ABSTRACT
Mass spectrometry (MS) starts with the ionization of molecular entities in vacuum, followed by the separation of these ions according to molecular mass, and then their detection. Analytical ultracentrifugation measures the sedimentation behavior of macromolecules in a gravitational field, which not only provides information on their mass, but also on their size and shape. MS relies on the ionization of molecules and the separation of these ions according to their mass in an electric field. In matrix-assisted laser desorption ionization (MALDI) the ionization is done out of the solid state under denaturing conditions whereas electrospray ionization can be performed under both denaturing and physiological conditions. Proteins and peptides usually form positive ions, and similar to MALDI the protonation efficiency of the solvent can be increased by a trace of formic acid. Carbohydrates and nucleic acids form negative ions, and deprotonation can be promoted by addition of volatile amines or ammonia to the solvent.
