250 ng of 13C6-labeled trans-permethrin, the surrogate recovery standard
(SRS), and vortexed with 12 mL hexane. Samples were sonicated for
20 min, centrifuged at 3000 rpm for 10 min, decanted and volume
reduced to 2 mL hexane. The extracts were subjected to alumina:silica
gel (1:1 by weight) column chromatography to remove interferences
following methods similar to those described in Hwang et al. (2008).
Prior to use, alumina and sodium sulfate were heated (450 °C for 4 h)
as well as the silica gel (170 °C for 24 h). All heated productswere stored
at 130 °C. When needed, alumina was deactivated (4% by weight) with
purified water. The columns were conditioned with hexane and eluted
with 50 mL of dichloromethane:hexane (1:1) mixture. The eluted solvents
were concentrated to 1 mL of hexane, and the internal standard
(IS) phenanthrene-d10 was added.