A Gas Chromatographic Method with Electron

Food Anal. Methods (2012) 5:1296–1302
DOI 10.1007/s12161-012-9382-x
A Gas Chromatographic Method with Electron-Capture
Detector (GC-ECD) for Simultaneous Determination
of Fenpropathrin, l-Cyhalothrin, and Deltamethrin Residues
in Tomato and Its Applications to Kinetic Studies
After Field Treatment
Abuzar E. A. E. Albadri & Abdalla A. Elbashir &
Hassan El-obid Ahmed & Ibrahim A. M. Mihaina &
Hassan Y. Aboul-Enein
Received: 17 December 2011 / Accepted: 13 February 2012 / Published online: 26 February 2012
# Springer Science+Business Media, LLC 2012
Abstract In this study, simultaneous determination of fenpropathrin, 1-cyhalothrin, and deltamethrin in tomato fruit
(Lycopesicon esculentum) grown in Khartoum, Sudan, was
carried out using gas chromatography with electron capture
detector (GC-ECD).The method was linear in the range of
0.001–0.01, 0.001–0.01 and 0.001–0.02 mg/ml for fenpropathrin, 1-cyhalothrin, and deltamethrin, respectively. The
limit of detection (LOD) and limit of quantification (LOQ)
were found to be 0.0012 and 0.0041, 0.0013 and 0.0041 and
0.0026 and 0.0087 mg/ml for fenpropathrin, 1-cyhalothrin,
and deltamethrin, respectively. The recoveries of fenpropathrin, 1-cyhalothrin, and deltamethrin at three concentration levels spiked to tomato were found to be in range
85.77±1.52–95.61±3.65%, 91.77±4.34–98.59±2.46% and
92.61±2.46–98.04±2.93%, respectively. The kinetic study
of the degradation of all pesticides was performed and the
ultimate evaluation of the kinetic data revealed a pseudo
first order kinetics pattern for fenpropathrin, 1-cyhalothrin,
and deltamethrin.
A. E. A. E. Albadri : A. A. Elbashir (*) : H. E.-o. Ahmed :
I. A. M. Mihaina
Faculty of Science, Chemistry Department,
University of Khartoum,
P.O. Box 321, Khartoum, Sudan
e-mail: [email protected]
H. Y. Aboul-Enein (*)
Pharmaceutical and Medicinal Chemistry Department,
Pharmaceutical and Drug Industries, Research Division,
National Research Centre,
Cairo 12311, Egypt
e-mail: [email protected]
Keywords Fenpropathrin . 1-Cyhalothrin . Deltamethrin .
Tomato . Kinetic degradation studies . GC-ECD
Introduction
Tomato (Lypersicon esculentum) is one of the most popular
and widely grown vegetables in the world, ranking second in
importance to potato in many countries. The fruits are eaten
raw or cooked. Tomato in large quantities is used to produce
soup, juice ketchup, puree, paste and powder. It supplies
vitamin C and adds variety of colors and flavors to the food.
Green tomatoes are also used for pickles and preserves. Its
many forms are adapted to wide range of soils and climates
extending from the tropics to almost the Arctic circle. It has
many other uses; tomato seeds contain 24% oil used as salad
oil and in the manufacture of margarine. By virtues of its many
attributes, tomato is considered a favorite crop for research in
physiology and cytogenetics all over the world API (Agriculture Planning and Information 2011; Basharat et al. 2007;
Adalberto et al. 2006; Gambacorta et al. 2005). Tomato crop
is attacked by a number of insect pests. Some important insect
pests of tomato are fruit worm (Heliothis armigera), Epilachna beetles (Epilachna vigintioctopunctata), Jassids
(Empoasca devastans), Tobacco caterpillar (Spodoptera littoralis), White fly (Bemesia tabaci), and Thrips (Thrips tabaci
and Frankliniella intonsa) (Agriculture Planning and Information 2011; Adalberto et al. 2006)
On the other hand, the tomato crop is susceptible to pest
attack throughout the season. Pesticides are extensively used
in this culture at various stage of cultivation to control pest
Food Anal. Methods (2012) 5:1296–1302
and diseases that may cause yield reduction (Adalberto et al.
2006). Therefore, residues of pesticide could affect the
ultimate consumers especially when these commodities are
freshly consumed. The total dietary intake of pesticide residues that remain on agricultural commodities are known as
carcinogens and/or toxin. Therefore, it is desirable to reduce
these residues. The levels of pesticide residues are controlled by the maximum residue limits (MRLs), which
are established by each country (Torres et al. 1996;
Zawiyah et al. 2007). The pesticides which are extensively used in Sudan belong to the classes of organophosphorus, organochlorine, pyrethroids, carbamates and
neonicotinoids. Many insecticides belonging to different
groups were found to be used on tomato by the farmers. Of
these, the most frequently used insecticides in Sudan were
fenpropathrin, 1-cyhalothrin, and deltamethrin.
The improper use of fenpropathrin, 1-cyhalothrin, and
deltamethrin can generate a considerable amount of
residues, higher than the MRL. The MRL for fenpropathrin, 1-cyhalothrin, and deltamethrin was 1.0, 0.5 and
0.3 mg/kg, respectively, as established by Codex Alimentarius
(FAO/WHO 2009).
Pyrethroid residues have been determined using chromatographic techniques. Gas chromatography is still the
method of first choice for the analysis of pyrethroid
residues with various detectors such GC with electron
capture detector (GC-ECD) (Chen et al. 2011; De Pinho
et al. 2010; Sandra et al. 2005; Su et al. 2007), GC-mass
spectrometry (GC-MS) (Albero et al. 2004; Beltran et al.
2003; Kazuaki et al. 1997; Tagami et al. 2009), highperformance liquid chromatography-ultraviolet (HPLCUV) (Metwally et al. 1997), and HPLC-mass spectrometry (HPLC-MS) (Klein and Alder 2003). Thus far, there
have been no reports in the literature of simultaneous
determinations of fenpropathrin, 1-cyhalothrin, and deltamethrin residues in tomato.
The dissipation rate of pesticides following application
depends mainly on many parameters, including chemical
and photochemical degradation, volatilization, climatic
conditions, plant species, formulation type and pesticide
application method (Sur et al. 2000). Thus, the disappearance curves reported in the literature are valid only
for one crop under specific conditions. Random use of
pesticides by local farmers is very dangerous to consumer,
because, after field treatment many farmers in Sudan
market their product unconcerned on the waiting period
for the pesticides degradation after spraying. Thus, a
high concentration of the pesticides residues may be
transferred to the consumer causing many health risks.
Therefore, the main objective of this work is to generate
data regarding the decline pattern and residue levels of fenpropathrin, 1-cyhalothrin, and deltamethrin in tomato cultivated
under field conditions.
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Experimental
Apparatus
A Shimadzu (GC-2010) Gas chromatograph apparatus
(Japan), supplied with a DB-5 (5% phenylmethylpolysiloxane; J&W Scientific, No. US6564667H, capillary column
30 m × 0.25 mm [i.d.], 0.25 μm film thickness), was used
under the following operating conditions: injection port temperature 280°C; ECD temperature 300°C; column temperature 240 °C; 1.5 ml/min nitrogen as carrier gas, N2/Air makeup gas, 30 ml/min; splitless injection opening splitter 1 min
after injection; purge flow, 9 ml/min.
The following equipment was used for sample preparation: balance (readability 0.0001 g; OHAUS, Model AS60s,
USA), homogenizer, rotary evaporator (Heidolph, laborota
4000 efficient, German), filtration unit (vacuum pump, filter
paper 12 cm, Buchner funnel 12 cm) and glassware (separatory funnel 500 ml, separatory funnel 100 ml, suction
flask 250 ml, Round-bottom 250 ml, glass column 400×22
mm and glass funnel).
Chemicals
Sodium sulfate anhydrous and sodium chloride, acetone,
acetonitrile, ethyl ether and n-hexane were obtained from
Scharlau (Gota Perez, Spain), and glass wool glass wool
was obtained from Loba Chemie (Mumbai, India).
Eluting Solvent: 6% Ethyl Ether in Hexane
Saturated acetonitrile. A total 300 ml of acetonitrile
and 100 ml of n-hexane were added to 500 ml separatory funnel and shaken for 5 min; then, the acetonitrile layer was drained in a storage bottle (Pang et al.
1999).
Deactivation of florisil. Florisil activated at 650°C for
4 h, was left to stand for 5 h at 130°C, stored in glass
stoppered bottle and cooled overnight. Then it was deactivated by adding 5% (w/w) deionized water and shaken for
1h, and subsequently left overnight (Pang et al. 1999).
Preparation of Chromatographic Column
Five milliliters of deactivated florisil was added to column
containing 50 ml hexane. The sides of the column were
taped for an even packing, and then the solvent was drained
until just above florisil packing (Pang et al. 1999).
Preparation of Calibration Curves
A standard solution of fenpropathrin, 1-cyhalothrin, and deltamethrin (1.0 mg/ml) was used to prepare serial dilutions in
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Food Anal. Methods (2012) 5:1296–1302
Fig. 1 a Chromatogram of
mixture standard solution for
three pyrethroids under
optimized GC-ECD conditions.
b The chromatogram of three
pyrethroid after 10 days of
treatment
a
uV(x1,000,000)
6.0
5.0
Fenpropathrin/8.145
3.0
2.0
Deltamethrin/31.990
Lambda-cyhalothrin/10.517
4.0
1.0
0.0
2.5
5.0
7.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
22.5
25.0
27.5
30.0
32.5
35.0 min
b
5.0
uV(x10,000)
Chromatogram
2.0
1.0
Deltamethrin
Fenpropathrin
3.0
Lambda-cyhalothrin
4.0
0.0
2.5
10.0
hexane in the range of 0.001–0.01, 0.001–0.01 and 0.001–
0.02 mg/ml for fenpropathrin, 1-cyhalothrin, and deltamethrin,
respectively.
Table 1 Retention time, linearity, LOD, and LOQ of pyrethroid pesticides (fenpropathrin, 1-cyhalothrin, and deltamethrin) by GC-ECD
Pyrethroid
Pesticide
Retention
of the
proposed
method
(min)
Fenpropathrin 8.145
λ-Cyhalothrin 10.517
Deltamethrin 31.990
Retention
of the
reference
methoda
(min)
(R2)
18.261
22.051
40.591
0.995
0.995
0.990
0.00122 0.00125 0.00260
0.00406 0.00418 0.00868
LOD
LOQ
(mg/ml) (mg/ml)
LOD limit of detection, LOQ limit of quantification, GC-ECD gas
chromatography with electron capture detector
a
Pang et al. (1999)
12.5
15.0
17.5
20.0
22.5
25.0
27.5
30.0
32.5
35.0 min
Sample Preparation and Fortification
Fenpropathrin, 1-cyhalothrin, and deltamethrin free tomato
sample was used for fortification. Fortified tomato sample
was prepared in three levels: 0.2 mg/kg, 1 mg/ml and
2 mg/ml for fenpropathrin, 1-cyhalothrin, and deltamethrin,
respectively, by adding a standard solution of fenpropathrin,
1-cyhalothrin, and deltamethrin to the sample. These were left
to stand for 30 min before extraction to allow the spiked
solution to penetrate into the matrix.
Extraction and Cleanup Procedures
Fifty grams of chopped samples was homogenized in blender with 120 ml acetone for 3 min at 18,000 rpm. The
homogenized sample was filtered through a 12-cm Buchner
funnel with filter paper into 500-ml suction flask. The solid
residues were placed in a blender jar rinsed with two 25-ml
Food Anal. Methods (2012) 5:1296–1302
Table 2 Recoveries percent and
relative standard deviation
(RSD %) For the three pyrethroids spike in tomato at three
different concentrations level
Pyrethroid
Fenpropathrin
λ-Cyhalothrin
Deltamethrin
1299
Spiked conc. 0.2 mg/kg
Spiked conc. 1 mg/kg
Spiked conc. 2 mg/kg
Recovery %
RSD %
Recovery %
RSD %
Recovery %
RSD %
85.77
91.77
92.61
1.52
4.34
2.46
95.61
96.56
98.42
3.65
0.73
1.49
91.26
98.59
98.04
4.09
2.46
2.93
portions of acetone, and rinses were used to wash residues in
Buchner funnel. The filtrate was transferred to 500-ml separatory funnel for liquid/liquid partition, and suction flask
was washed with two 10-ml portions of acetone and was
added to separatory funnel. Next, 60 ml hexane was added
to the separatory funnel containing the extract, which was
vigorously shaken with frequent venting (5 min). Then
200 ml 4% NaCl (w/v) was added and vigorously mixed
for approximately 30 s, and then the aqueous layer was
discarded. The hexane layer was filtered through the glass
funnel containing glass wool plug and around 15 g anhydrous sodium sulphate to eliminate residues water. Extract
was collected in 250-ml round-bottom flask, and the separatory funnel was rinsed with two 20-ml portions of hexane.
Next, then rinses were passed through funnel content to the
round bottom flask. Content of round bottom flask was
evaporated to dryness on rotary evaporator at 40 °C. The
residues in round bottom flask were dissolved with10 ml,
and two 5 ml hexane, and then transferred to 100 ml
separatory funnel for liquid/liquid partitioning with 30 ml
saturated acetonitrile with n-hexane for 5 min; the acetonitrile layer was drained into 250 ml round bottom
flask. The liquid/liquid partitioning with 30 ml acetonitrile saturated with n-hexane step was repeated again two
times, and the acetonitrile was collected and evaporated
flask to dryness, at 60°C.
The residue in round bottom flask was dissolved with
5 ml, and two 10 ml hexane, and was transferred to a florisil
column. Pyrethroid residues eluted by 150 ml of 6% elution
solvent described above. Elution was collected at 3 ml/min;
next, the elution was evaporated to less than 50 ml at 40 °C,
then was transferred in to 50-ml volumetric flask and was
diluted to volume with n-hexane. Finally, 1 μl of the solution was injected in GC (Pang et al. 1999).
Table 3 Fenpropathrin, 1-cyhalothrin and deltamethrin residues at
various time intervals following their application
Results and Discussion
Day after
application
0
2
4
6
8
10
12
14
16
Concentration
residue of
fenpropathrin
(Ct), mg/kg
Concentration
residue of
λ-cyhalothrin
(Ct), mg/kg
Concentration
residue of
deltamethrin
(Ct), mg/kg
40.58
31.28
23.04
17.78
15.98
14.11
12.78
10.45
8.10
3.18
2.04
1.38
1.02
0.98
0.79
0.59
0.49
0.44
2.40
0.761
0.53
0.52
0.40
0.39
0.28
0.262
0.19
Study of Degradation of Fenpropathrin, 1-Cyhalothrin
and Deltamethrin on Tomato
The site of this study lies in Elelfone area at the Southern
part of Khartoum North, Sudan. The area cultivated with
tomato was 12 Sarabs, 6 m in length and 4 m in width for a
total area of 288 m2. Every Sarabs contained 50 plants.
Tomato field was sprayed with a mixture of fenpropathrin,
1-cyhalothrin and deltamethrin commercial formulations in
level by backpack-spraying pump for 10 h on sunny day,
with a temperature of 32°C. The tomato fruits were collected before and after 1 h from spraying and then every day for
17 days.
Samples of 500–700 g were chopped, homogenized, and
then analyzed as described in spiked tomato samples. Fenpropathrin, 1-cyhalothrin and deltamethrin peak areas were
determined.
Optimized GC Conditions
The analytical method used in this study was developed
with the aim of providing a fast, accurate and efficient
means of determining fenpropathrin, 1-cyhalothrin, and deltamethrin residues in tomato. The best resolution was found
with the following conditions: injection port temperature
280 °C; ECD temperature 300 °C; column temperature
240 °C; 1.5 ml/min Nitrogen as carrier gas, N2/Air makeup gas, 30 ml/min, splitless injection opening splitter 1 min
after injection, purge flow, 9 ml/min.
The chromatograms of fenpropathrin, 1-cyhalothrin, and
deltamethrin are shown in Fig. 1a. The pesticides eluted by
the optimized GC condition faster than that of the reference
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Food Anal. Methods (2012) 5:1296–1302
Fig. 2 Plot ln concentration
(mg/kg) versus for degradation
of fenpropathrin (a),
1-cyhalothrin (b) and deltamethrin (c) on tomato after field
treatment
method (Table 1), indicating that the chromatographic conditions used in this study are better.
2
Table 4 Degradation rate (k), regression coefficients (R ), and half-life
(t½) of three pyrethroids on tomato after field treatment
Pyrethroid
Fenpropathrin
λ-Cyhalothrin
Deltamethrin
kobs (day−1)
R2
t1/2
−0.092
0.972
7.53
−0.117
0.96
5.92
−0.123
0.837
5.64
Calibration Curves
The calibration curves were obtained by plotting concentrations of fenpropathrin, 1-cyhalothrin, and deltamethrin standards (0.001–0.01, 0.001–0.01 and 0.001–
0.02 mg/ml, respectively) versus their corresponding peak
areas. The linearity of the GC–ECD procedure was
computed by regression analysis, and the values of
regression coefficient (R2), limit of detection (LOD) and limit
of quantification (LOQ) were calculated as shown in
Table 1.
Food Anal. Methods (2012) 5:1296–1302
Recoveries of Spiked Tomato
In order to assess the extraction efficiency and selectivity of
the method, tomato sample free of pesticides (before treatment pesticides application) was first analyzed by GC–ECD
before being spiked. None of the studied pesticides were
found at the corresponding retention times.
To determine the accuracy of the method, pesticide-free
tomatoes samples were fortified with 0.2, 1.0 and 2 mg
pesticides/kg sample (triplicates). The rates of recovery
obtained were in range of 85.77–95.61%, 91.77–98.59 and
92.61–98.04 for fenpropathrin, 1-cyhalothrin and deltamethrin, respectively, with relative standard deviation (RSD) of
less than 5% (Table 2).
Degradation Studies
Fenpropathrin, 1-cyhalothrin and deltamethrin residues after
the field treatment are shown in Table 3. The maximum
residue levels were detected on day 2, with concentrations of
31.28, 2.04 and 0.761 mg/kg for fenpropathrin, 1-cyhalothrin
and deltamethrin, respectively.
Results shown in Table 3 indicate that all pesticides
residues in the first 10 days were over the maximum levels
established for tomato by the Codex Alimentarius (FAO/
WHO 2009; 1.0, 0.5 and 0.3 mg/kg for fenpropathrin,
1-cyhalothrin and deltamethrin, respectively; Fig. 1b).
Meanwhile, on day 16 only the level of fenpropathrin was
over the maximum levels.
The disappearance of the three pesticides under study
were shown to fit a pseudo-first-order kinetics pattern
(Fig. 2), with correlation coefficients r2 of 0.972, 0.96 and
0.837 for fenpropathrin, 1-cyhalothrin and deltamethrin,
respectively.
The biological half-life (t1/2) was calculated as t1/2 0
(ln 2)/k, where k is the slope of the linear regression (degradation rate). The change in fenpropathrin, 1-cyhalothrin and
deltamethrin concentrations, indicating a half-life (t1/2) of
7.53, 5.92 and 5.64 days, respectively (Table 4), shows that
the degradation of deltamethrin is faster than that of 1cyhalothrin and fenpropathrin.This may be due to the
higher stability of cyhalothrin and fenpropathrin compared
with deltamethrin.
Conclusions
A method for simultaneous determination of fenpropathrin, 1cyhalothrin and deltamethrin residues using GC-ECD was
developed in this study. Based on the pattern of decline of
the fenpropathrin, 1-cyhalothrin and deltamethrin residues in
relation to the reported MRLs (1.0 mg/kg for fenpropathrin,
1301
0.5 mg/kg for 1-cyhalothrin and 0.3 mg/kg for deltamethrin),
a safety pre-harvest interval of 12 days for deltamethrin and
16 days for 1-cyhalothrin are suggested.
Acknowledgements The financial support provided by the University of Khartoum for the project entitled, “Analysis of pesticides
residues in food and environmental samples”, is greatly acknowledged.
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