What is electrospray ionisation?
Electrospray ionisation (ESI) is a mass-spectrometry ionisation method that converts neutral peptide molecules in solution into gas-phase ions suitable for mass-analyser separation. The dominant ionisation method for peptide identity verification in coupled LC-MS analytical methods.
What the research literature says
ESI works by applying a high voltage to a fine spray of peptide solution at the mass-spectrometer inlet. The voltage causes the solvent droplets to acquire charge; as the droplets evaporate, electrostatic repulsion causes them to fission into smaller droplets, eventually producing gas-phase peptide ions. The technique is gentle — it preserves peptide structure without fragmenting the backbone — and produces multiply-charged ions (typically [M+2H]²⁺ through [M+5H]⁵⁺ depending on peptide size and charge profile) that simplify the mass-analyser-resolution requirements.
For peptide identity verification, ESI is paired with a high-resolution mass analyser (typically time-of-flight or Orbitrap instruments) to provide the mass-accuracy needed to distinguish close-mass isobars. The combined LC-ESI-MS framework runs the sample through reversed-phase HPLC, ionises the eluate via ESI, and characterises each chromatogram peak by its mass spectrum.
The USP <1736> general chapter on mass spectrometry covers ESI and the broader mass-spectrometric methods framework. The analytical-validation considerations are in ICH Q2(R1).
Why this matters in research context
ESI matters in peptide-research contexts as the standard mass-spectrometry ionisation method for the LC-MS workflow that pairs with RP-HPLC for combined identity-and-purity verification on a peptide certificate of analysis. The multiply-charged-ion signature is the canonical pattern researchers should expect to see on the mass spectrum included on a credible COA.
Related compounds
- Mass spectrometry (glossary entry) — broader analytical methodology
Related research questions
References
- ICH Q2(R1) — Validation of Analytical Procedures: Text and Methodology. International Council for Harmonisation.
- USP <1736> Applications of Mass Spectrometry. United States Pharmacopeia.
Research-questions pages describe research-context use of peptide-research terminology. They do not constitute medical, veterinary, or clinical advice. Every compound in the Ronin catalog is sold strictly for laboratory and research use only.