Brazilian Journal of Analytical Chemistry - BRJAC - Brazilian Journal ...

With the purpose of minimizing the number of sample
manipulation steps, our research group has developed
methodologies for the determination of pesticide
residues in different matrices such as water [17],
milk [18] and tomato [20] using the method known
as liquid-liquid extraction with the low temperature
partition technique (LLE-LTP) for liquid matrices and
solid-liquid extraction with the low temperature partition
technique (SLE-LTP) for solid matrices. The SLE-
LTP method was originally utilized in the analysis of
residues of organochlorine and organophosphorus
pesticides for the removal of fat from extracts of
plants, animal tissues and foods [21, 22]. The extraction
technique is based on the partition of analytes
between a solid matrix and a water-miscible organic
phase, at room temperature (25 °C). By decreasing the
temperature to – 20 °C, the liquid aqueous phase is
solidified, entrapping the solid matrix, and the liquid
supernatant consists of organic solvent containing the
analytes. This organic extract obtained can be directly
analyzed by gas chromatography, with no need for
cleanup [20]. This technique was shown to be simple,
of low cost and with recovery rates between 80-120%
for most compounds, with a minimum consumption
of solvent and absence of purification steps before
chromatographic analysis of the extracts.
The aim of this work was to optimize and validate
the solid-liquid extraction technique with low temperature
partitioning (SLE-LTP) for the analysis of residues
of the pesticides chlorpyrifos, λ-cyhalothrin, cypermethrin
and deltamethrin in potatoes by gas chromatography
with electron capture detection (GC-ECD).
2. experImental
2.1. re a g e n t s a n d s o l u t Io n s
Solutions of the studied active principles were prepared
from standards of chlorpyrifos (99.0 % w/w
– Chem Service), λ-cyhalothrin (86.5 % w/w – Syngenta),
cypermethrin (92.4 % w/w – Chem Service)
and deltamethrin (99.0 % w/w – Chem Service) using
acetonitrile as a solvent (Mallinckrodt/HPLC). A bifenthrin
(92.2 % w/w – FMC do Brazil) solution, used as
an internal standard for the chromatographic analysis,
was also prepared in acetonitrile. The solutions were
prepared considering the purity of the standards.
2.2. potato samples
For optimization and validation of the SLE-LTP technique
for residue analysis of the pesticides chlorpyrifos,
λ-cyhalothrin, cypermethrin and deltamethrin,
samples of potatoes free of pesticides were used.
These samples were provided by the Associação de
Bataticultores do Sul de Minas Gerais (ABASMIG) and
the Empresa de Assistência Técnica e Extensão Rural
(EMATER-MG).
www.brjac.com.br
2.3. so l Id-lIquId extractIon w It h l o w temperature pu-
rIfIcatIon
2.3.1 experImental p l a n n In g o f mIxtures
For extraction and analysis of the active principles
of interest, experimental planning was performed of
mixtures limited to a sub-region of the experimental
range for mixtures of the three components. The upper
and lower limits for each solvent of the extraction
mixture were: 10% ≤ Water ≤ 20%; 65% ≤ Acetonitrile
≤ 75% and 15% ≤ Ethyl acetate ≤ 25%. Within these
limits, the extraction mixtures maintained the necessary
characteristics for the SLE-LTP technique where a single
phase is formed and part of the mixture remains in a
liquid state at -20 °C. The volumetric proportions of
the components used in each of the planning tests are
presented in Table I.
taBlE i. Co m P o s i t i o n o f thE ExtraCtion m i x t u rE s
EmPloyEd in thE slE-ltP o f Potato samPlEs fortifiEd w i t h thE
aCtivE PrinCiPlEs o f intErEst
components
Dardengo et al.
ex t r a c t I o n
m Ix t u r e
water
ac etonItrIle
et h y l
acetate
to t a l
v o l u m e o f
t h e m Ix t u r e
(%) (%) (%) (mL)
1 20 65 15 10.0
2 10 75 15 10.0
3 10 65 25 10.0
In a transparent glass flask with a plastic stopper
(30.0 mL capacity), 3.0 g of mashed potato (free of pesticides)
was fortified with 0.1 mL of the standard solution
containing the four pesticides at a concentration
of 50 mg L -1 . Then, water, acetonitrile and ethyl acetate
were added in accordance with the volumes presented
in Table I. The mixture obtained was agitated at 170
rotations per minute (rpm) in an orbital shaker (Tecnal
TE - 420) for 10 minutes at 28 °C. The resulting mixture
was placed in a freezer at a temperature of approximately
-20 °C for 12 hours. After phase separation by
the freezing of the aqueous phase and potato pulp, the
organic liquid phase was passed through a paper filter
containing 1.5 g of anhydrous sodium sulfate (Nuclear
- PA), previously washed with acetonitrile left in the
freezer at -20 °C. The volumes of the extracts obtained
were adjusted in volumetric flasks to 10.0 mL with acetonitrile
and stored in glass flasks at -20 °C until analysis
by GC-ECD. For GC-MS analysis the extracts (10.0 mL)
were dried in a rotary evaporator and reconstituted in
1.0 mL of acetonitrile. Extracts from pesticide-free potato
samples (blank) were obtained in a similar way.
2.3.2. ch r o m a t o g r a p h Ic a n a l y s Is
Quantitative and qualitative analysis of the active ingredients
was performed on a Shimadzu GC-17A gas
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