Table 1 Most common ionization techniques used for metabolomics applications

Electron impact

Most popular for organic compounds with molecular mass <600 Da, best-characterized ionization method

Spray ionization

Atmospheric pressure chemical ionization (APCI)

Applicable to relatively less polar and thermally stable compounds with an upper mass range of 1,500 Da, improved ionization efficiency and detection sensitivity

Electrospray ionization (ESI)

Characterization of small and large biomolecules (charged, polar, or basic), ultrahigh detection sensitivity, can control presence of fragmentation

Laser desorption ionization

Matrix-assisted laser desorption/ionization (MALDI)

Applicable to large biomolecules with masses >200 kDa, sensitivity of several orders of magnitude