ISOLATION AND QUANTIFICATION OF IVERMECTIN IN BOVINE-MILK BY MATRIX SOLID-PHASE DISPERSION (MSPD) EXTRACTION AND LIQUID-CHROMATOGRAPHIC DETERMINATION

A technique for the extraction and liquid chromatographic determination of ivermectin residues in bovine milk is described. Avermectin was used as an internal standard. Fortified and blank milk samples (5.0 mL) were blended with 2.0 g C-18 (octadecylsilyl derivatized silica) in a syringe barrel. After a 2 minute equilibration, the aqueous phase was removed from the column by vacuum aspiration. The ivermectin residues were eluted from the C-18/milk matrix with ethyl acetate. After further cleanup by silica solid phase extraction, ivermectin derivatives were formed and then quantified by liquid chromatography with fluorescence detection. The recoveries of fortified ivermectin residues (1.0 - 8.0 ppb) averaged 97.7%. The injected extracts are free from matrix interferences making it easy to calculate the amount of residue present.