Page 271 - Academic Press Encyclopedia of Physical Science and Technology 3rd Analytical Chemistry

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Encyclopedia of Physical Science and Technology EN009G-958 July 18, 2001 0:57

Mass Spectrometry

in Forensic Science

Jan Schuberth
National Laboratory of Forensic Chemistry,
University Hospital (Emeritus)

I. Data Generation
II. Data Evaluation

GLOSSARY General unknown A substance which perhaps is present
in a sample but whose identity then is not known. Its
Analyte The target substance in a sample that is searched revelation, which most often is an analytical challenge,
for and identified by chemical analytical means. may help explain a crime, death, or unexpected event.
Chemical ionization A low-energy mode of ionization Ion trap A type of mass filter. It has a closed space, in
by which a reagent gas, after having been ionized by which an oscillating electric field is generated to direct
electron impact, reacts with the analyte also in the gas the flow of ions made up by charged fragments, formed
phase. By causing only minor fragmentation of the an- from an analyte and accelerated into the field. Only
alyte, this soft ionization often results in a charged an- those ions with mass/charge ratios that do not suit the
alyte molecule. electric potentials of the oscillating field are thrown out
Electron ionization A high-energy mode of ionization of the cell to become recorded.
by which electrons are allowed to bombard an analyte Magnetic sector The part of a mass filter that gener-
molecule in the gas phase, whereupon it picks up en- ates a magnetic field used to direct the flow of ions
ergy enough to become ionized and fragmented. This made up by charged fragments, formed from an ana-
harsh ionization process often results in a number of lyte and accelerated into the field. Only those ions with
fragments that may form a “fingerprint” suitable for the mass/charge ratios that suit the acceleration voltage and
analyte identification. magnetic field strength pass the magnetic sector to be-
Electron multiplier A device that transforms the ion come recorded.
beam of charged fragments into an electrical signal to Mass/charge ratio The mass of a fragment divided by
be sent in a wire and monitored by a recorder or data the number of charges it carries. In most instances
system. only one charge is involved, and the mass/charge ratio
Forensic science Scientific methods that aim to solve le- is, therefore, generally equal with the mass of the
gal questions. fragment.

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