Thin-layer chromatographic determination of monensin in feeds: screening method

Monensin is extracted from feed with methanol and purified by solvent-partitioning solid-phase extraction. After solvent reduction, monensin is separated by thin-layer chromatography on silica gel and visualized by color development with vanillin. No false-positive results were obtained in validation studies by submitting or peer laboratories when blank samples were analyzed. Three of 20 samples spiked with 5 ppm monensin were reported as containing no monensin. All samples spiked with 10 ppm monensin were reported positive for monensin.