Oxidation Artifacts in the Electrospray Mass Spectrometry of A(beta) Peptide

摘要

Gradual corrosion of stainless steel electrospray emittersunder conditions of normal use generates surface irregularities that can promote electrical discharge. The increased emission current affects the electrochemical reactions associated with the spray process. When sampling the peptide A(beta)(1-40), this is manifest by oxidation of methionine at position 35 to methionine sulfoxide. The resultant mass shift and reduced sensitivity can adversely affect H/D exchange experiments. These effects can be avoided by adding a redox buffer or (preferably) by repolishing the emitter, especially to a rounded geometry.