Accepted Manuscript Removal of pesticides from wastewater by ion pair centrifugal partition extraction using betaine-derived ionic liquids as extractants Yannick De Gaetano, Jane Hubert, Aminou Mohamadou, Stéphanie Boudesocque, Richard Plantier-Royon, Jean-Hugues Renault, Laurent Dupont PII: DOI: Reference:
S1385-8947(15)01406-0 http://dx.doi.org/10.1016/j.cej.2015.10.012 CEJ 14281
To appear in:
Chemical Engineering Journal
Received Date: Revised Date: Accepted Date:
10 July 2015 30 September 2015 4 October 2015
Please cite this article as: Y. De Gaetano, J. Hubert, A. Mohamadou, S. Boudesocque, R. Plantier-Royon, J-H. Renault, L. Dupont, Removal of pesticides from wastewater by ion pair centrifugal partition extraction using betainederived ionic liquids as extractants, Chemical Engineering Journal (2015), doi: http://dx.doi.org/10.1016/j.cej. 2015.10.012
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Removal of pesticides from wastewater by ion pair centrifugal partition extraction using
betaine-derived ionic liquids as extractants
Yannick De Gaetano, Jane Hubert*, Aminou Mohamadou, Stéphanie Boudesocque, Richard
Plantier-Royon, Jean-Hugues Renault, Laurent Dupont*.
Université de Reims Champagne-Ardenne, Institut de Chimie Moléculaire de Reims (ICMR),
CNRS UMR 7312, UFR des Sciences Exactes et Naturelles, Bâtiment 18 Europol’Agro, BP
1039, F-51687 Reims Cedex 2, France.
The extraction of pesticides from aqueous solutions using new ionic liquids (ILs) derived
from glycine betaine as extractants was investigated. These ILs incorporate cationic esters of
trimethyl(2-alkoxy-2-oxoethyl) ammonium (GBOCn+) associated with inorganic ClO4- or BF4-
anions. First, batch extraction experiments were performed by using the liquid-liquid biphasic
system IL/ethyl acetate/water (1:1:1; v/v) for four commonly used pesticides: 4-
chlorophenoxyacetic acid (4-CPA), 2,4-dichlorophenoxyacetic acid (2,4-D), 2-[(4-methyl-5-
oxo-3-propoxy-1,2,4-triazolin-1-yl)carbamidosulfonyl]benzoic acid methyl ester sodium salt
(propoxycarbazone) and 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-5-methoxymethyl
nicotinic acid (imazamox). Then, the liquid-liquid extraction unit operation was intensified by
transposing the system into a Centrifugal Partition Extraction (CPE) device, using ethyl
acetate/n-butanol/water (1:4:5; v/v) as biphasic solvent system and potassium iodide, sodium
iodide or sodium perchlorate as potential displacers. The use of a lab-scale CPE column with
a capacity of 300 mL allowed the intensification of the extraction procedure. The extraction
and back-extraction of individual or mixture of pesticides were studied, with a particular
focus on the potential separation of individual pesticides and on the recyclability of the CPE
method. In optimal CPE conditions, a quantitative extraction for three of the four pesticides
was obtained, with recovery percentages of 95.6 %, 98.7 %, 99.0 %, and 100.0% for
imazamox, propoxycarbazone, 2,4-D, and 4-CPA, respectively. After the back-extraction
step, separated pesticides were recovered in fresh aqueous mobile phase. The recyclability
studies showed that the extraction/back-extraction process can be performed at least four
times while maintaining a quantitative extraction.
Keywords: Ionic liquid, pesticide, centrifugal partition extraction, water treatment,
(*) Corresponding author. Address: ICMR (Institut de Chimie Moléculaire de Reims), Université de Reims Champagne-Ardenne, BP 1039,
51687 Reims Cedex 2, France. Tel.: +33 (0) 3 26 91 33 36; fax: +33 (0) 3 26 91 32 43. E-mail address: [email protected]
DUPONT. [email protected]
37 38 39 40
The extensive use of pesticides in modern agriculture has become a major concern due to the
potential hazard that these compounds can cause to the environment and their known or
supposed toxic effects on human health, such as mutation, cellular degradation, and
interruption of hormone functions [1-2].
For this reason, the analytical control of pesticide concentrations is mandatory in different
water bodies within the EU including drinking waters . Thus the development of efficient
purification strategies focused on their elimination remains a critical issue. Industrially, the
most common removal techniques of pesticides from water rely on chemical oxidation,
filtration on activated charcoal or inverse osmosis. However these processes are still
expensive and research efforts are currently made to find other alternatives. To date, the most
common laboratory-scale methods to extract pesticides from aqueous media have been based
on liquid-liquid extraction [4, 5] and solid-phase extraction (SPE) [6, 7], with typical
extraction volumes ranging from around 10 to a maximum of 100 mL. These techniques
usually involve the use of chlorinated solvents that exhibit toxicity (such as tetrachloroethane,
chlorobenzene, carbon tetrachloride) or n-hexane [8-10]. ILs have been recently considered
as interesting ionic species to remove pesticides from water via extraction mechanisms. ILs
are non-flammable liquids, exhibiting a negligible vapour pressure and a high thermal
stability. Some of them are liquid at room temperature, able to solubilize a wide range of
organic and inorganic compounds .
The utilization of pure ILs for the extraction of pesticides has been already investigated in
liquid-liquid extraction [12-14], solid-liquid extraction , magnetic solid-phase extraction
, micro-solid phase extraction , dispersive micro-solid phase extraction , pipette
tip-solid phase extraction  and hollow fiber-solid phase microextraction procedures .
However these methods remain time consuming and still display some drawbacks such as low
extraction yields, multiple operation steps , and high IL consumption. The present work
aimed to develop a novel efficient method for the extraction of pesticides that combines the
use of ILs as extractants with Centrifugal Partition Extraction (CPE) as liquid-liquid efficient
CPE is a solid support-free liquid-liquid extraction technique involving transfer and
distribution of solutes between at least two immiscible liquid phases according to their
distribution and mass transfer coefficients.
A CPE column (Figure 1) consists in a series series of partition cells connected in cascade by ducts
and subjected to a centrifugal acceleration field . One liquid phase is maintained inside
the partition cells (the stationary phase) while the other liquid phase (the mobile phase) is
pumped through the stationary phase. The separation process is based on the interfacial mass
transfer of solutes between the two liquid phases in each cell .
Fig. 1. (a) Centrifugal Partition Extractor FCPE300®, (b) CPE column containing 7 circular
partition disks, (c) Scheme of a circular partition disk
The design of CPE partition cells inside the column allows the loading of sample solutions
continuously with flow rates ranging from 10 to 100 mL/min at the laboratory-scale, which is
of particular interest for the extraction of micropollutants such as pesticides present at low
concentrations in aqueous media.
Considering the ionic nature of ILs (cation/anion association), it can be expected that the ion-
pair displacement mode in CPE  would provide interesting results to extract pesticides
from water and possibly to separate pesticides from each other at the end of the process. The
ion pair displacement mode in CPE consists in diluting an anionic or cationic species (here
ILs) in the organic stationary phase. By this way ionisable analytes (such as most pesticides)
contained in the inlet aqueous solution are captured by the IL inside the CPE column. Then
during the back-extraction step, a displacer agent that presents a high affinity for the
extractant (i.e. the IL) is introduced into the aqueous mobile phase to force the analytes to
competitively progress along the column. As a result the analytes (here the pesticides) initially
introduced into the CPE column as a mixture of compounds in a liquid phase are not only
extracted from their initial media over the extraction step, but also displaced out of the
column during the back-extraction and possibly recovered in a fresh aqueous solution as
individual compounds. This method has been successfully applied for the separation and
purification of ionizable natural products .
To date only a few ILs have been synthesized and tested for the extraction of organic
compounds. The most common families of ILs employed for this purpose were the 1,3-
dialkylimidazolium salts with hexafluorophosphate or bis(trifluoromethylsulfonyl)imide
anion, but these ILs exhibited some toxicity .
2. Materials and methods
In the present work, we report the study of the extraction of some pesticides by six news ILs
obtained from esterified glycine betaine (Scheme 1) using Centrifugal Partition Extraction.
The effects of the nature of both cation and anion forms of the ILs, as well as CPE parameters
(e.g.volume of treated solutions, flow rate, nature of the displacer) on the pesticide extraction
percentage have been investigated. Results related to the back-extraction of pesticides are also
Scheme 1. Ionic liquids based on Glycine Betaine esters.
The CPE extraction method was developed by using four systemic herbicides commonly used
worldwide for the control of broadleaf weeds. Two members of the phenoxy family of
herbicides: the 4-chlorophenoxyacetic acid (4-CPA) and the 2,4-dichlorophenoxyacetic acid
(2,4-D), as well as propoxycarbazone and imazamox were selected as models (Scheme 2).
Scheme 2. Chemical structures of the four pesticides studied.
2.1. Reagents and solvents
All chemicals were of analytical grade. Ethyl acetate (EtOAc) and n-butanol (n-BuOH) were
purchased from Carlo Erba Reactifs SDS (Val de Reuil, France). 4-chlorophenoxyacetic acid
(4-CPA), 2,4-dichlorophenoxyacetic acid (2,4-D), propoxycarbazone salt and imazamox were
purchased from Sigma Aldrich (Saint Quentin, France). Sodium perchlorate and sodium
iodide were obtained from Acros (Illkirch, France) and potassium iodide from Alfa Aesar
(Schiltigheim, France). All aqueous solutions were prepared in distilled water and stored safe
from the light at 4°C.
2.2. Apparatus: Fast Centrifugal Partition Extractor FCPE300®
Extraction experiments were developed on a lab-scale Centrifugal Partition Extractor
(FCPE300®, Rousselet Robatel Kromaton, Annonay, France) containing a rotor of 7 circular
partition disks engraved with a total of 231 twin partition cells. The stationary phase was
maintained inside the CPE column by a centrifugal force field generated by rotation around a
single central axis. The total column capacity is 303.5 mL . The rotation speed can be
adjusted from 200 to 2000 rpm, producing a relative centrifugal acceleration in the partition
cell up to 437 g. The mobile phase was pumped through the stationary phase either in the
ascending or in the descending mode with low residual pulsation through a KNAUER
Preparative Pump 1800® V7115 (Berlin, Germany). Fractions were collected by a Pharmacia
Superfrac collector (Uppsala, Sweden). All experiments were conducted at room temperature
(20 ± 2 °C). The flow rate was fixed at 10 mL/min and the rotation speed at 1000 rpm for all
2.3. HPLC analyses
All CPE fractions were analyzed by HPLC on an Ultimate® 3000 HPLC system (Dionex)
equipped with a Dionex Ultimate pump (model 3000), a WPS-3000 (SL) autosampler, and a
diode array detector DAD-3000(RS). The chromatographic column (Myrsine, 250 × 4.6 mm,
5 µm particule size) was maintained at 21 °C. The mobile phases, 0.5% acetic acid in water
(solvent A) and acetonitrile (solvent B), were pumped isocratically at 1.5 mL/min with a ratio
60/40 (v/v). The injection volume was 20 µL. Data acquisition was controlled by the
Chromeleon Software and the chromatograms were recorded for 15 min.
UV detection was performed at λ = 254 nm for imazamox (λmax = 250 nm) and
propoxycarbazone (λmax = 253 nm) and λ = 280 nm for 4-CPA (λmax = 279 nm) and (λmax =
283 nm). Calibration curves were established by serial dilution of two independent stock
solutions of each pure pesticide (1 g/L) and by plotting the peak area recorded from HPLC
chromatograms as a function of pesticide concentration. The correlation coefficient (R2)
calculated from the calibration curves of standard solutions were higher than 0.9996 for all
compounds. The four pesticides were identified over CPE experiments by comparison with
the HPLC retention time of their corresponding standard molecules. The retention times of
imazamox, 4-CPA, 2,4-D and propoxycarbazone were 3.0, 6.8, 9.1 and 13.2 min,
2.4. Batch tests
2.4.1. Optimization of extraction conditions
Extraction conditions were optimized in batch tests by using the couple GBOC14-ClO4 and 4-
CPA as an IL/analyte test system. Experiments were performed using different molar ratios (
) ranging from 10 to 25 (corresponding to 8, 12, 16 and 20 mg of GBOC14-ClO4). An
aqueous solution containing 4-CPA at a concentration of 10-3 mol.L-1 (2 mL) was mixed with
an equal volume of IL diluted in ethyl acetate (2 mL). The mixture was stirred for 1 hour at
analyzed by HPLC. The efficiency of the extraction process was evaluated by determining the
extraction percentage (%E) using the following equation:
The liquid phases were then separated and the aqueous phase was
(Cin − C fin ) Cin
where Cin and Cfin (mol. L-1) represent the concentrations of the pesticide in the initial and in
the final aqueous solutions.
2.4.2. Choice of the base for the extraction
The first goal was to find the best pH conditions to ensure the ionization state of pesticides
(COO-, N-) while maintaining their chemical integrity. HPLC analyses of the four pesticides
revealed two different peaks for propoxycarbazone at pH > 9, suggesting that this compound
is stable only up to this value. The other pesticides were also stable up to pH 9. Therefore the
pH was fixed at 9 in all extraction experiments. The pKa values for 4-CPA, 2,4-D and
propoxycarbazone are respectively 3.6, 2.7 and 2.1. Imazamox has three protonation sites
corresponding to pKa values of 2.3, 3.3 and 10.8 . The first two pKas correspond
respectively to the deprotonation of pyridinium and carboxylic groups, whereas the third pKa 9
is ascribed to the neutralization of the protonated amidic nitrogen. Consequently, at pH 9,
Imazamox, 4-CPA, 2,4-D are present as their carboxylate salt and propoxycarbazone as its
anionic form (-N-). These observations are summarized in Table 1.
Several alkaline agents including ammoniac buffer (NH4OH), potassium hydroxide (KOH)
and sodium hydroxide (NaOH) were tested to adjust the pH of the aqueous solutions. For
experiments with NaOH and KOH, 18.6 mg of 4-CPA (corresponding to 0.1 mmol) were
firstly diluted in approximatively 100 mL of distilled water and then the pH was adjusted to 9
by adding few drops of concentrated solution of the base (1 mol.L-1), in order to obtain a
solution of 4-CPA at a concentration of 10-3 mol.L-1. For extraction experiments with
ammoniac buffer, 18.6 mg of 4-CPA corresponding to 0.1 mmol were directly diluted in
100 mL of ammoniac buffer at a concentration of 0.1 mol.L-1.
2.4.3. Extractant selection
GBOC12-ClO4, GBOC14-ClO4, GBOC16-ClO4, GBOC12-BF4, GBOC14-BF4 and GBOC16-BF4
were investigated as ILs for the extraction of 4-CPA. Experiments were performed at pH 9
using a molar ratio (
) equal to 25. All experiments were carried out at room
2.4.4. Extraction of individual pesticides with GBOC14-ClO4
The fresh pesticides solutions ([C] = 5.10-4 mol.L-1) were independently prepared by
dissolving 9.3 mg of 4-CPA; 11.0 mg of 2,4-D; 15.2 mg of imazamox or 21.0 mg of
propoxycarbazone in 100 mL of distilled water. Then, 2 mL of each solution containing
individual pesticide at a concentration of 5.10-4 mol.L-1 (pH = 9) were mixed with 2 mL of
ethyl acetate containing GBOC14-ClO4 at concentrations ranging from 0 to 25 equivalents of
pesticide (from 0 to 10.4 mg) for 4-CPA and 2,4-D and from 0 to 50 equivalents of pesticides 10
(0 to 20.7 mg) for imazamox and propoxycarbazone. The solutions were stirred for 1 h. The
liquid phases were then separated and the aqueous phases were all analyzed by HPLC to
determine the extraction percentage of individual pesticides. Extraction experiments were
repeated 5 times for each experimental condition.
2.5. Centrifugal Partition Extraction (CPE)
2.5.1. Optimization of the extraction and back-extraction steps with individual pesticides
Extraction and back-extraction of individual pesticides were investigated at the preparative
scale by using CPE. The extraction step consists in the capture of ionic species (among which
pesticides) by the ionic liquid inside the column through the formation of ion pairs, while the
other non-ionic compounds are eluted out of the column. In a second step, the back-extraction
consists in introducing in the mobile phase a displacer agent (here iodides) which exhibits a
higher affinity for the ionic liquid than the captured analytes. By this way a competitive
process takes place and the target ionic compounds are eluted selectively in the order of their
affinity for the ionic liquid.
A biphasic solvent system (2 L) was prepared by mixing EtOAc/n-BuOH/water in the
proportions 4:1:5 (v/v/v). The column was filled at 200 rpm with the organic phase used as
the stationary phase containing the IL extractant GBOC14-ClO4 at a molar ratio
25. Individual pesticides were dissolved in the aqueous phase of the solvent system at a
concentration of 62.5 mg/L. The pH was adjusted to 9 by adding KOH (1 mol.L-1) and the
aqueous phase containing the pesticide was pumped through the stationary phase at
After pumping slightly more than one column volume (320 mL), aqueous solutions of
potassium iodide (KI) or sodium iodide (NaI) were tested for the back-extraction step. In this
nIL n pesticides
process, the pesticide previously extracted, were stripped off the stationary phase, following
242 243 244
where R-COO- corresponds to the pesticide under his anionic form.
Fractions of 20 mL were collected over the whole experiments and analyzed by HPLC. The
back-extraction step was also studied using different molar ratios:
= 5 and
= 10. Finally, NaI and KI were investigated as displacers in order to
assess the influence of the cation on the back-extraction efficiency.
2.5.2. Extraction and back-extraction process description with mixtures of pesticides
Extraction and back-extraction of an equimolar mixture of the two phenoxyacetic acids 4-
CPA and 2,4-D were firstly investigated at a concentration of 2.8 x 10-4 mol.L-1 (21 mg of 4-
CPA and 25 mg of 2,4-D; 1.13 x 10-4 mol) were dissolved in 400 mL of distilled water. The
preparation of both the mobile and stationary phases is described above. The back-extraction
was carried out using a ratio
For the preparation of the mixture of the pesticides at a concentration of 2.0 x 10-4 mol.L-1,
14.9 mg of 4-CPA, 17.7 mg of 2,4-D, 24.4 mg of imazamox and 33.7 mg of
propoxycarbazone (8.0 x 10-5 mol) were dissolved in 400 mL of distilled water.
nKI = 10. nIL
2.5.3. Back-extraction with sodium perchlorate as displacer 12
This extraction was performed on the same pesticide mixture as described in § 2.5.2. Sodium
perchlorate was used as displacer. The back-extraction process was performed using a ratio
2.5.4. Recyclability of the process
In order to investigate the recyclability of the whole CPE procedure, 18.6 mg of 4-CPA (10-4
mol) were dissolved in 400 mL of distilled water to obtain a solution at a concentration of 2.5
x 10-4 mol.L-1. The preparation of the mobile and stationary phases are described in § 2.5.1.
The back-extraction process was performed using sodium perchlorate as displacer and a ratio
= 10. After one cycle of extraction/back-extraction, 18.6 mg of 4-CPA were dissolved
in 400 mL of the fresh aqueous phase of the CPE biphasic solvent system and loaded again
into the column to perform a second extraction/back-extraction cycle. In total, four
consecutive cycles were performed.
2.5.5. Resolution (Rs) and selectivity factor (α)
Resolution (Rs) and selectivity factor (α) were calculated for two consecutive peaks. The Rs
is calculated using this following equation:
Rs = 2
(t r ( B) − t r ( A)) wb + wa
where tr(A) and tr(B) represent the retention time for solutes A and B, with B the more
retained solute; wa and wb represent the curve width of solute A and solute B respectively.
Selectivity factor is given by this following equation:
k ' ( B) k ' ( A)
where k’(A) and k’(B) represent the capacity factor. These capacity factors are deduced by
these two equations:
k ' ( A) =
(t r ( A) − t 0 ) t0
k ' ( B) =
(t r ( B) − t0 ) t0
with t0 the time for the dead volume.
All GBOCn-X ILs were obtained from the esterification reaction of betaine with n-alkyl
alcohols using methanesulfonate acid as catalyser, follow by anionic metathesis from the
methanesulfonate derivative using sodium perchlorate or sodium tetrafluoroborate .
3.1. Optimization of the extraction conditions in batch tests with 4-CPA as pesticide model
The first goal was to evaluate the influence of the pH of the aqueous solution and the nature
of the base used to adjust the pH on the pesticide extraction percentage. percentage. For these
experiments, 4-CPA and GBOC14-ClO4 were selected as models. Indeed, alkaline conditions
are necessary to obtain pesticides in their anionic form and therefore facilitate the formation
of ion pairs with ILs. Due to the poor stability of pesticides, especially propoxycarbazone
which hydrolyses above pH 9, the pH was limited to this value (Table 1).
Chemical structure, molar mass (g.mol-1), stability under alkaline conditions and pKa values
of each pesticide. Chemical Structures of
Molar Mass Name
Pesticides 4-chlorophenoxyacetic acid
2,4-dichlorophenoxyacetic acid 221.04
(2,4-D) 2-[(4-Methyl-5-oxo-3-propoxy1,2,4-triazolin-1Stable at 420.37
2.10 pH < 9
acid methyl ester sodium salt
(propoxycarbazone) 2-(4 (4-Isopropyl-4-methyl-5-oxo-
methoxymethyl nicotinic acid
10.8 (Namide) (imazamox)
For the same experimental conditions with a ratio (
Table 2 demonstrate that the extraction of 4-CPA using NH4OH buffer or NaOH was less
effective (%E = 27.0 - 63.0%) than with KOH (%E (%E = 69.0%). The extraction of 4-CPA under
its potassium salt form with GBOC14-ClO4 IL is thus more efficient than under sodium or
ammonium salt forms.
) = 10, the results presented in
Extraction percentage (%E) of 4-CPA with three different bases (NH3, NaOH and KOH) and
two different ratios
n IL n 4−CPA
This tendency was confirmed by the results obtained with a ratio (
base lead to a nearly quantitative extraction of 4-CPA (99.1%) was observed. However, the
extraction percentage was below 90% when using NaOH and 50% with NH4OH buffer. The
best extraction conditions were thus fixed at pH 9 with KOH and using 25 equivalents of ILs.
To determine the most efficient IL, these conditions were applied for a range of glycine
betaine-derived ILs differing from each other by their anionic moiety (ClO4- or BF4-) and
alkyl chain length (n=12, 14, 16). The results are summarized in Table 3.
) = 25 using KOH as
Extraction percentage (%E) of 4-CPA, Experimental conditions: [4-CPA] = 10-3 mol.L-1, pH
9 (KOH), ratio (
) = 25.
Extraction yields obtained with ILs containing a tetrafluoroborate anion were comprised
between 59.6% and 71.4%, while all the extraction yields obtained with ILs containing a
perchlorate anion were higher than 90%. This effect is somewhat due to the ability of
perchlorate anions to precipitate in the presence of potassium as shown below.
Indeed, over the course of extraction, an anionic exchange occurs and the insoluble potassium
perchlorate salt is formed in the organic phase, thus enhancing the formation of GBOCn+ 416
CPA- and leading to a better extraction yield as compared to ILs with other anions. We also
observed that extraction yields were improved with ILs containing a longer alkyl chain as
observed in previous works . For instance the extraction yields obtained with the
tetrafluoroborate series were 59.6. 65.5 and 71.4% for n = 12, 14, and 16, respectively. For
the perchlorate series, extraction yields were 92.1, 99.1, and 96.7% for n = 12, 14, and 16,
respectively. The lower extraction percentage obtained with GBOC16-ClO4 could be explained
by its lower solubility in EtOAc, which limits its efficiency as an extractant. GBOC14-ClO4
was therefore selected to perform all others extraction experiments.
3.2. Influence of IL concentration on the extraction profile of pesticides from aqueous
The results depicted in Figure 2 represent the extraction trends for the four pesticides using
GBOC14-ClO4 as the extractant.
100 80 60 40
4-CPA 2,4D Propoxycarbazone Imazamox
20 0 0
Fig. 2. Extraction behaviors for 4-CPA, 2,4-D, propoxycarbazone and imazamox with
GBOC14-ClO4 IL (with a confidence interval +/- 0.3%).
Without IL, only 7.8% and 2.1% of the two chlorophenoxyacetic acids 4-CPA and 2,4-D were
transferred into the organic phase. For the two other pesticides, imazamox and
propoxycarbazone which are more soluble in water (4 g/L and 2.9 g/L, respectively), only 0.8
and 0.2 % of the pesticides were transferred into the organic phase.
With 25 equivalents of GBOC14-ClO4, the extraction percentages were 99.1 and 95.1% for 4-
CPA and 2,4-D, respectively. For imazamox and propoxycarbazone, the extraction
percentages were only 53.5 and 76.0 %, respectively. These lower values could be explained
by the higher hydrophilicity of these molecules as compared to 4-CPA and 2,4-D. With 50
equivalents of GBOC14-ClO4 ([C] = 2.5 x 10-2 mol.L-1), the extraction yields increased up to
61.0% for imazamox and up to 81.3% for propoxycarbazone. The extraction percentage
remained lower than those obtained for the two phenoxy herbicides. However, we expected
that the transposition of extraction experiments from batch test conditions to CPE by
exploiting the length (231 interconnecting partition cells) of the CPE column should provide
higher extraction percentages.
Each extraction experiment was replicated five times and the extraction percentage variations
were less than 1.5% between experiments, indicating a very good reproducibility (Figure 2).
3.3. Pesticide extraction by Centrifugal Partition Extraction (CPE)
Nowadays, ILs are mainly used in micro-extraction for the treatment of very low volumes of
aqueous solutions, typically from 2 to 10 mL, with a low amount of pure IL. Micro-extraction
is a very efficient process to obtain high enrichment factors (80-500) and extraction yields
higher than 90 % . But to our knowledge, no literature deals with the use of ILs for the
treatment of large volumes of aqueous solution contaminated with pesticides. The main goal
of this work was to develop a preparative-scale process for the extraction process of pesticides
by combining ILs as extractants and CPE. Our objective was to extract quantitatively the
pesticides from aqueous solutions and to investigate the selectivity of the process (i.e. the
separation of the different pesticides) and its recyclability.
3.3.1. CPE: Extraction and back-extraction results on individual pesticides
Extraction and back-extraction steps were firstly performed by CPE with each individual
pesticide. Experiments were performed at a flow rate of 10 mL/min by using a molar ratio
nIL/npesticides = 25 with a pesticide concentration of 62.5 mg/L in the aqueous mobile phase.
After pumping slightly more than one column volume (320 mL), no pesticide was detected for
4-CPA, 2,4-D and propoxycarbazone in the fractions collected during the extraction step
indicating that these compounds were quantitatively extracted from the aqueous mobile phase.
However under the same experimental conditions, the extraction of imazamox was less
effective with an extraction percentage of 58.0 %. In order to improve the extraction
percentage of imazamox, another experiment using twice more extractant GBOC14-ClO4 was
carried out, but the extraction percentage remained limited to 63.0 %.
For the back-extraction step, KI was first used as a displacer with
ranging from 1 to 10. The recovery of 4-CPA during this back-extraction step increased from
86 % to 100 % when the molar ratio
that a minimum of 10 equivalents of KI are required to obtain a complete back-extraction of
4-CPA. Under the exact same conditions, high recovery percentages were obtained for the
other pesticides as indicated in table 4. The use of NaI as a displacer instead of KI was also
investigated. The results showed that the nature of the cation on the displacer agent did not
significantly influence the back-extraction performance, except for 2,4-D for which the back-
extraction was slightly improved.
nKI nGBOC14 −ClO4
nKI nGBOC14 −ClO4
increased from 1 to 10. These results showed
Extraction percentage (%E), Recovery percentage (%R) of different pesticides; Experimental
conditions: mobile phase 1 (extraction process): mass of each pesticide = 25 mg, pH = 9
(KOH), ratio (
NaI (10 equivalents)
n IL n pesticide
) = 25; mobile phase 2 (back-extraction process): aqueous phase KI or
409 410 4-CPA
411 412 413
3.3.2. CPE: Extraction and Back-extraction results on mixture of pesticides
Support-free liquid-liquid separation techniques such as CPC (including CPE type devices) or
couter-current chromatography (CCC) are well-known for their large sample loading capacity
and scaling-up ability, but are also very attractive in terms of selectivity [31,32], especially
when the displacement mode (ion-exchange, pH-zone refining) is performed. Here the
selective recovery of pesticides was investigated.
Firstly, extraction and back-extraction were carried out for a binary mixture of the two
phenoxy-herbicides 4-CPA and 2,4-D. During the extraction step, 320 mL of the aqueous
mobile phase pumped at a flow rate of 10 mL/min and a rotation speed of 1000 rpm. The two
pesticides were quantitatively retained in the organic stationary phase. The extraction/back-
extraction profile of these pesticides when using NaI as a displacer (
Figure 3. This profile can be divided in three distinct zones: zone 1 covered the range between
160 mL and 240 mL (fraction 8-12, recovered mass = 17.0 mg, 9.1 x 10-5 mol), 4-CPA was
nNaI = 10) is shown in nIL
obtained as a pure compound; zone 2 covered the range between 260 mL and 320 mL
(fraction 13-16, m (CPA) = 4.1 mg, 2.1 x 10-5 mol and m (2,4-D) = 5.7 mg, 2.6 x 10-5 mol) in
which both compounds were obtained as a mixture, and zone 3 ranged above 320 mL
(fraction 17-30, recovery mass = 18.8 mg, 8.5 x 10-5 mol) only 2,4-D was recovered. These
results indicate a quite good pesticide separation. Pure fractions of 4-CPA represent 81% of
the total injected mass of 4-CPA, and 76% for 2,4-D. The total recovery percentage was
quantitative for 4-CPA and 2,4-D, respectively (Figure 3). For this experiment, the selectivity
factor (α) calculated was equal to 2.2 with a Rs of 0.86. Zone 1
quantity of pesticides (mol %)
25 20 15 10 5 0 0
200 300 400 Volume of displacer (mL)
Fig. 3. Back-extraction of the equimolar mixture of 4-CPA and 2,4-D with NaI as displacer,
Experimental conditions: ratio nNaI/nIL = 10, flow rate= 10 mL/min, rotation speed 1000 rpm,
The second experiment was the extraction and back-extraction of an equimolar mixture of the
four herbicides (8.0 x 10-5 mol). During the extraction step (
aqueous mobile phase pumped at a flow rate of 10 mL/min and a rotation speed of 1000 rpm),
nIL n pesticides
= 25, 320 mL of the
4-CPA, 2,4-D and propoxycarbazone were quantitatively retained in the organic stationary
phase. Only imazamox was partially extracted (%E = 68.7%). The back-extraction profile
obtained with NaI as a displacer (
between 80 mL and 120 mL (fraction 4-6, recovered mass = 17.0 mg, 5.6 x 10-5 mol), pure
fractions of imazamox were isolated. In zone 2, between 140 mL and 180 mL, a mixture of 4-
CPA, imazamox and propoxycarbazone was collected. Zone 3 (200–280mL) corresponds to a
mixture of 4-CPA and propoxycarbazone. In zone 4, between 300 and 380 mL, 4-CPA was
recovered as a pure compound. Finally zone 5, (400 mL- 600 mL) 2,4-D was isolated as a
pure compound. The total recovery percentages were 95.5% for 4-CPA, 98.7% for 2,4-D,
96.5% for imazamox and 96.0% for propoxycarbazone. (Figure 4)
nNaI = 10) can be divided in five distinct zones. In zone 1, nIL
453 Zone 5
Fig. 4. Back-extraction of the equimolar mixture of the four pesticides with NaI as displacer.
The selectivity factors α and Rs considering two consecutive peaks, between imazamox –
propoxycarbazone (peak 1 – peak 2), propoxycarbazone – 4-CPA (peak 2 – peak 3) and 4-
CPA – 2,4-D (peak 3 – peak 4) are summarized in Table 5.
Selectivity factor α and Resolution Rs calculated for the mixture of the four pesticides.
Selectivity factor (α) Resolution (Rs)
peak 1 – peak 2
peak 2 – peak 3
peak 3 – peak 4
During this back-extraction step, imazamox and 2,4-D were well separated with a selectivity
factor superior to 2.2, but the back-extraction profiles of 4-CPA and propoxycarbazone were
rather similar and their separation was less effective.
3.4. Back-extraction with sodium perchlorate as displacer
The regeneration, recyclability and reuse of ILs without significant loss remains a critical
issue to make the process economically viable and reduce the potential environmental burden.
The recyclability of the method was thus studied.
Back-extraction with NaClO4 as a displacer (
to regenerate the IL GBOC14-ClO4 directly in the organic stationary phase, and to investigate
the possibility to recycle the system (Figure 5).
= 10) was performed, the main goal being
Fig. 5. Extraction/Back-extraction cycle of 4-CPA ([C] = 2.5 x 10-4 mol.L-1) with GBOC14-
ClO4 IL as extractant and NaClO4 as displacer.
For this study, the extraction of an equimolar mixture of 4-CPA and 2,4-D, was investigated
at a concentration of 2.5 x 10-4 mol.L-1. During the extraction (
pesticides were quantitatively retained in the organic stationary phase. It was observed that
the back-extraction step was more efficient using NaClO4 as a displacer than with NaI.
Indeed, the back-extraction of 4-CPA was completed in only four fractions (80 mL) instead of
eight (160 mL) with NaI. In the same manner, the back-extraction of 2,4-D was realized in
180 mL instead of 320 mL. But in this latter case, the separation was less marked. The
selectivity factor was equal to 1.4 with a Rs value of 0.4. In the other hand, a selectivity factor
of 2.2 with a Rs of 0.9 were obtained for the back-extraction with NaI.
Only one fraction of pure 4-CPA was isolated (fraction 8). 2,4-D was isolated in fractions 12-
16. The total recovery percentage was 100% and 91% for 4-CPA and 2,4-D, respectively
nIL n pesticides
= 25), the two
Fig. 6. Back-extraction of the equimolar mixture of 4-CPA and 2,4-D ([C] = 2.8 x 10-4 mol.L-
) with NaClO4 as displacer.
3.5. Process recyclability
With regard to the efficiency of NaClO4 as a displacer, the recyclability of the process was
studied for four cycles with alternative extraction (0 - 350 mL, 700 - 1050 mL, 1400 - 1750
mL and 2100 - 2450 mL) and back-extraction (350 - 700 mL, 1050 – 1400 mL, 17500 – 2100
mL and 2450 – 2700 ml) steps. The quantitative extraction of 4-CPA for the two first cycles
proves that the regeneration of GBOC14-ClO4 was effective (Figure 7).
The high extraction percentages (98.3% and 97.1% for the third and the fourth cycle) showed
that IL maintained its extraction capacity over multiple extraction/back extraction cycles.
Fig. 7. (a) Profile curve for four cycles of Extraction/Back-extraction of 4-CPA with NaClO4
as displacer. (b) Percentage of 4-CPA recovered during extraction and back-extraction
process of 4-CPA with NaClO4 as displacer
The main focus of this work was to demonstrate the efficiency of Centrifugal Partition
Extraction to remove pesticides from water samples and optimize this extraction process. 26
The extraction potential of six new ILs derived from glycine betaine was investigated in batch
tests and then transposed to CPE. Batch tests have shown that GBOC14-ClO4 is the most
efficient IL for the extraction of the four model pesticides (4-CPA, 2,4-D, propoxycarbazone
and imazamox), and the transposition to a larger scale was successfully achieved by CPE.
Good extraction yields were obtained by CPE with a quantitative extraction for three of the
four pesticides and high recovery rate over the back-extraction step (up to 96%). Selective
back-extractions were also obtained for the separation of the two phenoxy herbicides. The
recyclability of the process has also demonstrated that the extractant can be regenerated and
the extraction/back-extraction cycle can be repeated at least four times. However, it seems
worthwhile to extend this work by replacing the perchlorate anion by other anions such as
amino-acid which are renewable and convenient, allowing the extension of this method to
larger effluent volumes.
We are grateful to Dr. Yamina Belabassi (UMR 7312, University of Reims Champagne-
Ardenne) for linguistic improvement of this manuscript. We thank the Conseil Régional de la
Marne for financial support.
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Pesticides are extracted from aqueous media using new bio-sourced ionic liquids
Extraction conditions were optimized in batch tests and transposed to Centrifugal
Partition Extraction •
Four model pesticides were successfully extracted by CPE in the ion-pair displacement mode
Pesticide mixtures were well separated and enriched over the back-extraction step
The recyclability of the process was demonstrated