X hits on this document

44 views

0 shares

0 downloads

0 comments

3 / 14

Field Ionization (FI) versus Field Desorption (FD)

! The Theory

A high electric voltage (potential) that gives rise to lines of equipotential result in an electric field crowd around the needle tip. The electric field is most intense at the surface (point) of the tip and is where ionization occurs.

FI : sample is heated in a vacuum so as to volatilize it onto an ionization surface. FI is suited for use with volatile, thermally stable compounds. FI sources are arranged to function also as FD sources

equipotental lines of the electric field

+

positive tip electrode

ion repelled

negative

towards negative

counter

electrode

electrode

to mass analyzer

FD : the sample is placed directly onto the surface (dipping emitter in an analyte solution) before ionization but FD is needed for non- volatile and/or thermally labile substances.

FI spectrum for D-glucose

FD spectrum for D-glucose

3

Document info
Document views44
Page views44
Page last viewedSun Dec 04 19:47:10 UTC 2016
Pages14
Paragraphs626
Words3706

Comments