The limits of detection,
limits of quantification and recoveries are given in Table 1.
For extraction, the tomatoes were blended and 10 g of sample was
added to a falcon tube. Acetonitrile (10 mL) was added and the sample
was mixed for a minute on a vortex shaker. Sodium chloride (1 g) and
magnesium sulfate (4 g) were added and samples were again shaken
for 1 min. The sample was transferred to a volumetric flask and the
volume was adjusted with acetonitrile to 25 ml. Four milliliters of
the extract was transferred to a falcon tube and the cleaning agent,
consisting of Primary-secondary Amine (PSA) (0.1 g), magnesium
sulfate (0.6 g) and activated carbon (0.03 g), was added. The solution
was mixed for 1 min and left to precipitate. The acetonitrile fraction
was removed and evaporated to dryness in a rotary evaporator at 40 °C
and 410 mm Hg pressure. The resulting residue was re-dissolved in
1 mL acetone and concentrated under nitrogen gas flow with SUPELCO
MINIVAP to a volume of 1 ml, and 80 μl of the internal standard
was added. For the organochlorine pesticide, pentachlornitrobenzene
in n-hexane (20 mg/l) was used as an internal standard and
dibutylchlorendate (20mg/l) was used as external standard. For the detection
of organophosphates, tributylphosphate in acetone (40 mg/l)
was used as internal standard and triphenyl phosphate (4 mg/l) was
used as external standard.
The quantification of the pesticide residues on the final extract
was performed using a SHIMADZU 17A gas chromatograph and