The potential of amine-containing dendrimer mass standards for internal calibration of peptides

In order to ensure accurate mass determinations, MALDI-TOF mass spectrometers must be calibrated regularly. While peptides and proteins represent the most widely used calibration standards due to their monodispersity, known masses and availability, their limited shelf-life complicates their use. Recently, polyester dendrimer calibrants have been introduced as an alternative because, in addition to monodispersity and relative molecular masses as high as 30,000, they exhibit vastly improved stability and broad compatibility with both matrices and solvents. However, the use of these initially reported polyester dendrimers as internal calibrants for the analysis of peptides or proteins presents a unique problem because these dendrimers typically require ionization with metal cations, while amino acid-based compounds preferentially ionize via protonation of an amine. To address this complication, dendrimers bearing a single amine were prepared which demonstrate the ability to easily ionize via protonation with either acidic matrices or dilute solutions of trifluoroacetic acid. This class of amine-containing dendrimers shows promise as a calibrant system specifically designed for the internal calibration of peptides.