Automated residue analysis of tetracyclines and their metabolites in whole egg, egg white, egg yolk and hen’s plasma utilizing a modified ASTED system

An automated analytical method is described allowing simultaneous determination of all tetracyclines and metabolites in whole egg, egg yolk, egg white and blood plasma of the hens. Sample pretreatment is restricted to homogenization and a dilution step. Clean-up is by on-line dialysis and on-line solid-phase extraction utilizing an extended ASTED system, followed by liquid chromatography with UV or fluorescence detection with post-column pH adjustment and confirmational analysis by LC–MS–MS. After feeding oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC) to laying hens, not only residual parent compounds could be found in the eggs but also in vivo formed 4-epimers, isochlortetracycline (ICTC) and tentatively identified N-desmethyl metabolites of OTC, TC and ICTC.