American Journal of Anal yt ical Chemistry, 2011, 2, 632-637
doi:10.4236/ajac.2011.25072 Published Online September 2011 (
Copyright © 2011 SciRes. AJAC
Determination of Amitraz in the Honey Samples by
Dispersive Liquid-Liquid Microextraction Followed by
Gas Chromatography—Flame Ionization Detection
Mostafa Bashiri-Juybari1, Ali Mehdinia*, Ali Jabbari1, Yadollah Yamini3
1Department of Chemistry, Faculty of Sciences, K. N. Toosi University of Technology, Tehran, Ira n
2Department of Marine Living Resources, Iranian National In stitute for Oceanography, Tehran, Iran
3Department of Chemistry, Tarbiat Modares University, Tehran, Iran
E-mail: *
Received June 15, 2011; revised July 2, 2011; accepted August 3, 2011
Dispersive liquid-liquid microextraction (DLLME) followed by gas chromatography–flame ionization detec-
tion (GC-FID), as a simple, rapid and efficient method, was developed for the determination of amitraz in
honey samples. This method involves the use of an appropriate mixture of the extraction and disperser sol-
vents for the formation of a cloudy solution in 5.0 mL aqueous sample containing amitraz. After extraction,
phase separation was performed by centrifugation and the concentrated amitraz in the sedimented phase was
determined by gas chromatography—flame ionization detection (GC-FID). Some important parameters such
as the type and volume of extraction and disperser solvents, and the effect of pH and salt on the extraction
recovery of amitraz were investigated. Under the optimum conditions (13 µL of carbon tetrachloride as an
extraction solvent, 1 mL of acetonitrile as a disperser solvent, no salt addition and pH 6) preconcentration
factor and the extraction recovery were 955 and 95.5%, respectively. The linear range was 0.01 - 1.0 mg·kg–1
and the limit of detection was 0.0015 mg·kg–1. The relative standard deviation (RSD, n = 4) for 0.1 mg·kg–1
of amitraz was 3.2%. The recoveries of amitraz from honey samples at the spiking levels of 0.1 mg·kg-1 were
78.8 and 98.2%. The results indicated that DLLME is an efficient technique for the extraction of amitraz in
honey samples.
Keywords: Dispersive Liquid-Liquid Microextraction, Amitraz, Honey Sample
1. Introduction
Amitraz (N-2,4-(dimethylphenyl)-N-[(2-4-di-amitmethyl-
phenyl)imino] methyl methanimid-amide) is a member
of formamidine pesticide family. It is widely applied on
beehives to control the beehive parasite Varroa lacobsoni
destructor which endangers beekeeping all over the
world [1]. Therefore, it can contaminate honey. Amitraz
produces behavioral, physiological and biochemical ef-
fects in humans [2]. The most characteristic symptoms
are the central nervous and respiratory systems depres-
sion, bradycardia, hypotension and convulsions [3-5].
Maximum residual limit in honey was set as 0.01
mg·kg–1 in Germany and Italy and 0.2 mg·kg–1 for Euro-
pean Union [6]. For these reasons, the development of
accurate and sensitive methods for the determination of
amitraz in honey samples is necessary.
Several instrumental techniques have been applied for
the determination of amitraz; these include high per-
formance liquid chromatography (HPLC) with UV de-
tection [7], gas chromatography with electron capture [8]
and thermionic specific [9] detectors, cyclic voltammetry
[10] and ultra-high-pressure liquid chromatography–
quadrupole time-of-flight mass spectrometry [11]. Low
concentration and matrix interference are two problems
in detecting amitraz. Therefore, in spite of developments
in modern analytical instruments, extraction and precon-
centration processes are needed for the determination of
In recent years, several pretreatment techniques have
been proposed for the extraction of amitraz such as solid
phase extraction (SPE) [12], solid phase microextraction
(SPME) [9] and headspace solvent microextraction
(HSME) [13].
Rezaee et al. have developed dispersive liquid–liquid
microextraction (DLLME) for the first time as a simple
and rapid microextraction method, which was initially
applied for the extraction of polycyclic aromatic hydro-
carbons (PAHs) from water samples [14]. The method
consists of two steps: 1) Injection of an appropriate mix-
ture of extraction and disperser solvents into the aqueous
samples, containing the analyte(s). In this step, the ex-
traction solvent is dispersed into the aqueous sample as
very fine droplets and the analytes are enriched into it.
Owing to the considerably large surface area between the
extraction solvent and the aqueous sample, the equilib-
rium state is achieved quickly and thus the extraction is
independent of time. This is the most important advan-
tage of the DLLME method. 2) Centrifugation of cloudy
solution. After centrifugation, the determination of the
analyte(s) in the sedimented phase can be performed by
instrumental analysis. Up to now, DLLME has been
successfully applied to the extraction of several families
of organic and inorganic species [15-18].
In this study, DLLME followed by gas chromatogra-
phy–flame ionization detector (GC-FID) has been inves-
tigated for the determination of amitraz in honey samples.
The effects of various experimental parameters, such as
the type and volume of extraction and dispersive solvent,
pH of sample solution and salt effect were studied and
optimized. The optimized method was applied to deter-
mine amitraz in honey in order to evaluate the applica-
tion of this method to real samples.
2. Experimental
2.1. Reagents and Standards
All the reagents and standards were of analytical grade
unless otherwise stated, and all dilutions were made with
twice distilled water. Stock standard (100 mg·L–1) of
amitraz was obtained by dissolving appropriate amounts
of analytical standards of amitraz (Fluka, Milwaukee, WI,
USA) in acetonitrile and stored in a refrigerator at 4˚C.
Other chemicals, such as carbon tetrachloride, carbon
disulfide, chloroform, chlorobenzene, methanol, acetone,
acetonitrile, HNO3 (>90%), and NaOH (>99%) were
purchased from Merck (Darmstadt, Germany).
The honey samples were obtained from Tabriz (Azar-
bayeja, Iran) and Juybar (Mazandaran, Iran).
2.2. Instrumentation
A gas chromatograph (Shimadzu GC-14B) equipped
with a split/splitless injector system and a flame ioniza-
tion detector was applied for the separation and determi-
nation of amitraz. Ultra-pure helium (99.9999%, Air
products, UK) that was passed through a molecular sieve
and oxygen trap (Crs, USA), was used as the carrier gas
at a constant flow of 3 mL·min–1. The injection port was
held at 260˚C and operated in the splitless mode for 1
min. Then the split valve was opened and a split ratio of
1:10 was applied. The separation was carried out on a
DB-5 (25 m × 0.32 mm × 0.25 µm film thickness) from
SGE (Victoria, Australia) capillary column. The oven
temperature was held at 120˚C for 2 min, then increased
to 270˚C at the rate of 20˚C·min–1 and finally held at
270˚C for 7 min. The total time for one GC run was
about 20 min. The FID oven temperature was maintained
at 280˚C. Hydrogen gas was generated by hydrogen gen-
erator (OPGU-2200s, Shimadzu) and used for FID at flow
rate of 40 mL·min–1. The flow rate of zero air (99.999%,
Air products, UK) was 400 mL·min–1 for FID. The model
2010D Centurion Scientific Centrifuges (West Sussex,
UK) was applied for the separation of the sedimented
phase from the sample solution.
2.3. Dispersive Liquid-Liquid Microextraction
A 5.0 mL of twice distilled water was placed in a 10 mL
screw cap glass test tube with conic bottom and spiked at
the level of 0.1 mg·kg–1 of amitraz. One mL of acetoni-
trile (as disperser solvent) containing 13.0 µL of CCl4 (as
extraction solvent) was rapidly injected into a sample
solution by 1.0 mL syringe, then, the mixture was gently
shaken. A cloudy solution (water, acetonitrile and carbon
tetrachloride) was formed. The cloudy state was stable
for a long time. The mixture was centrifuged for 1.5 min
at 6000 rpm and the dispersed fine particles of the ex-
traction phase were sedimented in the bottom of the
conical test tube. Finally, 2.0 µL of the sedimented phase
was injected into the GC for analysis. The volume of the
sedimented phase was about 5.0 µL which was measured
using a 10 µL microsyringe.
For the determination of amitraz in honey samples,
0.05 g of the honey samples was dissolved in 5 mL of
twice distilled water and a homogenized solution was
produced. Then, the DLLME procedure was done simi-
larly to the aqueous samples.
3. Results and Discussion
In order to obtain a high recovery and preconcentration
factor, the effect of different parameters such as type and
volume of the extraction and disperser solvents and salt
addition on the extraction recovery (ER) were examined
and the optimal conditions were obtained. The precon-
centration factor (PF) and extraction recovery were cal-
culated based on the following equations:
Copyright © 2011 SciRes. AJAC
PF CC (1)
where, Csed and C0 are the concentration of the analyte in
the sedimented phase and initial concentration of the
analyte in the aqueous sample, respectively.
%100 100
sed sedsed
aq aq
where, ER%, Vsed and Vaq are the extraction recovery and
volumes of the sedimented and aqueous sample, respec-
tively. Csed was calculated from the related calibration
curve, obtained by direct injection of amitraz standard
solutions into the extraction solvent with the concentra-
tions in the range of 10 - 100 mg·L–1.
3.1. Selection of Extraction Solvent
The suitable extraction solvent should have some proper-
ties such as (a) its density should be higher than that of
water, (b) it should have extraction capability of the de-
sired compound, and (c) it should have a good gas chro-
matographic behavior. Carbon disulfide, carbon tetra-
chloride, chloroform and chlorobenzene were tested as
extraction solvents. A series of sample solutions con-
taining 100 µg·L–1 of amitraz were prepared. Acetonitrile
(1.0 mL) of containing different volumes of the extrac-
tion solvents (12.0, 13.0, 25.6 and 45.0 µL of C6H5Cl,
CCl4, CS2 and CHCl3, respectively) was rapidly injected
into the sample solutions to achieve 5.0 µL volume of
sedimented phase. The average extraction recoveries
using different extraction solvents are shown in Figure 1.
The results revealed that CCl4 has the highest extraction
recovery in comparison with C6H5Cl, CS2 and CHCl3.
Thereby; CCl4 was selected as the extraction solvent in
the subsequent experiments.
3.2. Selection of Disperser Solvent
Miscibility of disperser solvent with extraction solvent
Figure 1. Effect of type of extraction solvent on the extrac-
tion recovery of amitraz. Extraction conditions: water sam-
ple volume, 5.0 mL; disperser solvent (acetonitrile) volume,
1.0 mL; extraction solvent volumes, 45.0 µL CHCl3, 12.0 µL
C6H5Cl, 13.0 µL CCl4 and 25.6 µL CS2; concentration of
amitraz, 0.1 mg·kg–1.
and aqueous phase is the main factor used for its selec-
tion. Thereby, acetone, acetonitrile and methanol were
selected as disperser solvents. A series of sample solu-
tions containing 100 µg·L–1 of amitraz were prepared and
extracted using 1.0 mL of each disperser solvent con-
taining 13.0 µL of CCl4. The extraction recoveries ob-
tained from acetone, acetonitrile and methanol were
76.5%, 96.4% and 77.7%, respectively. According to the
results, acetonitrile has the higher extraction recovery
and better gas chromatographic behavior in comparison
with the other disperser solvents. Thus, acetonitrile was
used as disperser solvent in the subsequent experiments.
3.3. Effect of Extraction Solvent Volume
To examine the effect of extraction solvent volume on
the extraction recovery, solutions containing different
volumes of CCl4 were used in DLLME procedure. The
experimental conditions included the use of 1.0 mL ace-
tonitrile containing different volumes of CCl4 (13.0, 18.0,
23.0 and 28.0 µL). According to Figure 2, the volumes
of the sedimented phase were changed from 5.0 to 14.0
µL by increasing the volume of CCl4 from 13.0 to 28.0
µL. As the volume of the sedimented phase increases,
the PF decreases due to the dilution of sedimented phase
(Figure 2). Thereby, the highest sensitivity was achieved
by using 13.0 µL of CCl4.
3.4. Effect of Disperser Solvent Volume
Variation of disperser solvent volume causes a change in
the volume of the sedimented phase; hence, it is neces-
sary to consider the influence of disperser solvent vol-
ume on the extraction efficiency. In order to achieve a
Figure 2. Effect of the extraction solvent (CCl4) volume on
the sedimented phase volume and preconcentration factor
of amitraz. Extraction conditions: water sample volume, 5.0
mL; disperser solvent (acetonitrile) volume, 1.0 mL; extrac-
tion solvent (CCl4) volumes, 13.0, 18.0, 23.0, 28.0 µL; con-
centration of amitraz, 0.1 mg·kg–1.
Copyright © 2011 SciRes. AJAC
constant volume of the sedimented phase, the volumes of
acetonitrile (disperser solvent) and CCl4 (extraction sol-
vent) were changed, simultaneously. The experimental
conditions were fixed and included the use of different
volumes of acetonitrile (0.5, 1.0, 1.5 and 2.0 mL) con-
taining 11.0, 13.0, 17.0 and 21.0 µL of CCl4, respectively.
Under these conditions, the volume of sedimented phase
remained constant (5.0 ± 0.3 µL). As shown in Figure 3,
the extraction recovery enhances by increasing of the
acetonitrile volume up to 1.0 mL and then decreases by
further increasing of acetonitrile volume. It seems that at
low volume of acetonitrile cloudy state is not well pro-
nounced and the extraction recovery decreases. On the
other hand, at high volumes of acetonitrile the solubility
of amitraz in water increases, and the extraction recovery
decreases. Therefore 1.0 mL of acetonitrile was chosen
as the optimum volume in the further works.
3.5. Effect of Ionic Strength
To investigate the influence of ionic strength on the ex-
traction recovery of amitraz, different amounts of NaCl
(0% - 10% w/v) were added to the solutions, whereas
other experimental conditions were kept constant. The
volume of the sedimented phase increased from 5 to 11
µL by increasing of the amount of NaCl from 0% to 10%
w/v, because of the decreasing solubility of the extrac-
tion solvent in the aqueous phase. According to Figure 4,
the preconcentration factor decreases as the volume of
sedimented phase increases. Therefore, all of the extrac-
tion experiments were carried out without salt addition.
Figure 3. Effect of the disperser solvent (acetonitrile) vol-
ume on the extraction recovery of amitraz. Extraction con-
ditions: water sample volume, 5.0 mL; disperser solvent
(acetonitrile) volumes, 0.50, 1.0, 1.5 and 2.0 mL; extraction
solvent (CCl4) volumes, 11.0, 13.0, 17.0 and 21.0 µL; con-
centration of amitraz, 0.1 mg·kg–1.
Figure 4. Effect of salt addition and pH on the extraction
recovery of amitraz. Extraction conditions: water sample
volume, 5.0 mL; disperser solvent (acetonitrile) volume, 1.0
mL; extraction solvent (CCl4) volume, 13.0 µL; concentra-
tion of amitraz, 0.1 mg·kg–1.
3.6. Influence of pH
The effect of pH on the extraction recovery of amitraz
was studied in the range of 4.0 - 10.0, using ammonium
acetate solution and step wise addition of NaOH. As
shown in Figure 4, the highest extraction recovery was
obtained at pH of 6.0. It is due to the lowest hydrolysis
of amitraz at pH 6.0.
3.7. Analytical Performance of the Method
Linearity of the method was over the range of 0.01 - 1.0
mg·kg–1(with nine standards, r2 = 0.998). The ER% and
PF of the method were 95.5% and 955, respectively at
spike level of 0.1 mg·kg–1. The relative standard devia-
tion (RSD, n = 4) at the concentration level of 0.1
mg·kg–1 of amitraz was 3.2%. The limit of detection
(LOD), based on the signal-to-noise ratio (S/N) of 3 was
0.0015 mg·kg–1. Table 1 comprises the figures of merit
of proposed extraction method with the other extraction
methods of amitraz. As shown, DLLME have shorter
extraction time and lower RSD and LOD value with ac-
ceptable linear range (LR) compared with the other ex-
traction methods.
3.8. Honey Samples Analysis
In order to test the applicability of the proposed method
Copyright © 2011 SciRes. AJAC
to real samples, two honey samples were extracted and
analyzed. The results showed that the analyzed samples
were free of amitraz. To study the matrix effect on the
extraction recovery of amitraz in the honey samples, 0.05
g of the honey samples was dissolved in 5 mL of the
twice distilled water and a homogenized solution was
produced. Both the honey samples were spiked with the
amitraz standard solution at 0.1 mg·kg–1 concentration
level to assess the recovery values. The obtained relative
recoveries were 78.8% and 98.2%. The results showed
that the matrix had little effect on the DLLME of amitraz.
Figure 5 shows GC-FID chromatograms of a honey
sample (a) before and (b) after being spiked of the honey
with amitraz at 0.1 mg·kg–1 level.
4. Conclusions
A rapid and sensitive method for the extraction and de-
termination of amitraz in honey samples by applying
DLLME-GC-FID was developed. The experimental re-
sults showed that the present method provides high ex-
traction recovery and preconcentration factor within a
short time. The extraction and determination of amitraz
from the honey samples by applying the proposed
Table 1. Comparison of DLLME-GC-FID with other me-
thods for determination of amitraz.
Methods LODb
(mg·kg–1) LRc
(mg·kg–1) RSDd
time (min)
HSMEa-GC-TSD13 0.01 0.1 - 10 10 10 5
SPME-GC-ITD 9 0.001 0.005 - 0.1 11.1 30 10
DLLME-GC-FID 0.0015 0.025 - 1 3.2 5 10
aHeadspace solvent microextraction; bLimit of detection for S/N=3; cLinear
range; dRelative standard deviation.
Figure 5. DLLME-GC-FID chromatograms of the honey
sample under optimum conditions (a) before and (b) after
spiking with 0.1 mg·kg-1 of amitraz.
method was satisfactory. The newly developed microex-
traction technique (DLLME-GC-FID) has distinct ad-
vantages over the conventional methods in terms of short
time of extraction, low volume of the solvents required
and low detection limits. Further, the proposed sample
preparation procedure is much simpler than the conven-
tional liquid-liquid extraction (LLE) and solid phase ex-
traction (SPE) methods.
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