Electrospray Ionization Theory

Electrospray Ionization (ESI) mode creates ions in solution. In the ESI mode, the liquid flow is forced through a stainless steel capillary where a high voltage (3-5 kV) and a nebulizing gas (Nitrogen) are applied. Small charged droplets are generated and undergo a process of solvent evaporation until ions leave the droplets in gas phase. Those ions enter in the mass spectrometer to be detected under a specific scan mode. 

ESI is suitable for polar compounds such as amino acids, phosphorylated compounds.