What is FI , FD , and LIFDI ?

Field Ionization (FI) is the formation of ions by "removal of electrons from any species by interaction with a high electrical field". (IUPAC 1997)

Gas samples are blown in the FI ion source e.g. via GC-capillary or by  evaporation from a crucible.

Field Desorption (FD) is "the formation of ions in the gas phase from a material deposited on a solid surface (known as an emitter) in the presence of a high electrical field". (IUPAC 1997)

Sample solution of 1 µL is "dripped onto the emitter" (according to Waters) outside of the ion source and introduced in the FD ion source via a vacuum interlock by means of the FD-probe.

Liquid Injection Field Desorption Ionization (LIFDI) is regarded as a convenient tool to ionize any solid, liquid, or gaseous species transferred to the emitter inside of the ion source through a capillary without breaking vacuum.

The entire LIFDI sample prep is dipping the capillary into the sample solution for 1-2 s. A volume of ca. 40 nL is aspirated automatically and forced through the capillary. Upon arrival at the emitter, osmotic and capillary forces between the dendrites distribute the solution over the entire emitter (see sample prep video). The small volume of solvent is evaporated in the vacuum within seconds, followed by acquiring spectra at a total sample prep of less than 30 s.

           empty emitter              wetted emitter                  sample coated emitter

The LIFDI emitter is safe in the ion source for many convenient sample preps for days or even weeks. The LIFDI emitter can not be harmed at all by the sample prep (in marked contrast to conventional FD emitters as per GCT manual).