Development and optimisation of a method for the extraction of benzimidazoles from animal liver using supercritical carbon dioxide

A multi-residue supercritical fluid extraction (SFE) method has been developed for extraction of 10 benzimidazole drug residues from animal liver. The method may be applicable also to some other benzimidazoles, but recovery was not quantitative. An oven dried sample-hydromatrix mixture was packed into an extraction vessel and rehydrated with water (I ml). The sample was extracted at 80 degreesC using 601 unmodified supercritical carbon dioxide (690 bar). Residues were trapped off-line on a neutral alumina trap, which was eluted with methanol + water (60 + 40, v/v, 18 ml). Sample extracts were acidified and cleaned-up using strong cation exchange solid phase extraction. After elution, sample extracts were evaporated to dryness under nitrogen, reconstituted in 400 mul methanol + water (50 + 50, v/v) and analysed by HPLC with UV photodiode array detection. The method was validated using ovine liver fortified at levels of 50, 100, 250 and 500 mug kg-1 with the drugs. Mean recovery ranged between 51 and 115% for the various benzimidazoles. The intra- and inter-assay variations showed R.S.D. values of <10 and <32%, respectively. The procedure was applied, also, to avian, bovine and porcine liver, giving similar results. The validated limit of determination of the method is 50 mug kg(-1) (C) 2002 Elsevier Science B.V. All rights reserved.