Determination of ionophoric polyether monocarboxylic acids in feedstuffs by HPLC with post-column derivatization

A fast HPLC method for determination of low contents of monensin, salinomycin and narasin in feedstuff was developed and validated. The ionophores were extracted from samples with a hexane - ethyl acetate mixture and, after purification on a Sep-Pak Silica column, they were determined by HPLC on C18 reverse phase using post-column derivatization with 4-(dimethylamino)benzaldehyde and UV detection at 598 run. The preseparation, separation and derivatization reaction of the ionophores were optimized. New derivatization reagents (salicylaldehyde, thiophene-2-carbaldehyde, 4-methoxybenz-aldehyde, 4-hydroxy-3,5-dimethoxybenzaldehyde and ethylvanilin) were tested. For monensin, salinomycin and narasin, the respective parameters were as follows: determination limit 7.5, 266 and 503 mug.kg(-1); repeatability 0.08 and 0.06 mg.kg(-1) (content 0.2-5 mg.kg(-1)); recovery 99.0 +/- 8.4, 97.0 +/- 6.0 and 99.2+/- 5.1% (content 1-5 mg.kg(-1)).