2.6. Endosulfan extraction and purification
All solvents of residue analysis quality and other reagents were
obtained from Merck Co. (Darmstadt, Germany). The endosulfan (a-
Endosulfan þ b-Endosulfan þ Endosulfan sulfate) was extracted
according to Metcalfe and Metcalfe (1997), with the modifications
of Miglioranza et al. (2003). Subsamples of 5 g of air-dried soil and
3 g of wet plant tissues were homogenized with sodium sulfate and
spiked with 20 ng of PCB #103 as a surrogate standard; these were
Soxhlet extracted (8 h) with a mixture of hexaneedichloromethane
(50:50), then concentrated using a vacuum pump, and finally
concentrated to 2-mL volume under nitrogen flow. The lipid percentage
was calculated after removing the plant extracts by gel
permeation chromatography in Bio Beads S-X3 (200e400 mesh
size, Bio-Rad Laboratories, Hercules, CA, USA), and then drying the
extracts under vacuum and nitrogen flow to a constant weight. The
cleaning of all extracts containing pesticides was performed by
silica gel chromatography, concentrated to 1 mL and maintained in
sealed vials at 20 C prior to gas chromatography analysis.