Development of an SI-Traceable HPLC-Isotope Dilution Mass Spectrometry Method To Quantify β-Lactoglobulin in Milk Powders

beta-Lactoglobulin (beta-LG) is one of the major allergenic proteins in milk. There is an urgent demand for an accurate and traceable method to develop beta-LG certified reference material (CRM). In this work, beta-LG was enzymatically digested and a specific peptide was chosen for quantitation by isotope-dilution mass spectrometry (IDMS). With amino acid CRMs as standards, the results could be traced to SI unit. By the proposed method, the recovery ranged from 86.0% to 118.3% with CVs <9.0%. The LOD and LOQ were 4.8 x 10(-5) g/g and 1.6 X 10(-4) g/g of beta-LG in milk powder, respectively. Ten samples from domestic market were analyzed with CVs <5.6%, and the relative expanded uncertainties ranged from 4.2% to 5.9% (k = 2). With the CRMs, it is expected that the comparability of beta-LG quantitation results will be improved among different laboratories.