Anal. Method Environ. Chem. J. 3 (4) (2020) 52-59
Research Article, Issue 4
Analytical Methods in Environmental Chemistry Journal
Journal home page: www.amecj.com/ir
AMECJ
Dispersive solid phase extraction using graphitic carbon
nitride microparticles for the determination of trace amounts
of lead in water samples
Ehsan Zolfonoun
a,*
a
Nuclear Fuel Cycle Research School, Nuclear Science and Technology Research Institute, Tehran, Iran
ABSTRACT
In this work, ultrasound-assisted dispersive micro-solid phase
extraction (USA-D-µSPE) technique using graphitized carbon nitride
(g-C
3
N
4
) is proposed for the preconcentration of low level of lead
in aqueous samples. In this method, microparticles of graphitized
carbon nitride sorbent were dispersed in the samples using ultrasonic
bath and Pb(II) ions were directly adsorbed on the surface of g-C
3
N
4
particles. After adsorption and desorption of lead ions from g-C
3
N
4
particles, the Pb concentration was determined by the inductively
coupled plasma- optical emission spectroscopy (ICP-OES). The main
advantages of this method are high speed, simplicity and cheapness.
The effects of pH, sorbent amount, eluent type and time on the recovery
of the analyte were investigated. Under the optimized conditions and
preconcentration of 10 mL of sample, the detection limit of 1.24 μg
L
-1
was obtained. The results were validated by standard reference
materials (NIST, SRM) and spiking of real samples by USA-D-µSPE
procedure.
Keywords:
Lead, Graphitic carbon nitride,
Water,
Ultrasound-assisted dispersive mi-
cro-solid phase extraction,
Inductively coupled plasma- optical
emission spectroscopy
ARTICLE INFO:
Received 6 Sep 2020
Revised form 10 Nov 2020
Accepted 28 Nov 2020
Available online 30 Dec 2020
*Corresponding author: Ehsan Zolfonoun
Email: ezolfonoun@aeoi.org.ir
https://doi.org/10.24200/amecj.v3.i04.118
------------------------
1. Introduction
With the development of various industries over the
past decades and increasing the amount of pollut-
ants entering the environment, the amount of heavy
metals in soil and water increased [1]. Most of these
heavy metals are not only environmentally destruc-
tive but also healthily hazardous even at trace lev-
els. Lead is one of the most hazardous elements to
human health. Metabolic poisoning, enzyme in-
hibition and nervous connection damages are the
most important toxic effects of lead on human [2].
The rst step in reducing or eliminating this met-
al is its accurate measurement. For this purpose,
various analytical techniques have been developed
[3-5]. In all of the reported analytical techniques,
sample preparation (separation and preconcentra-
tion) step is needed prior to instrumental analysis.
Among different sample preparation methods, sol-
id phase extraction is the most common one due
to its unique features such as simplicity, low cost,
high recoveries and low consumption of organic
solvents [6,7].Dispersive micro solid phase ex-
traction (D-µ-SPE) is a new version of solid phase
extraction (SPE) which simultaneously posses the
advantages of both dispersive liquid-liquid micro-
extraction and solid phase extraction [8]. In this
method a mixture of sorbent particles and carrier is
injected to the aqueous sample. After formation of
cloudy solution, extraction can be achieved with-
in a few seconds because of the large surface area
53
Extraction of lead by graphitic carbon nitride Ehsan Zolfonoun
between extraction sorbent and aqueous phase [9].
Recently, D-µ-SPE has received much attention in
analytical chemistry because it is a simple, fast and
inexpensive method [11,12]. One of the most im-
portant parameters that affect the performance of
this method is the type of sorbent [12]. The advan-
tages of using nanoparticles as sorbent in D-µ-SPE
have been demonstrated in recent reports [13-15].
Unique size and desirable physicochemical prop-
erties of nanoparticles have made them suitable
options for improving DSPE method. Among dif-
ferent nanosorbents, cheaper and more stableones
such as graphene and carbon nanotubes have been
used more frequently [16-18]. Graphitic carbon ni-
tride (g-C
3
N
4
) is a non-toxic analogue of graphene
which is very stable and inexpensive and has suit-
able band structure, easy synthesis method and
unique physicochemical properties [19,20]. It has
a 2D layered structure (2D sheets of tri-s-triazine
connected via tertiary amines) and is synthesized
from various simple and green nitrogen rich precur-
sors such as melamine, thiourea, urea, cyanamide
[21]. Due to the hydrophobicity, large π-conjugated
structure and polar functional groups , g-C
3
N
4
can
be a suitable and ecofriendly candidate for conven-
tional sorbents in extraction methods [22].
In the current study, we propose a simple, fast and
ligandless preconcentration technique based on
ultrasound-assisted dispersive micro-solid phase
extraction (USA-D-µSPE) using graphitic carbon
nitride for the determination of lead by inductively
coupled plasma-optical emission spectrometry.
2. Experimental
2.1. Reagents and materials
All chemicals used in this work were of analytical
grade. All aqueous solutions were prepared in dou-
ble-distilled deionized water (Milli-Q system, Mil-
lipore, USA). Pb(II) stock solution was supplied by
Merck (Darmstadt, Germany). The standard solu-
tion of lead (Pb
2+
) was purchased with a concen-
tration of 1000 mg L
-1
in 1 % HNO
3
. Another con-
centration of lead was daily prepared by dilution
of the standard lead solution with DW. Ultrapure
water was purchased from Millipore Company.
The g-C
3
N
4
was synthesized according to the previ-
ously reported method. The syntheses of graphitic
carbon nitrides ( g-C
3
N
4
)by heating at 300-600 °C
of a mixture of melamine with the formula C
3
H
6
N
6
and uric acid ( C
5
H
4
N
4
O
3)
in the presence of crys-
talline form of alumina (Al
2
O
3
) has been reported.
Alumina favored the deposition of the graphitic
carbon nitrides layers on the exposed surface [19].
2.2. Instrumentation
A Perkin Elmer inductively coupled plasma optical
emission spectroscopy (ICP-OES, Optima 7300
DV) equipped with a charge-coupled device de-
tector (CCD) and a cyclonic spray chamber with a
concentric nebulizer was used for the determination
of the target element. The detection wavelength for
lead was 220.353 nm. A Metrohm model 744 digital
pH meter, equipped with a combined glass-calomel
electrode, was employed for the pH measurements.
An ultrasonic water bath with temperature control
(Tecno-Gaz SpA, Italy) was applied to disperse of
adsorbent particles in aqueous solution. The centri-
fuge accessory based on the rotor with high speed
(speed 2000-30.000 rpm x g, Sigma 3K30 centri-
fuge, UK) was used for separation nanoparticles
from water samples. For sampling, all glass tubes
were cleaned with a 1.0 mol L
-1
HNO
3
solution for
24 h and washed 10 times with DW. The water pre-
pared and stored by standard method for sampling
from water by adding nitric acid to waters.
2.3. On-line extraction procedure
Due to Figure 1, 6.0 mg of g-C
3
N
4
was added to 10
mL of water sample or standard solution and soni-
cated by an ultrasonic bath for 5 min. The chemical
and physical adsorption of lead ions carried out by
g-C
3
N
4
at optimized pH
.
The covalence bonding
between nitrate and Pb cause to increase extraction
efciency in water samples. After extraction of
lead ions with g-C
3
N
4
, the solution was then cen-
trifuged for 5 min at 5,000 rpm, and the aqueous
phase was removed. The preconcentrated target an-
alyte was eluted using 1.0 mL of a 1 mol L
−1
solu-
tion of HNO
3
. Finally, the concentration of Pb(II)
in acidic aqueous phase was determined by ICP-
54
Anal. Method Environ. Chem. J. 3 (4) (2020) 52-59
OES. The proposed procedure developed based on
g-C
3
N
4
nanostructure with lower and upper limit
quantication (5.0–600 µg L
−1
) for lead analysis in
water and standard samples by ultrasound-assisted
dispersive micro-solid phase extraction (USA-D-
µSPE).
3. Results and discussion
The USA-D-µSPE procedure based on g-C
3
N
4
as
adsorbent was used for the extraction and separa-
tion of lead ions in water samples. In order to obtain
the favorite lead speciation with high extraction,
the analytical parameters such; pH, the amount of
adsorbent, the sonication time, the eluent type and
interference ions must be optimized.
3.1. Effect of pH
The pH of the sample solution is one of the most
important factors in metal–adsorbent interac-
tion in the SPE procedure. The effect of pH on
the extraction of Pb(II) by g-C
3
N
4
was studied in
the range of 3.0–8.0 using nitric acid or sodium
hydroxide. The results in Figure 2 show that the
adsorption of Pb(II) is maximum in the pH range
of 6.0 to 7.5. So, pH 6.0 was chosen as the opti-
mum value. The mechanism of extraction of lead
achieved based on the coordination of covalent
bond of N in g-C
3
N
4
with the positively charged
inorganic lead (Pb
2+
), which is highly dependent
on pH (Pb→:N-C).
3.2. Effect of g-C
3
N
4
amount
The effect of amount of g-C
3
N
4
on the quantitative
extraction of Pb(II) was examined in the range of
1–10 mg by ultrasound-assisted dispersive mi-
cro-solid phase extraction (USA-D-µSPE). The re-
sults are shown in Figure 3. The obtained results
revealed that by increasing the sorbent amounts
from 1 up to 6 mg, due to increasing accessible sites,
the extraction efciency increased and after that re-
mained constant. Hence, the subsequent extraction
experiments were carried out with 6 mg of g-C
3
N
4
.
3.3. Effect of sonication time
By USA-D-µSPE procedure, the sonication time
is one of the main factors inuencing the target
analytes extraction. By favorite time for solid dis-
persion in liquid phase, the mass-transference was
increased and so, the efcient extraction of lead
based on the g-C
3
N
4
was obtained in water sam-
ples. The effect of the sonication time on the ex-
traction and recovery of Pb(II) was studied in the
range of 1–20 min. The obtained results indicated
that there was no signicant effect on the extraction
efciency when the ultrasonication time increased
from 5 to 20 min. So, an ultrasonication time of 5
min was selected for the entire procedure.
3.4. Effect of eluent type
The kind and value of elution for back extraction
lead ions from g-C
3
N
4
were optimized at pH=6.
Fig.1. On-line extraction procedure for lead extraction by g-C
3
N
4
particles
55
Extraction of lead by graphitic carbon nitride Ehsan Zolfonoun
Low pH caused to dissociate N-lead bonding and
release the Pb (II) into the liquid phase. So, a differ-
ent acid solution such as HCl, HNO
3
, H
2
SO
4
, and
CH
3
COOH with different concentration was used
for back extraction Pb(II) in blood samples (0.5-3
mol L
-1
) by USA-D-µSPE procedure. In order to
nd the best eluent, different mineral acids were
examined as striping agents. The results revealed
that among the tested eluents, nitric acid
was the
superior striping agent for the quantitative elution
of Pb(II). Therefore, HNO
3
solution was selected
for Pb(II) desorption. The effect of nitric acid
con-
Fig. 2. Effect of pH on the recovery of Pb(II). Conditions: g-C
3
N
4
amount,
10 mg; concentration of analyte, 50 µg L
–1
.
Fig. 3. Effect of the g-C
3
N
4
amount on the recovery of Pb(II). Conditions: pH, 6.0;
concentration of analyte, 50 µg L
–1
.
56
Anal. Method Environ. Chem. J. 3 (4) (2020) 52-59
centration on the recovery of the adsorbed analyte
was studied in the range of 0.1 to 3 mol L
−1
. Based
on the obtained results, 1.0 mol L
−1
HNO
3
was suf-
cient for complete desorption of the target analyte
from the sorbent surface (Fig.4).
3.5. Effect of diverse ions on the recovery
In order to evaluate the analytical applicability of
the developed method, the effect of commonly
occurring ions in natural water samples on the ex-
traction and determination of lead was studied. In
these experiments, 10 mL of sample solutions con-
taining 50.0 μg L
−1
of Pb(II) and various amounts
of interfering ions were treated according to the
recommended procedure. Tolerable limit was set
as the highest amount of foreign ions which cause
an approximately ± 5 % relative error in the de-
termination of the analyte. The results showed that
40,000-fold Li
+
, Na
+
, K
+
, Cl
-
, NO
3
-
, 20,000-fold
Ca
2+
, Mg
2+
, Ba
2+
, Sr
2+
, 400-fold Ag
+
, Cd
2+
, Co
2+
,
Zn
2+
, Mn
2+
, 200-fold Fe
3+
, Ni
2+
, Cr
3+
, Ce
3+
, and 100-
fold Al
3+
, Cu
2+
, Hg
2+
ions had no signicant inu-
ence on the extraction and determination of Pb(II).
3.6. Analytical gures of merit
The analytical parameters of the proposed are sum-
marised in Table 1. Linear working range of the
method for determination of Pb(II) was found to be
5.0–600 µg L
−1
. The limit of detection (LOD) of the
proposed method was calculated as three times the
standard deviation of 10 measurements of the blank
solution over the slope of the calibration curve. The
LOD for the determination of Pb(II) was found to
be 1.24 µg L
−1
. The relative standard deviation
(R.S.D) of the proposed method for determination
of 50.0 µg L
−1
Pb(II) (n= 10) was 2.3 %.
Table 1. Analytical parameters of the proposed method
Parameter Analytical feature
Linear range (µg L
−1
) 5.0–600
r
2
0.998
LOD (ng L
−1
) 1.24
R.S.D. % (n = 10) 2.3
Enrichment factor 10
Fig.4. The effect of eluents on lead extraction based on g-C
3
N
4
particles
by USA-D-µSPE procedure
57
Extraction of lead by graphitic carbon nitride Ehsan Zolfonoun
3.7. Application
The developed method was applied to nd the
amount of Pb(II) in tap water, well water and river
water samples by USA-D-µSPE procedure. The
analytical results, along with the recovery for the
spiked samples, are given in Table 2. The recovery
values calculated for the spiked samples were in
the range of 94–105 %. The results demonstrat-
ed that the UA-D-µSPE can be used as a reliable
sample treatment technique for extraction and de-
termination of Pb(II) in real samples. Moreover,
the standard reference materials (NIST; SRM)
were used for validating of proposed procedure by
g-C
3
N
4
nanostructure in water and urine samples
(Table 3).
4. Conclusions
A preconcentration technique based on ultrasound-as-
sisted micro-solid phase extraction using graphitic
carbon nitride microparticles was developed for the
extraction and preconcentration of Pb(II) from aque-
ous samples, prior to ICP-OES determination. In the
proposed method there is no need to use any chelat-
ing agent. The obtained results indicate that the pro-
posed method gives a high enhancement factor and
low LOD and can be used for the preconcentration
and determination of lead in real water samples.
5. Acknowledgements
The authors wish to thank Nuclear Fuel Cycle Re-
search School, Nuclear Science and Technology
Research Institute, Tehran, Iran
Table 2. Recovery of lead from water samples based on g-C
3
N
4
particlesby USA-D-µSPE procedure
Sample Added (µg L
−1
) Found (µg L
−1
) Recovery (%)
Tap water 0.0 <LOD –
10.0 10.2 (2.5)
a
102
Well water 0.0 5.1 (3.2) –
10.0 14.5 (3.0) 94
River water 0.0 4.3 (2.9) –
10.0 14.8 (2.6) 105
a
Values in parentheses are R.S.D.s based on three replicate analyses
Table 3. Validation of USA-D-SPE procedure in water by standard reference materials (SRM, NIST)
Recovery (%)
Found
*
( μg L
-1
)Added( μg L
-1
)SRM( μg L
-1
)
Sample
-----17.4 ± 0.9-----18.2 ± 0.6
a
SRM1643d
96.631.9 ± 1.415.0
-----138.6 ± 6.5-----137.9 ± 3.6
b
SRM 2668
99.4287.7± 11.4150.0
*
Mean of three determinations of samples ± SD (P = 0.95, n =10)
a
SRM1643d, trace element in water
b
SRM 2668, Human Freeze-Dried Urine, level (II), μg L
-1
Anal. Method Environ. Chem. J. 3 (4) (2020) 52-59
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