Ionization Methods
The ionization method will depend in part on the nature of the sample and in part on the information sought. The LTQ linear ion trap mass spectrometer has electrospray ionization (ESI). 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.
The foregoing is a rather brief and broad generalization and exceptions do exist.