Technical data

18 Agilent 6200 Series TOF and 6500 Series Q-TOF LC/MS System Concepts Guide
1Overview
Electrospray ionization (ESI) and Dual ESI
1 Formation of ions
2 Nebulization
3 Desolvation
4 Ion evaporation
Formation of ions
Ion formation in API-electrospray occurs through more than
one mechanism. If the chemistry of analyte, solvents, and
buffers is correct, ions are generated in solution before
nebulization. This results in high analyte ion concentration and
good API-electrospray sensitivity.
Preformed ions are not always required for ESI. Some
compounds that do not ionize in solution can still be analyzed.
The process of nebulization, desolvation, and ion evaporation
creates a strong electrical charge on the surface of the spray
droplets. This can induce ionization in analyte molecules at the
surface of the droplets.
Nebulization
Nebulization (aerosol generation) takes the sample solution
through these steps:
a Sample solution enters the spray chamber through a
grounded needle called a nebulizer.
b For high-flow electrospray, nebulizing gas enters the spray
chamber concentrically through a tube that surrounds the
needle.
c The combination of strong shear forces generated by the
nebulizing gas and the strong voltage (2–6 kV) in the spray
chamber draws out the sample solution and breaks it into
droplets.
d As the droplets disperse, ions of one polarity
preferentially migrate to the droplet surface due to
electrostatic forces.
e As a result, the sample is simultaneously charged and
dispersed into a fine spray of charged droplets, hence the
name electrospray.