ELECTROSPRAY IONIZATION

In electrospray ionization, a liquid is pushed through a very small, charged and usually metal, capilary. This liquid contains the substance to be studied, the sample, dissolved in a large amount of solvent, which is usually much more volatile than the sample. Volatile acids, bases or buffers are often added to this solution too. The sample exists as an ion in solution either in its anion or cation form. Because like charges repel, the liquid pushes itself out of the capillary and forms an aerosol, a mist of small droplets about 10 μm across.

The aerosol is at least partially produced by a process involving the formation of a Taylor cone and a jet from the tip of this cone. An uncharged carrier gas such as nitrogen to evaporate the neutral solvent in the droplets. As the solvent evaporates, the analyte molecules are forced closer together, repel each other and break up the droplets. This process is called Coulombic fission because it is driven by repulsive coulombic forces between charged molecules. The process repeats until the analyte is free of solvent and is a lone ion. In electrospray processes, the ions observed may be quasimolecular ions created by the addition of a proton or cation(Na⁺).