Definition
A soft ionization method for mass spectrometry that produces multiply charged peptide ions from solution.
Electrospray ionisation sprays a liquid sample through a fine, high-voltage capillary, forming charged droplets that shrink by evaporation until gas-phase ions are released. It is a soft technique, so peptides usually reach the analyser intact. Peptides typically acquire several protons, giving a series of peaks such as [M+2H]2+ and [M+3H]3+ at different m/z values; software deconvolutes this envelope to calculate the neutral mass. Because ESI works directly from liquid, it couples naturally to HPLC as LC-MS, which links each chromatographic peak to a mass. John Fenn shared the 2002 Nobel Prize in Chemistry for its development. Salts and TFA can suppress the ESI signal, so volatile buffers are preferred.