Validation and robustness testing of a HPLC method for the determination of avermectins and moxidectin in animal liver samples using an alumina column clean-up

A multi-residue method has been developed for the quantitative determinatio n of moxidectin, abamectin, doramectin and ivermectin in liver samples, wit h capability for qualitative identification of the presence of eprinomectin . Liver samples are extracted with isooctane, followed by clean-up on alumi na-N solid phase extraction (SPE) cartridges. Extracts are derivatised and determined by high-performance liquid chromatography (HPLC) with fluorescen ce detection. The method was validated using bovine liver fortified at leve ls of 4 and 20 mu g kg(-1) with the drugs. The mean recovery from bovine li ver ranged between 90 and 96%. The intra and inter-assay variations showed RSD typically of < 5% and < 10%, respectively. The procedure was applied al so to ovine and porcine liver, giving similar results. A robustness study, carried out on the alumina clean-up step, indicated that the step is relati vely insensitive to method changes. However, significant differences overal l were found for the type of alumina and/or commercial SPE cartridge used. The limit of quantitation of the method is 2 mu g kg(-1) (ppb).