Sample preparation for residue determination of gentamicin and neomycin byliquid chromatography

The effect of sample preparation on the determination of gentamicin and neo mycin residues in animal tissues was investigated. The extract was mixed wi th an ion-pair reagent and applied to an octadecyl cartridge. The cartridge s were washed with buffer followed by water, and analytes were eluted with ion-pair buffer-acetonitrile mixture. The aminoglycosides were derivatized with 9-fluorenylmethyl chloroformate prior to liquid chromatography using a reversed-phase column and fluorescence detection. Under the conditions app lied neomycin was fully separated from all the gentamicin compounds. The hi ghest recoveries of gentamicin and neomycin from spiked tissues were obtain ed using trichloroacetic acid after initial extraction with phosphate-buffe red saline. No interfering peaks from endogenous compounds of matrix were n oted at the elution position of the analytes. An intra-laboratory validatio n of the whole procedure was performed. The calibration graphs were linear from 0.1 to 1.0 mg/kg for gentamicin, and from 0.2 to 1.0 mg/kg for neomyci n. Limits of detection were 0.05 mg/kg and 0.10 mg/kg for gentamicin and ne omycin, respectively. Limits of quantitation for gentamicin and neomycin we re 0.1 and 0.20 mg/kg muscle, liver or kidney tissue, respectively. Recover ies of gentamicin spiked at levels of 0.1 mg/kg porcine tissues ranged from 76 to 86%. Recoveries of neomycin spiked at levels of 0.2 mg/kg porcine ti ssues ranged from 77 to 83%. The validated procedure was used to determine gentamicin concentrations in porcine tissue after dosing with gentamicin at a level of 5 mg/kg body mass. (C) 2001 Elsevier Science B.V. All rights re served.