabricated on ITO glass slab of about

microscope slide size. The individual micro wells had identical volume and the

poly(luminol) layer immobilized on their bottom had identical activity. The wells could

be used for “single shot” determination of free chlorine content of drinking water. The

long storage stability, the simple measurement procedure and low feasible

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concentration range makes the array an attractive analytical tool. Its applicability was

proved measuring dissolved chlorine concentration of tap water samples.

Keywords:

luminol, poly(luminol), electropolymerization, chemiluminescence, dissolved chlorine

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1. Introduction

Chlorine gas or hypochlorite ionic species are used in broad scale in water treatment as

disinfectant. The amount of disinfectant needed to be added depends on the level of

bacterial contamination. High excess of active chlorine in tap water is a health hazard, it

must be avoided. Therefore monitoring of the dissolved chlorine content of drinking

water is an important analytical task. The ratios of hypochlorous acid / hypochlorite /

dissolved chlorine depend on the pH and temperature of the sample. Therefore the

content of this disinfectant is given as free chlorine concentration. Its value must be in

concentration range of 1-10 μM [1] for drinking water. High number of different

instrumental methods has been worked out for determination of active chlorine

concentration of water samples. Among them several are based on chemiluminescence

generating reactions. Different chemiluminescent indicators, such as fluorescein

disodium salt [2], rhodamine 6G [3] or the well-known luminol (3-

aminophtalhydrazide) [4-6] have been used in these methods. Lophine (2,4,5-triphenyl-

1H-imidazole) [7] and hydrogen peroxide [8] are frequently applied as reagents in the

chemiluminescence based analytical procedures. An excellent review [9] has been

published about literature dealing with application of hypohalites and related oxidants

as chemiluminescence reagents.

Several reports appeared about electrochemical ways of polymerization of luminol [10-

12]. Usually poly(luminol) is electrodeposited from the acidic solution of the monomer

as thin layer on the surface of different electrodes. Gold, Glassy carbon, platinum

[10,11,26], transparent indium-tin oxide (ITO) [12] or screen printed [25] electrode

surfaces have been successfully coated with the polymer. Poly(luminol) is a conductive

polymer. It gained already application in electrochemical sensors [11,13], in electro-

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optical sensors as well as in biosensors [10,12,14, 22]. To enhance the sensing

properties of the electrodeposited layers co-polymerization of luminol with aniline have

been reported [23,24] recently. Interestingly nanowire structured polymer formation

could be observed on graphite surfaces [27], when galvanostatic or constant potential

oxidation of both luminol and aniline in different solution, were performed.

In our previous work electropolymerized thin transducer layers were prepared from o-

phenylendiamine and of methyleneblue on ITO coated planar glass substrates [15, 16].

These could be well applied as optrode sensors in free chlorine measurements. In the

presence of chlorine the sensing membranes changed absorbance characters, and the

color change was measured in attenuated total internal reflection (ATIR) mode by a

fiber optic photometer. The detection limit for dissolved chlorine of these optode based

method was about 4 μM. It was an important advantage that the electropolymerized

optrode film could be regenerated after measurements.

In this work we describe a poly(luminol) based free chlorine measuring array sensor

prepared on ITO coated glass slab. In earlier published works the determination was

based on electrogenerated chemiluminescence (ECL) [10-14] signal. In our recent

work however, the signal is generated by chemical interaction between hypochlorite

form of the analyte and the poly(luminol) layer. In this paper we are reporting the

results obtained recently with this chemoluminescence version. It has been reported

[4,5,9] that hydrogen peroxide enhances the sensitivity of similar measuring methods,

therefore we also employed it. The optimal conditions of the hypochlorite

determination, such as layer preparation, buffer pH and composition, were investigated.

An array of 24 micro wells was fabricated on microscope slide size ITO glass slab. The

individual microwells of identical volume of the array contained immobilized

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poly(luminol) reagent of identical activity. The wells could be used for “single shot”

determination of free chlorine content of drinking water.

2. Experimental

2.1. Chemicals

Luminol (3-aminophtalhydrazide), tris (hydroxymethyl)amine hydrochloride and

phosphoric acid used for the experiments were purchased from Fluka (Buchs,

Switzerland). Ethylenediamine-tetraacetate disodium salt, iron(II)sulfate, sodium

chloride were obtained from Reanal (Budapest, Hungary). The other chemicals used for

preparing the buffer solutions were Riedel de Haen products. All the chemicals were

analytical grade and used as received. Sodium hypochlorite stock solution was prepared

by dissolving NaOCl in phosphate buffer (pH=8). Iodometric titration [17] was used for

determination of its free chlorine content. The calibrating standards were made freshly

diluting the stock solution. Indium-tin-oxide (ITO) glass plates having a resistivity less

than 10 Ohm·cm-2 was obtained from Prazisions Glass Optik (Iserlohn, Germany).

They were cut to 76x26 mm2 pieces (common microscope slide size).

Solutions were prepared with deionized water; its specific conductivity was less than

0.8 μS cm-1. The pH of the buffer solutions was adjusted by using a WTW 325 digital

pH meter calibrated with buffers pH = 4.00 and pH = 10.00. 1.0 mM luminol stock

solution was prepared by dissolving luminol in 0.1 M sulfuric acid. The

electrochemically active area of the ITO electrodes were measured by recording

voltammograms in a phosphate buffer solution (pH=7.00) containing 5 mM Fe(II)

sulfate and 5 mM Na2-EDTA.

2.2. Instrumentation

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An Autolab PGSTAT 10 (Eco Chemie, The Netherlands) potentiostat and a PalmSens

(Palm Instruments, The Netherlands) portable potentiostat were used for electro

polymerization with three electrode arrangements. The software of the Autolab was

used to measure the electric charge consumed in polymer deposition steps, as well as in

studying the electro activity character of the poly(luminol) films by recording CV-s in

monomer free sulfuric acid solution.

Exerimental arengements used in chemiluminescence measurements is shown in Fig.1.

A stand of an old microscope was used for holding and positioning the sensor (A) and

the optics. All of these were placed into a dark box. A 5x5x10 mm prism (D) was fixed

below the movable sample holding stage. The window of the photomultiplier tube

(PMT), (E) optimized for phosphorescence and chemiluminescence measurements

(Hamamatsu, H5783P), was positioned to face the lower end of the prism. A

mechanical shutter (not shown in figure 1.) was inserted between the prism and the

multiplier to protect the sensitive PMT from the ambient light in open box conditions.

The PMT was connected through an IUC 01-01 preamplifier (Pannonlaser, Hungary)

(F) to a DAQPad 1200 data acquisition board (National Instruments, USA) to collect

the data. The data acquisition software was written in Visual Basic 6 in our laboratory.

2.3. Layer preparation

The microscope slide sized ITO slabs were washed three times with distilled water, the

organic residual were removed from their surface with acetone. After drying on air they

were washed again with water, dried and kept dry until use. Before

electropolymerization the ITO slabs were electrochemically pretreated in 0.1M sulfuric

acid by running 3 cycles with 100 mV/s scan rate in the potential range of -500 to

+1100 mV versus SCE. After the pretreatment the ITO was ready for the electro

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polymerization process. For these 50 mL of 1 mM luminol solution in 0.1 M sulfuric

acid was introduced into an electrochemical cell. The electro polymerization was

carried out by using common three electrode arrangement. The electrochemical

deposition of PL with the three methods and the determination of the residual

electrochemically active surfaces have been performed on 26x10 mm slides. A silver

wire was glued by silver-epoxy to one of the shorter side and the slab was partly

covered by silicon rubber (Wacker E4). A square of 10x10 mm ITO surface was left

free of coating. In those cases 1x1 cm Pt counter electrode has been applied during the

electro deposition. Also the corresponding CL measurements have been made on those

supports. The electro chemical cell setup was similar to that used previously [15, 16].

Microscope slide sized (76x26 mm) PL coated ITO glass slabs have been used for the

tests and demonstration of the analytical performances of the poly(luminol) layers.

They were prepared separately, while a large Pt mesh served as counter electrode.

Because of the relatively low conductivity of the electrode material a silver wire was

fixed by silver-epoxy glue along the 76 mm side of the ITO coated glass slab, and

connected to the working electrode port of the potentiostat. The ITO working electrode,

the saturated calomel (SCE) reference electrode and a platinum counter electrode were

fixed into the cell. There is no evidence that the presence of oxygen affects the layer

deposition, however the solution was degassed in an ultrasonic bath and then purged

with argon for 10 minutes before measurements to remove the oxygen.

Different electrode potential – time programs were used for electro polymerization.

In CV technique the potential was cycled from -0.2 to +0.9 V with a 100mV/s scan rate.

Constant potential (PSE) (+0.9 V) as well as pulsed potential (PA) deposition were also

used. In case of pulsed potential deposition the potential was set to -0.2 V for 0.5

seconds and a pulse of +0.9 V was applied also for 0.5 s. The cycles were repeated until

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a poly(luminol) layer was formed on the ITO surface. The electric charge passed

through the cell during electrolysis steps was measured and displayed by the

electrochemical work station.

2.4. Chemiluminescence measurements

After polymerization the ITO slab was washed with distilled water. A 2 mm thick

chlorinated PVC sheet containing 24 holes (6 mm in diameter) was glued with Decosa

universal adhesive on the polymer coated surface. In this way 24 small reaction cells

(wells) (with an individual volume of approximately 80 μL) were obtained. The

poly(luminol)-coated (PL-coated) ITO glass was placed on the stage of the microscope

and the first cell was positioned over the prism. The buffer solution and the sample

were injected from the top by micro syringes; the total volume of the solutions injected

was 60 µl.

3. Results and discussion

3.1. Electro deposition and investigation of the poly(luminol) film

Preliminary electrochemical tests indicated that reproducibility of the poly(luminol)

film preparation on the ITO slabs was poor. In many cases the electrochemical

treatment has not resulted detectable poly(luminol) film deposition regardless careful

application of the method taken fro earlier reports (e.g. [10-12]). Therefore in order to

improve the success rate of polymer layer formation, an ITO glass surface pretreatment

procedure was worked out in our laboratory. This pretreatment procedure – described in

experimental section- was employed in each case before electropolymerization.

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Necessity of electrochemical or plasma pretreatment of ITO surface have been reported

[19] by other groups, too.

Three different electropolymerization methods were used for preparation of the PL

film: cyclic voltammetry (CV) (Fig.2), pulsed potential (PA) and potentiostatic

electrolysis (PSE). All of these have already been used for making electrically

conductive polymers [20]. After electro polymerization the layers were tested in

monomer free sulfuric acid solution by recording cyclic voltamograms. In these anodic

and cathodic peaks appeared. The current integral under the anodic and cathodic peaks

that is the electric charge value shows the redox active amount of the polymer. These

charges obtained for polymers prepared in the three different ways were compared. The

polymers prepared with the CV method showed fare the highest redox activity. Only

15% and 5% of their one were measured for pulsed potential (PA) and constant

potential depositions (PSE), respectively. Fig. 2 shows typical CV curves recorded for

luminol during its electro polymerization on the ITO surface. As it can be seen in the

inset, the oxidation peak appears at quite high potential, over 1V. It was found earlier

that long time exposition of the ITO coating in acidic solution for higher than 1.2 V

could damage it. Therefore oxidation potentials not higher than 0.9 V vs. SCE were

imposed in doing electro polymerization of luminol. It can be seen in Fig. 2 that despite

of applying this reduced oxidation potential the polymer layer was growing.

The poly(luminol) layer deposited partly covers the ITO coated glass surface, however

part of the layer stays accessible for electroactive species. In another set of experiments

the efficiency of the coating that is the ratio of the coated and the free areas of the ITO

surface were compared for the three differently prepared coatings. In these experiments

first cyclic voltammograms with the bare ITO coated slides were taken in the presence

of Fe(II)-EDTA complex and the current of the oxidation peaks were measured. These

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values could be used for calculating the total electrochemical area. Then poly(luminol)

was deposited onto the same ITO layer and finally the CV of the Fe-EDTA was

recorded again. In doing the electro polymerization coulostatic conditions were

employed, that means the charge passing through the electrolysis cell was kept equal in

case of the three different methods as fare as it was feasible. The oxidation and

reduction peak of the complex appears at +0.3 V and +0.0 V, and that values are out of

the potential range of the oxidation and reduction (+0.55 and +0.65 V, respectively) of

poly(luminol). The ratio of peak currents of Fe-EDTA measured after and before the

layer formation, corresponds to the ratio of the free and total electroactive area of the

ITO (see Table I). It was found that 83, 35 and 20% of the ITO were covered with the

polymer when using CV, pulsed amperometry (PA) and constant potential electrolysis

(PSE), respectively. It should be mentioned, that the functionally best layers have been

obtained when 4 CV cycles (-500 - +1100 mV potential range) have been performed

after the pretreatment of the ITO glass in sulfuric acid solution and before the

deposition in the narrow potential range. However it would make the comparison of the

layer deposition methods more difficult. Therefore it was not used in this study.

3.2. Chemiluminescence measurements

The light producing pathway for the oxidation of luminol is a complex process, it is

very much affected by the properties of the oxidizing agents used [18]. According to the

general scheme [9], hypohalites react with luminol to form diazoquinone [21]. Then it

reacts with hydrogen peroxide producing the light emitting aminophtalate species.

To perform the chemiluminescence tests, a plate of microscope slide size surface was

cut from a 2mm thick plastic sheet. An array of 24 holes with identical diameter (6mm)

was prepared through it. The poly(luminol) coated surface of the ITO glass was

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covered with the plastic plate. They were pasted together like a mask and the substrate.

In this way we obtained 24 independent reaction wells having identical volumes and

poly(luminol) layers of identical activity at their bottom.

Chemiluminescence (CL) measurements could be carried out in each micro wells. For

these, buffer solution containing 0.1 M hydrogen peroxide was used as reagent. In order

to make one measurement 30 microliters of this buffer solution was introduced into a

micro well (see Fig.1), and the CL signal was followed, and recorded in time. After a

few seconds a 30 µl dose of sample or standard solution was pipetted in. As the reaction

proceeded in the microwell in the presence of free chlorine a short light pulse (ca. for 1-

2 s) could be observed. No CL signal could be detected with reagent blank that means

in presence hydrogen peroxide (0.3 %) but in absence of free chlorine. Fig. 3 shows

comparison of the CL signal obtained in reagent blank and in the hypochloride (4 µM)

containing sample. Each CL measurement was done in a new compartment after

mechanic positioning the optics. The effect of the hydrogen peroxide concentration on

the CL intensity was tested at constant (0.1 mM) hypochlorite concentration. It was

found that the CL intensity increses with increasing H2O2 concentration of the reagent

up to 0.1 M. For example the CL peak height was 3.4 times higher with 0.1 M H2O2

concentration than with of 0.01 M. It should be note, however that the area under the

CL intensity – time peak obtained with 0.1 M reagent concentration was 1.3 times

higher than that with 0.01 M. This indicates that at higher peroxide concentration the

reaction rate is accelerated. Above 0.1 M peroxide concentration a slight decrease of the

CL sign was measured, therefore 0.1 M H2O2 concentration was selected and used in

the further experiments.

The chemiluminescence (by using the same conditions) of the PL layers prepared by the

three different method has been compared in Fig. 4. The CL versus time plots have

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been recorded separately and then copied into one figure for easier comparison. Letters

A, B and C in the figure indicate the peak of the CL signal. The highest

chemiluminescence (CL) intensity was recorded in case of layers prepared by CV

deposition method, while no CL signal could be detected using PSE films (see also in

Table I).

This is in good agreement with the earlier described results obtained comparing the

surface areas of electrodes prepared with different electro polymerization methods.

Therefore for further experiments the sensor layers were prepared with CV deposition.

The superiority of poly(luminol) layers prepared with CV technique was proved,

however, it was important to see how many electrode potential cycle results polymer

giving optimal CL signal in the free chlorine concentration range needed to measure. In

order to answer this poly(luminol) layers were prepared with different number of

potential cycles, and the CL signal intensity was measured using 0.01 mM hypochlorite

sample and 0.1 M hydrogen peroxide reagent (phosphate buffer, pH=8.0). It was

obtained, that the CL signal increased with increasing cycle number up to 200 cycles.

Although at 200 cycles the CL intensity was about 10 times higher than at 50 cycles, we

decided to use 50 cycles for preparing the poly(luminol) layers, simply because the CV

deposition is a very time consuming process (50 cycles - 18 minutes, 200 cycles – 72

minutes).

It is known that the CL intensity of luminol depends also on the buffer composition and

on the pH. For selecting the appropriate buffer the performance of the method was

tested with pH = 8 borate, phosphate and Tris buffers. The CL signal was about 16-18

times higher in Tris buffer (0.01 M, pH = 8.0) than in phosphate or borate ones.

However, unfortunately the CL intensity in Tris had poor reproducibility.

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The effect of the pH on the CL was tested in phosphate buffer in the pH = 5-10 range.

The results obtained show that CL increased by increasing pH. It was observed,

however that the stability of the ITO film is limited in alkaline solution, e.g. it was

removed completely when soaked in a pH=10.0 solution for several hours. Therefore

pH = 8.0 was selected for further measurements.

3.3. Determination of hypochlorite

Calibration curve was taken in the concentration range of 5·10-7 – 4·10-3 M of sodium

hypochlorite in the presence of hydrogen-peroxide (0.1 M) in phosphate buffer (pH =

8.0) by using poly(luminol) sensing layers prepared by the CV method with 50 cycles.

Measurements with all sample concentrations were repeated three times with different

sample wells. At low concentrations (0-30 μM) linear dependence was obtained

between the CL signal and the hypochlorite concentration (Fig. 5.), with a slope of 1017

RLU/mM hypochlorite. Between 30 and 110 μM the relationship is still linear, but the

slope increases. Over 1 mM the CL signal drops with increasing hypochlorite

concentration (see inset in Fig 5.). The reason of these could be the change of the

oxidation mechanism at high concentration. There are (at least) two known ways for

OCl- decomposition [4, 5, 9, 18]:

2 OCl- → 1O2 + 2 Cl- (1)

HOOH + OCl- → 1O2 + H2O + Cl- (2)

Cl- is produced in both reactions that lead to free chlorine production:

OCl- + Cl- + H2O → Cl2 + 2 OH-. (3)

When the OCl- concentration is increased, the chance for Cl-, and thus Cl2 production is

also increasing. Assuming that the reaction rates of poly(luminol)-OCl- and the

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poly(luminol)-Cl2 reactions are different, the reason of the two different linear ranges

could be understood. The observed decreasing signal intensity (inlet in Fig 5) at

concentrations over 0.5 mM has been explained in the literature [28] by a quenching

mechanism caused by the high amount of free chlorine or of the analyte. The (3σ)

detection limit for hypochlorite was below 5x10-7 M.

Chlorine concentration in tap water was determined by standard addition method. In

these experiments 30-30 μl buffer was injected into 9 reaction wells. Then, 25 μl tap

water was injected into the first cell. The CL signal was recorded and the measurement

was repeated with tap water spiked with different amount of NaOCl solution. The CL

intensities were measured and plotted against the concentration added (Fig.6). The

hypochlorite concentrations calculated from the CL measurements for three different

tap water samples (18, 23 and 20 μM) were in good agreement with those obtained by

the standard [17] method (20, 25 and 25 μM, respectively). However the relative error

of the measurements seems to be high. The reason for that could be the moderate

reproducibility of the chemiluminescent signal. Three results obtained with identical

hypochlorite concentration (4 μM) are shown in Fig. 7. The calculated relative standard

deviation of the peak height from the average value is 6%. Almost the same deviation

(4-6%) was calculated for other batches, too. The reason for the moderate

reproducibility is not clear. By checking the activity of the layers electrochemically,

less than 1 % difference could be measure in the peak heights.

4. Conclusions

Solid state chemiluminescent sensor array based on electro polymerized luminol was

prepared, characterized and used for dissolved chlorine detection. Three different

methods for PL deposition were used and the resulting layers were tested. Highest CL

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intensities were recorded by using CV deposition technique. The resulting sensing layer

showed a fast response (<5s) and an acceptable measuring ranges (0-40 and 50-800

μM) for chlorine determinations. Highly concentrated samples could be diluted readily

to the lower linear concentration range. The layer preparation is simple and the obtained

layer activity is reproducible. However, because of the 6% variations in the

chemiluminescence signal, the sensors can be used only in those applications where

10% relative error in the concentration is tolerable. The high storage stability (Table 2.),

simple analytical procedure and low concentration range feasible make the “single

shot” measuring wells containing array an attractive analytical tool in application in

water quality tests.

5. Acknowledgement

The authors, M. Szili, G. Nagy, B. Kovács appreciate the support of the foundation

„Synthesis of supramolecular systems, examination of their physicochemical properties

and their utilization for separation and sensor chemistry” (SROP-4.2.2.A-11/1)

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Biographies

Barna Kovács studied chemistry at the University of Szeged and obtained his diploma

in 1989. After finishing his doctoral work in 1991 on potentiometric surfactant sensitive

electrodes, he moved to Graz and worked as postdoc in the group of O.S. Wolfbeis.

From 1994 to1999 he has been working at the University of Pécs as assistant. In 2000

he received associate professor position. His main interests are luminescent based

analytical techniques and optical sensors for environmental analysis.

Monika Szili received her diploma in biology and chemistry at the University of Pecs

in 2004. She studied for the PhD at the same university since 2004; currently she is

employed as a research fellow supported by the Science Please Project at the University

of Pecs. Her main research interest is optical sensor development.

Géza Nagy is a full professor of physical chemistry at the University of Pécs. He

obtained MSc from Kossuth Lajos University Debrecen, Hungary, PhD from Technical

University of Budapest, DSc from Hungarian Academy of Sciences. He worked as

post.doc. fellow with G.G. Guilbault at LSUNO (New Orleans, LA), with R.N. Adams

(KU, Lawrence), as visiting scholar at UF (Gainesville, FL) with Roger Bates, at UNC

(Chapel Hill) with R.P. Buck, at TU (Austin, TX) with A.J. Bard. He is author of more

than 250 scientific papers.

Vlastimil Matejec received his PhD degree in chemistry from the Institute of Chemical

technology in Prague in 1981. From 1983 to 1993 he worked as a scientist at the

Institute of Chemistry of Glass and Ceramic Materials, Czechoslovak Academy of

Sciences, dealing with technology of optical fibers. Since 1993 he has been with the

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Institute of Radio Engineering and electronics ASCR (now the Institute of Photonics

and Electronics ASCR, v.v.i.) as a scientist. Currently, he is director of the above

Institute. His research interest is in the preparation of special optical fibers for

telecommunications and sensors by using the MCVD and sol–gel methods. He has

published over 100 journal and conference papers.

Ivan Kasik received his PhD degree in technology of silicates from the Institute of

Chemical Technology in Prague in 1995. From 1981 to 1987 he worked in the field of

special inorganic glasses and since that time he has dealt with specialty silica optical

fibers for fiber lasers and fiber sensors and with methods of their preparation. Since

1993 he has been working in the Institute of Radio Engineering and Electronics ASCR,

now the Institute of Photonics and Electronics ASCR, v.v.i.

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Figure legends

Table 1. Comparison of the properties of PL layers prepared with three different

techniques, by using the same amount of charge (2.38*10-5 C) for polymerization.

Table 2. Shelf life determination of the PL layer. Tests were performed with 0.3 %

H2O2 and 4 µM HOCl dissolved in 0.01M, pH=8 phosphate buffer. Three parallel

measurements have been done; the averages and the standard deviation of PL intensities

are given in column 2.

Fig. 1. Instrumental setup: A – PL film on ITO glass; B – sample compartment; C –

pipette or capillary tube for sample; D – prism; E – photomultiplier; F – amplifier; G –

power supply; H – computer; J – cells in the pvc-body on PL coated ITO glass

Fig. 2. Consecutive cyclic voltammograms recorded during the electro polymerization

of luminol by CV method (-200 to +900 mVvs. SCE, scan rate 100 mV/s) on ITO

electrode. 50 cycles are represented. The inset shows the first 10 runs when using a

broad potential window (-500 to +1200 mV vs. SCE)..

Fig. 3. CL signal at addition of 0.1M H2O2 and 4 µM HOCl (the polymer was

synthesized with 50 potential program cycles).

Fig. 4. CL signal of PL films deposited by different methods (A – constant potential

(PCE), B – pulsed amperometry (PA), C – cyclic voltammetry). 4 µM HOCl and 0.01

M pH=8 TRIS buffer was used in the reaction.

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Fig. 5. Calibration curve for NaOCl between 5*10-7 and 1,2*10-5 mol (0,3% H2O2 in

pH=8 phosphate buffer was used). Grey lines indicate the linear fits; the corresponding

equations are presented in the lower-right corner. The islet shows the calibration curve

in a broad concentration range (5*10-7 – 4*10-3 M).

Fig. 6. Determination of dissolved chlorine concentration of tap water sample by

standard addition method

Fig. 7. Reproducibility of the signal on PL prepared during 50 cycles. 0.1 M H2O2 and

4µM HOCl was used.

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Table 1.

2.36*10-3 CCovered

area(%)

Deposition time(s)

CL signal (a.u.)

Cyclic voltammetry-0.2 – 0.9 V

100 mV/s, 50 cycles 83 1100 6760.5

Pulsed amperometry-0.2 V 0.5 s0.9 V 0.5 s

35.1 73 955.5

Constant potential electrolysis

0.9 V20.2 35 0

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Table 2.

elapsed timepeak height (RLU)

n=3freshly prepared 457.2 ± 26

1 day 418.4 ± 201 week 423.7 ± 243 weeks 412.1 ± 181 month 419.8 ± 213 months 405.4 ± 17

1 year 374.2 ± 25

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Figure(s)

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*Manuscript

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Figure(s)