Determination of amoxicillin in trout by liquid chromatography with UV detection after derivatization

A liquid chromatographic (LC) method based on solid-phase extraction was de veloped for determination of amoxicillin in muscle tissue of rainbow trout. The compound was extracted in an aqueous solution by precipitation of orga nic material with a mixture of sulfuric acid and sodium tungstate. The extr act was processed by solid-phase extraction on an end-capped phenyl sorbent , and concentrated on a divinylbenzene-co-N-vinylpyrrolidone polymeric sorb ent. The extract was derivatized and analyzed by reversed-phase gradient LC on a C-18 column with UV detection at 323 nm. The method detection limit w as 2.9 mu g/kg. Mean recovery in muscle was 80.5% (range 10-200 mu g/kg). T he method was applied to fillets from trout offered feed containing amoxici llin in an aquaculture pilot plant. Amoxicillin was detected in muscle tiss ue shortly after administration but not 3 weeks later. The relative repeata bility standard deviation for incurred residues in muscle tissue was 6.4% ( range 11-143 mu g/kg).