electrospray

Electrospray is a technique for generating ions in the gas phase from a liquid sample by applying a high electric potential to the liquid as it exits a capillary, producing a fine aerosol of charged droplets. In its most common form, electrospray ionization (ESI), the solution is sprayed at a metal capillary tip, forming a Taylor cone and a spray of charged droplets.

As droplets travel, solvent evaporates and desolvation aids in shrinking the droplets and concentrating charges. This leads to Coulombic fission and progressively smaller droplets, culminating in gas-phase ions. Biomolecules often acquire multiple charges, enabling their analysis with mass spectrometers that have a limited m/z range. ESI is considered a soft ionization method because it tends to preserve intact molecular ions with minimal fragmentation.

Developed in the 1980s by John B. Fenn and colleagues, electrospray ionization transformed coupling of liquid chromatography to mass spectrometry. Fenn and colleagues were awarded the 2002 Nobel Prize in Chemistry for the development of electrospray ionization.

A typical system includes a sample solution delivered to a conductive capillary, a high-voltage power supply, and a desolvation interface to a mass spectrometer (such as a quadrupole, time-of-flight, or Orbitrap). Nanoelectrospray (nESI) uses smaller capillaries and lower flow rates, increasing sensitivity and reducing sample consumption. ESI is widely used in tandem with LC-MS for a range of analyses.

Applications include proteomics, metabolomics, lipidomics, and analysis of large biomolecules, with widespread use in direct infusion, LC-MS workflows, and MS/MS. Limitations include dependence on suitable solvents and salts, formation of adducts, and spectra influenced by multiple charging.