Anal. Method Environ. Chem. J. 4 (1) (2021) 5-15  
Research Article, Issue 1  
Analytical Methods in Environmental Chemistry Journal  
AMECJ  
Separation and determination of cadmium in water samples  
based on functionalized carbon nanotube by syringe filter  
membrane-micro solid-phase extraction  
Jamshid Rakhtshah a,*  
a Department of Inorganic Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran  
A B S T R A C T  
A R T I C L E I N F O :  
Received 19 Nov 2020  
Revised form 25 Jan 2021  
Accepted 22 Feb 2021  
Asimple and fast separation of cadmium (Cd) based on functionalized  
carbon nanotubes with 2,3-dimercapto-1-propanol (CNTs@DHSP)  
was achieved in water samples before a determination by atom trap  
flame atomic absorption spectrometry (AT-FAAS). In this study,  
Cd(II) ions were extracted by syringe filter membrane-micro solid  
phase extraction procedure(SFM-μ-SPE). Firstly, 20 mg of the  
CNTs@DHSP as solid-phase added to 20 mL of water sample in  
a syringe, then dispersed for 3 min after adjusting pH up to 7 and  
pass through SFM very slowly. After extraction, the Cd(II) ions  
were back-extracted from SFM/CNTs@DHSP by 1.0 mL of eluent  
in acidic pH. Finally, the cadmium concentration was measured by  
AT-FAAS. Under the optimal conditions, the linear range (2–90 µg  
L−1), LOD (0.75 µg L−1) and enrichment factor (19.6) were obtained  
(RSD<1.5%). The adsorption capacity of Cd(II) with the CNTs@  
DHSP was obtained about 152.6 mg g-1. The method was validated  
by certified reference materials (SRM, NIST) and ET-AAS in water  
samples.  
Available online 28 Mar 2021  
------------------------  
Keywords:  
Cadmium,  
Separation,  
Water,  
Functionalized carbon nanotubes,  
Syringe filter membrane micro solid  
phase extraction,  
Atom trap flame atomic absorption  
spectrometry  
gastrointestinal and respiratory tract system  
1. Introduction  
from food, water, air pollution and smoking. The  
cadmium exposure causes to hepatic dysfunction,  
the pulmonary edema, the testicular damage, the  
osteoporosis and cancer in different organs such as,  
breast, renal, lung and pancreas [3,4]. The Cd ions  
absorb through the respiratory tract or the gastro-  
intestinal tract and enters into the bloodstream via  
erythrocytes and accumulated in the kidneys liver [5].  
Cadmium ions excrete from the human body through  
urine. The liver and kidneys are able to synthesize  
metallothioneins (MT) which protect the cells from  
cadmium toxicity through bonding to cadmium  
(Cd- MT) [6]. Mitochondria play a crucial role in  
the formation of ROS (reactive oxygen species) for  
cadmium [7]. Moreover, the different methodologies  
Cadmium (Cd) as a toxic non-essential metal  
release from industrial activity to water, soil, food,  
agricultural product and air, then, cadmium ions  
cause to environmental and human health hazards.  
Cadmium is naturally creating in the environment  
matrixes from agricultural and chemical industrial  
sources. The sources of cadmium have various  
applications in different industry such as PVC  
products in petrochemical industries, pigments  
in color factories, and Ni-Cd batteries [1,2].  
The cadmium enters to the human body through  
*Corresponding Author: Jamshid Rakhtshah  
Anal. Method Environ. Chem. J. 4 (1) (2021) 5-15  
6
such as microbial fermentation based on TiO2  
nanoparticles have been used to remove cadmium  
from waters efficiently [8,9]. The cytotoxic effects of  
cadmium cause to apoptotic effect in human which  
was reported by internationalAgency for research on  
cancer (IARC) [10]. Itai itai disease or osteomalacia  
is chronic cadmium poisoning was reported in Japan.  
The cadmium intake to the human body is about 7 µg  
Cd per week. This value cause to create the cadmium  
concentration in renal and urine between 100-200 µg  
g-1 and less than 0.5 µg g-1 creatinine, respectively.  
Blood and urinary cadmium at 0.38 µg L-1 and  
0.67 µg g-1 creatinine were associated with tubular  
impairment. Urinary cadmium at 0.8 µg g-1 creatinine  
was associated with glomerular impairment [11]. So,  
the extraction and determination of Cd(II) in waters  
is very important, due to the environment and human  
health safety. Recently, various analytical techniques  
can be used for cadmium extraction in different  
water, foods and environmental samples. The  
various methods such as flame atomic absorption  
spectrometry (AAS) [12], the optical microscopy  
based on laser-induced photoluminescence (UV–  
VIS-NIR) [13], the SrFe12O19@CTAB magnetic  
nanoparticles with electrothermal atomic absorption  
spectrometry (ET-AAS) [14-17], the colorimetric  
sensor [18], the electrothermal vaporization coupled  
with optical emission spectrometry with inductively  
coupled plasma (ETV-ICP-OES) [19] and laser-  
induced breakdown spectroscopy (LIBS) [20]  
were used for cadmium determination in various  
environmental samples. Due to the low concentration  
of cadmium in water samples and difficulty matrixes  
in wastewater samples, the pretreatment is required  
before the determination of cadmium by instrumental  
analysis. The different extraction methods such as,  
the ultrasound-assisted liquid–liquid spray extraction  
(USA-LLSE) [21], the solvent extraction [22], the  
liquid–liquid extraction [23], the cloud point assisted  
dispersive ionic liquid-liquid microextraction  
[24] the dispersive solid-phase extraction (DSPE)  
combined with ultrasound-assisted emulsification  
microextraction [25], solid-phase extraction  
(SPE) [26, 27], the coagulating homogenous  
dispersive micro solid-phase extraction exploiting  
graphene oxide nanosheets (CHD-µSPE)[28] and  
graphene oxide-packed micro-column solid-phase  
extraction[29] were used before cadmium analysis in  
water samples. Recently, the membrane micro solid-  
phase extraction procedure (M-μ-SPE) was reported  
as micro SPE (μ-SPE) for separation/determination  
of cadmium in water samples. This method showed  
several advantages, such as easy and fast extraction  
of cadmium in water samples. The properties of  
adsorbents have a main role for cadmium extraction  
by the syringe filter membrane micro solid-phase  
extraction procedure (SFM-μ-SPE). In this study, a  
novel sorbent based on CNTs@DHSP was used for  
extraction of Cd(II) in water and wastewater samples  
by SFM-μ-SPE at pH of 7. The proposed method was  
validated with CRM and spike samples in waters and  
high recovery was obtained by AT-FAAS.  
2. Experimental  
2.1. Material and Methods  
Atomtrapflameatomicabsorptionspectrophotometer  
(GBC 932, AT-FAAS, Aus) was used for cadmium  
determination in water and wastewater samples.  
The atom trap accessory /air-acetylene controlled  
by AVANTA software which was placed on the air-  
acetylene burner. The cadmium determines in water  
and wastewater samples with 1.0 mL of the sample  
with LOD of 0.025 mg L-1, the wavelength of 283.3  
nm and 5 mA. The lower limit of quantitation  
(LLOQ), ULOQ and linear range for AT-FAAS  
was obtained 100 µg L−1, 1800 µg L−1 and 100-  
1800 µg L−1, respectively. All water samples were  
injected by an auto-sampler to the injector of AT-  
FAAS for 1-1.5 min. The electrothermal atomic  
absorption spectrophotometer (ET-AAS) was  
used for the validation of water samples in ultra-  
trace analysis of Cd(II). The Metrohm pH meter  
was used for measuring pH in water samples (E-  
744, Switzerland). The shacking of water samples  
was used based on 250 rpm speeds by vortex  
mixer (Thermo, USA). The standard solution of  
cadmium (Cd2+) was purchased from Sigma Aldrich.  
(Germany) with a concentration of 1000 mg L-1 in  
1 % HNO3. The various concentration of cadmium  
was daily prepared by dilution of the standard Cd  
Cadmium extraction by CNTs@DHSP  
Jamshid Rakhtshah  
7
solution with DW. Ultrapure water was purchased  
from Millipore Company (USA) for the dilution  
of water samples. 2,3-Dimercapto-1-propanol  
(CASN:59-52-9, HOCH2CH(SH)CH2SH) was  
prepared from Sigma Aldrich, Germany. The pH  
was adjusted pH by 0.2 mol L-1 of sodium phosphate  
buffer solution (Merck, Germany) for a pH of 7.0  
(Na2HPO4/NaH2PO4). The analytical grade of  
reagents such as HNO3, HCl, acetone, and ethanol  
were prepared from Merck, Germany. The syringe  
Whatman filter membrane (SFM) with glass  
microfiber pre-filter (100 nm, Anotop filters, SN:  
WHA68091112, D:10 mm, polypropylene housing  
polypropylene membrane) was purchased from  
Sigma Aldrich, Germany. Anotop syringe filters  
contain the proprietary alumina and use for difficult  
separation samples.  
mixture, drop by drop, at room temperature. After  
sonicating for 15 min, the resulting mixture was  
refluxed at 60 °C under N2 atmosphere to remove  
the produced HCl. In order to obtain the CNTs@Cl,  
it was dried at 100 °C under vacuum. Then, 1 g of  
CNTs@Cl and 1 mL of DMP were mixed in 60 mL  
ethanol using an ultrasonic bath for 30 min. Then, a  
few drops of triethylamine were added to the above  
slurry, and the mixture was refluxed at 60 °C for  
three extra hours. The product was separated from  
the reaction mixture by a PTFE membrane filter and  
washed with ethanol three times and finally dried  
under vacuum at 100 °C.  
2.4. Extraction Procedure  
By SFM-μ-SPE procedure, 20 mL of water and  
standard samples (3 µg L−1 and 90 µg L−1) were  
used for the separation and determination of  
cadmium ions at pH 7. Firstly, the CNTs@DHSP  
added to water or cadmium standard solution  
and shaked for 3 min at pH=7. Then, the water  
sample was slowly passed through SFM with  
glass microfiber pre-filter and the solid-phase was  
separated by filtering (100 nm, polypropylene  
housing polypropylene membrane). After shaking,  
the Cd(II) ions were extracted by sulfur group of  
CNTs@DHSP as coordination bond or dative bond  
at pH from 6-8 (Cd2+→: SH @CNTs) and then the  
Cd (II) ions on SFM/CNTs@DHSP back-extracted  
by 0.5 mL of eluent (1.5 M, HNO3) at pH 2. Finally,  
the cadmium concentration in remained solution  
was determined by AT-FAAS after dilution with  
DW up to 1 mL (Fig.1). The procedure was used  
for a blank solution without cadmium ten times.  
The calibration curve for Cd in standards solutions  
was prepared (3- 90 µg L−1) and enrichment factor  
(EF) was calculated. The analytical parameters  
showed in Table 1. Validation of methodology  
was achieved by CRM for cadmium samples  
and ETAAS analysis. The recovery was obtained  
for cadmium by equation 1. The Cp and Cf is the  
primary and final concentration of Cd(II), which  
was determined by SFM-μ-SPE procedure coupled  
to AT-FAAS (n=10, Eq. 1).  
2.2. Human sample preparation  
The glass analysis was washed with a HNO3 solution  
(1 M) for at least 12 h and rinsed 10 times with DW.  
The cadmium concentrations in water and wastewater  
have a low concentrations less than 50 µg L-1 and low  
contamination for sampling and determination caused  
to low accuracy of results. By procedure, 20 mL of  
the water samples were prepared from well water,  
drinking water and wastewater factories from Iran.  
Clean syringes were prepared for sample treatment.  
The water is prepared and stored by standard method  
for sampling from water by adding nitric acid to waters.  
2.3. Synthesis of CNTs@DHSP adsorbent  
First, the CNTs@COOH was prepared according to  
the acid oxidation method reported in the literature  
[30]. In the final step, 1 g of CNTs@COOH was  
added in 50 mL of methanol and maintained  
under ultrasonic conditions for 15 min. Sodium  
borohydride was also simultaneously added to the  
solution. Then, the mixture was stirred at room  
temperature for 3 h. Then, the product was washed  
with methanol three times and dried under vacuum.  
Typically, CNTs@OH (0.5 g) and dry xylene (40  
mL) were sonicated for 15 minutes in a 100 mL  
round-bottomed flask. 3 mL of (3-chloropropyl)  
trimethoxysilane (CPTMS) was added to the above  
Re (%) = (Cp-Cf)/Cp×100  
(Eq.1)  
Anal. Method Environ. Chem. J. 4 (1) (2021) 5-15  
8
Table 1. The analytical features for determination cadmium by SFM-μ-SPE procedure  
Features  
Working pH  
value  
6-8  
Amount of CNTs@DHSP (mg)  
20.0  
Sample volume of water (mL)  
20 .0  
Volume of sample injection (mL)  
1.0  
Linear range for water (μg L-1)  
working range for water (μg L-1)  
Mean RSD %, n=10  
3.0-90  
3.0-170  
1.5  
LOD (μg L-1)  
0.75  
Enrichment factor for water  
Volume and concentration of HNO3  
Shaking time  
19.6  
1 mL, 1.5 M  
3.0 min  
R2 = 0.9998  
Correlation coefficient  
Fig. 1. Cadmium extraction in water sample based on CNTs@DHSP by SFM-μ-SPE procedure  
functionalized CNTs were functionalized by  
(3-chloropropyl) trimethoxysilane (CPTMS) to  
provide chloroalkylsilane. Finally, thiol derivative  
as a DHSP was covalently immobilized on CNTs.  
Finally, SH group of DHSP on the surface of CNTs  
can be complexed with cadmium ions in a water  
solution (Fig.2).  
3. Results and discussion  
3.1. Extraction Mechanism  
The carboxylic acid-functionalized CNTs were  
synthesized by using the acid oxidation method.  
Then, for the generation of OH groups on surface  
CNT, these materials were treated with sodium  
borohydride in methanol. Afterward, hydroxyl-