Page 257 - Academic Press Encyclopedia of Physical Science and Technology 3rd Analytical Chemistry

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Encyclopedia of Physical Science and Technology EN009N-406 July 18, 2001 23:32

Mass Spectrometry

Kenneth L. Busch
Kennesaw State University

I. Instrumentation
II. Launch Points for the Next Fifty Years

GLOSSARY by a process of surface ablation, and ionized by proton
transfer from the acidic matrix molecules.
Chemical ionization An ion/molecule reaction that leads Quadrupole mass filter A mass analyzer that uses a stru-
to ionization of the neutral gas-phase sample molecule cture of four colinear rods of hyperbolic cross section
via its reaction with an ion generated from the reagent (energized with a combination of DC and rf fields) that
gas present in excess in the ionization source. creates trajectory oscillations in low-kinetic-energy
Electron ionization The direct ionization of a neutral ions passing through the rods. At a particular set of
gas-phase sample molecule via loss of an electron in- DC and rf values, only ions of one mass maintain a
duced by interaction with a high energy (70 eV) elec- stable trajectory that allows passage through the mass
tron emitted from a metal filament. filter.
Electron multiplier A transducer for creation of a cas- Sector mass analyzer A mass analyzer that uses either
cading electron flow initiated by the initial impact of an a magnetic field, or a combination of magnetic and
energetic particle on the front electro-emissive surface. electric fields, to change the direction of travel of high-
Electrospray ionization A process through which isola- kinetic energy ions. Ions of different masses are influ-
ted and usually highly charged ions of sample mole- enced to different degrees, providing the basis for a
culesarecreatedbysprayingafinestreamofdropletsof mass separation.
sample solution from a highly charged needle, followed Time-of-flight mass analyzer A mass analyzer that sep-
by progressive loss of solvent molecules. arates a mixture of ions generated in an ionization pulse
Ion trap A mass analyzer that traps all ions from a pulse by providing all ions with an equal kinetic energy, and
of ionization at the center of a ring and cap electrode then noting the different ion transit times (due to dif-
structure energized with DC and radio frequency (rf) ferent velocities for ions of different masses) through
fields. Ions of different masses are accelerated out of a flight tube of fixed length.
the trap to an external detector by selective addition of
energy.
Matrix-assisted laser desorption ionization A process MASS SPECTROMETRY (MS) today is certifiably dis-
by which sample molecules cocrystallized with a laser- tinct from the analytical method of five, ten, and cer-
energy-absorbing matrix are transferred without de- tainly fifty years ago when it was first used as a gen-
composition directly from the solid into the gas phase eral purpose analytical tool. Its fundamental principles

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