Determination of dexamethasone in feed by TLC and HPLC

Two detection methods are described for the determination of dexamethasone in feed, which may be used as screening and confirmatory methods. The procedures were developed after studying different extraction and clean-up procedures: feed extraction was optimized using methylene chloride and hexane followed by a tandem solid-phase clean-up step with silica and C18 cartridges. The confirmatory method presented is based on normal-phase high-performance liquid chromatography on a Diol 5 microns column, with hexane-propan-2-ol (90:10 v/v) as mobile phase, followed by diode array detection and confirmation. All parameters are discussed, especially the extraction and clean-up steps. Recovery studies after application of the proposed method to different kinds of feed samples spiked with dexamethasone at levels between 120 and 1600 ng g-1 yielded a mean value of 55.4% with an overall standard deviation of 15.6%. The proposed procedure allows the determination of dexamethasone in feed at levels lower than 50 ng g-1.