Electrospray Ionization (ESI) Definition:

It is a technique used in mass spectrometry to produce Ions using an electrospray, in which high voltage is applied to a liquid to make aerosol.

Electrospray Ionization (ESI) Explained:

In mass spectrometry, the ionization technique in which the compound is first dissolved in a solvent and then sprayed via a high-voltage needle into a vacuum chamber. The tiny droplets of the solution become charged by the needle, and subsequent evaporation forms gas-phase molecular ions that typically carry one or more charges.