of durian fruits is not edible, only the inner parts (flesh or
pulp) were used for the analysis. The sample preparation for
durian did not follow the protocols of Codex Alimentarius
Commission [14], but the guidelines given by the Department
of Food Safety, Ministry of Health, Labour and
Welfare, Japan [15]. The durian samples consisted of flesh
separated from peeled fruit. These samples were analyzed
without seeds. The representative portion (150–200 g) of
the fresh fruit was cut into small pieces, blended using a
food processor, and mixed thoroughly. For durian samples,
10 % distilled water was added to the sample before homogenization.
When calculations were made for durian
samples, the correction for sample dilution was taken into
account. The homogenized samples were then extracted and
processed as described below.
Determination of pesticide levels in flesh and unpeeled
watermelon samples
The same watermelon fruits were cut and divided into two
portions, one without peel (i.e., flesh watermelon) and
another with peel (unpeeled watermelon). The sample size
employed for this experiment was 8 samples (n = 8 each).
These samples were analyzed for pesticide residues in the
same way as ordinary samples.
Sample preparation
To determine the concentrations of pesticide residues, the
extraction procedure was performed following a modified
acetate-buffered version of the quick easy cheap effective
rugged and safe (QuEChERS) method as previously described
[16–19]. In brief, the procedure for sample preparation
was as follows: 15 g of homogenized fruit was extracted
with 15 ml acetonitrile saturated with 6 g of magnesium
sulfate and 1.5 g of sodium chloride. After the sample mixture
was vigorously shaken and centrifuged, the sample was
subjected to a cleaning up procedure. For watermelon samples,
this was accomplished by transferring an aliquot of
1 mL of supernatant into a dispersive solid-phase extraction
tube containing 50 mg of primary–secondary amine (PSA)
and 150 mg magnesium sulfate. For durian samples, 1 mL of
the supernatant was transferred into a dispersive solid-phase
extraction tube containing 50 mg of primary–secondary
amine (PSA), 50 mg C18 sorbent, and 150 mg magnesium
sulfate. After shaking and centrifugation, the extract supernatant
was then transferred to an autosampler vial for direct
injection into the Bruker GC/MS/MS system.quadrupole mass spectrometer (GC–MS/MS). Details of
the GC–MS/MS conditions were as in a previous report
[20]. Multiple reaction monitoring (MRM) acquisition
method and two-ion transition at the experimentally optimized
collision energy (CE) were monitored for each
pesticide analyte.
Recovery studies for method validation were made by
adding appropriate volumes of working solution to blank
samples. The method of validation with respect to recovery,
reproducibility, calibration linear range, limit of detection
(LOD), and limit of quantification (LOQ) was
carried out for the fruit matrix as described previously