Analytical Methods in Environmental Chemistry Journal Vol 1(2018) 5-10

Research Article, Issue 1

Analytical Methods in Environmental Chemistry Journal

Journal home page: www.amecj.com/ir

AMECJ

Solid phase extraction and determination of indium using

multi-walled carbon nanotubes modified with magnetic

nanoparticles

Ehsan Zolfonoun ^a,*

^a Material and Nuclear Fuel Research school, Nuclear Science and Technology Research Institute, Tehran, Iran

A R T I C L E I N F O:

A B S T R A C T

Received 18 Aug 2018

In this work MWCNTs-Fe₃O₄ nanocomposite was used as an adsor-

bent for extraction and preconcentration of indium from aqueous so-

Revised form 20 Oct 2018

lutions. The magnetic MWCNTs with adsorbed analytes were easily

Accepted 28 Nov 2018

separated from the aqueous solution by applying an external magnetic

Available online 31 Dec 2018

field. After elution of the adsorbed analytes, the concentration of indi-

um was determined using inductively coupled plasma optical emission

------------------------

spectrometry determination. The effects of pH, sorbent amount, eluent

type, chelating reagent concentration, sample volume, and time on the

Keywords:

recovery of the In(III) were investigated. Moreover, under the opti-

mum conditions, the detection limit for In(III) was 0.28 µg L⁻¹. The

Indium

precision of the method, evaluated as the relative standard deviation

Preconcentration

obtained by analyzing a series of ten replicates, was 3.1 %. Ultimately,

Carbon nanotubes

the method was successfully applied for the determination of In(III) in

Fe₃O₄ nanoparticles

.environmental water samples

1. Introduction

and biological samples. The quantification of metal

Indium is an important element in the semiconductor

ions in various matrices has been performed by

industry, in the nuclear studies and in the production

different techniques, including spectrophotometry,

of high purity materials

[1]. Indium and its

atomic absorption spectrometry

(AAS), and

compounds have numerous industrial applications

inductively coupled plasma optical emission

including the manufacture of liquid crystal displays

spectrometry (ICP-OES) [3]. In addition, using the

(LCD), semiconductors, low-temperature solders,

mentioned methods directly for determining indium

and infrared photodetectors

[2]. Also, indium

at very low concentrations is difficult because of

compounds damage the heart, kidney, and liver.

insufficient sensitivity of this technique, as well

Thus, there is a need for specific and precise

as the matrix interferences which occur in real

determination of indium traces in environmental

samples, and an initial sample pretreatment, such

as preconcentration of the analyses (or analytes)

*Corresponding author: Email: ezolfonoun@aeoi.org.ir

https://doi.org/10.24200/amecj.v1.i01.14

and matrix separation, is often necessary [4]. Solid

Analytical Methods in Environmental Chemistry Journal; Vol. 1 (2018)

phase extraction

(SPE) is a routine extraction

were used as supplied. HNO₃, ammonia solution,

method for preconcentration of organic and

FeCl₃·6H₂O, and FeCl₂·4H₂O, were purchased

inorganic analytes. This technique reduces solvent

from Merck (Germany). MWCNTs (purity> 95%)

usage and exposure, disposal costs, and extraction

were obtained from Sigma-Aldrich. Standard stock

time. In addition, based on the references,

[5]

solution (1000 μg mL^-1) of In(III) was prepared

and [6], various adsorbents have been used for

by dissolving appropriate amounts of In(NO₃)₃ in

adsorption of analytes in SPE methods.

water. A solution of 1.0×10⁻³ mol L⁻¹ quinalizarine

Magnetic nanoparticles, mainly including Fe₃O₄

(Merck) was prepared by dissolving appropriate

nanoparticles, received increasing attention in the

amounts of this reagent in 0.01 mol L⁻¹ NaOH

recent years due to its unique properties and high

(Merck).

potential applications in various fields such as cell

separation, magnetically assisted drug delivery,

2.2. Instrumentation

enzyme immobilization, and protein separation

All the measurements were carried out using a

[7, 8].. Recently, using magnetic nanoparticles for

Perkin Elmer

(Optima 7300 DV) simultaneous

extraction of analytes in SPE methods is gaining

ICP-OES coupled to a concentric nebulizer and

research interest [9, 10]. In addition, multi-walled

equipped with a charge coupled device (CCD)

carbon nanotubes

(MWCNTs) have received

detector. Moreover, Metrohm model 744 digital

great attention due to their exceptional electronic,

pH meter, equipped with a combined glass-

mechanical, thermal, chemical properties, and

calomel electrode, was employed for the pH

significant potential applications in many fields

adjustments.

[11]. Owing to their large surface area and high

reactivity, MWCNTs based adsorbents have been

2.3. Preparation of MWCNTs-Fe₃O₄ nanocomposite

used for solid phase extraction and preconcentration

MWCNTs-Fe₃O₄ nanocomposite was synthesized

of organic compounds and metal ions [12,13]. The

according to the previously reported methods,

decoration of MWCNTs with various compounds

which were mentioned in the references,

[14]

can modify their physicochemical properties. Also,

and

[15]. First, MWCNTs were dispersed in

this character makes them more suitable for chemical

concentrated nitric acid for 4 hours with ultrasonic

and biological applications. Functionalizing

treatment. Then purified MWCNTs were separated

MWCNTs with magnetic nanoparticles can

by filtering. Afterwards, they washed repeatedly

combine the features of magnetic nanoparticles

with distilled water followed by ethanol and dried

and MWCNTs, which may result in materials with

°C. The MWCNTs-Fe₃O₄ nanocomposite

potential applications in biological labelling, drug

was prepared by chemical coprecipitation method.

delivery, and magnetic storage media [14, 15]. In

First, FeCl₃·6H₂O (1.18 g) and FeCl₂·4H₂O (0.43

this paper, a magnetic solid phase extraction method

g) were dissolved in

200 mL deionized water

based on Multi-walled carbon nanotubes decorated

under nitrogen gas with vigorous stirring at 60

with Fe₃O₄ nanoparticles is developed for the

^◦C. Then 1.0 gram of MWCNTs was added in the

extraction and preconcentration of trace amounts of

solution with ultrasonic treatment for about

indium, prior to their determination by ICP-OES.

min. Finally, NH₄OH solution was added dropwise

into the solution until its pH was adjusted to 11.

2. Experimental Procedure

After stirring for 30 min at 50 °C, the obtained

2.1. Reagents

MWCNTs-Fe₃O₄ nanocomposite was separated

All reagents used were of analytical grade and

from the reaction medium by magnetic field, and

Solid phase extraction of indium; Ehsan Zolfonoun

washed with 200 mL deionized water four times.

The obtained results showed that by increasing the

sorbent amounts from 2 up to 5 mg due to increasing

2.4. Magnetic solid-phase extraction procedure

accessible sites, extraction recovery increased, and

A 100-mililiter sample or standard solution

then it remained constant. A 5-miligram of the

containing In(III)

(pH

6), and QA

(1.0×10⁻⁵

MWCNTs-Fe₃O₄ nanocomposite was selected for

mol L⁻¹), was transferred in a glassware beaker.

subsequent experiments.

Then 5 mg MWCNTs-Fe₃O₄ nanocomposite was

added into the sample solution. Afterwards, the

3.3. Effect of eluent type

mixture was stirred for 3 min. Subsequently, the

In order to find the best eluent, different eluting

sorbent particles were isolated by placing a strong

solutions such as HCl, H₂SO₄, HNO₃ and acetic

magnet, and the supernatant was poured away. The

acid, were tested. The results revealed that a

preconcentrated target analyte was eluted using 1.0

1.0-mililiter of 1.0 M concentration of all acids

mL of a 1 mol L⁻¹ solution of HNO₃. Finally, the

could afford the quantitative elution of In³⁺ from

concentration of In(III) in acidic aqueous phase

the sorbent. Finally, subsequent elutions of In³⁺

was determined by ICP-OES.

were carried out with 1 M HNO₃ solution

3. Results and discussion

3.4. Effect of chelating reagent concentration

3.1. Effect of pH

The effect of QA concentration on the extraction

The effect of pH on the extraction of indium was

of indium was studied, and the results are shown

studied in the range of 2.0-8.0 using nitric acid or

in Fig. 3. Also, QA concentration in the range of 0

sodium hydroxide. The resulting percent recovery-

to 5.0×10⁻⁵ mol L⁻¹was investigated by us. Then,

pH plots are shown in Fig. 1. These plots indicate

maximum recovery was obtained at a concentration

that sorption is maximum and quantitative in the

of 1.0×10⁻⁵ mol L⁻¹ of the ligand and at higher

pH range of 6.0-7.0. Consequently, a solution pH

concentrations, the extraction recovery remained

of 6.0 was used in further experiments.

constant.

3.2. Effect of the sorbent amount

3.5. Effect of solution volume

In order to study the effect of the sorbent, 2 to

The effect of solution volume was examined by

10 mg of MWCNTs-Fe₃O₄ nanocomposite was

added to 100 mL of the sample solution (Fig. 2).

Fig. 2. Effect of the MWCNTs-Fe₃O₄

amount on the

Fig. 1. Effect of pH on the recovery of In(III) ion.

recovery of In(III) ion.

Analytical Methods in Environmental Chemistry Journal; Vol. 1 (2018)

In(III) was studied in the range of 1-15 min. The

experimental results indicated that there was no

significant effect on the extraction efficiency when

the extraction time increased from 3 to 10 min.

Based on the above considerations, the extraction

time that is equal to 3 min was selected for further

studies.

3.7. Effect of diverse ions on the recovery

In order to assess the possible analytical applications

of the recommended procedure, the effect of

Fig. 3. Effect of chelating reagent concentration on the

common coexisting ions in natural water samples

recovery of In(III) ion.

on the preconcentration and determination of

indium ion was studied. In these experiments, 100

preconcentrating different volumes (20-250 mL)

mL solutions containing 50 μg L⁻¹ of indium and

of aqueous solutions spiked with a constant mass

various amounts of interfering ions were treated

of 10.0 μg of In(III), and the results are depicted

according to the recommended procedure. In

in Fig. 4. The obtained results showed that when

addition, tolerable limit was defined as the highest

aqueous solution volume was up to

100 mL,

amount of foreign ions that produced an error not

recoveries above 95% were obtained. Thus, 100

exceeding ±5% in the determination of investigated

mL was considered to be the maximal enrichment

analyte ion. The results are summarized in Table

volume for water samples. Consequently, since the

1. As seen, a large number of ions used have no

final solution volume to be measured by ICP-OES

considerable effect on the determination of indium.

was 1.0 mL, the preconcentration factor for In(III)

was evaluated as 100.

3.8. Analytical figures of merit

In Table

2, the analytical characteristics of the

3.6. Effect of extraction time

proposed method, including linear range, limit

The effect of extraction time on the extraction of

of detection, reproducibility, and enrichment

factor have been summarized. In the optimum

conditions, a calibration graph was constructed by

preconcentrating a series of the solutions according

to the recommended procedure. There is an

important tip, that the calibration curve for In(III)

was linear form 1.0 to 500 µg L⁻¹ with a regression

Table 1. Tolerance limits of some cations and anions on

the sorption and determination of indium.

Ion

Tolerance limit (µg mL⁻¹)

Li⁺, Na⁺, K⁺, Cl^-, NO3-

>2000

Ca²⁺, Mg²⁺, Ba²⁺, Sr²⁺

1000

Ag⁺, Hg²⁺, SO4-

Cu²⁺, Fe³⁺, Pb²⁺, Ni²⁺, Co²⁺,

Fig. 4. Effect of sample volume on the recovery of

Cr³⁺, Mn²⁺, Cd²⁺, Zn²⁺

In(III) ion.

Solid phase extraction of indium; Ehsan Zolfonoun

Table 2. Analytical parameters of the proposed method.

Table 3. Recovery of indium from water samples.

Parameter

Analytical feature

Sample

Indium

Added

Found

Recovery

Linear range (µg L⁻¹)

1.0−500

(µg L⁻¹)

(%)

r²

0.995

Tap water

0.0

<LOD

LOD (µg L⁻¹)

0.28

10.0

9.7 (1.8)^a

R.S.D. % (n = 10)

3.1

Mineral water

0.0

<LOD

Enrichment factor

100

10.0

10.9

(1.4)

109

River water

0.0

<LOD

coefficient of 0.995. The limit of detection (LOD)

10.0

9.4

(2.6)

of the proposed method for the determination of

^a Values in parentheses are R.S.D.s based on three

indium was studied under the optimal experimental

replicate analyses.

conditions. The LOD, defined three times by

paying attention to the standard deviation of 10

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4. Conclusions

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In this study, a fast and simple method based was

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