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Analysis of Nosiheptide in Food Animal Tissues via Its Unique Degradation Product by Liquid Chromatography Tandem Mass Spectrometry After Alkaline Hydrolysis.

Very weak signals of fragment ions of nosiheptide could be observed using liquid chromatography-tandem mass spectrometry. The preparation of 4-hydroxymethyl-3-methyl-1H-indole-2-carboxylic acid (HMIA), a specific fragment of nosiheptide, by alkaline hydrolysis is described. HMIA showed good mass spectrometric signal in negative electrospray ionization mode. In the new method, nosiheptide residue in muscle tissue was hydrolyzed with sodium hydroxide aqueous solution, followed by the cleanup using the mixed mode cartridges. Identification and quantification of nosiheptide were carried out by analyzing HMIA in hydrolysate of muscles. Nosiheptide showed good linear relationship (r > 0.996) in the calibration range of 2 - 500 µg/kg, and low limit of quantification of 2 μg/kg was obtained in swine, chicken and fish muscles. Recoveries of nosiheptide from spiked muscle samples were 85% - 108% with relative standard deviations less than 10%. The proposed method was successfully applied for the detection of nosiheptide residue in medicated animal tissues samples.