Electrospray Ionization (ESI) Explained | And why ESI is useful in Mass Spectrometry

0:00-0:48 | What is electrospray ionization?
0:48-2:21 | How does electrospray ionization work?
2:21-3:41 | What are the advantages and disadvantages of ESI?
3:41-4:54 | Why is electrospray ionization useful?

Electrospray ionization is a technique which allows us to ionize a sample. That is to say to turn our sample into charged ions. In the case of ESI a high voltage is applied to a liquid producing an aerosol which can be used in a number of chromatography techniques. Normally ionizing biomolecules is difficult due to their fragile nature. Electrospray ionization can successfully bypass this effectively increasing the mass range of for instance the mass spectrometer to magnitudes of kDa-mDa.

In a nutshell Electrospray ionization works by applying a high voltage to the outlet of a capillary atomizing the particles into tiny charged droplets. As the solvent evaporates this charged intensity exerted on the droplets increases further eventually causing them to split into charge ions which creates the gas phase ion. Let us take a closer look at how this process works.

Electrospray ionization can be thought of as 3 distinct steps:

1. Droplet formation during which the sample solution is ejected from the capillary and exposed to a high voltage electric field, forcing the sample to form small charged droplets.
2. Desolvation during which these charged droplets are evaporated by a countercurrent of heated gas, further decreasing their diameter and as a result increasing their surface charge density. When this charge becomes too great, the Coloumb repulsive forces within them exceeds the surface tension it causes them to undergo fission, in other words divide into even smaller charged droplets.
3. Finally follows the gas phase ion formation because at this point the charged droplets have reached the nm level, turning them into gas phase ions.