Determination of isometamidium residues in animal-derived foods by liquid chromatography–tandem mass spectrometry

In this paper, a new determination method for isometamidium residues in animal-derived foods was developed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Isometamidium residues in bovine tissues and milk were extracted with the mixed solution of acetonitrile and 0.25 mol/L of ammonium formate–methanol (v/v, 1:1), concentrated and degreased, and determined by LC–MS/MS with quantification by external standard method. The results showed that the peak area of chromatogram was linearly related to the concentration of isometamidium in the range of 1–100 μg/L, and the limits of detection (LOD) and quantification (LOQ) were 0.05 μg/kg and 5 μg/kg, respectively. The average recoveries of spiked samples were in the range of 73.8–93.9% with relative standard deviations ranged from 2.3% to 7.5%. This method is simple, accurate and suitable for the identification and quantification for isometamidium in animal-derived foods.