Question

Describe the difference between gaseous field ionization sources and field desorption sources.

Short answer

Mostly ion sources are categorized as two types; they are gas phase sources and desorption sources. In gas phase sources, the sample is first vaporized and then ionized. In desorption sources, the solid or liquid sample is converted directly into gaseous ions. Here, field ionization is belongs to gas phase sources and field desorption is belongs to desorption sources.

Step-by-step solution

Common difference

A high-potential electric field is applied to an emitter with a sharp surface, such as a razor blade, or, more typically, a filament from which small "whiskers" have developed, in the field desorption.

The sample is first volatilized and then transferred to the ionisation region for ion production in a gaseous ionisation source.

Differences

S.No	Field ionization sources(FI)	Field desorption sources(FD)
1.	The sample is directly evaporated from the insection probe or gas inlet. So, the gaseous molecules reach the emitter and then they are ionized by electron tunneling.	The sample is deposited at the emitter which is biased to high potential when a current is passed through emitter to heat up the filament. So, the emitter current increases gradually as results the sample evaporates from emitter into gas phase.
2.	It is mostly used for small organic molecules and some petrochemical reactions.	It is mostly used for thermally stable nonvolatile, polar organic, and organometallic compounds.
3.	There is no chemical reaction occur	There is no chemical reaction occur
4.	Mass spectrum range is low nearly less than 1000 Da	Mass spectrum range is high approximately between 2000 to 3000 Da
5.	Mixture of ion species are recognized by this sources per molecules at a time.	One moelcular ion species is recognized by this sources per moleucle at one time