Electrospray Ionization (ESI) and Atmospheric Pressure Chemical Ionization (APCI) in Mass Analysis

Electrospray Ionization (ESI) and Atmospheric Pressure Chemical Ionization (APCI) are two widely used techniques in mass spectrometry, each best suited for specific types of molecules. Let’s explore their unique principles, ideal uses, and applications in a reader-friendly way.

ESI vs APCI

ESI vs APCI

Electrospray Ionization (ESI)

How It Works: In ESI, a high voltage is applied to a liquid sample, creating a fine mist of charged droplets. As the solvent evaporates, the analytes in the droplets gain charge and transition into gas-phase ions.

Best For: ESI is ideal for analyzing large, polar, or non-volatile molecules, such as:

  • Proteins
  • Peptides
  • Nucleic acids
  • Other complex biomolecules

Common Applications:

  • Protein and Peptide Analysis: Useful for studying structures and functions of large biomolecules.
  • Biomolecular Studies: Helps in identifying and quantifying complex biomolecules.
  • Pharmacokinetics and Drug Discovery: Supports research into how drugs interact within the body.
  • Quantitative and Qualitative Analysis: Well-suited for polar compounds.

Atmospheric Pressure Chemical Ionization (APCI)

How It Works: APCI uses a corona discharge needle to ionize vaporized samples in the presence of nitrogen gas. This method is highly effective for ionizing less polar and medium-polarity molecules.

Best For: APCI is ideal for smaller, less polar, and more volatile compounds, such as:

  • Lipids
  • Small organic molecules
  • Pharmaceuticals

Common Applications:

  • Small Molecule Analysis: Provides insights into simple organic and inorganic molecules.
  • Lipidomics: Aids in studying lipids and lipid-containing structures.
  • Pharmaceutical Testing: Useful for drug development and quality control.
  • Environmental Analysis: Enables analysis of pollutants and other environmental samples.

Quick Comparison

  • Polarity: ESI works best for highly polar compounds, while APCI is suited for moderately polar to nonpolar compounds.
  • Volatility: ESI handles larger, less volatile molecules, whereas APCI is ideal for smaller, more volatile compounds.

Conclusion

Together, ESI and APCI significantly broaden the capabilities of mass spectrometry, providing tools to analyze a vast array of molecular structures. They support applications across biological research, drug discovery, environmental science, and more, allowing for versatile and precise molecular analysis.

Ref:

Lee HR, Kochhar S, Shim SM. Comparison of electrospray ionization and atmospheric chemical ionization coupled with the liquid chromatography-tandem mass spectrometry for the analysis of cholesteryl esters. Int J Anal Chem. 2015;2015:650927.

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