2.4. Sample preparation
Thatch material (0.3 g) and breast milk (0.1 g dry weight) were placed in 40 mL glass-centrifuge tubes. They were fortified with d6-trans-permethrin (4.5 ng) and d6-trans-cypermethrin (2.5 ng) as surrogate standards. The samples were stirred and extracted by sonication with 20 mL of hexane:dichloromethane (2:1) in a Raypa, UCI-200 bath for 15 min. Then, the samples were centrifuged at 3500 rpm for 5 min. The organic phase remained at the top of the conical tube and was entirely transferred to a vial and evaporated under a nitrogen stream. This extraction step was repeated two additional times and all the solvent residues were collected together.
Thatch material extracts were cleaned up by elution through Florisil cartridges (2 g/15 mL). Each cartridge was conditioned with 15 mL of ethyl acetate:dichloromethane (2:1). The sample was loaded onto the cartridges and the pyrethroids were eluted with 25 mL of ethyl acetate. The eluate was evaporated under a nitrogen stream and re-dissolved with 100 μL ethyl acetate for GC–NCI-MS–MS analysis (Feo et al., 2010a and Feo et al., 2010b).
The breast milk extracts were cleaned up by elution through C18 cartridges (2 g/15 mL) coupled to basic alumina (5 g/25 mL) and conditioned with 25 mL of acetonitrile. Then the sample was eluted with 30 mL of acetonitrile. The acetonitrile extract was evaporated under a nitrogen stream and the residue was dissolved in 100 μL of ethyl acetate for GC–NCI-MS–MS analysis.