The ionization method will depend in part on the nature of the sample and in part on the information sought. The TSQ7000 triple quadrupole mass spectrometer has both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources. ESI is the most frequently used and works well for many analytes; it is particularly useful for large biomolecules, and usually can ionize any molecule having some degree of hydrophilicity. APCI is better suited to small molecules which can be volatilized with relative ease, and is better than ESI for molecules that are less polar.

The foregoing is a rather brief and broad generalization and exceptions do exist. Should you have any questions about the ionization method to be used on your sample, please contact the MS facility manager.