A sensitive enzyme immunoassay (EIA) for the determination of melengestrolacetate (MGA) in adipose and muscle tissues

The development of a sensitive screening method of MGA residues in bovine p erirenal fat and muscle based on a competitive microtitration plate enzyme immunoassay is descried. The samples were extracted with petroleum ether an d purified with octadecyl-silica-cartridges. The detection limit for fat wa s 0.4 ng/g and for muscle tissue 0.05 ng/g, much lower than required for re liable detection of positive samples. The mean recovery rates of fortified samples amount to 75%, the mean intraassay variations to 7% and the interas say variation to 13%. Determination limits were validated for fat at 2 ng/g and for muscle at 0.1 ng/g. The efficiency of the new screening method was successfully demonstrated by the direct comparison to GC-MS and LC-MS meth ods performed at natural positive samples originating from an animal experi ment in which the labelled dose (0.5 mg per animal and day) with and withou t a 48 h withdrawal period or 3-fold or 10-fold the amount of MGA, respecti vely was fed to Holstein Frisian heifers. In conclusion, this new screening method can be used for sensitive determination of MGA residues in adipose tissues even after low treatment doses or longer withdrawal periods.