Polymeric membrane sensors based on Cd(II) Schiff base complexes forselective iodide determination in environmental and medicinal samples
Ashok Kumar Singh ∗, Sameena MehtabDepartment of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
Received 9 June 2007; received in revised form 12 July 2007; accepted 13 July 2007Available online 25 July 2007
bstract
The two cadmium chelates of schiff bases, N,N′-bis(salicylidene)-1,4-diaminobutane, (Cd-S1) and N,N′-bis(salicylidene)-3,4-diaminotolueneCd-S2), have been synthesized and explored as ionophores for preparing PVC-based membrane sensors selective to iodide(I) ion. Potentiometricnvestigations indicate high affinity of these receptors for iodide ion. Polyvinyl chloride (PVC)-based membranes of Cd-S1 and Cd-S2 using asexadecyltrimethylammonium bromide (HTAB) cation discriminator and o-nitrophenyloctyl ether (o-NPOE), dibutylphthalate (DBP), acetophe-one (AP) and tributylphosphate (TBP) as plasticizing solvent mediators were prepared and investigated as iodide-selective sensors. The besterformance was shown by the membrane of composition (w/w) of (Cd-S1) (7%):PVC (31%):DBP (60%):HTAB (2%). The sensor works wellver a wide concentration range 5.3 × 10−7 to 1.0 × 10−2 M with Nernstian compliance (59.2 mV decade−1 of activity) within pH range 2.5–9.0
ith a response time of 11 s and showed good selectivity for iodide ion over a number of anions. The sensor exhibits adequate life (3 months) withood reproducibility (S.D. ± 0.24 mV) and could be used successfully for the determination of iodide content in environmental water samples andouth wash samples.2007 Published by Elsevier B.V.
Iodine is an indispensable microelement to humans. Iodines toxic and its vapors irritate the eyes and lungs. The maximumllowable concentration in air when working with iodine is justmg m−3 [1]. Iodine-131 is one of the radionuclides involved
n atmospheric testing of nuclear weapons. Iodine plays a keyole in many biological activities such as brain functions, cellrowth, neurological activities, metabolism and thyroid func-ions [2]. Iodide ions also present in the composition of variousrugs. I−/I3
− redox couple contributes to the high performancef dye-sensitized solar cells. Due to vital importance of iodiden environment, medicines and industry, determination of iodideon is very important in clinical and chemical analysis [3,4].
Numerous analytical methods have been reported for itsetermination at low concentration levels. These include gashromatography with mass spectrometry detection [5]; induc-
ively coupled plasma atomic emission mass spectrometry [6];eutron activation analysis [7]; chemiluminescence [8]; polarog-aphy [9]; pulse stripping analysis [10] and flow injectionnalysis [11]. These methods are time consuming, require largenfrastructure backup, high operational cost and not very appro-riate for analysis of large number of samples. On the otherand potentiometric sensors offer an inexpensive and convenientethod for fast analysis with high sensitivity and selectivity. Ion
lective electrodes have emerged as one of the most promisingools for direct determination of various species in biologicalnd industrial analysis. In view of such advantages, efforts haveeen made to make selective sensors for different anions.
Anion sensing and recognition remains a challenging taskecause of the limited availability of suitable molecular hostsor anions. In order to have selective sensor for iodide, theost important requirement is to have an ionophore in the
ensor which show high affinity towards iodide ion and poor
or other anions. Thus, quest for new materials capable ofpecific and effective recognition of iodide is a topic of cur-ent interest. It has been shown that the anion selectivity ofhe membrane electrodes that are based on metal complexes
3Yield: 78%. m.p.: 112 ◦C. Anal. Calc. for (%) C21H18N2O2:C, 76.36; H, 5.45; N, 8.48. Found (%): C, 76.33; H, 5.42; N,
A.K. Singh, S. Mehtab /
s influenced by both the structure of the ligands and theroperties of the metal ions [12]. Many sensing agents haveeen described for the preparation of iodide sensors includingn(II)porphyrinato [13], Iodide-miconazole ion pair [14], urea
erivative [15], silver wire [16], Co(II) and Ni(II) cyclam deriva-ives [17], Hg(II) bis(benzoin)-semiethylenediamine complex18], Salophen complex of Co(II) [19]. However, most of thesefforts have not been very fruitful. The developed sensorsosses narrow working concentration range [14,15,17] and suf-er serious interference from lipophilic anions like SCN−, CN−,lO4
− and Sal−. Recently, N,N′-bis(salicylaldehyde-n-octyl)iimine cobalt(II) [20] and copper(II) of N,N′′-bis(salicylidene)-,2-bis(p-aminophenoxy)ethane tetradentate complex [21] havelso been explored as ionophores in the construction ofon-selective electrodes for iodide. In this manuscript, weave synthesized cadmium complexes of two schiff bases,N′-bis(salicylidene)-1,4-diaminobutane (Cd-S1) and N,N′-is(salicylidene)-3,4-diaminotoluene (Cd-S2) and studied theses ionophores in the preparation of polymeric membrane sensorsor low level determination of iodide ion.
. Experimental
.1. Reagents
Salicylaldehyde, 1,4-diaminobutane, 3,4-diaminotoluene,riethyleneamine and cadmium(II) perchlorate were pur-hased from Aldrich and used as received. For membranereparation, high molecular weight polyvinyl chloride (PVC), o-itrophenyloctyl ether (o-NPOE), dibutylphthalate (DBP), ace-ophenone (AP), tributylphosphate (TBP), hexadecyltrimethy-ammonium bromide (HTAB) and tetrahydrofuran (THF) weresed as received from Fluka. Reagent grade sodium salts of allnions used were of highest purity available from SRL (Mum-ai, India) and used without any further purification except foracuum drying over P2O5. Anionic salt solutions were preparedn doubly distilled water and standardized whenever necessary.
.2. Conditioning of membranes and potentialeasurements
The membranes were equilibrated for 2 days in 0.01 M NaIolutions. The potentials have been measured by varying theoncentration of NaI in test solution in the range 1.0 × 10−8
o 1.0 × 10−2 M. The standard NaI solutions had been obtainedy gradual dilution of 0.01 M NaI solution. The potential mea-urements were carried out at 25 ± 1 ◦C using saturated calomellectrodes (SCE) as reference electrodes with the following cellssembly:
PVC membranes have been fabricated as suggested byraggs et al. [22]. Membranes have been prepared by dissolving
8υ
((
ta 74 (2008) 806–814 807
ppropriate amounts of ionophores (Cd-S1 or Cd-S2), cationicdditives (HTAB), plasticizers (DBP, o-NPOE, AP or TBP) andVC in THF (5 mL). The components were added in terms ofeight percentages. The homogeneous mixture obtained after
omplete dissolution of all the components, was concentratedy evaporating THF at room temperature and then poured intoolyacrylate rings placed on a smooth glass plate. Membranesf ∼0.4 mm thickness were removed carefully from the glasslate and glued to one end of a “Pyrex” glass tube. It is knownhat the sensitivity, linearity and selectivity obtained for a givenonophore depends significantly on the membrane compositionnd nature of plasticizer used [23]. Thus, the ratio of membranengredients, time of contact and concentration of equilibratingolution were optimized after a good deal of experimentation.
embranes which generate reproducible and stable potentialsave been studied. The blank membranes having only PVC asembrane ingredients was also prepared and studied. Whileembrane having PVC with plasticizer small potentials with
lope of ∼5 mV were generated. The activities of ions were cal-ulated from the modified form of the Debye–Huckel equation24].
. Results and discussion
.1. Synthesis of Cd-S1 and Cd-S2 complexes
The ionophore ligands N,N′-bis(salicylidene)-1,4-iaminobutane (S1) N,N′-bis(salicylidene)-3,4-diaminotolueneS2) were synthesized by the previously described methods25,26].
.1.1. Preparation of ligands S1 and S2
To a solution of 1.0 g (7.2 mmol) of salicylaldehyde in0 mL of ethanol, 3.6 mmol of the appropriate amine (1,4-iaminobutane or 3,4-diaminotoluene) was added. The contentsere refluxed for 12 h. The products were precipitated after cool-
ng. The precipitates were filtered, washed with cold diethylther and dried in vacuum. The ligand products were purified bye-crystallization from ethanol.
.1.1.1. N,N′-bis(salicylidene)-1,4-diaminobutane (S1). Yield:3%. m.p.: 125 ◦C. Anal. Calc. for (%) C18H20N2O2: C, 72.95;, 6.80; N, 9.45. Found (%): C, 72.82; H, 6.72; N, 9.50. Maas
.1.2. Synthesis of prepared salanes complexesTo a solution of 1 mmol of the salane (S1 or S2) in 15 mL of
reshly distilled acetonitrile solution, 0.351 g (1 mmol) of cad-ium(II) perchlorate salt was added. After 15 min. of stirringmL of triethyleneamine was added to the reaction mixturend these contents were further stirred for 5 h at room temper-ture. The precipitated product were filtered, washed with coldcetonitrile and dried under vacuum.
.1.2.1. Cd(II)-S1 complex. Yield: 65%. m.p.: 152 ◦C. Anal.alc. for (%) C18H20CdClN2O6: C, 42.71; H, 3.58; N, 5.53.ound (%): C, 42.62; H, 3.47; N, 5.84. FAB + Mass (m/z): 506M+). FT-IR (KBr) cm−1: υ(C N) 1617 (vs), υ(C–H) 1452 (vs),(C–O) 1312 (vs) cm−1 (Fig. 1a).
.1.2.2. Cd(II)-S2 complex. Yield: 62%. m.p.: 166 ◦C. Anal.alc. for (%) C21H16CdClN2O6: C, 46.69; H, 2.99; N, 5.19.ound (%): C, 46.25; H, 2.82; N, 5.43. FAB + Mass (m/z): 540M+). FT-IR (KBr) cm−1: υ(C N) 1613 (vs), υ(C–H) 1459 (vs),(C–O) 1319 (vs) cm−1 (Fig. 1b).
.2. Response of different anions
In preliminary experiments, various PVC-membrane ion-
elective electrodes with the synthesized schiff base metalomplexes were prepared and tested for different anions. Theotential response of the electrodes based on Cd-S1 and Cd-S2or different anions are shown in Figs. 2 and 3, respectively. The
ig. 1. Structure of N,N′-bis(salicylidene)-1,4-diaminobutane cadmium com-lex (Cd-S1) (a), Structure of N,N′-bis(salicylidene)-3,4-diaminotolueneadmium complex (Cd-S2) (b).
3r
i1pPtapa
Ff
ig. 2. Potential responses of ion-selective membrane sensor based on Cd-S1
or various anions.
esults exhibited significantly high selectivity to iodide ion overther anions. Hence, the complexes were selected as a carrieror preparation of iodide-selective electrodes.
.3. The effect of membrane composition on potentialesponse of the iodide sensor
Potential of the membranes of (Cd-S1) and (Cd-S2) werenvestigated as a function of iodide ion activity in the range.0 × 10−8 to 1.0 × 10−2 M and the results obtained are com-iled in Tables 1 and 2. The electrodes with no carrier (containingVC, plasticizer and HTAB) displayed insignificant sensitivity
owards iodide. The influence of plasticizer on the response char-cteristics of the iodide electrodes was investigated by using fourlasticizers of different polarities including DBP, o-NPOE, APnd TBP. The sensor nos. 3 and 16 having membranes with-
ig. 3. Potential responses of ion-selective membrane sensor based on Cd-S2
or various anions.
A.K. Singh, S. Mehtab / Talanta 74 (2008) 806–814 809
Table 1Optimized membrane compositions and their potentiometric response as in iodide sensor (based on Cd-S1)
Sensor no. Composition (w/w, %) Slope (mV decade−1 of activity) Linear range (M)
ut plasticizer exhibits a narrow working concentration rangef 10−4 to 10−2 M with a sub Nernstian slope. Improvement inensors performance was observed by the addition of plasticizer.mong the several membranes tested for each of the carriers,
he membranes incorporating DBP showed better potentiomet-ic responses, i.e. higher sensitivity and wider linearity of thealibration plots (sensor nos. 12 and 23). It seems that DBP,s a low polarity and a relatively high mobility, with respecto other plasticizers examined, provides appropriate conditionsor incorporation of highly lipophilic iodide ion into the mem-ranes prior to its coordination with the cadmium atom in theomplexes [27].
The addition of lipophilic cationic additive in anion selectiveembranes is necessary to introduce permselectivity [28]. The
nfluence and concentration of the membrane additives was alsonvestigated by incorporating HTAB into the membranes. Theotentiometric sensitivity of the membranes based on both carri-rs was greatly improved in the presence of HTAB as a lipophilic
ationic additive, compared to the membranes with no additivet all. Previous studies have shown that there is an optimal con-entration of lipophilic ionic additives in the membranes andhat gives the best electrode performance. The effect of HTAB
3
p
able 2ptimized membrane compositions and their potentiometric response as in iodide se
58.4 3.5 × 10 to 1.0 × 1059.2 5.3 × 10−7 to 1.0 × 10−2
59.8 8.2 × 10−7 to 1.0 × 10−2
oncentration in the membrane was investigated at several addi-ive/ionophore mole ratios. The sensors with HTAB/ionophore
ole ratios of ∼0.55 for both of the carriers exhibited maximumensitivity over a wide range of iodide concentration.
.4. Calibration characteristics
Among the different membrane compositions, membranesith ionophore/HTAB/PVC/DBP in (w/w, %) 7(Cd-S1)/2/31/60
nd 6(Cd-S2)/4/31/59 showed highest sensitivity and widest lin-ar range and were selected as the optimum composition forurther studies (Fig. 4). These sensors exhibit the maximumorking concentration range of 5.3 × 10−7 to 1.0 × 10−2 M withslope of 59.2 mV decade−1 of activity (sensor no. 12, Table 1)nd working concentration range 8.1 × 10−6 to 1.0 × 10−2 Mith Nernstian slope of 59.3 mV decade−1 of activity (sensoro. 23, Table 2).
.5. Effect of internal solution
The influence of the concentration of internal solution on theotential response of the polymeric membrane electrodes for
nsor (based on Cd-S2)
Slope (mV decade−1 of activity) Linear range (M)
VC
N.M. N.M.62.4 2.4 × 10−4 to 1.0 × 10−2
47.8 7.7 × 10−4 to 1.0 × 10−2
69.2 6.7 × 10−5 to 1.0 × 10−2
67.5 2.8 × 10−5 to 1.0 × 10−2
58.0 9.4 × 10−5 to 1.0 × 10−2
59.0 1.1 × 10−5 to 1.0 × 10−2
57.2 5.2 × 10−5 to 1.0 × 10−2
55.3 5.5 × 10−5 to 1.0 × 10−2
59.3 8.1 × 10−6 to 1.0 × 10−2
58.4 9.8 × 10−6 to 1.0 × 10−2
58.8 8.4 × 10−5 to 1.0 × 10−2
58.9 2.8 × 10−5 to 1.0 × 10−2
810 A.K. Singh, S. Mehtab / Talanta 74 (2008) 806–814
Fi
iTawcott
3
essic
F
lrtiC
3e
srelt
ig. 4. Calibration plots of iodide-selective sensors based on Cd-S1 and Cd-S2
onophores.
odide ion based on Cd-S1 and Cd-S2 ionophores were studied.he concentration was varied from 1.0 × 10−1 to 1.0 × 10−5 Mnd the potential response of the sensors has been observed. Itas found that the best results in terms of slope and working
oncentration range have been obtained with internal solutionf activity 1.0 × 10−3 M. Thus, 1.0 × 10−3 M concentration ofhe reference solution was quite appropriate for the smooth func-ioning of the proposed sensors.
.6. Influence of pH on the on sensors performance
The influence of pH on the response of the potential wasxamined by use of 10−3 M and 10−4 M potassium iodide
olutions over the pH range 1.0–12.0. To adjust the pH, verymall volumes of HNO3 and NaOH were used. The results foronophores Cd-S1 and Cd-S2 are shown in Fig. 5, which indi-ated that the sensors exhibits a better response and extended
ig. 5. Effect of pH on potential response of the iodide ion-selective sensors.
Aa
psfrwvc
3
sppA5tsca
Fig. 6. Dynamic response of the membrane sensor based on Cd-S1.
inearity at lower pH values. In alkaline media, the potentiomet-ic response properties of the electrode slightly deteriorated dueo hydroxide-coordinated central metal interference. The work-ng pH range for ionophore Cd-S1 (sensor no. 12) is 2.5–9.0 andd-S2 (sensor no. 23) is 3.0–8.5.
.7. The dynamic response time behavior of the proposedlectrode
Dynamic response time is an important factor for iodide sen-itive sensor. In this study, the practical response time has beenecorded (for sensor no. 12) by changing solutions with differ-nt I− concentrations. The measurement sequence was from theower (1.0 × 10−6 M) to the higher (1.0 × 10−2 M) concentra-ion. The actual potential versus time traces is shown in Fig. 6.s it is seen, the electrode reached the equilibrium response invery short time of about 11 s.
To evaluate the reversibility of the electrode, a similarrocedure in the opposite direction was adopted. The mea-urements have been performed in the sequence of high-to-lowrom (1.0 × 10−2 to 1.0 × 10−3 M) sample concentrations. Theesults showed that, the potentiometric response of the electrodesas reversible; although the time needed to reach equilibriumalues (42 s) were longer than that of low-to high sample con-entrations.
.8. Lifetime of proposed sensor
The lifetime of the sensor (no. 12), which is a measure of sen-ors durability, was studied over a 4 months period. During thiseriod, the electrode was daily used over extended period (2 her day), and its slopes and detection limits have been measured.fter 3 months changes were observed in the slope (from 59.2 to8.6 mV decade−1 of activity) and detection limit (1.9 × 10−7
o 2.5 × 10−6 M). The reproducibility of the proposed iodideensor was also investigated. The standard deviations of 10 repli-ate measurements at 1.0 × 10−3 and 1.0 × 10−4 M were ± 0.24nd ± 0.38 mV decade−1, respectively. Cd-S1 complex is suffi-
Talanta 74 (2008) 806–814 811
cTfAtotstu
3
dmutst(
bmrss
K
I5idtmiuTesmto
Table 3Selectivity coefficients of iodide-selective sensor nos. 12 and 23 based on themembranes of (Cd-S1) and (Cd-S2), respectively
Interfering ion (B) Selectivity coefficient (−log kPotI−,B
iently lipophilic, i.e. has very low solubility in aqueous solution.his factor imparts minimizes leaching (loss of components)
rom the membrane and produces a long and stable response.fter life time period swelling in membrane was too high
hat the membrane became mechanically weak and leachingf ionophore and plasticizer from membrane to aqueous solu-ion took place. Therefore, deviation in potential occurs andlight gradual decrease in slope. It is important to emphasizehat sensors were stored in 0.01 M NaI solutions when not inse.
.9. Selectivity of ion sensing membranes
Selectivity is an important characteristic of a sensor thatelineates the extent to which the device may be used in the esti-ation of analyte ion in the presence of other ions and extent of
tility of any sensor in real sample measurement. In this work,he selectivity coefficients of the sensors toward different anionicpecies (An−) were evaluated by using both the matched poten-ial method (MPM) [29,30] and the fixed interference methodFIM) [31].
In the MPM, the selectivity coefficient (KPotI,B) was determined
y measuring the change in potential upon increasing the pri-ary ion (I−) activity from an initial value of aI to a′
I and aBepresents the activity of interfering ion added to the referenceolution of primary ion of activity aI which also brings aboutame potential change. It is given by expression:
PotI,B = �aI
aB= a′
I − aI
aB(1)
n the present studies aI and a′I were kept at 1.0 × 10−4 and
.0 × 10−4 M I− and aB was experimentally determined. FIMs the most widely used procedure as per IUPAC recommen-ation for determining selectivity coefficients [32]. In the FIM,he selectivity coefficient was evaluated from potential measure-
ent on solutions containing a fixed concentration of interferingon (1.0 × 10−2 M) and varying amount of I− ions. The val-es of selectivity coefficient so determined are compiled inable 3. A value of selectivity coefficient equal to 1.0 indicatesqual response to both primary ion and interfering ions. A value
maller than 1.0 shows that the sensor is selective to the pri-ary ion over the interfering ion. It is seen from the Table 3,
hat the selectivity coefficients determined by both the meth-ds are sufficiently smaller than 1.0 indicating that the present
caod
Fig. 7. Response mechanism of ion
CO3− 5.13 5.02 5.22 5.13
2O42− 5.56 5.28 5.78 5.56
ensors are significantly selective to iodide ion over all the inter-ering ions. Of the two sensors, selectivity of the sensor no. 12based on Cd-S1) was found better than sensor no. 23 (based ond-S2).
Thus, sensor no. 12 was compared with some reported iodide-elective sensors (Table 4). It is seen that the selectivity, workingoncentration range and pH range of the proposed sensor towardodide is better as compared to reported sensors.
.10. Response mechanism of the sensor
Fig. 7 demonstrates the suggested the coordination schemef I− with cadmium centre in schiff base complexes. The selec-ivities were mainly controlled by specific interactions between
etal centre and anions in the structure of ionophore. The naturef spacer that joins the two imines groups in the schiff base struc-ure has an influence upon the interaction of metal centre withnions. The higher selectivity of iodide towards sensor no. 12
ould be explained by the presence of four carbon containinglkyl carbon chain instead of the phenyl moiety in the structuref Cd-schiff base ionophore. An alkyl chain has fewer electronsonating property than a phenyl group, and increases the acidity
ophores towards iodide ion.
812 A.K. Singh, S. Mehtab / Talanta 74 (2008) 806–814
Table 4Comparison of the potentiometric parameters of the proposed iodide-sensor with the literature reported iodide sensors
Ref. no. Ionophore name Linear range (M) Slope(mV decade−1
4.2. Determination of iodide containing mouth washsamples
In order to test the analytical utility of sensor it was used todetermine iodide in KEXIDONE (Cadex India Ltd.), ALPHA-
Table 5Performance of sensor no. 12 in partially non-aqueous media
Non-aqueouscontent (%v/v)
Working concentrationrange (M)
Slope (mV decade−1
activity)
0 5.3 × 10−7 to 1.0 × 10−2 59.2
Methanol10 5.3 × 10−7 to 1.0 × 10−2 59.220 6.8 × 10−7 to 1.0 × 10−2 59.230 4.2 × 10−6 to 1.0 × 10−2 58.435 1.5 × 10−5 to 1.0 × 10−2 56.5
Ethanol10 5.3 × 10−7 to 1.0 × 10−2 59.220 6.1 × 10−7 to 1.0 × 10−2 59.030 3.8 × 10−6 to 1.0 × 10−2 58.235 5.2 × 10−5 to 1.0 × 10−2 55.9
f the metal ion, so as to improve the interaction of iodide ionsnd metal centre.
.11. Effect of non-aqueous content
The sample may contain the non-aqueous content sohe performance of the proposed sensor (no. 12) was alsossessed in partially non-aqueous media using methanol–water,thanol–water and acetonitrile–water mixtures. The membraneoes not show any appreciable change in working concentra-ion range or slope in mixtures up to 20% (v/v) non-aqueousontent (Table 5). Above this, the potentials show an erraticehavior.
. Analytical performance
.1. Titration of iodide solution with a standard silveritrate solution
The proposed iodide membrane sensor (no. 12) was found to
ork well under laboratory conditions. It was applied success-
ully as an indicator electrode in the potentiometric titration of0 mL of 1.0 × 10−4 M KI with 1.0 × 10−3 M AgNO3 and theesulting titration curve are shown in Fig. 8. As can be seen, themount of iodide can be determined with sensor.
A
(4.62), NO3− (4.5), HPO4
2− (4.52),CH3COO− (4.51), Cit3− (4.56), HCO3
−(5.13), C2O4
2− (5.56); by MPM method
cetonitrile10 5.3 × 10−7 to 1.0 × 10−2 59.220 5.3 × 10−7 to 1.0 × 10−2 59.230 5.3 × 10−7 to 1.0 × 10−2 57.635 5.3 × 10−7 to 1.0 × 10−2 57.0
A.K. Singh, S. Mehtab / Talan
Fig. 8. Potentiometric titration curve for 20 mL of 1.0 × 10−4 M KI with1.0 × 10−3 M AgNO3 using the proposed sensor (no. 12).
Table 6Results of determination of iodide ion in mouthwash samples
INE (Nicholas Piramal India Ltd.) and POVIDINE (Stadmedrivate India Ltd.) mouth wash samples. A sample of 10 mLf sample was burned with 10 mL of 5% H2O2 and 4.0 mL of.5 M NaOH. The mixture was heated, acidified with H2SO4nd diluted with water. The sample solution obtained were anal-sed by proposed membrane sensor and the results obtained byriplicate measurement are compiled in Table 6. One can seerom the table that there is a satisfactory agreement between theetermined value and the labeled iodide content.
.3. Determination of iodide in sea water and river wateramples
To demonstrate the usefulness of the proposed sensor for
he environmental analysis, its potentiometric response to seand river water samples were investigated. River water samplerom Ganga river (Roorkee, India) and sea water samples from
able 7nalytical results (mean ± S.D., n = 3) for iodide in water samples by proposed
ensor
ample Added (�g L−1) Found (�g L−1) Recovery (%)
ea water 0 6110 70 98.520 88 97.8
iver water 0 4610 55 98.220 73 97.3
[[[
[
[
[[
[
ta 74 (2008) 806–814 813
ea coast (Bombay, India). The sample solutions were filteredhrough 0.45 �m membrane filter (Millipore) within 24 h of col-ection. Filtrates were stored in polyethylene bottles at 4 ◦C inhe dark. Water samples were used directly by adjusting pH 5.5y dilute HCl solution. The results of analysis of water samplesre compiled in Table 7.
. Conclusion
Among the synthesized cadmium complexes of salens viz.,,N′-bis(salicylidene)-1,4-diaminobutane (Cd-S1) and N,N′-is(salicylidene)-3,4-diaminotoluene (Cd-S2) the Cd-S1 shownigh affinity for iodide ion. The sensor no. 12 basedn Cd-S1 with membrane composition 7:2:60:31 (w/w, %)Cd-S1:HTAB:DBP:PVC) best. It exhibits widest workingoncentration range (5.3 × 10−7 to 1.0 × 10−2 M), Nernstianompliance (59.2 mV decade−1 of activity), fast response time11 s), and high selectivity for iodide. Its performance was com-ared with reported sensors, where it is seen that reported sensorshows significant superiority over them in many aspects likeide concentration range and high selectivity for I− even over
ipophilic anions Sal−, ClO4− and SCN−. Thus, the sensor pre-
ared is advancement over the reported systems. It also offers aossibility for practical sensing and the determination of iodideon in real sample solutions.
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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