Electrospray ionisation (revision 4)
Old revision·11:52, 2 Oct 2024·TechnicianTeal
| Electrospray ionisation | |
|---|---|
| Abbreviation | ESI |
| Produces | Multiply charged ions from solution |
| Nature | Soft; molecule survives intact |
| Compatible with | Liquid chromatography |
| Analytical method infobox · conventions | |
Electrospray ionisation transfers molecules from solution into the gas phase as ions. A solution is sprayed from a capillary held at high potential, producing charged droplets whose solvent evaporates until ions are released.[1]
It is a soft technique — the molecule survives largely intact — and it produces multiply charged ions from peptides and proteins, so a large molecule appears at a mass-to-charge ratio within the range of ordinary analysers. A single peptide therefore produces a series of peaks at successive charge states, deconvolved by software into one neutral mass.[2]
Mechanism
[edit]The applied potential draws the liquid into a cone from whose tip a fine spray of charged droplets emerges. Solvent evaporates, the droplets shrink until charge repulsion exceeds surface tension, and they divide. Ions are ultimately released either by field-driven ejection from very small droplets or by complete evaporation of the solvent around them.[1]
The charge states observed depend on the number of ionisable sites and on solution conditions. Acidic mobile phases favour protonation and positive-mode operation, which is why peptide LC-MS is usually run in positive mode with an acidic modifier.[2]