Current Electrospray Mass Spectrometry: An Overview. PartB. Analyte Charging

Abstract

Electrospray ionization(ESI) is an atomization and ionization method through which a solution‐phase analyte can be transferred into the gas‐phase as an ion via minute charged droplets. The second part of this two‐part review on electrospray mass spectrometry reviews the final part of the charged droplet trajectory and covers transfer into the gas‐phase and ionization of the analyte. The now customary separation into the ion evaporation model (for small analytes) and the charged residue model (for large analytes) is followed and reviewed. These models yield insight into the charging process, but observations made with newer atomization techniques and quantitation limitations imposed by ionization suppression (matrix effect) indicate that a complete understanding is not available yet. Deviations from expected charged residue or ion evaporation behavior will be indicated. Chemical and charge‐driven surfactancy is discussed in relation to small analyte ionization and quantitation, whereas hydration and kinetic trapping of protein conformers are treated as part of the charged residue model.