Abstract: A rapid method for the determination of lysinoalanine in milk products by ultra-high performance liquid chromatography-quadrupole/electrostatic field orbitrap high resolution mass spectrometry (UPLC-Q-Exactive Orbitrap HRMS) was developed. Samples were hydrolyzed with hydrochloric acid to remove impurities such as proteins and then separated on an Ascentis C8 column (100 mm × 4.6 mm, 3 μm) by gradient elution using a binary solvent system composed of acetonitrile and 0.1% formic acid in water. The analytes were detected by quadrupole-orbitrap high resolution mass spectrometry in full-MS and data dependent scan (ddMS2) mode. The results showed that the deviation between the theoretical and measured accurate mass to charge ratio of lysinoalanine was lower than 1.0 × 10-6, and a good linear relationship was observed in the concentration range of 1–200 μg/L with a correlation coefficient higher than 0.999. The limit of detection (LOD) was 0.01 mg/kg and the limit of quantitation (LOQ) was 0.025 mg/kg. Recoveries of the method were in the range of 78.7%–117.1% at spiked concentration levels of 0.025, 0.1, and 0.25 mg/kg, and the relative standard deviation (RSD) for precision was 3.64%. The method had high accurate, repeatability and sensitivity, and consequently was suitable for the qualitative and quantitative screening of lysinoalanine in milk products. Furthermore, the pattern of variation in lysinoalanine content of liquid milk processed using small-scale simulated processing equipment at different temperatures was studied.

Key words: utlra-high performance liquid chromatography, high resolution mass spectrometry, lysinoalanine, milk, determination