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Karbala International Journal of Modern Science 3 (2017) 185e190
http://www.journals.elsevier.com/karbala-international-journal-of-modern-science/

Ionic liquid based dispersive liquideliquid microextraction

procedure for the spectrophotometric determination of copper using
3-dimethylamino rhodanine as a chelating agent in natural waters
Yasemin Ça

glar a,*, Ece Tu

gba Saka b
a
Department of Genetic and Bioengineering, Giresun University, 28200 Giresun, Turkey
b
Department of Chemistry, Karadeniz Technical University, 61080 Trabzon, Turkey
Received 27 March 2017; revised 11 September 2017; accepted 23 September 2017
Available online 15 October 2017

Abstract

In this work, a novel ionic liquid based dispersive liquideliquid microextraction (IL-DLLME) method has been developed for
spectrophotometric copper determination in natural waters. The method is based on the extraction of Cu(II) in the form of a
complex with 3-dimethylamino rhodanine and determination using spectrophotometry. In the IL-DLLME, 3-dimethylamino
rhodanine and Triton X-100 were used as chelating agent and anti-sticking agent. 1-Heptyl-3-methylimidazolium hexa-
fluorophosphate and ethanol were selected as extractive and disperser solvents, respectively. The following experimental conditions
were optimized: pH 3.0, 5
106 mol L1 complexing reagent, centrifuge for 1 min at 5000 rpm. The method is linear in the range
from 2.2 to 12.2 mg/mL with a correlation coefficient (R2) of 0.9968 and a limit of detection (LOD) of 0.81 mg/mL. The proposed
method was successfully applied to the determination of Cu(II) in water samples.
© 2017 The Authors. Production and hosting by Elsevier B.V. on behalf of University of Kerbala. This is an open access article
under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: IL-DLLME; Preconcentration; Copper; Spectrophotometric determination; 3-Dimethylamino rhodanine

1. Introduction organisms [3]. Excess levels of Cu can cause the

neurological ailments such as schizophrenia, depres-
Copper, found only in very low levels in the human sion, epilepsy [4] and irritation of nose and throat,
body, is a trace element that performs a significant role nausea, vomiting and diarrhea [5].
in various biochemical reactions, hemoglobin synthesis, Some procedures have been developed to determina-
usual task of the central nervous system and oxidative tion of Cu(II) from environmental samples such as liq-
phosphorylation [1]. It is also required in growth of both uideliquid extraction (LLE) [6], solid phase extraction
plants and animals [2]. The maximum daily intake of Cu (SPE) [7], cloud point extraction (CPE) [8]. Nowadays,
is 0.5 mg/L for the normal metabolism of many living these methods are replaced by microextraction methods
minimizing organic solvent consumption, simplifying
sample preparation steps, providing high enrichment
* Corresponding author. rates and appropriate to automation [9].
E-mail address: go_yasemin@hotmail.com (Y. Ça
glar).
Peer review under responsibility of University of Kerbala.

https://doi.org/10.1016/j.kijoms.2017.09.002
2405-609X/© 2017 The Authors. Production and hosting by Elsevier B.V. on behalf of University of Kerbala. This is an open access article under
the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
186 Y. Ça
glar, E.T. Saka / Karbala International Journal of Modern Science 3 (2017) 185e190

Dispersive liquideliquid microextraction (DLLME) 2.2. Apparatus

was demonstrated by Rezaee and co-workers in 2006
[10]. In this process, a convenient mixture of the high Thermo Scientific Evaluation Array UveVis spec-
density extracting solvent and the disperser solvent trophotometer equipped with 250 mL quartz micro
which can be mixed in both the extractant and aqueous cuvette was used for absorbance measurements. A
phase are quickly syringed into the aqueous solution by centrifuge (Benchtop Centrifuges, K2015R) was used
a syringe, resulting in a blurred solution. After extrac- to speed up the separation of sedimented phase. The
tion, the blurred solution is centrifuged and the sedi- pH was determined using a Ohaus pH-meter (Starter
mented phase is collected on the lower of conical glass 5000) with combined a glass electrode.
test tube. Specification of analytes in the residue can be
achieved by appropriate analytical techniques. The 2.3. Dispersive liquideliquid microextraction
main advantages of DLLME method are good repeat- procedure
ability, high enrichment factor, small sample amount,
rapidity, high recovery and low LOD values [11e14]. A mixture of 5 mL sample solution including Cu(II)
Several DLLME methods including flame atomic analyte and 250 mL 3-dimethylamino rhodanine
absorption spectrometry [15e21], electrothermal atomic (5.0
106 mol L1) as chelating agent were placed
absorption spectrometry [22,23], capillary electropho- into 10 mL conical test tube with addition of 200 mL
resis [24], inductively coupled plasma-optical emission Triton X-100. The pH was adjusted to 3.0 using buffer
spectrometry [25], X-ray fluorescence spectrometry solution. Then 750 mL ethanol (disperser solvent)
[26], spectrophotometry [27e30] have been reported for containing 250 mL 1-heptyl-3-methylimidazolium
the preconcentration and determination of Cu(II) from hexafluorophosphate (extraction solvent) was rapidly
many types of samples. injected to the mixture by a 2.0 mL syringe. The so-
Inthiswork,wedevelopedafacileIL-DLLME process lution became blurred rapidly and the complex of
for copper preconcentration and determination using Cu(II) ion was drawn into the droplets of 1-heptyl-3-
UVeVis spectrophotometry. The method is based on the methylimidazolium hexafluorophosphate within a few
extraction of Cu(II) in the ionic liquid droplets after seconds. After centrifugation step for 1 min at
complex formation with 3-dimethylamino rhodanine 5000 rpm, the upper bulk aqueous phase was carefully
compound. removed with a pipette. Then the volume of the
extraction phase was diluted to 250 mL with methanol.
2. Experimental Finally, about 250 mL resultant sample solution was
transferred into a 250 mL quartz cell for spectropho-
2.1. Reagents tometric Cu(II) detection at 280 nm.

All the reagents that used were bought from Merck 3. Results and discussion
(Darmstadt, Germany) and SigmaeAldrich (Tauf-
kirchen, Germany) and all in analytical purity. The ionic 3.1. Optimization of IL-DLLME procedure
liquids were bought from Merck (Darmstadt, Germany),
abcr (Karlsruhe, Germany) and Carl Roth (Karlsruhe, 3.1.1. Effect of the disperser solvent type and volume
Germany). The certified reference materials (TMDA 70) A suitable disperser solvent must be miscible with
was supplied from the National Water Research Institute, both the aqueous and organic phases [21e24]. There-
Environment Canada. Ultra pure water from Sartorius fore, acetone, acetonitrile, ethanol and methanol were
(Arium-Pro) was used through the study. A stock stan- tested as nominees of disperser solvent. Based on the
dard solution of copper ion (Cu II) at a concentration of obtained results (Fig. 1), ethanol was selected as
1000 mg L1 was prepared from Cu(NO3)2$3H2O in disperser solvent and used for further experiments.
water. Copper working solution (50 mg/mL) was ob- The IL-DLLME efficiency when using varied vol-
tained through sequent dilution of the standard stock umes of ethanol ranging from 300 to 1500 mL was
solution. The complexing agent, 3-dimethylamino rho- studied. Based on the obtained results, 750 mL of
danine solution (5
106 M), was used by dissolving an ethanol was selected as optimal.
proper supply of agent in methanol on a daily basis. The
required pH values for the extraction of copper was 3.1.2. Effect of the extraction solvent type and volume
adjusted using citric acid, sodium hydroxide, hydrogen In this work, chloroform, dichloromethane, 1-
chloride tampon (Certipur Merck). butyl-3-methylimidazolium hexafluorophosphate ([C4-
 Y. Ça
glar, E.T. Saka / Karbala International Journal of Modern Science 3 (2017) 185e190 187

1e10 range when the other experimental conditions

were kept constant. As can be seen in Fig. 3, the highest
extraction efficiency of Cu(II)-3-dimethylamino rho-
danine complex from aqueous phase was observed at pH
3.0. When the pH increased from 2.0 to 3.0 the
maximum absorbance was obtained at lower pH levels
were higher than those at higher pH levels. However,
after pH 3.0 the absorbance dramatically decreased
because of the hydrolysis of copper. The absorbance
remained constant from pH 6.0e10.0.
Fig. 1. Effect of disperser solvent. Extraction conditions: sample
volume, 10.0 mL; extraction solvent, 250 mL 1-hexyl-3- 3.1.4. Concentration of chelating reagent
methylimidazolium hexafluorophosphate; 3-dimethylamino rhoda-
nine concentration 5
106 mol L1; extraction time, 1 min; pH,
The effect of 3-dimethylamino rhodanine amount
3.0. on the extraction of Cu(II) was investigated in the
range of 1
105e1
106 mol L1. The absorbance
mim][PF6]), 1-hexyl-3-methylimidazolium hexafluor- has been increased by increasing the 3-dimethylamino
ophosphate ([C6-mim][PF6]), 1-heptyl-3-methylimid- rhodanine up to 5
106 mol L1 at certain amount of
azolium hexafluorophosphate ([C7-mim][PF6]), 1- Cu(II) at pH 3.0.
methyl-3-octylimidazolium hexafluorophosphate ([C8-
mim][PF6]) and 1-butyl-3-pentylimidazolium hexa- 3.1.5. Selection of anti-sticking agent
fluorophosphate ([C4-C5im][PF6]) were examined. Ionic liquid droplets can adhere to the test tube and
When 1-hexyl-3-methylimidazolium hexafluorophos- reduce the effectiveness of the DLLME procedure.
phate was used as extraction solvent the highest When an anti-sticking agent is used, the ionic liquid
absorbance was watched (see Fig. 2). droplets are surrounded by its molecules. Thus this
Various volumes of 1-hexyl-3-methylimidazolium reducing effect is minimized [31]. In this work, some
hexafluorophosphate in 750 mL ethanol was studied. surfactants such as Triton X-100, Triton X-114 and
The absorbance increased with increasing volume of 1- SDS that is various volumes were studied. The best
hexyl-3-methylimidazolium hexafluorophosphate up to result was showed with the 200 mL of Triton X-100.
250 mL. When greater volumes of extraction solvent
were used, the absorbance decreased because of the 3.2. Interferences
increasing sedimented phase volume.
To appraise the selectivity of the suggested method,
3.1.3. Effect of pH some ions that most frequently interference with Cu(II)
The influence of pH on the extraction of copper was were studied individually. The cation solutions were
researched by altering the pH of aqueous solution in the

Fig. 3. Effect of pH on the extraction of copper. Extraction condi-

Fig. 2. Effect of extraction solvent. Extraction conditions: sample tions: sample volume, 10.0 mL; extraction solvent, 250 mL 1-hexyl-
volume, 10.0 mL; disperser solvent, 750 mL ethanol; 3- 3-methylimidazolium hexafluorophosphate; disperser solvent,
dimethylamino rhodanine concentration 5
106 mol L1; extrac- 750 mL ethanol; 3-dimethylamino rhodanine concentration
tion time, 1 min; pH, 3.0. 5
106 mol L1; extraction time, 1 min.
188 Y. Ça
glar, E.T. Saka / Karbala International Journal of Modern Science 3 (2017) 185e190

prepared from nitrate salts and the anion solutions from water collected from the Black Sea in Giresun
sodium, potassium and ammonium salts. The tolerable (Turkey), the lake water collected from Sera Lake in
limit of each interferent was taken as a relative error Trabzon (Turkey), the stream water collected from
not exceeding ±5%. The concentration of the analyte Hars‚it Stream in Giresun (Turkey) and tap water
ions used during experiment was 3.32 mg/mL. Ac- collected from our laboratory were passed through a
cording to the data, the anions (NO3  , 800 mg/mL; 0.45 mm filter and acidified to pH 2.0 with HCl to avoid
Cl, 706 mg/mL; ClO4  , 678 mg/mL; SO4 2 , 590 mg/ adsorption of metal ions on the flask walls. Then all
mL; PO4 3 , 300 mg/mL; H2 PO4  , 612 mg/mL) did not natural waters were stored in the dark at 4  C
interfere more than the cations (Ca2þ, 406 mg/mL; until preconcentration procedure. The suggested
Mg2þ, 378 mg/mL; Co2þ, 192 mg/mL; Cr3þ, 270 mg/ method was performed to extract of Cu(II) from these
mL; Ni2þ, 345 mg/mL; Cd2þ, 367 mg/mL; Zn2þ, natural waters. The results obtained for three deter-
408 mg/mL, Fe3þ 349 mg/mL). The most of the inter- mination of each samples are shown in Table 2. The
fered ions are Agþ (53 mg/mL), Mn2þ (67 mg/mL) and recovery values ranged from 99.33 to 100.00%.
Pb2þ (105 mg/mL).
3.6. Comparison with other dispersive liquideliquid
3.3. Analytical performance microextraction methods

The analytical characteristics of the proposed pro- The linear range, LOD and RSD, % obtained by the
cess were determined under the optimized experi- developed DLLME method were compared with other
mental conditions. The LOD calculated as 3 times the DLLME methods combined with different analytical
SD of the blank (n ¼ 11). The LOQ calculated as 10 techniques in the literature. The results are given in
times the SD of the blank (n ¼ 11). The enhancement Table 3. Stanisz et al. (2014) used sodium dieth-
factor, calculated using the slope ratio of the two yldithiocarbamate (DDTC) as complexing reagent and
calibration curves of the analyte with and without obtained a better limit of detection than this work's
preconcentration. The figures of merit of the intro- detection limit, but this method required the use of an
duced method are summed up in Table 1. additional chemical (LiNTf2) to start metathesis reac-
tion. The method developed by Shariati and Golshekan
3.4. Analysis of certified sample (2011) using neocuproine as ligand has low limit of
detection. However, their method used chloroform as
To validate of the developed IL-DLLME procedure extraction solvent and an additional chemical (hy-
integrated with UVeVis. spectrophotometry, TMDA droxylamine hydrochloride) as reducing agent of
70 (Cu2þ concentration, 399 ± 21.2 mg/L) was used as 
Cu(II). The method developed by Skrlíkov a et al.
certified reference material. According to t-test, there (2011) using 1,3,3-trimethyl-2-[5-(1,3,3-trimethyl-1,3-
is no considerable difference between the results. dihydroindol-2-ylidene)-penta-1,3-dienyl]-3H-indo-
Calculated Student's t value (0.02) was less than the lium (DIDC) as chelating reagent has very low limits
theoretical value (0.07) at a 95% confidence level. of detection, but this method uses an extra solvent
(tetrachloromethane) as auxiliary solvent. Farajzadeh
3.5. Analysis of natural waters et al. (2008) using 8-hydroxyquinoline as ligand
require an extra step to evaporate the sedimented phase
After the developed process passed the accuracy test before measurement. Khani et al. (2011) used thio-
that was done using the certified reference material, the benzophenone (TMK) as ligand and required a home-
process was performed to the natural waters. The sea made microsample unit. Acar and Kara (2014) using

Table 1
The analytical characteristics of the proposed method for copper Table 2
determination under the optimized conditions. Analytical results for determination of Cu(II) in natural waters.

Parameter Sample Concentration (mean, n ¼ 3) (mg/mL)

2
Correlation coefficient (R ) 0.9968 Cu added Cu found Recovery
Linear range (mg/mL) 2.2e12.2 (±RSD) (%)
LOD (mg/mL) 0.81 Sera Lake 3.00 3.00 ± 0.11 100.00
LOQ (mg/mL) 2.43 Hars‚it Stream 3.00 3.02 ± 0.09 99.33
RSD, % (n ¼ 6) 1.09 Black Sea 3.00 3.01 ± 0.04 99.67
Enhancement factor 5 Tap water 3.00 3.01 ± 0.13 99.67
 Y. Ça
glar, E.T. Saka / Karbala International Journal of Modern Science 3 (2017) 185e190 189

Table 3
Comparison of some reported methods with present work.
Procedure Analytical technique Linear range (mg/L) LOD (mg/L) RSD (%) Ref.
DLLME FAAS 50e2000 3.00 5.1 [32]
IL-DLLME FAAS 2e50 0.45 3.3 [33]
DLLME UVeVIS 1e200 0.33 4.0 [27]
DLLME UVeVIS 0.02e0.09 0.005 1.3e5.4 [30]
DLLME FO-LADS 2e70 0.34 <1.3 [34]
DLLME-SFO FAAS 2e600 0.69 e [35]
In-situ IL-DLLME ET-FAAS 20e150 1.8 7.0 [23]
IL-DLLME UVeVIS 2.0e12.0a 0.83a 1.09 This work
a
mg/mL.

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