Research Article, Issue 1
Analytical Methods in Environmental Chemistry Journal
Journal home page: www.amecj.com/ir
AMECJ
------------------------
Nafiseh Esmaeili
a
, Nadia Kokabi
a
, and Eskandar Kolvari
a,*
a
Department of chemistry, Faculty of Science, Semnan University, Semnan, Iran
rock and sulfide mineral has high levels about 12
mg L
-1
. Mean arsenic concentrations in sediment
the mean of As has ranges from 5 to 3000 mg kg
-1
[2, 3]. The occupational exposure and oral intake
(food and water) of arsenic are the most important
route in humans. The mean daily intake of arsenic
from drinking water to human body must be less
than 10 µg. By increasing of arsenic concentration
in waters, dangerous diseases created in human
body after drink waters for many times. Many
changes in CNS and peripheral nervous system
(PNS) such as, tenderness and vomiting headaches
occurred for arsenic exposure. Liver and renal may
moved to cancer problem as different toxicity and
Speciation of arsenic in wastewater samples based on
pyributicarbamate /ionic liquids by dispersive liquid-liquid
microextraction
1. Introduction
The toxicities of heavy metals in waters cause to
main problem in humans and environment and
cannot be biodegraded as VOCs. The factories and
chemical activity are real source of heavy metals
such arsenic which can entrance to environment
and caused different disease in humans such as,
renal, liver and brain [1]. The most of arsenic in
waters has two forms As(III) and AS(V). The
arsenic concentration in waters has generally
ranged between 1 and 2 µg L
-1
. Water in volcanic
* Corresponding author: Bahareh Fahimirad
Email: kolvari@semnan.ac.ir
DOI: https://doi.org/10.24200/amecj
A R T I C L E I N F O:
Received 6 Dec 2019
Revised form 30 Jan 2020
Accepted 15 Feb 2020
Available online 28 Mar 2020
Keywords:
Arsenic, Speciation,
Wastewater,
Pyributicarbamate,
Task specific Ionic liquid,
Dispersive liquid-liquid
microextraction
A B S T R A C T
A simple and applied method based on O-3-Tert-butylphenyl N-(6-methoxy-2-
pyridyl)-N-methylthiocarbamate (Pyributicarbamate; TBMPMTC) was used
for arsenic speciation (As
III
and As
V
) in urine and water samples by dispersive
liquid-liquid microextraction (DLLME) procedure. The concentrations of
arsenic in the liquid phase were determined by hydride generation atomic
absorption spectrometry in the presence of flame accessory (HG-AAS).
By procedure, a mixture of ionic liquid (0.1 g, [APMIM][PF6]@[HMIM]
[PF
6
]), acetone (0.2 mL) and pyributicarbamate was injected into wastewater
sample containing arsenic (As
III
and As
V
) ions, which were already extracted by
pyributicarbamate at the optimized pH. The task-specific ionic liquid (TSIL)
of 1-3-aminopropyl)-3-methyl-imidazoliumhexafluorophosphate [APMIM]
[PF6] was chemically synthesized and used for increasing of As(V)
extraction in the liquid phase. As(III) was extracted based on the sulfur bond
of pyributicarbamate at pH=5.3. As (V) can be extracted by amine group of
TBMPMTC and [APMIM][PF6] at pH=3.0 (As(V)---:NH2). The influence
of parameters such as, pH, amount of ionic liquid, and ligand was studied.
Based on results, the LOD, enhancement factor (EF) and linear range (LR)
were obtained 3.2 ngL
-1
, respectively. The procedure
validated by certified reference material (CRM).
Speciation of arsenic by pyributicarbamate Nafiseh Esmaeili et al
Anal. Method Environ. Chem. J. 3 (1) (2020) 41-48
42
Anal. Method Environ. Chem. J. 3 (1) (2020) 41-48
oxidation state of arsenic [4-7]. Different analytical
procedure used for arsenic determination of
speciation/determination in water samples. A few
of them only determination without speciation such
as graphite furnace atomic absorption spectrometry
(GF-AAS) [8], Flame atomic absorption
spectrometry (F-AAS) [9], hydride generation
atomic absorption spectrometry (HG-AAS)
[10], capillary electrophoresis with inductively
coupled plasma-mass spectrometry (CE-ICP)[11]
and arsenic species can be determined with ion
chromatography coupled to inductively coupled
plasma mass spectrometry (IC-ICP-MS)[12]. As
low concentration of arsenic species in waters
(sub ppb), sample preparation must be used before
instrumental analysis. Recently, solid-phase
extraction (SPE) based on nanomaterials was
used to improve the extraction procedure. For this
purpose, many carbon structure such as, modified
activated carbon [13], carbon nanotubes [14], and
alumina supported on graphene oxide [15], were
reported by researchers. In addition, the liquid-
liquid extraction technique (LLE) and dispersive
liquid-liquid microextraction (DLLME) was used
for extraction analyte from liquid phase based
on ligand by immiscible solvents or ionic liquid
which was directly immersed in water samples and
dispersed by acetone [16-22]. The organic solvents
such as tetrachloride carbon are toxic. Therefore,
the ionic liquids (ILs) as green solvents have used
as extracting solvent. ILs has many advantages as
compared to organic solvents, such as favorite vapor
pressure, viscosity and density. Therefore, ILs have
used as benign solvent in DLLME procedure.
In this study, a new procedure based on
TBMPMTC -DLLME coupled to HG-AAS for the
speciation and determination of trace amount of As
(III) and As (V) in wastewater samples at pH of
5.3 and 3.0, respectively. Flame conditions with 1.2
Lmin
-1
fuel and minimum flow air have used.
2. Experimental
2.1. Apparatus
The experiments were performed using a GBC-932
atomic absorption spectrometer equipped with a
hydride generation module (HG3000-AAS -AUS).
A hollow cathode lamp operated at a current of 8
mA and a wavelength of 193.7 nm with a spectral
band width of 1 nm and deuterium background
corrector was applied. The deuterium-lamp
background corrector, As hollow-cathode lamp,
and a circulating reaction loop was used for arsenic
determination.
The instrument conditions of HG-AAS have
showed in Table 1. The pH values of the solutions
have adjusted by a digital pH meter (Metrohm 744,
Herisau, Switzerland). A Hettich centrifuge (model
EBA 20, Germany) and an ultrasonic bath with
heating system (Tecno-GAZ SPA, Italy) have used.
Table 1. The instrumental parameters for analysis of
arsenic
Features Value
Precision (%RSD, N=10) 1.4
LOD
-1
Linear range, PA
-1
Wavelength 193.7 nm
Spectral band width 1 nm
Lamp current 8 mA
Correlation coefficient R = 0.9997
PA = Peak Area, PH = Peak Height
2.2. Reagents and Materials
All the reagents were of analytical grade. Arsenic
standard solutions were prepared from a stock
solution of 1000 mg L
-1
as ultra trace in 2% nitric
acid from Fluka Switzerland (CAS N: 39436).
Arsenic (V) oxide prepared from Sigma, Germany
(As
2
O
5
; CAS N: 1303-28-2). The powder of
O-3-Tert-butylphenyl N-(6-methoxy-2-pyridyl)-
N-methylthiocarbamate (pyributicarbamate;
TBMPMTC) purchased from Sigma which was
prepared daily by DW (C
18
H
22
N
2
O
2
S; CAS N: 88678-
67-5, Germany). 1-Hexyl-3-methylimidazolium
hexafluorophosphate (C
10
H
19
F
6
N
2
P; CID 2734175;
[HMIM][PF
6
]) was purchased from Sigma,
Germany. The ionic liquid of 1-(3-aminopropyl)-
3-methyl-imidazoliumhexafluorophosphate
[APMIM][PF6] synthesis in center of organic
chemistry in Semnan University, Iran. Sodium
acetate /acetic as buffer solutions for pH 3–6 was
43
prepared from Sigma, Germany (1.5 mol L
-1
).
Ultrapure water has obtained from a water system
of RIPI. The plastic, vials and glasses equipments
were cleaned by soaking in HNO
3
(1 M) and were
rinsed with deionized water for 10 times prior to
use.
2.3. Sampling
Drinking and river water samples were collected
paint and chemical wastewaters from Iran. These
samples were immediately acidified with 0.1% of
concentrated HCl which provided a pH lower than
2. The samples have then filtered in the laboratory
Nagel, PTFE) to remove suspended solids.
2.4. Synthesis of [APMIM][PF6]
As reported by Hu and Yeon, the procedure of
synthesis of [APMIM][PF6], was done by center
of organic chemistry, Semnan. For this purposed
methylimidazole and bromopropylammonium
bromide (C
3
H
9
Br
2
N) dissolved in acetonitrile in
boiling flasks with magnetic stirrer and refluxed at
90°C. Finally, the solution of [APMIM][Br] was
obtained. After cooling, the KPF6 (10 g) added to
20 mL of DW) and after 24 h, the solvents were
separated and the ionic liquid was removed by
extraction in methanol/chloroform. The suspension
was then filtered and washed with diethyl ether (10
times) to remove impurities [23, 24].
2.5. Procedure
After synthesis of [APMIM][PF6], the procedure
followed by 0.5 mL of TBMPMTC solution (2%,
w/w), 0.1 g of 1-Hexyl-3-methylimidazolium
hexafluorophosphate in acetone solution (0.2 mL)
which was mixed and injected to 10 mL of sample
solution containing As(III)/As(V). The cloudy
solution has shaken with a vortex for 5 min and
pH adjusted up to 5.3 based on favorite buffer
solutions. Then, the arsenic (III) was efficiently
extracted (As-:SR) in [APMIM][PF6] @ [HMIM]
Fig. 2. The mechanism of extraction of As(III) and As(V) based on TBMPMTC by DLLME procedure
Fig. 1. The procedure for speciation of arsenic in wastewater samples based on pyributicarbamate /ionic liquids
44
Anal. Method Environ. Chem. J. 3 (1) (2020) 41-48
[PF
6
]. Finally, the IL separated in conical tube by
centrifuging accessory for 7 min at 4000 rpm. The
water sample removed from upper phase, arsenic
(III) back extracted from IL with 0.25 mL of nitric
acid solution (0.5M) in lower phase, dilution with
DW up to 1 mL and determined by HG-AAS.
As(V) was also extracted with same procedure
in pH=3.0 by mixture of TBMPMTC/[APMIM]
[PF6]@[HMIM][PF
6
]. Total As was calculated
by summarizing of As(III) and As(V) which was
shown in Figure 1. In addition, the mechanism of
proposed procedure has presented in Figure 2.
3. Results and Discussion
Analytical conditions for HG-AAS determination
have optimized in this work. Absorption (S/N) and
repeatability that were investigated for speciation
and determination As(III) and As(V) in wastewater
samples in paint factories and chemical industries
by HG-AAS. In view of the possibility of As
extraction with TBMPMTC, this ligand was used
to chelated of arsenic in ionic liquids phase. All
conditions such as pH, amount of Il, amount of
TBMPMTC, sample volume and shaking time
were optimized by DLLME procedure.
3.1 Effect of pH
The complexation phenomenon has strongly
conditioned by the pH of solutions and subsequently
affects on the extraction efficiency of the As
III
-
SR and As
V
-SR. For this reason, the pH between
2-10 was examined for As (III) and As(V) in water
samples by DLLME method. Two groups of
ligands include N and S bonding have important
role in speciation arsenic in liquid phase when
pH optimized. Based on solubility and charge of
ions, they can be extracted by bonding group of
TBMPMTC. The results showed, As (III) extracted
with sulfur group of TBMPMTC at pH=4.8-5.5 and
As (V) captured by amine group of TBMPMTC/
[APMIM][PF6] at pH=2.5-3.2. S0, pH of 3.0
and 5.0 was selected as optimum pH in this study
(Fig.3). The pH adjustments of samples were
made using nitric acid (0.1 mol L
-1
) for pH 1-2,
and appropriate buffer solutions including sodium
acetate (CH
3
COONa/CH
3
COOH, 1-2 mol L
-1
)
for pH 3.75-5.75, sodium phosphate (Na
2
HPO
4
/
NaH
2
PO
4
, 0.2 mol L
-1
) for pH of 5.8-8.0, and
ammonium chloride (NH
3
/NH
4
Cl, 0.2 mol L
-1
) for
pH 8-10.
3.2. Effect of amount of TBMPMTC
It is important to establish the favorite concentration
of ligand for arsenic extraction with high recovery
as shown in Figure 4. The different concentration
of TBMPMTC was used for optimization of
arsenic extraction from 0.5 -50 micro molar.
The results showed that the 17
micro molar has
Fig. 3. The effect of pH on arsenic speciation based on TBMPMTC by DLLME procedure
45
maximum recovery for arsenic (III, V) extraction
from wastewater samples by DLLME. Based
on statistical report in analytical chemistry the
minimum ligand concentration was necessary to
use with maximum extraction efficiency. So, the 20
micro molar selected as optimum concentration by
proposed procedure.
3.3. Effect of amount of ionic liquid
The amount of ionic liquid as green organic
solvent for extraction of arsenic in wastewaters
must be optimized by DLLME. For this purpose,
the different mass and kind of ionic liquid was
studied. The results showed [HMIM][PF
6
] have
more extraction as compared to others ([BMIM]
[PF
6
], [EMIM][PF
6
], [MMIM][PF
6
]). So, the 0.05-
0.2 g of [HMIM][PF
6
] examined by procedure.
The quantitative extraction was observed for more
than 0.08 g of [HMIM][PF
6
] and therefore, 0.1 g
of [HMIM][PF
6
] was chosen as optimum IL for
further works (Fig. 5). The [APMIM][PF6] had no
effect on separation process but helped to increase
efficiency extraction of As(V) from liquid phase.
3.4. Effect of sample volume and elution
The effect of sample volume was examined in a
As
(III) and As(V).
The quantitative extraction has observed less
than15 mL wastewaters. So, 10 mL of sample
volume was selected in optimum conditions.
The acid concentrations were used in order to
obtain the maximum extraction with the minimal
concentration and volume of the acid solution. The
presented DLLME method based on the elution of
arsenic species from IL phase with a mineral acidic
solution achieved. Low pH leads to dissociation
and releasing of As (III) and As(V) into the
aqueous phase. So, 100-500 µL of different mineral
Fig. 4. The effect of amount of TBMPMTC on arsenic speciation by DLLME procedure
Fig. 5. The effect of amount of ionic liquid on arsenic speciation based on TBMPMTC by DLLME procedure
46
Anal. Method Environ. Chem. J. 3 (1) (2020) 41-48
acids such as HCl, HNO
3
, H
2
SO
4
and H
3
PO
4
(0.1-1
mol L
-1
) were examined. The results showed that
0.5 mol L
-1
HNO
3
(250 µL)
quantitatively back-
extracted arsenic from IL.
3.5. Effect of dispersion time
Dispersion is the main factor in arsenic extraction
by DLLME method and so, allows the direct contact
of the analytes with TBMPMTC ligand and then
extracted. Due to the dispersion of TBMPMTC/
ILs into the aqueous phase, the mass-transference
phenomenon was obtained with high efficiency in
short time. The influence of the shaking time was
studied within the 1–5 min. The results showed that
the relative response increased at 4 min and then
remained constant. So, 5 min was chosen as favorite
time as shaking. By centrifuging, the extraction was
accelerated for phase separation between IL and
liquid phase. The different times for centrifuging
were tested from 2 to 10 min at 4000 rpm. The
result showed that 5 min centrifugation time was
sufficient to get a satisfactory biphasic system.
3.6. Interference of coexisting ions
As efficient analytical procedure in water samples,
the interference of some coexisting ions was
investigated in optimized condition. By DLLME
procedure, the different concentration of the
interfering ions added to 10 mL of standard sample
-1
of As (III) and As
(V). The results showed that most of concomitant
ions have no effect on the extraction efficiencies
of As (III) and As (V) at the optimized pH. The
tolerable concentration ratio of metals per As (III)
and As (V) for Ni
2+
, Co
2+
,
Cd
2+
, Mn
2+
, Cu
2+
, Zn
2+
,
K
+
, Na
+
, Pb
2+
, Hg
2+
, NO
3
-
, Cl
-
, F
-
, CO
3
2-
and SO
4
2-
was obtained in water samples (Table 2).
3.7. Validation
The DLLME method based on TBMPMTC as a
ligand was used for determination of As (III) and
As (V) in 10 mL of wastewater and water samples
by HG-AAS. The results were verified by spiking
water samples with nickel standard solution. Based
on results, the acceptable recovery was achieved
by adding standard solution (As (III) and As (V)
to real samples as a found analyte amount. The
recoveries of spiked samples were 95-103% by
DLLME methods (Table 3). Wastewaters of a
chemical factory (A), a paint factory (B), well water
(C), and drinking water (D) were selected as real
samples which were used by procedure. The results
demonstrated that TBMPMTC-DLLME can used
for speciation of As (III) and As (V) in wastewater,
and water samples which were determined by HG-
AAS. In addition, the certified reference material
(CRM, NIST 2670) was used for validation As
(III) and As (V) in urine samples by TBMPMTC-
DLLME (Table 4).
4. Conclusions
The procedure has many advantage such as
simplicity, reliability and high extraction efficiency
in short time for arsenic speciation based on
TBMPMTC-DLLME by sensitive HG-AAS
technique. By improving the procedure, the favorite
and acceptable preconcentration/separation/
speciation of the trivalent and pentavalent inorganic
Table 2. The effect of interferences ions on extraction
of As (III) and As (V) in water samples by DLLME
procedure
Interfering Ions
(M)
Mean ratio
(C
M
/C
As(III)
)
Recovery
(%)
Ni
2+
, Co
2+
,
Cd
2+
600 96.9
Mn
2+
, Cu
2+
, Zn
2+
900 98.7
I
-
, Br
-
, F
-
, Cl
-
1100 99.2
Na
+
, K
+
, Ca
2+
, Mg
2+
900 98.2
NO
3
-
, Cl
-
, F
-
, CO
3
2-
1200 97.4
Hg
2+
100 95.5
NH
4
+
, SO
4
2-
400 96.8
Pb
2+
250 97.3
Interfering Ions
(M)
Mean ratio
(C
M
/C
As(V)
)
Recovery
(%)
Ni
2+
, Co
2+
,
Cd
2+
500 96.9
Mn
2+
, Cu
2+
, Zn
2+
800 98.7
I
-
, Br
-
, F
-
, Cl
-
900 99.2
Na
+
, K
+
, Ca
2+
, Mg
2+
900 98.2
NO
3
-
, Cl
-
, F
-
, CO
3
2-
1200 97.4
Hg
2+
200 95.5
NH
4
+
, SO
4
2-
500 96.8
Pb
2+
300 97.3
47
forms of arsenic was achieved as alternative to
HPLC-ICP-MS. The results showed the quantitative
recovery more than 96% and EF of 9.85 as curve
fitting analysis for As(III) /As(V) were obtained at
pH of 5.0 and 3.0, respectively. If the ionic liquid of
[APMIM][PF6] as TSIL wasn’t used, the recovery
obtained up to 73% for As(V) in optimized
conditions. The certified reference material and
spiking real samples showed the high accuracy
and precisions results which were agreement with
the certified values. In DLLME procedures, the
satisfactory results based on TBMPMTC ligand
was achieved for arsenic species in wastewater
samples.
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Table 3. Speciation and determination of As (III) and As (V) in spiked water samples by TBMPMTC-DLLME method
Sample
a
Added
(μg L
-1
)
a
Found (μg L
-1
)
Total
Recovery (%)
As (III) As (V) As (III) As (V) As (III) As (V)
A ------ ------ 0.432 ± 0.023 0.266 ± 0.014 0.698 ± 0.037 ------ ------
0.4 ------ 0.827 ± 0.043 0.262 ± 0.015 1.089 ± 0.052 98.8 ------
------ 0.3 0.435 ± 0.022 0.568 ± 0.028 1.003 ± 0.049 ------ 100.6
B ------ ------ 0.501 ± 0.023 0.197 ± 0.011 0.698 ± 0.034 ------ ------
0.5 ----- 0.993 ± 0.048 0.195 ± 0.009 1.188 ± 0.057 98.4 ------
----- 0.3 0.498 ± 0.024 0.504 ± 0.026 1.002 ± 0.055 ------ 102.3
C ------ ------ 0.102 ± 0.006 0.068 ± 0.003 0.170 ± 0.009 ------ ------
0.1 ----- 0.203 ± 0.009 0.064 ± 0.003 0.267 ± 0.012 101.0 ------
----- 0.1 0.098 ± 0.005 0.165 ± 0.013 0.263 ± 0.018 ------ 97
D ------ ------ 0.032 ± 0.001 ND 0.032 ± 0.001 ------ ------
0.05 ------ 0.081 ± 0.004 ND 0.081 ± 0.004 98 ------
------ 0.05 0.030 ± 0.001 0.002 ± 0.048 0.078 ± 0.003 ------ 96
a
Mean of three determinations ± Confidence interval (P = 0.95)
Table 4. Method validation for speciation of arsenic based on TBMPMTC-DLLME by standard reference material
(ng L
-1
)
sample
Certified value
As (III)
Certified value
As (V)
*Found
As (III)
*Found
As (V)
Recovery
As (III) (%)
Recovery
As (V) (%)
CRM 833.3 500.0 827.4 ± 45.6 488.7 ± 24.6 99.3 97.7
Added 400.0 ------ 1209.8 ± 58.5 482.3 ± 26.3 95.6 ------
Added ------ 500.0 831.2 ± 51.2 990.2 ± 47.7 ------ 100.3
a
NIST CRM 2670, Arsenic in frozen dried urine, pH 4.0, - 20°C, diluted with DW(1:3)
b
Mean of three determinations ± confidence interval (P = 0.95)
48
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