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Analytica Chimica Acta 575 (2006) 25–31

Selective electrochemical sensor for copper (II) ionbased on chelating ionophores

Ashok Kumar Singh ∗, Sameena Mehtab, Ajay Kumar JainDepartment of Chemistry, Indian Institute of Technology at Roorkee, Roorkee 247667, India

Received 8 February 2006; received in revised form 17 May 2006; accepted 22 May 2006Available online 2 June 2006

bstract

Plasticized membranes using 3-(2-pyridinyl)-2H-pyrido[1,2,-a]-1,3,5-triazine-2,4(3H)-dithione (L1) and acetoacetanilide (L2) have been pre-ared and explored as Cu2+-selective sensors. Effect of various plasticizers, viz. chloronaphthalene (CN), benzyl acetate (BA), o-nitrophenyloctylther (o-NPOE), and anion excluders, sodium tetraphenylborate (NaTPB) and oleic acid (OA) was studied in detail and improved performance wasbserved at several instances. Optimum performance was observed with dithione derivative (L1) having a membrane composition of L1 (5):PVC120):o-NPOE (240):OA (10). The sensor works satisfactorily in the concentration range 5.0 × 10−8 to 1.0 × 10−2 M (detection limit 4.0 × 10−8 M)ith a Nernstian slope of 29.5 mV decade−1 of activity. Wide pH range (3.0–9.5), fast response time (12 s), non-aqueous tolerance (up to 20%)

nd adequate shelf life (4 months) indicate the vital utility of the proposed sensor. The potentiometric selectivity coefficient values as determined

y match potential method (MPM) indicate good response for Cu2+ in presence of interfering ions. The proposed electrode comparatively showsood selectivity with respect to alkali, alkaline earth, transition and some rare earth metals ions. The electrode was used for the determination ofopper in different milk powder, water samples and as indicator electrode in potentiometric titration of copper ion with EDTA.

2006 Elsevier B.V. All rights reserved.

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eywords: Chelating ionophore; Poly(vinylchloride) membranes; Copper-selec

. Introduction

The determination of trace metals is important in the contextf environmental protection, food and agricultural chemistry.opper is an essential trace element and present in all land andarine organisms. It is widely used for industries, agriculture

nd domestic purposes and is therefore most widely distributedlement in the environment of industrialized countries. It is aroven fact that copper plays an important role in many bio-ogical processes, such as blood formation and functioning ofarious enzymes [1,2]. The maximum tolerable level for coppers 2.0 mg L−1 [3]. However, large concentration of copper cane tolerated by human beings but excessive intake of this ele-ent manifest certain diseases in humans for example, Menke’s

yndrome and Wilson’s disease [4,5]. Thus, the determinationf copper is important in view of its utility as well as toxicity.number of instrumental methods such as AAS, ICP, stripping

∗ Corresponding author.E-mail address: akscyfcy@iitr.ernet.in (A.K. Singh).

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003-2670/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.aca.2006.05.076

lectrode; Electrochemical sensors; Selectivity

oltammetry and flame photometry are employed for the deter-ination of copper at low concentration levels. These methods

enerally require sample pretreatment and infrastructure backupnd are not very convenient for routine analysis of large num-er of environmental samples. Ion-sensors provide analyticalrocedures that overcome the above drawbacks since they areast convenient and require no sample pretreatment and are alsouitable for online analysis.

The specific metal–ligand interaction is the most importantecognition mechanism that can be utilized in the develop-ent of potentiometric sensors [6]. Due to urgent need for

elective potentiometric determination of trace amounts of cop-er ions, especially in food and water samples, many coor-ination compounds have been employed as an ionophore inhe construction of ISEs of copper ion [7–21]. The copperII)–nitrogen–sulfur ligands frame provides remarkable contri-ution to determine copper ions in various samples [22]. Suc-

essful attempts have been made in the design and synthesisf highly selective ionophores as sensory molecules for Cu2+-on selective electrodes, but they show a poor detection limit8,9,12] narrow concentration range [11,14] and serious interfer-

26 A.K. Singh et al. / Analytica Chim

Fig. 1. Structure of chelating ligand (L1) 3-(2-pyridinyl)-2H-pyrido[1,2,-a]-1,3,5-triazine-2,4(3H)-dithione.

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Fig. 2. Structure of chelating ligand (L2) acetoacetanilide.

ng effect of other ions [15]. So the purpose of the present works the construction of selective and sensitive copper ion selec-ive electrode. For this purpose nitrogen, sulphur and oxygenontaining chelating ligands 3-(2-pyridinyl)-2H-pyrido[1,2,-a]-,3,5-triazine-2,4(3H)-dithione (Fig. 1, L1) and acetoacetanilideFig. 2, L2) have been investigated as sensing materials to pre-are copper selective electrode. In the screening of response tooth ionophores, we found that L1 is quite suitable for makingcopper (II) ion-selective electrode.

. Experimental

.1. Reagents

3-(2-Pyridinyl)-2H-pyrido[1,2,-a]-1,3,5-triazine-2,4(3H)-ithione (L1) and acetoacetanili-de (L2) were procured fromigma–Aldrich. Reagent grade sodium tetraphenylborateNaTPB), oleic acid (OA), chloronaphthalene (CN), benzylcetate (BA), o-nitrophenyloctyl ether (o-NPOE), tetrahydro-uran (THF) and high molecular weight PVC were purchasedrom Merck and used as received. Copper nitrate (Merck) wassed without any further purification. Double distilled wateras used for the preparation of metal salts solutions of different

oncentrations by diluting stock solution (0.1 M).

.2. Electrode preparation

Besides the critical role of the nature of ion carrier in prepar-

ng membrane-selective sensors, some other important featuresf the PVC based membrane electrode, such as amount ofonophore, nature of solvent mediator, plasticizer/PVC rationd especially the nature of additive used are known to signifi-

ttwp

ica Acta 575 (2006) 25–31

antly influence the sensitivity and selectivity [23–29]. Varyingmount of the ion-active phase and anion excluder OA andaTPB were dissolved with an appropriate amount of PVC inmL THF. To these, solvent mediators, viz. CN, BA and NPOEere added to get membranes of different compositions. Theixture was shaken vigorously with a glass rod. When the solu-

ion became viscous it was poured in acrylic ring placed onmooth glass plate. The solution was then allowed to evaporateor 24 h at room temperature. Transparent membranes of about.1 mm thickness were obtained, which were then cut to sizend glued to one end of a pyrex glass tube with araldite. Theatio of membrane ingredients, time of contact and concentra-ion of equilibrating solution were optimized so that the potentialecorded were reproducible and stable within the standard devi-tion. Membrane to membrane reproducibility was assured byarefully following the optimum condition of fabrication. Theembrane that gave reproducible result and best performanceas selected for detailed studies.

.3. Equilibration of membranes and potentialeasurements

The membranes were equilibrated for 3 days in 1.0 × 10−1 Mu(NO3)2 solution. The potentials were measured by varying

he concentration of Cu(NO3)2 in test solution in the range.0 × 10−8 to 1.0 × 10−2 M. Standard Cu(NO3)2 solutions werebtained by the gradual dilution of 0.01 M Cu(NO3)2 solution.he potential measurements were carried out at 25 ± 1 ◦C usingaturated calomel electrodes (SCE) as reference electrodes withhe following cell assembly:

g/Hg2Cl2|KCl (satd.)|0.1 M Cu(NO3)2‖PVC membrane‖test solution|Hg/Hg2Cl2|KCl (satd.)

. Results and discussion

.1. Optimization of membrane composition

The selectivity, linearity and sensitivity obtained for a givenonophore depends significantly on the membrane composition,ature of plasticizer and additive used [30–32]. The potentialsf membrane of two chelating ligands L1 and L2 were investi-ated as a function of copper ion concentration and the results areummarized in Table 1. The addition of plasticizer improves theensitivity and stability of the sensor. A good plasticizer shouldxhibit high lipophilicity and capacity to dissolve the membraneomponents [33]. We tested several membranes of varying com-ositions and different plasticizers o-NPOE, CN and BA wereested in PVC matrix and some of the results obtained are shownn Figs. 3 and 4. Copper electrodes without these plasticizershow weak response but the presence of plasticizers affect theesponse characteristics of the electrodes, due to its influence on

he dielectric constant of the membrane phase [34]. The elec-rodes based on L1 and L2 exhibit a nice Nernstian behaviorith o-NPOE and CN, respectively. It is well known that theresence of lipophilic additive improves the selectivity of an

A.K. Singh et al. / Analytica Chimica Acta 575 (2006) 25–31 27

Table 1Potentiometric response characteristics of copper (II) PVC membrane sensors based on ionophores L1 and L2 using different plasticizers and additives

Membrane no. Composition of membrane (mg) Slope (mV decade−1

of activity)Linear range (M) Detection

limit (M)Responsetime (s)

Ionophore Plasticizer Additive PVC

1. L1, 5 BA, 240 NaTPB, 3 120 25.2 7.9 × 10−7 to 1.0 × 10−2 2.5 × 10−7 252. L1, 5 BA, 240 OA, 10 120 26.5 5.0 × 10−7 to 1.0 × 10−2 1.2 × 10−7 283. L1, 5 NPOE, 240 NaTPB, 3 120 31.5 3.2 × 10−7 to 1.0 × 10−2 2.0 × 10−7 204. L1, 5 NPOE, 240 OA, 10 120 29.5 5.0 × 10−8 to 1.0 × 10−2 4.0 × 10−8 125. L1, 5 CN, 240 NaTPB, 3 120 35.0 8.9 × 10−7 to 1.0 × 10−2 4.5 × 10−7 326. L1, 5 CN, 240 OA, 10 120 32.2 4.0 × 10−7 to 1.0 × 10−2 3.2 × 10−7 307 L1, 4 NPOE, 240 OA, 10 120 29.0 1.2 × 10−7 to 1.0 × 10−2 8.6 × 10−8 188. L1, 6 NPOE, 240 OA, 10 120 30.1 2.2 × 10−7 to 1.0 × 10−2 9.1 × 10−8 259. L2, 5 BA, 240 NaTPB, 3 120 35.3 2.2 × 10−6 to 1.0 × 10−2 4.5 × 10−7 41

10. L2, 5 BA, 240 OA, 10 120 39.7 4.0 × 10−6 to 1.0 × 10−2 2.5 × 10−6 4311. L2, 5 NPOE, 240 NaTPB, 3 120 36.4 6.3 × 10−6 to 1.0 × 10−2 3.2 × 10−6 3512. L2, 5 NPOE, 240 OA, 10 120 39.9 2.8 × 10−5 to 1.0 × 10−2 2.0 × 10−5 3813. L2, 5 CN, 240 NaTPB, 3 120 29.2 2.2 × 10−7 to 1.0 × 10−2 1.1 × 10−7 151 8 −7 −2 −7

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4. L2, 5 CN, 240 OA, 10 120 33.5. L2, 4 CN, 240 NaTPB, 3 120 25.6. L2, 6 CN, 240 NaTPB, 3 120 34.

on sensor by decreasing the membrane resistance and co-ionnterference [35]. In our experiments, we examined the effect ofaTPB and OA as suitable lipophilic additives in conjugationith ionophores L1 and L2 on the potentiometric response of Cu

II) selective electrode. As is obvious from Table 1, the use of0% OA and 3% NaTPB significantly improves the performanceharacteristics of the membrane sensors.

The variation in potential response with different amountsf ionophore was also examined as shown in Table 1 (sensoros. 4, 7, 8, 13, 15 and 16). In the case of carrier type ion-elective electrodes, the extraction equilibrium in the vicinity ofhe interface between the membrane and aqueous layer affectshe potentiometric response of membranes [36,37]. In spite of

hese considerations, a carrier content of 5 mg was chosen ashe optimum ionophore amount, because the surface conditionsf the PVC membrane deteriorated on decreasing and increas-

ig. 3. Potentiometric response of membrane sensors based of L1 using differentlasticizers and additives (nos. 1–6).

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Fp

7.9 × 10 to 1.0 × 10 3.9 × 10 247.3 × 10−6 to 1.0 × 10−2 4.6 × 10−7 229.0 × 10−6 to 1.0 × 10−2 7.0 × 10−7 28

ng the carrier content. Hence, the membranes obtained withVC:NPOE:L1:OA in the ratio of 120:240:5:10 (w/w) (sen-or no. 4) and PVC:CN:L2:NaTPB ratio as 120:240:5:3 (w/w)sensor no. 13) show nice Nernstian slope over wide Cu2+ con-entration range.

.2. Working concentration range and slope

The results thus obtained indicate that the best elec-rode (no. 4) based on L1 exhibits nice Nernstian slope29.5 ± 0.2 mV decade−1) over a wide concentration rangef 5.0 × 10−8 to 1.0 × 10−2 M with a limit of detection

−8

.0 × 10 M while electrode (no. 13) based on L2 exhibitsNernstian slope (29.2 ± 0.2 mV decade−1) and concentration

ange of 2.2 × 10−7 to 1.0 × 10−2 M with limit of detection.1 × 10−7 M.

ig. 4. Potentiometric response of membrane sensors based of L2 using differentlasticizers and additives (nos. 9–14).

2 Chimica Acta 575 (2006) 25–31

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8 A.K. Singh et al. / Analytica

.3. Response and lifetime

The response time of the electrode was determined by mea-uring the time required to achieve a 95% of the steady potential.t can be seen from Table 1 that the best performance, with regardo response time, is 12 s for sensor based on L1 (no. 4) and 15 sor sensor based on L2 (no. 13) as compared to the rest. The highipophilicity of ionophore and plasticizer ensures stable poten-ials and longer lifetime [38,39] for the membrane. Among allhe membranes prepared, the lifetime of membrane sensor basedn L1 (no. 4) found to be 4 and 3 months for sensor based on L2no. 13). During this period, changes in potential were withinhe standard deviation (±0.2 mV). However, it is important tomphasize that the membranes were stored in a 0.1 M Cu2+ solu-ion when not in use.

.4. Solvent effect

The real samples may contain non-aqueous content, so theerformance of the sensor was also investigated in partiallyon-aqueous media using 10%, 20%, 30% and 40% usingon-aqueous content in methanol–water, ethanol–water andcetonitrile–water mixtures (Table 2). It was found that theembranes do not show any appreciable change in working

oncentration range and slope in mixtures up to 20% (v/v) non-queous contents. However, above 20% non-aqueous content,otentials show drift with time. The drift in potentials in therganic phase may be probably due to leaching of the ionophoret higher organic content.

.5. Effect of pH change

The dependence of sensor’s potential response has beennvestigated over the pH range 1.0–12.0 for 1.0 × 10−3 and.0 × 10−4 M Cu2+ solution (Fig. 5). The operational range was

able 2ffect of partially non-aqueous medium on the working of Cu2+ sensor basedn L1 (sensor no. 4)

on-aqueousontent (% v/v)

Working concentrationrange (M)

Slope (mV decade−1

activity)

1.0 × 10−2 to 5.0 × 10−8 29.5

ethanol10 1.0 × 10−2 to 5.0 × 10−8 20.220 1.0 × 10−2 to 5.0 × 10−8 29.230 1.0 × 10−2 to 7.3 × 10−8 12.535 1.0 × 10−2 to 4.6 × 10−7 24.2

thanol10 1.0 × 10−2 to 5.0 × 10−8 29.520 1.0 × 10−2 to 5.0 × 10−8 29.130 1.0 × 10−2 to 6.7 × 10−8 28.735 1.0 × 10−2 to 2.2 × 10−7 27.6

cetonitrile10 1.0 × 10−2 to 3.2 × 10−8 29.520 1.0 × 10−2 to 3.2 × 10−8 29.430 1.0 × 10−2 to 7.3 × 10−8 28.635 1.0 × 10−2 to 1.5 × 10−7 25.8

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ig. 5. Effect of pH on cell potential of sensor no. 4 based on L1 at 1.0 × 10−3 MA), 1.0 × 10−4 M (C) and sensor no. 13 based on L2 at 1.0 × 10−3 M (B),.0 × 10−4 M (D), respectively.

tudied by varying the pH of the test solution with nitric acidr sodium hydroxide. As can be seen from Fig. 5, the poten-ial is independent of pH in the range 3.0–9.5 and 4.0–9.0 forlectrodes based on L1 and L2, respectively. Therefore, the sameas taken as the working pH range of the sensor assemblies. The

hange in potential below pH 3 is apparently due to interferencef H+ and above pH 9.5 due to hydrolysis of Cu2+.

.6. Selectivity

Selectivity is the most important characteristic as it deter-ines the extent of utility of any sensor in real sample mea-

urements. It gives the response of ion-sensitive sensor for therimary ion in the presence of other ions present in solution,hich is expressed in terms of the potentiometric selectiv-

ty coefficients. Potentiometric selectivity coefficient (KpotCu,B)

escribes the preference by the membranes for Cu2+ relativeo an interfering ion B. IUPAC recommended match poten-ial method (MPM) was used to determine the selectivity ofu2+ with respect to alkali, alkaline earth and several common

ransition metal ions [40,41]. This method has an advantage ofemoving limitations imposed by Nicolsky–Eisenman equationhile calculating selectivity coefficient by other methods. These

imitations include non-Nernstian behavior of interfering ion androblem of inequality of charges of primary and interfering ions.

In this method selectivity coefficient KpotCu,B is given by the

ollowing equation:

potCu,B = �aCu

aB= a′

Cu − aCu

aB(1)

nd is determined by measuring the change in potential uponncreasing by a definite amount of the primary ion activity (Cu2+)

rom an initial value of aCu to a′

Cu and aB represents the activityf interfering ion added to the same reference solution of activityCu which bring about the same change in potential. The activ-ty of Cu2+ as reference solution was taken as 1.0 × 10−2 M in

A.K. Singh et al. / Analytica Chimica Acta 575 (2006) 25–31 29

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ig. 6. Selectivity coefficient values as determined by matched potential methodor ionophores L1 and L2 based membrane sensors, respectively.

his study. The selectivity coefficients so calculated are shownn Fig. 6. The selectivity coefficients are of the order of 10−2

r smaller which indicate that these ions cause negligible inter-erence on the functioning of the proposed copper electrode.he concentration level of interfering ions that can be toler-ted depends on the value of selectivity coefficient. Smaller ishe value the higher is the concentration that can be tolerated.t is also seen from Fig. 6 that the selectivity coefficient foro2+ and Ag+ is more than that for other metal ions and it isxpected that the sensor would not tolerate very high concentra-ion levels of these ions in Cu2+ ion estimation. In order to haven estimate of tolerance levels, mixed run studies were carriedut. In these runs, the potentials of the sensor were determineds a function of Cu2+ concentration in the presence of fixed

oncentrations 1.0 × 10−5, 5.0 × 10−5, 1.0 × 10−4, 1.0 × 10−3,.0 × 10−2 M of Co2+ and Ag+ ions. It is seen from Figs. 7 and 8hat the presence of these ions at concentrations of 1.0 × 10−5

nd 5.0 × 10−5 M caused no significant divergence in the poten-

ig. 7. Variation of membrane potential as a function of Cu2+ ion activity in theresence of different activities of Co2+ ions.

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ig. 8. Variation of membrane potential as a function of Cu2+ ion activity in theresence of different activities of Ag+ ions.

ial against concentration plot while increase in the concentrationf Co2+ and Ag+ ions in the solution, decreases limit of the detec-ion of Cu (II) sensor.

. Analytical applications

To assess the applicability of proposed copper selective elec-rode (based on L1, sensor no. 4) in real samples an attempt was

ade to determine copper in milk powder and different wateramples. To determine copper in milk powder, 2 g of milk pow-er was ashed at ∼400 ◦C in a crucible for 3 h. Then 2 mL ofoncentrated nitric acid was added and the mixture was heated toissolve residue. The resulting solution was diluted with watern a 25 mL volumetric flask. Then solution was used to deter-

ine copper content by proposed sensor. The electrode was alsouccessfully applied to determine copper directly in differentnvironmental (drinking water, river water and sea water) sam-les. The water samples were acidified with 0.1 M HNO3 todjust stable pH at 5.5. The results obtained from the triplicateeasurement of proposed copper sensor (for both milk powder

nd water samples) are compared with that determined by atomicdsorption spectroscopy (AAS) and are summarized in Table 3.rom the given data it is seen that there is satisfactory agree-ent between the results obtained by the proposed electrode

able 3uantification of copper in health drinks and water samples using AAS androposed Cu2+ sensor based on L1 (sensor no. 4)

ample Average Cu2+ concentration (mg L−1)

Determined by(proposed sensor)a

Determined by(AAS)a

ilk powder 3.5 ± 0.09 3.5 ± 0.05rinking water 1.8 ± 0.05 1.7 ± 0.05iver water 15.5 ± 0.06 15.2 ± 0.05ea water 24.8 ± 0.02 24.6 ± 0.05

a Average of three replicates.

30A

.K.Singh

etal./Analytica

Chim

icaA

cta575

(2006)25–31

Table 4Comparison of the proposed Cu2+-selective electrodes (sensor nos. 4 and 13) with the reported electrode

Ref. no. Carrier name Linear range (M) Detectionlimit (M)

Slope (mV decade−1

of activity)pH range Selectivity coefficients (−log K

potCu,B) Response

time (s)

This work 3-(2-Pyridinyl)-2H-pyrido[1,2,-a]-1,3,5-triazine-2,4(3H)-dithione

5.0 × 10−8 to 1.0 × 10−2 4.0×10−8 29.5 3.0–9.5 Ca2+ (3.5), Mg2+ (4.5), Sr2+ (3.9), Ba2+ (4.2),Ni2+ (2.9), Co2+ (1.1), Cd2+ (2.2), Pb2+ (1.5),Zn2+ (2.4), Hg2+ (0.8), Ag+ (0.5), Li+ (4.7),Na+ (2.9), K+ (4.9), Ce3+ (4.7)

12

This work Acetoacetanilide 2.2 × 10−7 to 1.0 × 10−2 1.1×10−7 29.2 4.0–9.0 Ca2+ (2.7), Mg2+ (4.4), Sr2+ (3.4), Ba2+ (3.9),Ni2+ (3.0), Co2+ (0.9), Cd2+ (3.2), Pb2+ (2.1),Zn2+ (1.7), Hg2+ (2.2), Ag+ (1.3), Li+ (3.7),Na+ (2.5), K+ (4.6), Ce3+ (4.7)

15

[9] Schiff’s base 8.0 × 10−6 to 1.0 × 10−1 3.0 × 10−6 29.5 3.0–6.5 Ca2+ (2.6), Mg2+ (2.3), Sr2+ (2.1), Ba2+ (2.1),Ni2+ (2.4), Co2+ (2.2), Cd2+ (2.2), Pb2+

(0.5),Zn2+ (2.3), Na+ (3.78), NH4+ (2.74), Zn2+

(2.25), K+ (2.02)

15

[11] Ethambutol–Cu (II) complex 7.9 × 10−6 to 1.0 × 10−1 7.0 × 10−6 29.9 2.1–6.3 Ca2+ (1.0), Mg2+ (0.9), Sr2+ (0.8), Ba2+ (0.6),Ni2+ (0.8), Co2+ (0.2), Cd2+ (0.7), Pb2+ (0.6),Zn2+ (1.0), Hg2+ (0.9), Ag+ (0.6), NH4

+ (0.6),Li+ (0.7), Na+ (0.2), K+ (0.2)

11

[12] o-Vanilin 5.0 × 10−6 to 1.0 × 10−1 8.0 × 10−7 28.5 1.9–5.2 Ca2+ (1.2), Mg2+ (1.2), Sr2+ (1.1), Ba2+ (1.3),Ni2+ (1.1), Co2+ (1.1), Cd2+ (1.1), Zn2+ (1.1),Na+ (1.1), Hg2+ (0.4), Ag+ (0.3), K+ (1.2), Li+

(2.4)

30

[15] Salens 1.0 × 10−5 to 1.0 × 10−1 3.1 × 10−6 29.7 3.5–6.5 Ca2+ (3.0), Ni2+ (2.0), Co2+ (2.0), Cd2+ (3.2),Zn2+ (4.0), Na+ (3.3), Hg2+ (3.0), Ag+ (2.5), K+

(4.1), Pb2+ (2.3)

10

[16] Porphyrin 4.0 × 10−6 to 1.0 × 10−1 4.4 × 10−6 29.3 2.8–7.9 Ca2+ (1.4), Sr2+ (1.6), Ni2+ (1.2), Co2+ (2.0),Cd2+ (1.5), Pb2+ (1.2), Zn2+ (1.9), Hg2+ (1.0),Ag+ (1.2), NH4

+ (3.0), Li+ (1.2), Na+ (2.0), K+

(1.2)

8

[17] Cyclic tetrapeptide derivative 1.0 × 10−5 to 1.0 × 10−2 2.1 × 10−7 25.9 4.5–7.0 Li+ (5.1), Na+ (5.2), K+ (5.1), Mg2+ (3.2), Ca2+

(3.4), Ag+ (3.1), Sr2+ (2.8), Ba2+ (3.0), Ni2+

(2.5), Co2+ (2.7), Hg2+ (2.52), Cd2+ (2.4), Zn2+

(1.7), Pb2+ (0.5)

15

[18] Phenylglyoxal-�-monoxime 1.0 × 10−6 to 1.0 × 10−1 5.0 × 10−7 28.2 3.3–6.5 Ca2+ (2.9), Ni2+ (3.0), Co2+ (3.0), Cd2+ (2.9),Pb2+ (4.7), Zn2+ (1.7), Hg2+ (4.1), Ag+ (3.7),NH4

+ (2.5), Li+ (2.3), K+ (2.9), Mg2+ (2.4)

10

[19] Napthol-derivative Schiff’s base 5.0 × 10−8 to 2.0 × 10−2 3.1 × 10−6 29.8 4.0–7.0 Ca2+ (3.0), Mg2+ (3.0), Ba2+ (3.1), Ni2+ (1.5),Co2+ (2.1), Cd2+ (2.1), Zn2+ (2.1), Na+ (1.3),Hg2+ (1.2), K+ (3.9), Pb2+ (2.4)

5

[20] Hexadendate Schiff’s base 6.0 × 10−8 to 1.0 × 10−1 6.0 × 10−7 29.8 3.0–7.5 Ca2+ (3.4), Mg2+ (3.5), Ni2+ (3.7), Co2+ (3.6),Cd2+ (3.5), Zn2+ (3.4), Na+ (4.0), Ag+ (4.0), K+

(3.7), Li+ (4.4), Pb2+ (3.7)

15

[21] o-Xylene bis(dithiocarbamates) 10−6 to 10−1 1.4 × 10−7 29 3.2–5.5 Ca2+ (3.6), Ni2+ (3.2), Co2+ (4.0), Cd2+ (4.5),Pb2+ (0.7), Zn2+ (2.2), K+ (2.3), Mg2+ (3.6),Na+ (2.6)

9

[22] 3,4-Ethylenedioxythiophene 10−6 to 10−2 2.4 × 10−7 29.6 – Ni2+ (6.9), Na+ (9.3), K+ (5.9), Mg2+ (7.4),Ca2+ (6.8), Co2+ (7.3), Cd2+ (3.3), Zn2+ (6.8),Pb2+ (2.9)

60

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[[[[[[38] M. Telting-Diaz, E. Bakker, Anal. Chem. 73 (2001) 5582.

ig. 9. Potentiometric titration curve for 20 mL of 2.5 × 10−3 M Cu2+ with.0 × 10−2 M EDTA, at constant pH range 6 using the proposed sensor.

nd those by AAS. This sensor was also found useful as an indi-ator electrode in potentiometric titration of Cu (II) with EDTA.

20 mL solution of 2.5 × 10−3 M Cu2+ was titrated against a.0 × 10−2 M EDTA solution within constant pH range 5–7. Asndicated from Fig. 9, the sharp inflection point, showing perfecttoichiometry was observed in the titration plot. Thus, the sensoran be used to determine Cu2+ ion accurately under laboratoryondition.

. Conclusions

The investigations on PVC based membranes of two chelates,iz. L1 and L2 have shown that they act as Cu2+ selec-ive sensors. However, of the two chelates, the sensor no.

based on 3-(2-pyridinyl)-2H-pyrido[1,2,-a]-1,3,5-triazine-,4(3H)-dithione (L1) shows maximum selectivity, widest work-ng concentration range and minimum response time. The pro-osed sensor is superior to the reported sensors (Table 4) withegards to detection limit, response time and selectivity. Further,he proposed sensor can also be used for the determination ofu (II) ions in real samples both by direct potentiometry as wells by potentiometric titration.

cknowledgement

Ms. Sameena Mehtab is grateful to Council of Scientific andndustrial Research, New Delhi, India for providing financialssistance for this work.

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