Methods for quantification of amyloid β peptides in plasma by mass spectrometry

A method for preparing a plasma sample comprising amyloid beta peptides for analysis by mass spectrometry, wherein the plasma sample comprises intact amyloid beta peptides Aβ40 and Aβ42, comprising:

• a) contacting said plasma sample with a denaturing agent to obtain a denatured solution;
• b) performing a first solid phase extraction on the denatured solution to recover a first eluate,
• c) performing a second solid phase extraction step on said first eluate to recover a second eluate, and
• d) drying said second eluate and processing the dried second eluate for analysis by mass spectrometry to obtain the plasma sample,
• wherein the first solid phase extraction step is a reversed-phase solid phase extraction and the second solid phase extraction step is a cation exchange solid phase extraction,
• wherein the first solid phase extraction step is an anion exchange solid phase extraction and the second solid phase extraction step is a cation exchange solid phase extraction, or
• wherein the first solid phase extraction step is a cation exchange solid phase extraction and the second solid phase extraction step is an anion exchange solid phase extraction,
• and
• wherein the denaturing agent is an acidic denaturing agent if the first solid phase extraction step is a reversed-phase solid phase extraction or a cation exchange solid phase extraction, or
• wherein the denaturing agent is a basic denaturing agent if the first solid phase extraction step is an anion exchange solid phase extraction.