The extraction device consists of 20mg of sorbent packed
inside a (1.5 cm×1.5 cm) porous polypropylene membrane envelope
made from two overlapping sheets whose open edges were
heat-sealed. The detailed fabrication of the device has been
previously reported [32–34]. Each device was cleaned by ultrasonication
in methanol for 10min. It was then stored in the
clean methanol until use. The -SPE device was placed in a
soil sample (20 g with 15 ml of ultrapure water, pH was not
adjusted and no salt was added) that was stirred at ca. 105 rad s−1
(1000 rpm; 1rpm= 0.1047 rad s−1). After extraction (90 min), the
device was removed, rinsed in ultrapure water, dabbed dry with
lint-free tissue and placed in a 200-l crimper vial. The analytes
were desorbed by ultrasonication in acetonitrile (150l) and the
100l extract was injected directly into the HPLC for analysis.
The -SPE device could be reused after cleaning with the same
solvent.