[Determination of free selenomethionine in cow milk by UPLC-MS/MS].

To establish an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the quantification of free selenomethionine (SeMet), and be applied to the quantification of free SeMet in cow milk.The analyte was separated on a BEH C18 column (2.1 mm x 100 mm, 1.7 μm) at 40 degrees C with a mobile phase of water: acetonitrile: formic acid (95: 5: 0.1, V/V) , a flow rate of 0.3 mL/min, and an analysis time of 2. 5 min. At positive electrospray ionization mode, multiple reaction monitoring of the precursor-product ion transitions of m/z 198.0 --> 181.1 was used for the quantification.The linear calibration curve was obtained in a concentration range of 0.5 - 100 ng/mL with a lower limit of quantification of 0.5 ng/mL. The value of intra- and inter-day accuracy for SeMet fell in the range of 97.6%-100.6% and 97.7%-99.2%, and value of intra- and inter-day precision 0.53%-4.49% and 1.03%-4.54%.The method is specific, sensitive, rapid, and accurate, suitable for the quantification of free SeMet in cow milk.