A new LC-MS method has been established for determination of momoiodotyrosine(MIT) and diiodotyrosine(DIT) in the hydrolysate of premix feeds.Samples was hydrolyzed with 4.0 mol·L-1 NaOH for 16 h at 110 ℃,then the hydrolysate was cleaned up with a SPE cartridge and injected directly for LC-MS analysis.Chromatographic separation was performed on a 2.1 mm×150 mm,5 μm particle,C18 column with a mixture of acetonitrile and 0.1%(by volume) acetic acid as mobile phase at a flow rate of 0.2 mL· min-1.ESI+ mass spectrometry detection was run on SIR mode with m/z 308,262 for MIT,and m/z 434,388 for DIT.Quantification was carried out with external standard method.Validation data indicated the method was linear in the concentration ranges investigated with regression coefficients(R2) of more than 0.99.The limits of detection(LOD) were 8 μg·L-1 and limits of quantification(LOQ) were 30 μg·L-1.The recoveries were range of 93%-110% with relative standard deviations of 6.5%-13.2%.The method was sensitive,accurate,and was applied in the determination of MIT and DIT in real sample with satisfactory results.
