An ultra performance liquid chromatography-triple quadrupole tandem mass spectrometric(UPLC-MS/MS) method was developed for the determination of α-lactalbumin(α-La) and β-lactoglobulin(β-Lg) in whey powder under positive ion multiple reaction monitoring(MRM) mode.The samples were firstly alkylated with iodoacetamide

followed by enzymatic hydrolysis with alkaline trypsin

then separated on a Waters ACQUITY UPLC-BEH C18

300 - column with 0.1% formic acid water solution and 0.1% formic acid acetonitrile solution as mobile phases by gradient elution.Results showed that there were good linear relationships for α-La and β-Lg in the ranges of 40-1 000 nmol/L and 80-2 000 nmol/L

respectively.The limits of quantitation(S/N=10) for α-La and β-Lg were 0.020 g/100 g

respectively.The average recoveries of two analytes from spiked whey powder samples were in the range of 84.7%-95.6%

with relative standard deviations(RSDs

n=6) of 1.6%-5.8%.Based on the above method

the targets in four kinds of whey powder samples

i.e.70% demineralised whey powder

90% demineralised whey powder

whey protein concentrate and α-lactalbumin powder from five countries were determined and contrasted.With the advantages of simple operation

accuracy and reliability

the established method was suitable for the determination of α-La and β-Lg in whey powder.