For SPE assays, each cartridge was conditioned with 3 ml ofmethanol
and 3 mL of ultra-pure water. After loadedwith 5 mL of the spikedwater
samples, the columnwas washed with 1.5 ml of ultra-purewater and by
5 mL of hexane, followed by vacuum dry with nitrogen for 2 min.
Subsequently, the elution took place with 5 mL of MTBE (methyltertiobutylether).
After drying with anhydrous sodium sulphate (Na2SO4)
(2 g) by homogenization followed by centrifugation at 2000 rpm for
5 min, the extract was concentrated under a stream of nitrogen. The
residues were than dissolved in 0.1 mL mobile phase and analyzed by LCMS
/MS (ESI). For blank assays the same procedure as above was
performed using ultra-pure water samples without spiking. All steps of
the sample preparation procedure were programmed on and automatically
controlled by means of Zymark RapidTrace SPE Workstation.