Development of amyloid β (1-42) certified reference material NMIJ CRM 6210-a.

Amyloid β is a well-known peptide biomarker for Alzheimer's disease. Various methods for amyloid β such as immunological assays have been reported. It is important to establish metrological traceability using a certified reference material (CRM) at the highest level in the calibration hierarchy to assess equivalence of measured values obtained from each method. Herein, we developed a CRM for amyloid β, named as NMIJ CRM 6210-a, with a concentration traceable to the International System of Units (SI). This CRM comprises a lyophilized synthetic peptide with a human amyloid β (1-42) sequence (hereafter, amyloid β) and includes oxidated, deamidated, and isomerized forms of amyloid β. Two certified values were assigned for the mass concentration of total amyloid β (a mixture of amyloid β and its oxidized, deamidated, and isomerized forms) and amyloid β, determined via amino acid analyses with two different hydrolysis methods with different liquid chromatography mass spectrometry methods coupled to isotope-dilution mass spectrometry on the reconstituted solution of the candidate material with (1.00 0.01) g of 0.1% ammonia aqueous solution. The quantitative results obtained from amino acid analyses were converted into mass concentration using the density and molar mass, resulting in certified values of (46 11) mg/L for total amyloid β and (42.6 7.0) mg/L for amyloid β, respectively. The amyloid β content in total amyloid β was determined by calculating the relative area percentage using liquid chromatography with ultraviolet detection. Furthermore, the storage stability of this CRM was evaluated along with its stability in use, both of which were shown to be stable.