Synthesis of a New Cu(II)-Ion ImprintedPolymer for Solid Phase Extractionand Preconcentration of Cu(II)

Dhruv K. Singh&, Shraddha Mishra

Analytical Research Laboratory, Department of Chemistry, Harcourt Butler, Technological Institute, Kanpur 208002, India;E-Mail: dhruvks123@rediffmail.com

Received: 9 July 2009 / Revised: 7 September 2009 / Accepted: 22 September 2009Online publication: 1 November 2009

Abstract

A new Cu(II)-ion imprinted polymer (IIP) has been synthesized by copolymerizing salicylicacid and formaldehyde as a monomer and crosslinker, respectively in the presence of Cu(II)-4-(2-pyridylazo) resorcinol complex. The imprinted Cu(II) ions were completely removed byleaching the IIP with 0.05 M EDTA. The maximum adsorption capacity for Cu(II) ions was310 lg g-1 at pH 6. The IIP was repeatedly used in adsorption–desorption experiments forseven times with recoveries *95%. The relative selectivity factor (ar) values of Cu(II)/Zn(II),Cu(II)/Cd(II), Cu(II)/Ni(II) and Cu(II)/Co(II) are 3.17, 2.90, 2.47 and 3.37, respectively. Thedetection limit corresponding to three times the standard deviation of the blank was found tobe 3.0 lg L-1. The developed IIP has also been tested for preconcentration and recovery ofCu(II) ions from water samples.

Keywords

Ion imprinted polymerSolid phase extractionPreconcentrationCu(II)4-(2-Pyridylazo) resorcinol

Introduction

Copper is an essential trace nutrient to

all higher plants and animals. In animals

including humans, it is found primarily

in the blood stream, as a co-factor in

various enzymes, and in copper based pig-

ments. Environmental Pollution Agency

(EPR)has established concentration action

level as 1.3 ppm for public water supplies.

Too much copper in the human body

can cause stomach and intestinal distress

such as nausea, vomiting, diarrhea and

stomach cramps. It is well known that the

free cupric ion is highly toxic for marine

organisms and its determination is an

important analytical task [1–4]. A great

variety of analytical procedures for Cu(II)

enrichment have been proposed, based

mainly on liquid–liquid extraction [5–7],

co-precipitation [8, 9] and solid phase

extraction (SPE) [10–12]. The SPE pro-

cedures are faster, reproducible and sludge

free.

The ion imprinted polymers have out-

standing advantages such as predeter-

mined selectivity in addition to its simple

preparation. The high selectivity of the

IIPs can be explained by the polymer

memory effect toward the metal ion inter-

action with a specific ligand, coordination

geometry,metal ion coordination number,

charge and size [13]. Nishide et al. utilized

for the first time ion template effect in the

synthesis of chelating polymers way back

in 1976. They [14, 15] cross-linked poly

(4-vinylpyridine) with 1,4-dibromobutane

in the presence of metal ions as templates.

The adsorption behaviour of obtained

resins for Cu(II), Zn(II), Co(II), Ni(II),

Hg(II), and Cd(II) was studied. The resins

preferentially adsorb the metal ion, which

had been used as template. Numerous

studies on IIPs and their applications for

selective preconcentration and separation

of metal ions have been reported: Cu(II)

[16–19], Hg(II) [20, 21], UO2(II) [22, 23],

Ni(II) [24, 25], Pd(II) [26], Cr(II) [27],

Cd(II) [28].

4-(2-Pyridylazo) resorcinol (PAR)

was found to possess high selectivity for

2009, 70, 1539–1545

DOI: 10.1365/s10337-009-1379-20009-5893/09/12 � 2009 Vieweg+Teubner | GWV Fachverlage GmbH

Original Chromatographia 2009, 70, December (No. 11/12) 1539

extraction of Cu(II) from aqueous solu-

tions [29–31]. Salicylic acid chelates have

been known for many years [32, 33].

Formaldehyde is a well known crosslink-

ing agent used in the synthesis of copoly-

mers such as phenol–formaldehyde and

salicylic acid–formaldehyde [28, 34]. Ion

imprinted polymer based on salicylic acid

and formaldehyde copolymer has not

been reported. Although some of the re-

ported IIPs [16–19] have higher selectivity

as well as adsorption capacity for Cu(II),

the high cost of these polymers limits their

use as an adsorbent. The objective of this

study was to investigate a new Cu(II)

selective and economic IIP for removal of

Cu(II). The route of synthesis of devel-

oped IIP is easy and its cost is low. The

percentage adsorption of developed IIP

(77.5%) is higher than other IIPs (14.2–

42.2%) reported in the literature [18, 19,

35]. The adsorbent is good enough for

separation and determination of Cu(II) in

matrixes containing components with

similar chemical properties and ionic radii

[Cu(II), 0.080 nm; Ni(II), 0.069 nm;

Co(II), 0.078 nm; Zn(II), 0.074 nm].

Experimental

Reagents and Apparatus

4-(2-Pyridylazo) resorcinol (C.D.H., In-

dia), salicylic acid and formaldehyde

(B.D.H., India) were used. The pH was

adjusted using the buffer solutions: HCl/

CH3COONa for pH 1–3; CH3COOH/

CH3COONaforpH4–7.Allother reagents

were of AR grade. Temperature con-

trolled rotary shaking machine (IEC-56),

Systronics digital pH meter, Systronics

double beam spectrophotometer 2203,

magnetic stirrer with hot plate, vacuum

oven, Heraeus-Carlo-Erba 1108 analyzer,

Shimadzu 8201 PC FTIR spectropho-

tometer, Atomic Absorption Spectrome-

ter-Graphite Tube Atomizer (GTA-AAS)

GTA-96 were used for shaking, pH mea-

surements, spectrophotometric measure-

ments, stirring, drying, elemental analysis,

FTIR studies and selectivity studies,

respectively.

Synthesis of Cu(II)-IonImprinted Polymer

The synthesis of IIP was carried out in

two steps;

1. Binary complex formation; and

2. Copolymerization of binary complex

with salicylic acid and formaldehyde.

The binary complex of Cu(II) ion

with PAR was prepared by stirring

1 mmol of copper(II) acetate and

1 mmol of PAR (dissolved in 10 mL

of demineralized water) for 2 h at

25 ± 2 �C. The formation of binary

complex was confirmed by UV–VIS

absorption spectral studies. Curve ‘a’ in

Fig. 1 shows the absorption spectrum of

PAR solution (1 9 10-4 M) against

DMW with absorption peaks at 211 and

410 nm. On addition of Cu(II) to the

above solution resulted the formation of

red colour complex with additional

absorption peaks at 516 nm (Fig. 1

curve b) and 519 nm (Fig. 1 curve c)

against DMW and PAR solution as

blanks, respectively. This evidence clearly

proves the formation of binary complex

Cu(II)-PAR.

This binary complex was mixed with

salicylic acid (0.1 mol), formaldehyde

(0.8 mol) and HCl (20 mL, 2 M), and

refluxed for 10 h. The resulting polymer

was dried in a vacuum oven at

50 ± 1 �C, ground and sieved to 60–100

mesh. The selected particles were treated

with DMW and then with 0.05 M

EDTA to remove Cu(II) linked to im-

printed polymer. The mechanism of

synthesis of IIP is given in Fig. 2. Non-

imprinted polymer (NIP) was also pre-

pared under similar experimental condi-

tions without Cu(II).

Preconcentration Procedure

For preconcentration of Cu(II) ions,

100 mL of the aqueous solution con-

taining 20–100 lg L-1 of Cu(II) was

stirred with 25 mg imprinted polymer

for 1 h at pH 6. Then, Cu(II)-ion im-

printed polymer was separated from the

adsorption media by filtration and

20 mL of 0.05 M EDTA solution was

added to IIP and stirred for 1 h. Im-

printed polymer was separated from the

desorption media and the concentration

of Cu(II) ions in the desorption media

was determined using GTA-AAS sys-

tem.

Surface Area Measurement

The surface area of the leached IIP

and NIP was measured by methylene

blue adsorption method [36]. A stan-

dard solution of methylene blue

(0.0178 g L-1) was prepared. Calibra-

tion curve for methylene blue was drawn

at k 600 nm. 0.1 g of IIP and NIP each

was equilibrated with 25 mL of methy-

lene blue solution until the absorbance

became constant. The amount of meth-

ylene blue adsorbed was calculated

based on concentration difference be-

tween the initial and equilibrium values,

which were measured by spectropho-

tometry. The surface area of leached IIP

and NIP was calculated using the fol-

lowing equation

Fig. 1. UV–VIS absorption spectra of PAR (1 9 10-4 M) a, PAR + Cu(II) (1:1 mole ratio)against DMW as blank b, PAR + Cu(II) (1:1 mole ratio) against PAR as blank c

1540 Chromatographia 2009, 70, December (No. 11/12) Original

As ¼GNAV[ 10�20

MMW

where, As is the surface area in m2 g-1, G

the amount ofmethylene blue adsorbed (g),

NAV the Avogadro’s number (6.0291023

mol-1), [ the methylene blue molecular

cross section (197.2 A2), MW is the molec-

ular weight of methylene blue (373.9

g mol-1) andM the mass of adsorbent (g).

Ion Exchange Capacity

The leached IIP and NIP (1 g) each was

taken in a glass column (i. d. 1.0 cm) and

the H+ ions were eluted by percolating a

neutral sodium chloride solution (1 M)

through the column at flow rate *0.5

mL min-1.The feedwaspasseduntil its pH

became equal to that of the eluent collected.

TheH+ ions so eluted were titrated against

standardized 0.01 MNaOH solution.

Batch Experiments

The imprinted polymer (25 mg) was

equilibrated with 20 mL of metal ion

solution (400 lg L-1) and 5 mL buffer

solution (pH 1–7) at 25 ± 2 �C in a

100 mL stoppard conical flask. The

amount of metal ion in the solution after

and before treatment with imprinted

polymer was determined by spectropho-

tometry [37] or GTA-AAS depending

upon concentration of metal ion and

sensitivity of the method. For compari-

son, adsorption experiments under simi-

lar experimental conditions were

conducted for NIP. The adsorption

capacity, distribution ratio, selectivity

factor of Cu(II) with respect to Zn(II),

Cd(II), Ni(II) and Co(II) and relative

selectivity factor were calculated using

following equations:

Q ¼ ðCo � CeÞ V =WD ¼ Q=Ce

a ¼ DCu=DM

ar ¼ ai=an

where, Q represents the adsorption

capacity (lg g-1), Co and Ce the initial

and equilibrium concentrations of Cu (II)

(lg L-1), W the mass of polymer (g) and

V the volume of metal ion solution (mL),

D the ratio of amount of metal ions in

polymer g-1 and amount of metal ion in

solution mL-1, a the selectivity factor,

DCu and DM represent the distribution

ratios of Cu(II) and Zn(II), Cd(II), Ni(II)

or Co(II), ar the relative selectivity factor,Di,Dn and ai, an represent the distributionratios and selectivity factors of IIP and

NIP, respectively.

Column Experiments

1 g of IIP/NIP was slurred with DMW

and then poured in to a pyrex glass col-

umn (i. d. 4.0 mm) plucked with small

portion of glass wool at the bottom. The

column was preconditioned by passing

DMW and then 100 mL of Cu(II) solution

(4 lg 10 mL-1) was passed through the

column at a flow rate of *0.5 mL min-1.

Results and Discussion

FTIR

FTIR spectra of PAR and Cu(II)-ion im-

printed polymer are given in Fig. 3. Both

spectra of pure PAR and Cu(II)-ion im-

printed polymer have the characteristics

stretching vibration bands of OH at 3,277

and 3,058 cm-1, respectively. The shifting

of OH peak towards lower wave number

in case of Cu(II)-ion imprinted polymer

seems due to dimer formation [38]. The

FTIR spectrum of Cu(II)-ion imprinted

polymer shows characteristic absorption

peaks of >C=N and –N=N– at 1,490

and 1,445 cm-1, respectively. Absorption

peak at 1,204 cm-1 seems due to C–N

stretching vibration.

Elemental Analysis

To evaluate the degree of PAR incorpo-

ration, elemental analysis of the IIP and

NIPwas performed. The incorporation of

PAR was found 0.070 mmol g-1 in IIP

and 0.069 mmol g-1 in NIP from N

stoichiometry.

Surface Area

Porosity is an important factor as it can

change the surface area of the adsorbent

and thus increases the selective removal

of Cu(II) ions from complex matrices.

Surface area measurements done by

methylene blue adsorption experiments

revealed a higher surface area of

95.26 m2 g-1 for leached IIP than sur-

face area of 42.87 m2 g-1 for NIP. In IIP

the cavities are created after removal of

template and hence porosity seems to be

responsible for its higher surface area

than NIP.

Ion Exchange Capacity

The ion exchange capacities of leached

IIP and NIP were found to be 0.372 and

0.368 mmol g-1, respectively for H+/

Na+ ion exchange. This seems due to the

replacement of H+ ions of polymer

containing –COOH and –OH groups by

Na+ ions. Probably, due to steric hin-

drance all the H+ are not replaced by

Na+ resulting in poor ion exchange

capacity in both polymers.

Fig. 2. Scheme for the preparation of sali-cylic acid–formaldehyde-PAR-Cu(II) imprintedpolymer

Original Chromatographia 2009, 70, December (No. 11/12) 1541

Adsorption Capacity

Adsorption of Cu(II) onto IIP and NIP

was investigated by batch experiments

in the concentration range 100–600

lg L-1. The amount of Cu(II) ions ad-

sorbed per unit mass of the IIP and NIP

increases with the increased initial con-

centration of Cu(II) up to 400 lg L-1

(Fig. 4). Above 400 lg L-1 concentra-

tion, the adsorption capacity remains

constant in IIP (310 lg g-1) and NIP

(195 lg g-1) both. In IIP, the cavities

created after removal of template is

complementary to the imprint ion in size

and coordination geometries. Whereas,

in NIP adsorbent, the random distribu-

tion of the ligand functionalities in

polymeric network results in no speci-

ficity in rebinding affinities.

Effect of pH

The metal ion complexation of Cu(II)-

PAR is highly dependent on pH of the

medium. The effect of pH on Cu(II)

adsorption onto IIP and NIP was

studied by varying the pH from 1 to 7

and the results are plotted in Fig. 5.

The adsorption of Cu(II) increases as

the pH increases. In acidic solution

below pH 3, adsorption is very low.

This seems due to protonation of the

functional groups of the polymers and

competing H+ ions as well. The opti-

mum pH 6 was chosen for further

adsorption experiments.

Effect of Flow Rate

The flow rate of Cu(II) solution through

the packed bed column is an important

parameter for the time controls of

adsorption and analysis using the col-

umn procedure. The effect of flow rate

on adsorption of Cu(II) onto IIP and

NIP was investigated. The results show

that Cu(II) can be adsorbed quantita-

tively onto Cu(II)-ion imprinted polymer

up to a flow rate of 1.0 mL min-1.

Above 1.0 mL min-1, the recovery was

less than 95% (Fig. 6). However, in case

of NIP, the recovery was only 82% at a

flow rate of 1.0 mL min-1. The decrease

in adsorption of Cu(II) ions with

increasing flow rate seems due to de-

crease in contact time of Cu(II) with the

adsorbent. For IIP, the flow rate of

0.5 mL min-1 was chosen as optimum in

further column experiments.

Cu(II) Adsorption–DesorptionStudies

The adsorbed Cu(II) ions onto IIP were

desorbed by treatment with 0.05 M

EDTA. The Cu(II) ions adsorbed im-

printed polymer was placed in the

desorption medium and stirred at room

temperature for different time intervals.

Maximum desorption was observed

within 1 h. In order to test the reusability

of Cu(II)-ion imprinted polymer, Cu(II)

adsorption–desorption procedure was

repeated seven times with recoveries not

less than 95% by using the same im-

printed polymer.

Equilibrium Adsorption Time

The time dependence of Cu(II) adsorp-

tion onto the IIP and NIP from aqueous

solution was determined by batch

experiments. Higher adsorption rates are

observed at the beginning of adsorption

process, and then saturation values (i.e.

adsorption equilibrium) are gradually

reached within 60 min (Fig. 7). The

adsorption equilibrium seems due to

Fig. 3. FTIR spectra of PAR a and Cu(II)-ion imprinted polymer b

Fig. 4. Effect of concentration on the adsorption of Cu(II) on IIP and NIP; pH 6.0; T 25 ± 2 �C

1542 Chromatographia 2009, 70, December (No. 11/12) Original

complexation between Cu(II) ions and

template group in the imprinted poly-

mer. However, saturation value ap-

proached after 80 min in case of NIP.

Maximum Sample Volumeand Eluent Type

The enrichment of Cu(II) ions onto IIP

was studied by standard column proce-

dure. A Cu(II) solution (100–1,200 mL)

containing 200 lg of Cu(II) in each was

equilibrated with 1 g of IIP at room

temperature. The result revealed that a

maximum sample volume can be upto

1,000 mL with 98% recovery. The choice

of eluent type (HCl, HNO3 and EDTA)

was also studied in column procedure.

The results showed that 20 mL of 0.05 M

EDTA was sufficient for 98% recovery.

However, in case of 0.1 M each of HCl

and HNO3, the recovery was 85–90%. So

20 mL of 0.05 M EDTA was used as

eluent in all further experiments.

Competitive Adsorption

The result of competitive adsorption in

batch experiments of Zn(II)/Cu(II),

Cd(II)/Cu(II), Ni(II)/Cu(II) and Co(II)/

Cu(II) from their binary mixtures are

given in Table 1. Although, these ions

possess a similar chemical properties, the

competitive adsorption capacity of

Cu(II)-ion imprinted polymer for Cu(II)

is higher than NIP due to molecular

geometry. The D value for Cu(II) is sig-

nificantly higher than for Zn(II), Cd(II),

Ni(II) and Co(II) in IIP which is not

applicable in NIP (Table 2). The ar val-ues are 3.17, 2.90, 2.47 and 3.37 respec-

tively, which are greater than 1 for

Cu(II)-ion imprinted polymer of Cu(II)/

Zn(II), Cu(II)/Cd(II) Cu(II)/Ni(II) and

Cu(II)/Co(II). It shows that IIP can be

utilized for determination of Cu(II) even

in the presence of Zn(II), Cd(II), Ni(II)

and Co(II) interferences.

Analytical Parameters

Under the optimum conditions described

above, the calibration curve was linear

over the concentration range 20–100 lg

L-1 of Cu(II). The linear equation with

regression is as follows.

A ¼ 0:001C þ 0:097

where, correlation coefficient is 0.999,A is

the absorbance and C the concentration

in microgram of Cu(II) ion per 1.0 L. The

lowest concentration that could be

Fig. 5. Effect of pH on the adsorption of Cu(II) on IIP and NIP; 400 lg L-1 Cu(II); T25 ± 2 �C

Fig. 6. Effect of flow rate on the adsorption of Cu(II) on IIP and NIP; 400 lg L-1 Cu(II); pH6.0; T 25 ± 2 �C

Fig. 7. Adsorption rates of Cu(II) on IIP and NIP; 400 lg L-1 Cu(II); pH 6.0; T 25 ± 2 �C

Original Chromatographia 2009, 70, December (No. 11/12) 1543

determined by GTA-AAS method below

which the recoveries become non-quan-

titative is 3.0 lg L-1. All the statistical

calculations are based on the average of

triplicate readings for each standard

solution in the given range.

Applications

Theproposedmethodhas been applied for

the determination of Cu(II) in tap water

(hardness = 262.3 ppm, pH 7.5), distilled

water (pH 7.0) and synthetic sea water [39]

samplesusingbatchprocedure.The results

listed in Table 3 indicate the suitability of

the present polymer for preconcentration

ofCu(II) fromwater samples (98.4–99.9%

recovery). The decrease in recovery from

sea water seems due to its high salinity.

Conclusions

Cu(II)-ion imprinted polymer is a new

type of carrier that can considerably en-

hance the adsorption capacity and the

selectivity for Cu(II). The imprinted

polymer, thus obtained, adsorbed the

corresponding guest Cu(II) ions more

effectively than did the non-imprinted

polymer. The cross-linked imprinted

polymer has good chemical and physical

stability, rapid equilibration in adsorbing

Cu(II) ions and can be repeated to use

seven cycles with recoveries of not less

than 95%. Cu(II)-IIP shows good selec-

tivity for Cu(II) ions even in the presence

of complex matrices, such as tap water

and sea water. The procedure for the

preconcentration and solid phase extrac-

tion of Cu(II) is simple, reproducible and

less susceptible to contamination.

Acknowledgements

The authors thank the Director of

HBTI, Kanpur for providing necessary

research facilities.

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Table 1. Adsorption of metal ions on the Cu(II)-ion imprinted and non-imprinted polymers

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Imprinted polymer Non imprinted polymer

Cu(II) 310 195Zn(II) 182 169Cd(II) 103 87Ni(II) 81 59Co(II) 54 51

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