Anal. Method Environ. Chem. J. 3 (3) (2020) 18-24
Research Article, Issue 3
Analytical Methods in Environmental Chemistry Journal
Journal home page: www.amecj.com/ir
AMECJ
Dispersive liquid–liquid microextraction technique combined
with UV–Vis spectrophotometry for determination of
zirconium in aqueous samples
Ehsan Zolfonoun
a,*
a
Nuclear Fuel Cycle Research School, Nuclear Science & Technology Research Institute, Tehran, Iran
ABSTRACT
Dispersive liquid–liquid microextraction coupled with UV–Vis
spectrophotometry was applied for the determination of zirconium
in aqueous samples. In this method a small amount of chloroform as
the extraction solvent was dissolved in pure ethanol as the disperser
solvent, then the binary solution was rapidly injected by a syringe
into the water sample solution containing Zr(IV), xylenol orange and
cetyltrimethylammonium bromide (CTAB). The formed ion-associate
was extracted into the ne chloroform droplets. The detection limit for
Zr(IV) was 0.010 µg mL
−1
. The precision of the method, evaluated as
the relative standard deviation obtained by analyzing of 10 replicates,
was 2.7 %. The practical applicability of the developed method was
examined using natural waters and ceramic samples.
Keywords:
Zirconium;
Dispersive
liquid–liquid microextraction;
Xylenol orange;
Cetyltrimethylammonium bromide.
ARTICLE INFO:
Received 28 May 2020
Revised form 20 Jul 2020
Accepted 26 Aug 2020
Available online 27 Sep 2020
* Corresponding Author: Ehsan Zolfonoun
Email: ezolfonoun@aeoi.org.ir
https://doi.org/10.24200/amecj.v3.i03.107
------------------------
1. Introduction
Zirconium is used in the nuclear industry as a fuel
rod cladding, as a catalyst in organic reactions and,
additionally, in the manufacture of water repellent
textiles, in metal alloys and in dye pigments and
ceramics [1, 2]. Most of zirconium compounds
have low solubility and as a result have low
toxicity. However, chronic exposure to the soluble
compounds of zirconium such as zirconium
tetrachloride may cause skin and lung granulomas
[3, 4]. Industrial wastewater can increase the amount
of zirconium in the environment. Contaminated
soil and water can expose humans to this metal.
Therefore, extraction and determination of trace
levels of zirconium is necessary.
Spectrophotometric methods are most commonly
used for the determination of zirconium [5, 6].
However, the direct determination of zirconium at very
low concentrations by traditional spectrophotometric
techniques is difcult because of insufcient
sensitivity of this technique as well as the matrix
interferences occurring in real samples, and an initial
sample pretreatment, such as preconcentration of the
analyte and matrix separation, is often necessary.
Several methods have been reported for the
separation and preconcentration of metal ions, such
as liquid–liquid extraction (LLE) [7], coprecipitation
[8], solid phase extraction (SPE) [9, 10] and cloud
point extraction (CPE) [11], but the disadvantages
such as time-consuming, unsatisfactory enrichment
factors, large organic solvents and secondary
wastes, limit their applications.
Dispersive liquid–liquid microextraction
(DLLME) is a modied solvent extraction method
19
Determination of zirconium in aqueous samples Ehsan Zolfonoun
and provides the advantages of ease of operation,
rapid extraction, and use of small volume of
organic solvent [12, 13]. In DLLME, a water-
immiscible organic extractant and a water-miscible
dispersive solvent are two key factors to form ne
droplets of the extractant, which disperse entirely
in the aqueous solution, for extracting analytes.
The cloudy sample solution is then subjected to
centrifuge to obtain sedimented organic extractant
containing target analytes. This method has been
applied for the determination of trace organic
pollutants and metal ions in the environmental
samples [14-17].
Xylenol orange (XO) is a metal indicator, which is
widely used for analytical determination [18, 19]. It
can react with many metal ions in various oxidation
states and the solution chemistry of its chelates is
known to be complex [20]. However the utility of
XO for extraction of metal ions is reported rarely.
As the XO is a nonselective methallochromic
indicator it’s complexes with the cited ion has
severe spectral interferences and this makes the
determination to be very difcult or practically
impossible. For a successful determination a prior
separation step is mandatory for elimination of the
cationic interferences.
In the present study we introduce a simple and fast
dispersive liquid–liquid microextraction (DLLME)
method for the separation and preconcentration
of trace amounts of zirconium, prior to
spectrophotometric determination. The point of
the present method is using of an accessible and
inexpensive reagent, XO, with a cationic surfactant
as a new extractant.
2. 2. Experimental
2.1. Reagents
All reagents were of analytical grade, purchased
from the Merck Company. Standard stock solution
(1000 μg mL
−1
) of Zr(IV) was prepared by
dissolving appropriate amounts of ZrOCl
2
·8H
2
O,
in water. Stock solutions of diverse elements were
prepared from the high purity salts of the cations
(all from Merck, Germany). A solution of 1.0×10
−3
mol L
−1
xylenol orange was prepared by dissolving
appropriate amounts of this reagent in distilled
water.
2.2. Instrumentation
A Perkin Elmer (Lambda 25) spectrophotometer
with 10 mm quartz cells (500 µL) was used for
UV−Vis spectra acquisition. A Metrohm model
744 digital pH meter, equipped with a combined
glass-calomel electrode, was employed for the
pH adjustments. A Hettich centrifuge model EBA
20 (Oxford, England) was employed for phase
separation.
2.3. Dispersive liquid–liquid microextraction
procedure
A 5 mL sample or standard solution containing
Zr(IV) (pH 3.0), XO (3.0×10
−5
mol L
−1
), and
CTAB (2.0×10
−5
mol L
−1
) was transferred in a 10
mL conical-bottom polypropylene centrifuge tube.
Then 1.5 mL ethanol (disperser solvent) containing
120 µL chloroform (extraction solvent) was
injected rapidly into the sample solution using a
syringe and a stable cloudy solution (water, ethanol
and chloroform) was formed. In order to separate
the phases, the cloudy solution was centrifuged
for 5 min at 3000 rpm and the aqueous phase was
removed with a transfer pipette. Afterwards, the
sedimented phase was dissolved in 500 µL of pure
ethanol and transferred to a quartz cell and then the
absorbance was measured at 592 nm.
2.4. Analysis of the real samples
A 5 mL of tap water, well water, and mineral
water samples were ltered through 0.45 µm
membrane lter, adjusted to the optimum pH and
subjected to the recommended procedure for the
preconcentration and determination of metal ions.
To 1.0 g of ceramic samples in a platinum crucible,
10 mL of HF, 1 mL of H
2
SO
4
, and 1 mL of HClO
4
were added and heated to 150
◦
C on a hot plate.
The process was repeated three times. The residue
was cooled and dissolved in 50 ml of 0.1 mol L
–1
HCl and made up to 100 mL. Suitable aliquots
were taken and subjected to preconcentration and
determination by the procedure described above.
20
Anal. Method Environ. Chem. J. 3 (3) (2020) 18-24
3. 3. Results and discussion
3.1. Effect of pH
The formation of metal chelate and its chemical
stability are the two important inuence factors for
the extraction of metal ions, and the pH plays a unique
role on metal chelate formation and subsequent
extraction. The effect of pH on the complex formation
and extraction of zirconium was studied in the range of
1.0–5.0 using hydrochloric acid or sodium hydroxide.
As can be seen in Fig. 1, the highest signal intensity
was obtained at pH 3.0–4.0. In more acidic or more
alkaline solutions, absorbance decreased because of
incomplete complex formation and hydrolysis of
the complex. Therefore, pH 3.0 was selected for
further study.
3.2. Effect of xylenol orange concentration
The effect of xylenol orange concentration on
the absorbance was studied, and the results are
shown in Fig. 2. We investigated xylenol orange
concentration in the range of 5.0×10
−6
to 5.0×10
−5
mol L
−1
. Maximum absorbance was obtained at a
concentration of 3.0×10
−5
mol L
−1
of the ligand and
after that, absorbance approximately stays constant.
Fig. 1. Effect of pH on the absorbance of
metal–xylenol orange complex.
Fig. 2. Effect of xylenol orange concentration on the absorbance of
metal–xylenol orange complex.
21
Determination of zirconium in aqueous samples Ehsan Zolfonoun
3.3. Effect of CTAB concentration
Effect of CTAB concentration on the extraction
and determination of zirconium was investigated
in the range of 0 to 1.0×10
−4
mol L
−1
. The results
are shown in Fig. 3. The amount of the absorbance
for sample increased by increasing CTAB
concentration. The blank signal also increased
by increasing CTAB concentration. This is due to
more extraction of xylenol orange by increasing
CTAB concentration, but the difference between
the sample and blank signals increased by
increasing CTAB concentration up to 2.0×10
−5
mol L
−1
and decreased at higher concentrations.
Therefore, 2.0×10
−5
mol L
−1
CTAB was chosen as
the optimum.
3.4. Effect of type and volume of the extraction
solvent
Selecting the extraction solvent by paying attention
to its characteristic properties is very important.
Chloroform and carbon tetrachloride were
compared in this extraction and obtained recoveries
were higher for chloroform. To examine the effect
of the extraction solvent volume, 1.5 mL of ethanol
Fig. 3. Effect of CTAB concentration on the absorbance of
metal–xylenol orange.
Fig. 4. Effect of amount of chloroform on the absorbance of
metal–xylenol orange.
22
Anal. Method Environ. Chem. J. 3 (3) (2020) 18-24
Ion Tolerance limit (µg mL
−1
)
Li
+
, Na
+
, K
+
, Cl
−
, NO
3
−
1000
Ca
2+
, Mg
2+
, Ba
2+
, SO
4
2−
50
Co
2+
,Cr
3+
, Zn
2+
, Cd
2+
, Ni
2+
, Pb
2+
5
Cu
2+
, Hg
2+
, La
3+
, Ce
3+
, UO
2
2+
2
Fe
3+
0.5
Table 1. Tolerance limits of some cations and anions on the determination of zirconium
containing different volumes of chloroform in the
range of 60–150 µL were subjected to the same
procedures. According to Fig. 4, increasing the
volume of chloroform, initially increases the
absorbance until at 120 µL it reaches the maximum
amount. Thereby, the 120 μL of chloroform was
employed to extract the zirconium from the
aqueous samples.
3.5. Effect of type and volume of the disperser
solvent
The main criterion for the selection of the disperser
solvent is its miscibility in the extraction solvent
and aqueous solution. In addition, the type of
disperser directly inuences the viscosity of the
binary solvent. Thus, this solvent can control
droplet production and extraction efciency.
To study this effect, two different solvents such
as acetone and ethanol were tested. A series of
sample solutions were studied using 1.5 mL of
each disperser solvent with 120 µL of chloroform
as the extraction solvent. The obtained enrichment
factors for these two dispersers show no statistically
signicant differences between them; however we
selected ethanol as the disperser because it was
cheaper and more accessible than acetone. The
effect of the volume of ethanol on the extraction
recovery was also studied. The different volumes
of ethanol (0.50, 1.00, 1.50, 2.00 and 2.50 mL)
containing 120 µL chloroform were examined.
For the rst two tests, the droplets were big and
the surface area was low, so the droplets rapidly
settled at the bottom of the tube and low extraction
efciencies were obtained. Maximum extraction
was observed when the disperser solvent volume
was 1.5 mL. Thus 1.5 mL of ethanol was chosen as
the proper amount.
3.6. Effect of diverse ions on the recovery
In order to assess the possible analytical
applications of the recommended procedure, the
effect of common coexisting ions in natural water
samples on the preconcentration and determination
of zirconium was studied. In these experiments, 5.0
mL solutions containing 0.10 μg mL
−1
of zirconium
and various amounts of interfering ions were
treated according to the recommended procedure.
Tolerable limit was dened as the highest amount
of foreign ions that produced an error not exceeding
±5% in the determination of investigated analyte.
The results are summarized in Table 1. As it is seen,
large numbers of ions used have no considerable
effect on the determination of zirconium.
3.7. Analytical performance of the method
The linear working range of the method for
determination of Zr(IV) was found to be 0.04−0.35
µg mL
−1
. The limit of detection (LOD) of the
proposed methodology was calculated as three times
the standard deviation of 8 blank solution readings
over the slope of the calibration graph. The LOD for
the determination of Zr(IV) was found to be 0.010
µg mL
−1
. The relative standard deviation (R.S.D) for
analysis of 0.10 µg mL
−1
Zr (IV) (n= 10) was 2.7 %.
3.8. Applications
The accuracy of the proposed method was tested
by separation and determination of Zr(IV) ion in
tap water, well water and mineral water samples.
In order to validate the method, analytes were
determined in spiked real samples. Also this method
was applied to the determination of zirconium in
ceramic materials. The results obtained are shown
in Tables 2 and 3. The results demonstrated that the
proposed method was suitable for the determination
of Zr(IV) in real samples.
23
Determination of zirconium in aqueous samples Ehsan Zolfonoun
4. Conclusions
In the present study, a novel method for the
preconcentration and spectrophotometric
determination of zirconium in water samples is
proposed. Dispersive liquid–liquid microextraction
is a sensitive, efcient, and simple method for
preconcentration and separation of trace metals
with the use of low sample volumes. The proposed
preconcentration and determination method gives a
low limit of detection and good R.S.D. values. The
method can be successfully applied to the separation
and determination of zirconium in real samples.
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