“…Because MRLs (maximal residue limits) or MRPLs (minimum required performance limits) the progestogens residue in animal food were as low as 1 to 10 μg/kg (Impens et al, 2003;Giannetti et al, 2005), complex and cost-consuming sample clean-up methods have to be adapted for animal fat and meat specimen. Some sample pretreatment and clean-up methods for progestogens in fat and meat have been established including combination of matrix solid phase dispersion and solid phase extraction (Rosen et al, 1994), accelerated solvent extraction and supercritical fl uid extraction for kidney fat (Stolker et al, 2002;Hooijerink et al, 2003) and most of them are solvent extraction and solid phase extraction method (Hageleit et al, 2001;Impens et al, 2002;Giannetti et al, 2005) for kidney fat or meat. Feed containing below 10 μg/kg progestogens is usually ineffective for bringing drug residue in animal tissues, because most of progestogens will be metabolized.…”