Ad

VD

h

I

I

I

a

ARRAA

KBDePP

1

aueisN

0h

Analytica Chimica Acta 749 (2012) 44– 50

Contents lists available at SciVerse ScienceDirect

Analytica Chimica Acta

jo u rn al hom epa ge: www.elsev ier .com/ locate /aca

new beryllium ion-selective membrane electrode based onibenzo(perhydrotriazino)aza-14-crown-4 ether

inod Kumar Gupta ∗, Ashok Kumar Singh, Naveen Merguepartment of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India

i g h l i g h t s

It is the first report on an ion sensorusing substituted aza-14-crown-4for Be2+.Response time is 15 s and life timeis more than 4 months with goodreproducibility.The proposed electrode works well ina wide pH range 3.0–9.0.

g r a p h i c a l a b s t r a c t

Variation of potential with Be2+ activity for membrane sensors based on dibenzo(perhydrotriazino)aza-14-crown-4 ether.

r t i c l e i n f o

rticle history:eceived 20 June 2012eceived in revised form 21 August 2012ccepted 29 August 2012vailable online 6 September 2012

a b s t r a c t

Beryllium(II) selective electrodes have been fabricated based on poly(vinyl chloride) (PVC) matrixmembranes containing newly synthesized neutral carrier dibenzo(perhydrotriazino)aza-14-crown-4 ethers as ionophore. Best performance was exhibited by the membrane having a compositionionophore (IIa):PVC:sodium tetraphenylborate (NaTPB):tributyl phosphate (TBP) in the ratio (w/w; mg)of 5:30:3:65. This membrane worked well over a wide concentration range 7.6 × 10−6 to 1.0 × 10−1 M of

eywords:eryllium selective electrodeibenzo(perhydrotriazino)aza-14-crown-4theroly(vinyl chloride) membrane

Be2+ with a Nernstian slope of 30.7 mV per decade of beryllium activity. The response time of the sensoris 15 s and the membrane can be used over a period of 4 months with good reproducibility. The proposedelectrode works well in a wide pH range 3.0–9.0. It was successfully applied to the determination ofberyllium in a mineral sample.

© 2012 Elsevier B.V. All rights reserved.

otentiometry

. Introduction

At present, crown ethers are essential for the organic andnalytical chemistry, since crown ethers are useful in removingnnecessary metal cations. The other important role of the crownther is its capability of recognizing metal cations through cav-

ty [1]. Oxygen donor macrocycles such as crown ethers form atrong complexes with alkali and alkaline earth metal ions [2].itrogen–oxygen mixed donor macrocycles such as aza crown

∗ Corresponding author. Tel.: +91 1332 285801; fax: +91 1332 286202.E-mail addresses: vinodfcy@iitr.ernet.in, vinodfcy@gmail.com (V.K. Gupta).

003-2670/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.aca.2012.08.050

ethers can form stable complexes with both alkali and transitionmetal ions [3,4].

Beryllium is useful in many fields, such as aircraft, nuclearreactor, telecommunication, X-ray tubes and computer indus-tries. Beryllium is unfortunately associated with severe respiratorydiseases, i.e. chronic beryllium disease (CBD) [5], acute clinicalpneumonitis [6] and lung cancer [7]. So it is necessary to detect theberyllium in the vicinity of ore-processing plants and their disposalsites and industry.

Different techniques have been used for the determination ofthe beryllium ion in the different samples, e.g. spectrophotom-etry [8–10], gravimetry [11], chromatography [12–14], spectrofluorimetry [15], gas chromatography [16,17], atomic absorption

Chimica Acta 749 (2012) 44– 50 45

ssaoc

fscmst

est

2

2

(ettAat

2

tdtdT2t2t

1

47

p1((7

th15J

2

eaCg

6 5 4 3 2 1

140

120

100

80

60

40

20

0

Pote

nti

al (

-mV

)

membrane

1

2

3

4

5

6

7

V.K. Gupta et al. / Analytica

pectrometry (AAS) [18–21], inductively coupled plasma masspectrometry (ICP-MS) [22] and inductively coupled plasmatomic emission spectrometry (ICP-AES) [23–26]. However, mostf these methods require very expensive instruments and are timeonsuming.

The ion selective electrodes (ISEs) have been successfully usedor the determination of different metal ions, such as lithium [27],odium [28], potassium [29], beryllium [30–34], magnesium [35],alcium [36], strontium [37], terbium [38], and holmium [39]. Thisethod provides easy construction and manipulation, has good

electivity in a wide concentration range, has a relatively low detec-ion limit, fast response and is non-destructive.

In this paper, we report for first time an ISE based on aza crownther as a neutral carrier, in the construction of a beryllium ionelective electrode. The developed electrode showed good selec-ivity and working range over other cations.

. Experimental

.1. Reagents and materials

Reagent grade tributyl phosphate (TBP), 1-chloronaphthaleneCN), dibutyl phthalate (DBP), dioctyl phthalate (DOP), Bis(2-thylhexyl)sebacate (BEHS), 2-nitrophenyloctyl ether (o-NPOE),etrahydrofuran (THF), high relative molecular weight PVC, sodiumetraphenylborate (NaTPB) and beryllium nitrate (Merck andldrich). The pH adjustments were made with dilute hydrochloriccid, sodium hydroxide, triply distilled deionized water was usedhroughout.

.2. Synthesis of ionophore

The aza crown ethers were synthesized [40,41] accordingo Scheme 1, salicylaldehyde was reacted with 2,2′-ichloro ethyl ether in dimethyl sulfoxide under nitrogeno give 1,7-Bis(2′-formylphenyl)-1,4,7-trioxa heptane(I). Theibenzo(perhydrotriazino)aza-14-crown-4 ethers: IIa (8,11,14-rioxa-22,24,25-triazatetracyclo[19.3.1.02,7.015,20]pentacosa-,4,6,15(20),16,18-hexaene-23-thione) and IIb (23-Imino-8,11,14-rioxa-22,24,25-triazatetracyclo[19.3.1.02,7.015,20]pentacosa-,4,6,15(20),16,18-hexa-ene) were obtained by reaction of I withhiourea and guanidine.

1,7-Bis (2′-formylphenyl)-1,4,7-trioxa heptane (I). mp 74 ◦C.H NMR spectrum, ı, ppm (J, Hz): 4.00 (t, J = 4.5, 4H); 4.28 (t, J = 4.5,H); 7.00 (d, J = 8.5, 2H); 7.05 (t, J = 7.5, 2H); 7.52 (dt, J = 2.0, 7.5, 2H);.83 (dd, J = 2.0, 8.0, 2H); 10.50 (2H, s).

8,11,14-Trioxa-22,24,25-triazatetracyclo[19.3.1.02,7.015,20]entacosa-2,4,6,15(20),16,18-hexaene-23-thione (IIa). mp88 ◦C. IR spectrum, �, cm−1: 3397, 3321 and 3196 (NH), 1059C S). 1H NMR spectrum, ı, ppm (J, Hz): 4.03–4.27 (m, 9H); 5.33d, J = 12.0, 2H); 6.65 (br. s, 2H); 6.87 (d, J = 8.0, 2H); 6.93 (dt, J = 1.0,.5, 2H); 7.25 (d, J = 2.0, 2H); 7.33 (dt, J = 2.0, 8.5, 2H).

23-Imino-8,11,14-trioxa-22,24,25-riazatetracyclo[19.3.1.02,7.015,20]pentacosa-2,4,6,15(20),16,18-exa-ene (IIb). mp 220 ◦C. IR spectrum, �, cm−1: 3313, 3243 (NH),614 (C N). 1H NMR spectrum, ı, ppm (J, Hz): 4.03–4.18 (m, 9H);.45 (d, J = 12.5, 2H); 6.40 (br. s, 2H); 6.99 (t, J = 7.5, 2H); 7.10 (d,

= 8.0, 2H); 7.37 (d, J = 7.5, 2H); 7.43 (t, J = 7.5, 2H); 8.48 (br. s, 1H).

.3. Electrode preparation

PVC membranes have been prepared as suggested by Craggs

t al. [42]. Membranes were prepared by dissolving appropriatemounts of ionophore, PVC, plasticizers (TBP, DOP, DBP, o-NPOE,N and BEHS) and anion additive (NaTPB) in THF (5 mL). The homo-eneous mixture obtained after completion of dissolution of all

-lo gaBe

2+

Fig. 1. Variation of potential with Be2+ activity for membrane sensors based on IIa.

ingredients was concentrated by evaporation of THF at room tem-perature. This homogeneous mixture was poured into poly acrylaterings placed on a smooth glass plate. THF was allowed to evaporateat room temperature about 24 h and carefully removed the mem-brane from glass plate and attached to one end of a pyrex glass tube.The membrane which is attached to the glass tube was equilibratedfor 2–3 days in a 0.1 M Be (NO3)2 solution.

2.4. Potential measurements

The potentials have been measured by varying the concentra-tion of test solution of beryllium nitrate in the range 1.0 × 10−8

to 1.0 × 10−1 M. The potential measurements were carried out atroom temperature using saturated calomel electrodes (SCE) as areference electrode with the following cell assembly:

SCE||test solution|PVC membrane|0.1 M Be(NO3)2||SCE

3. Results and discussion

3.1. The effect of plasticizer and membrane composition onpotential response

The linear range, slope and response time significantly dependon the nature and amount of ionophore, plasticizers and theamount of lipophilic additive used. Potential of the membranes(with IIa and IIb as ionophores) were investigated in the range1.0 × 10−8 to 1.0 × 10−1 M and the results obtained are shown inTables 1 and 2. Generally plasticizer is the one of the major compo-nent in the fabrication of ion selective electrode, which enhancesthe flexibility and softness of the membrane, ensures the mobil-ity of the ionophore, determines membrane polarity and providessuitable mechanical properties to the membrane. The influence ofplasticizer on the Beryllium electrode was investigated by usingdifferent plasticizers such as TBP, DOP, DBP, CN, o-NPOE and BEHS(Figs. 1 and 2). A narrow working concentration range (7.4 × 10−4

to 1.0 × 10−1 M) with a slope of 10.4 mV perdecade of activity wasexhibited by the membrane (with IIa) without plasticizer (mem-brane no. 7), on the addition of plasticizers significant change

was observed in slope and response time of electrodes and theresults are tabulated in Table 1. Membrane with CN as a plasti-cizer (no. 5) showed linearity in the concentration range 6.8 × 10−4

to 1.0 × 10−1 M with a slope of 39.1 mV perdecade of activity. The

46 V.K. Gupta et al. / Analytica Chimica Acta 749 (2012) 44– 50

CHO

OH

Cl O Cl

CHO

OO

O

OHC

O

NH

HN NH

O

O

X

+DMSO, NaOH

N2, 180 oC, 72 h

H2N NH2

X

NH4OAc

20 oC

13 h

(I)

(IIa,b)

IIa: X=SIIb: X=NH

Scheme 1. Dibenzo(perhydrotriazino)aza-14-crown-4 ethers.

Table 1Effect of plasticizer on the potentiometric response of IIa based PVC membrane sensors.

Membrane no. Composition of membrane (mg) Linear range (M) Slope (±0.5 mV/decade) Response time (s)

Ionophore Plasticizer NaTPB PVC

1 5 65 (TBP) 3 30 7.6 × 10−6 to 1.0 × 10−1 30.7 152 5 65 (DOP) 3 30 5.6 × 10−4 to 1.0 × 10−1 19.5 183 5 65 (DBP) 3 30 7.9 × 10−4 to 1.0 × 10−1 13.9 284 5 65 (o-NPOE) 3 30 8.3 × 10−4 to 1.0 × 10−1 19.1 325 5 65 (CN) 3 30 6.8 × 10−4 to 1.0 × 10−1 39.1 28

−4 −1

mBtt(ft

TE

6 5 65 (BEHS) 3 30

7 5 – 3 30

embranes with DOP (no. 2), DBP (no. 3), o-NPOE (no. 4) andEHS (no. 6) as plasticizers did not improve the performance ofhe electrodes (Fig. 1). Similar results were also obtained withhe membranes (IIb as a ionophore) with and without plasticizers

membrane no. 8–14). It is seen from Table 2 and Fig. 2. Further, dif-erent amounts of ionophore, plasticizer and anionic additive wereried to get the optimum composition (Table 3). The membrane (no.

able 2ffect of plasticizer on the potentiometric response of IIb-based PVC membrane sensors.

Membrane no. Composition of membrane (mg)

Ionophore Plasticizer NaTPB PVC

8 5 65 (TBP) 3 30

9 5 65 (DOP) 3 30

10 5 65 (DBP) 3 30

11 5 65 (o-NPOE) 3 30

12 5 65 (CN) 3 30

13 5 65 (BEHS) 3 30

14 5 – 3 30

7.8 × 10 to 1.0 × 10 16.5 307.4 × 10−4 to 1.0 × 10−1 10.4 35

1) with 5 mg of the ionophore and 3 mg of ionic additive showedthe best performance. It is clear that the linear range of electrodeincrease with increase in the amount of the ionophore from 1 mgto 5 mg. Hence, the best composition of the membrane was found

to be 5:65:30:3 (ionophore (IIa):TBP:PVC:NaTPB), exhibited highworking concentration range of 7.6 × 10−6 to 1.0 × 10−1 M with aslope of 30.7 mV per decade of activity, i.e. membrane no. 1.

Linear range (M) Slope (±0.5 mV/decade) Response time (s)

5.7 × 10−5 to 1.0 × 10−1 33.0 173.3 × 10−4 to 1.0 × 10−1 22.6 201.9 × 10−4 to 1.0 × 10−1 18.3 271.5 × 10−4 to 1.0 × 10−1 18.2 328.9 × 10−4 to 1.0 × 10−1 36.5 312.1 × 10−4 to 1.0 × 10−1 20.0 291.3 × 10−4 to 1.0 × 10−1 14.3 38

V.K. Gupta et al. / Analytica Chimica Acta 749 (2012) 44– 50 47

Table 3Effect of membrane composition on the potentiometric response of IIa based PVC membrane (no. 1).

Membrane no. Composition of membrane (mg) Linear range (M) Slope (±0.5 mV/decade)

Ionophore TBP NaTPB PVC

15 1 69 1 30 1.58 × 10−5 to 1.0 × 10−1 27.216 2 68 1 30 1.00 × 10−5 to 1.0 × 10−1 28.117 3 67 1 30 8.90 × 10−6 to 1.0 × 10−1 29.518 4 66 1 30 8.71 × 10−6 to 1.0 × 10−1 19.819 5 65 1 30 8.60 × 10−6 to 1.0 × 10−1 22.820 6 64 1 30 8.65 × 10−6 to 1.0 × 10−1 23.121 7 63 1 30 8.83 × 10−6 to 1.0 × 10−1 20.922 8 62 1 30 9.12 × 10−6 to 1.0 × 10−1 26.223 1 69 2 30 1.07 × 10−5 to 1.0 × 10−1 28.024 2 68 2 30 1.02 × 10−5 to 1.0 × 10−1 26.525 3 67 2 30 8.70 × 10−6 to 1.0 × 10−1 29.526 4 66 2 30 8.67 × 10−6 to 1.0 × 10−1 26.327 5 65 2 30 8.58 × 10−6 to 1.0 × 10−1 22.728 6 64 2 30 8.63 × 10−6 to 1.0 × 10−1 21.729 7 63 2 30 8.70 × 10−6 to 1.0 × 10−1 20.230 8 62 2 30 1.02 × 10−5 to 1.0 × 10−1 28.531 1 69 3 30 1.07 × 10−5 to 1.0 × 10−1 28.232 2 68 3 30 9.12 × 10−6 to 1.0 × 10−1 29.533 3 67 3 30 9.12 × 10−6 to 1.0 × 10−1 29.534 4 66 3 30 8.70 × 10−6 to 1.0 × 10−1 28.8

−5 −1

3

wgiw

3

aAinsstsp

F

35 6 64 3

36 7 63 3

37 8 62 3

.2. Calibration characteristics

Among the different membrane compositions, has membraneith ionophore (IIa)/TBP/PVC/NaTPB in (w/w, %) 5/65/30/3 showed

ood sensitivity and linear range. This sensor exhibited the max-mum working concentration range of 7.6 × 10−6 to 1.0 × 10−1 M

ith a slope of 30.7 mV per decade of activity (sensor no. 1, Table 1).

.3. Response and life time

The membrane of (IIa) and (IIb) without any plasticizer (no. 7nd 14) exhibited the response time of 35 and 38 s (Tables 1 and 2).s a result of the addition of solvent mediators, the response time

mproved significantly. The better results exhibited by membraneo. 1 and 8 (with TBP) in the form of response time for theseensors are 15 and 17 s, respectively. The membranes with DOP

howed good performance, there is no significant change with addi-ion of other plasticizers (Tables 1 and 2). The life time of theensor (no. 1) was studied over a 6 months period. During thiseriod, the electrode was daily used over extended period (3–4 h

7 6 5 4 3 2 1

140

120

100

80

60

40

20

0

Pote

nti

al (

-mV

)

-lo gaBe

2+

membrane

8

9

10

11

12

13

14

ig. 2. Variation of potential with Be2+ activity for membrane sensors based on IIb.

30 1.02 × 10 to 1.0 × 10 29.030 1.02 × 10−5 to 1.0 × 10−1 26.730 1.12 × 10−5 to 1.0 × 10−1 29.5

per day), its slopes and working concentration ranges have beenmeasured. After 4 months the changes were observed continuouslyin the slope (from 30.7 to 28.1 mV per decade of activity), workingrange (7.6 × 10−6–1.0 × 10−1 M to 5.80 × 10−5–1.0 × 10−1 M) andresponse time (15–20 s), membranes were stored in 0.1 M Be(NO3)2solution when not in use.

3.4. Selectivity coefficient

The selectivity coefficients were investigated by fixed interfer-ence method [43–53]. In this method the interfering ion containeda fixed concentration and varying amount of Be2+ ions. The val-ues of selectivity coefficient determined are showed in Table 4. Avalue of selectivity coefficient of 1.0 indicates equal response toprimary as well as interfering ions. A value of selectivity coefficientof smaller than 1.0, indicates an equal response to primary andthe interfering ions. The selectivity coefficient determined by thismethod is smaller than 1.0, thus indicating that the present sensor

(no. 1) is selective even over a number of monovalent, bivalent andtrivalent cations. The obtained selectivity coefficient values showedthat they did not cause interference when present in equal or lessconcentration than Be2+. In this measurement, the potential of the

Table 4Selectivity coefficients (Kpot

Be,B) of various Interfering cations for membrane no. 1.

Interfering ion Selectivity coefficient (KpotBe,B

)

Li+ 7.76 × 10−2

Na+ 4.46 × 10−2

K+ 2.95 × 10−2

Ag+ 7.94 × 10−2

NH4+ 6.16 × 10−2

Mg2+ 9.33 × 10−2

Ca2+ 6.45 × 10−2

Mn2+ 6.60 × 10−2

Fe2+ 6.16 × 10−2

Co2+ 9.77 × 10−2

Ni2+ 5.01 × 10−2

Cu2+ 5.88 × 10−2

Zn2+ 7.40 × 10−2

Cd2+ 6.76 × 10−2

Al3+ 7.41 × 10−2

Cr3+ 8.91 × 10−2

48 V.K. Gupta et al. / Analytica Chimica Acta 749 (2012) 44– 50

Table 5Determination of beryllium ion in beryl and tap water samples.

S. no. Be2+ content in final solution ofberyl samples (mg L−1)

Be2+ content in tap water (mg L−1)

ISE AAS ISE

Added Found Recovery (%)

soptdK

3

et

TC

1 25.4 ± 0.4 26.2 ± 0.2

2 25.8 ± 0.6 26.0 ± 0.2

3 24.8 ± 0.3 25.5 ± 0.5

ensor (no.1) was found as a function of Be2+ concentration of vari-us K+ concentrations, and the results are shown in Fig. 3. The linearortion of the graph is showing that the reduced working concen-ration range is cause of the K+ concentration. Activity of Be2+ atifferent concentrations of 1.0 × 10−2, 1.0 × 10−3 and 1.0 × 10−4 M+ resulted in the deviation in the pure solution plot.

.5. pH effect

The effect of pH on the performance of the most responsivelectrode (no. 1) was studied over the pH range of 1–12 usingwo different concentrations 1.0 × 10−3 M and 1.0 × 10−4 M of Be2+.

able 6haracteristics comparison between the proposed sensor and previously.

Reference Ionophore Linear range (M) Det

[26]

O

O

O 2.5 × 10−6 to 4.0 × 10−3 1.0

[27]

**

O

O

O

OO

O

m m'

1.0 × 10−6 to 1.0 × 10−3 8.0

[28]

NH2

O O

H2N

OMe

Br

3.0 × 10−6 to 7.0 × 10−2 2.0

[29]

HNXNH

O O O

n

OO3.0 × 10−6 to 3.0 × 10−2 2.0

[30] 1.0 × 10−7 to 1.0 × 10−1 4.0

This workNH

O O

O

HN NH

S

7.6 × 10−6 to 1.0 × 10−1 5.0

40 40.4 ± 0.30 101.050 49.6 ± 0.56 99.2100 98.3 ± 0.21 98.3

The pH was adjusted by using dilute hydrochloric acid and sodiumhydroxide. The results are shown in Fig. 4, which indicated thatthe potential remains constant over the pH range of 3.0–9.0. Thedeviation in electrode potential at pH <3.0 may be due to interfer-ence of H+ ions and at pH >9.0 could be due to the formation ofsome hydroxy complexes of beryllium ions. Hence, the working pHrange of electrode is 3.0–9.0.

4. Analytical applications

The Be2+ ion selective electrode was found to work well underlaboratory conditions. It was successfully applied to the direct

ection limit (M) Response time (s) Slope (mV/decade) pH range

× 10−6 50 29.5 2.0–6.0

× 10−7 30 29.0 4.0–8.0

× 10−6 14 29.6 4.0–7.0

× 10−6 15 29.4 4.0–7.5

× 10−8 10 29.6 4.5–8.0

× 10−6 15 30.7 4.5–8.0

V.K. Gupta et al. / Analytica Chim

7 6 5 4 3 2 1

140

120

100

80

60

40

20

0

Pote

nti

al (

-mV

)

-logaBe

2+

a

b

c

d

Fig. 3. Variation of potentials of sensor no. 1 with Be2+ activity in the presence of(a) 0.0 M, (b) 1.0 × 10−2 M, (c) 1.0 × 10−3 M and (d) 1.0 × 10−4 M K+.

0 2 4 6 8 10 12

140

120

100

80

60

40

20

0

Pote

nti

al (

-mV

)

pH

a

b

FI

mowaissfaw

5

1a57dspvt

[[

[

[[[

[[[[[[

[

[[[[[

[[[[

[

[

[

[[[

[

[

[

[

[[[[

[

ig. 4. Effect of pH on potentials of sensor no. 1 (composition of 5:30:3:65 ofIa:PVC:NaTPB:TBP) at: (a) 1.0 × 10−3 and (b) 1.0 × 10−4 M Be2+.

easurement of Be2+ in beryl samples after suitable treatmentf the mineral [54]. The beryllium content of the final solutionas determined using the proposed membrane sensor and atomic

bsorption spectrometry and the results are shown in Table 5. Ast is seen, the obtained results by the ion selective electrode are inatisfactory agreement with those obtained by atomic absorptionpectrometry (AAS). It could successfully recover beryllium ionrom tap water containing different foreign ions [55–70]. Differentmounts of Be2+ were spiked into tap water samples and the Be2+

as measured, the obtained results are shown in Table 5.

. Conclusion

The membrane incorporating dibenzo(perhydrotriazino)aza-4-crown-4 ether (IIa) as the ionophore, TBP as the plasticizernd NaTPB as the anion additive in a PVC matrix in the ratio:65:3:30 can be used to determine Be2+ in the concentration range.6 × 10−6 to 1.0 × 10−1 M with a Nernstian slope of 30.7 mV perecade of activity. The functional pH range is 3.0–9.0. The sen-

or shows a fast response time of 15 s and performed well for aeriod of 4 months. The proposed sensor is compared to the pre-iously reported beryllium ion selective electrodes with respecto the characteristics such as linear range, response time and pH

[

[[

ica Acta 749 (2012) 44– 50 49

range. The sensor showed good pH range and wide concentrationrange than previously reported electrodes (Table 6). The electrodecan be successfully applied to the determination of Be2+ in berylsamples and recovery of Be2+ from tap water.

Acknowledgement

M. Naveen is thankful to Ministry of Human Resource Develop-ment (MHRD), New Delhi, India for financial support.

References

[1] Y. Maruyama, M. Matsugami, Y. Kuta, Condens. Matter Phys. 51 (2007) 315–322.[2] F. Vogtle, Top. Curr. Chem. 98 (1981) 1–41.[3] V.J. Tom, M.S. Shaikjee, R.D. Hancok, Inorg. Chem. 25 (1986) 2992–3000.[4] R.M. Izatt, J.S. Bradshaw, S.A. Nielsen, J.D. Lamb, J.J. Christensen, D. Sen, Chem.

Rev. 85 (1985) 271–339.[5] M. Eisenbud, J. Lisson, J. Occup. Med. 25 (1983) 196–202.[6] American College of Chest Physicians, Dis. Chest 48 (1965) 550–558.[7] G.L. Finch, M.D. Hoover, F.F. Hahn, K.J. Nikula, S.A. Belinsky, P.J. Haley, W.C.

Griffith, Environ. Health Perspect. 104S (1996) 973–979.[8] E.B. Sandell, H. Hnishi, Photometric Determination of Trace Metals, Part 3,

Wiley, New York, 1978.[9] Y.Y. Vin, S.M. Khopkar, Analyst 113 (1988) 175–177.10] H.B. Singh, N.K. Agnihotri, V.K. Singh, Talanta 47 (1998) 1287–1296.11] F.D. Snell, C.L. Hilton, Encyclopedia of Industrial Chemical Analysis, vol. 7, John

Wiley, New York, 1968, pp. 112–115.12] M.J. Shaw, S.J. Hill, P. Jones, P.N. Nesterenko, J. Chromatogr. A 876 (2000)

127–133.13] H. Matsumiya, H. Hoshino, Anal. Chem. 75 (2003) 413–419.14] W. Bashir, B. Paull, J. Chromatogr. A 910 (2001) 301–309.15] F.D. Snell, Beryllium, in: Photometric and Fluorometric Methods of Analysis

Metals, Part 1, Wiley, New York, 1978, pp. 661–701.16] K.J. Eisentraut, D.J. Griest, R.E. Sievers, Anal. Chem. 43 (1971) 2003–2007.17] C.I. Measures, J.M. Edmond, Anal. Chem. 58 (1986) 2065–2069.18] L.C. Robles, C. Garciolalla, M.T. Alemany, A.J. Aller, Analyst 116 (1991) 735–737.19] H. Lana, P.M.A. Bruno, Analyst 114 (1989) 1331–1333.20] M. Hiraide, T. Uchida, H. Kawaguchi, Analyst 118 (1993) 537–539.21] J.L. Burguera, M. Burguera, C. Rondon, P. Carrero, M.R. Brunetto, Y. Petit de Pena,

Talanta 52 (2000) 27–37.22] F. Pilon, S. Lorithioir, J.C. Birolteau, S. Lafontan, J. Anal. At. Spectrom. 11 (1996)

759–764.23] S.Q. Tao, Y. Okamoto, T. Kumamaru, Anal. Chim. Acta 309 (1995) 379–385.24] L. Halicz, I.B. Brenner, O.J. Yoffe, J. Anal. At. Spectrom. 8 (1993) 475–480.25] F. Buhl, W. Galas, Z. Fresenius, Anal. Chem. 332 (1988) 366–367.26] D.E. Kimbrough, I.H. Suffet, Analyst 121 (1996) 309–315.27] V.K. Gupta, S. Chandra, S. Agarwal, H. Lang, Sens. Actuators B 107 (2005)

762–767.28] S. Chandra, H. Lang, Sens. Actuators B 114 (2006) 849–854.29] S. Kim, H. Kim, K. Ho Noh, S. Ho Lee, S.K. Kim, J.S. Kim, Talanta 61 (2003) 709–716.30] M.R. Ganjali, A. Moghimi, M. Shamsipur, Anal. Chem. 70 (1998) 5259–5263.31] M. Shamsipur, M.R. Ganjali, A. Rouhollahi, A. Moghimi, Anal. Chim. Acta 434

(2001) 23–27.32] A. Soleymanpour, N. Ahmadi Rad, K. Niknam, Sens. Actuators B 114 (2006)

740–746.33] M. Shamsipur, A. Soleymanpour, M. Akhond, H. Sharghi, Electroanalysis 16

(2004) 282–288.34] M.R. Ganjali, M.R. Nasrabadi, B. Maddah, A. Moghimi, M.F. Rastegar, S. Borhany,

M. Namazian, Talanta 63 (2004) 899–906.35] V.K. Gupta, R. Prasad, A. Kumar, Talanta 63 (2004) 1027–1033.36] A. Kumar, S.K. Mittal, Sens. Actuators B 99 (2004) 340–343.37] H.A. Zamani, M.R. Ganjali, P. Norouzi, M. Adib, Mater. Sci. Eng. C 28 (2008)

157–163.38] H.A. Zamani, M.R. Ganjali, P. Norouzi, A. Tadjarodi, E. Shahsavani, Mater. Sci.

Eng. C 28 (2008) 1489–1494.39] M.R. Ganjali, P. Norouzi, M. Adib, A. Ahmadalinezhad, Anal. Lett. 39 (2006)

1075–1086.40] K.R. Alam, A.J. Leong, L.F. Lindoy, H.C. Lip, B.W. Skelton, A.H. White, J. Am. Chem.

Soc. 105 (1983) 4645–4651.41] C.H. Hieu, L.T. Anh, A.N. Levov, E.V. Nikitina, A.T. Soldatenkov, Chem. Heterocycl.

Compd. 45 (2009) 1406–1407.42] A. Craggs, G.J. Moody, J.D.R. Thomas, J. Chem. Educ. 51 (1974) 541–544.43] F.J. Sa’ez de Viteri, D. Diamond, Analyst 119 (1994) 749–758.44] V.K. Gupta, R. Mangla, S. Agarwal, Electroanalysis 14 (2002) 549, 1127–1132.45] S.K. Srivastava, V.K. Gupta, M.K. Dwivedi, S. Jain, Anal. Proc. 32 (1995) 21–23,

533.46] V.K. Gupta, M. Al Khayat, A.K. Singh, M.K. Pal, Anal. Chim. Acta 634 (2009) 36–43,

582.47] V.K. Gupta, R.N. Goyal, R.A. Sharma, Int. J. Electrochem. Sci. 4 (2009) 156–172,

580.48] A.K. Jain, V.K. Gupta, U. Khurana, L.P. Singh, Electroanalysis 9 (1997) 857–860.49] R.N. Goyal, V.K. Gupta, M. Oyama, N. Bachheti, Talanta 71 (2007) 1110–1117.

5 Chim

[[[[

[[

[[

[

[

[[

[[

[

[[

0 V.K. Gupta et al. / Analytica

50] R.N. Goyal, V.K. Gupta, M. Oyama, N. Bachheti, Talanta 72 (2007) 976–983.51] V.K. Gupta, A. Rastogi, J. Hazard. Mater. 163 (2009) 396–402.52] V.K. Gupta, A.K. Singh, B. Gupta, Anal. Chim. Acta 583 (2007) 340–348.53] R.N. Goyal, V.K. Gupta, A. Sangal, N. Bachheti, Electroanalysis 17 (2005)

2217–2223.54] E. Stocchi, Industrial Chemistry, vol. 1, Ellis Harwood, New York, 1990.55] M. Shamsipur, A. Soleymanpour, M. Akhond, H. Shargi, Electroanalysis 16

(2004) 282–288.56] V.K. Gupta, R. Prasad, A. Kumar, Talanta 60 (2003) 149–160.57] A.K. Jain, V.K. Gupta, L.P. Singh, Anal. Proc. Including Anal. Commun. 32 (1995)

263–265.58] A.K. Jain, V.K. Gupta, B.B. Sahoo, L.P. Singh, Anal. Proc. Including Anal. Commun.

32 (1995) 99–101.59] V.K. Gupta, A.K. Jain, P. Kumar, S. Agarwal, G. Maheshwari, Actuators B: Chem-

ical 113 (2006) 182–186.

[[[

[

ica Acta 749 (2012) 44– 50

60] V.K. Gupta, I. Ali, V.K. Saini, Water Res. 41 (2007) 3307–3316.61] R.N. Goyal, V.K. Gupta, S. Chatterjee, Biosens. Bioelectron. 24 (2009)

1649–1654.62] A.K. Jain, V.K. Gupta, L.P. Singh, U. Khurana, Analyst 122 (1997) 583–586.63] R.N. Goyal, V.K. Gupta, Neeta Bachheti, R.A. Sharma, Electroanalysis 20 (2008)

757–764.64] A.K. Jain, V.K. Gupta, S. Radi, L.P. Singh, J.R. Raisoni, Electrochim. Acta 51 (12)

(2006) 2547–2553.65] V.K. Gupta, R. Mangla, U. Khurana, P. Kumar, Electroanalysis 11 (1999) 573–576.66] V.K. Gupta, S. Chandra, H. Lang, Talanta 66 (2005) 575–580.

67] V.K. Gupta, R.N. Goyal, R.A. Sharma, Anal. Chim. Acta 647 (2009) 66–71.68] V.K. Gupta, S. Chandra, Rajni Mangla, Electrochim. Acta 47 (2002) 1579–1586.69] V.K. Gupta, A.K. Jain, G. Maheshwari, H. Lang, Sens. Actuat. B: Chem. 117 (2006)

99–106.70] V.K. Gupta, S. Jain, U. Khurana, Electroanalysis 9 (1997) 478–480.