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Summary of Ionization Methods

Ionization Method	Ions Formed	Sensitivity	Advantage	Disadvantage
Electron impac	M⁺	ng – pg	Data base searchable Structural information	M⁺ occasionally absent
Chemical ionization	M+1 M+18, etc	ng – pg	M⁺ usually present	Little structural information
Field desorption	M⁺,	μg − ng	Nonvolatile compounds	Specialized equipment
Fast atom bombardment	M+matrix	μg − ng	Nonvolatile compounds Sequencing information	Matrix interference Difficult to interpre
Plasma desorption	M⁺	μg − ng	Nonvolatile compounds	Matrix interference
Laser desorption	M+1 M+matrix	μg − ng	Nonvolatile compounds Burst of ions	Matrix interference
Thermospray	M⁺	μg − ng	Nonvolatile compounds	Outdated
Electrospray	M⁺, M⁺⁺, M⁺⁺⁺, etc.	ng − pg	Nonvolatile compounds interfaces w/LC Forms multiply charged ions	Limited classes of compounds Little structural information