Page 200 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

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excellent standards for the extraction of ignitable liquids and for the clas-
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sification and interpretation of the analytical results from this examination.
It is when the sample contains these compounds in very low concentrations
or in the presence of a large amount of background substrate that more
sensitive techniques are required. In the absence of these sensitive techniques,
the samples would be determined as negative for the presence of ignitable
liquid residues. This chapter describes the recent application of a tandem
(MS/MS) mass spectrometry experiment for the purposes of isolating and
identifying ignitable liquid residues in the presence of background products
that may mask the target analytes of interest. Our approach involves com-
pound specific MS/MS experiments that can be used to first isolate a specific
compound of interest by isolating the parent ion (or one of the fragment
ions) in the first MS experiment, conducting a collisional-induced dissocia-
tion, and then resolving the resulting daughter ions for compound identifi-
cation, all within the approximate time frame of a single mass spectrometry
experiment. The approach, previously described for the identification of
ignitable liquid residues from fire debris, 9–12 is widely used in analytical
chemistry for the identification of many different analytes of interest, includ-
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ing drugs of abuse. Other researchers are currently investigating MS/MS
methods for the analysis of fire debris evidence in order to distinguish pyroly-
sate markers from fuels.
5.1.2 Tandem Mass Spectrometry (MS/MS)

Mass spectrometry is now widely used in the identification of organic com-
pounds such as the components found in ignitable liquid residues. The result
of an MS experiment is an ion that could represent the molecular ion or one
of the fragment ions of the target analyte. Tandem mass spectrometry
involves a second MS experiment on the isolated ion from the first experi-
ment. MS/MS can be achieved in space (spatial resolution) with magnetic
sector or quadrupole instruments connected in series or in time (temporal
resolution) with the use of an ion trap mass spectrometer instrument. The
triple-quadrupole mass spectrometer was developed and commercialized
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for routine use of this technique. Following the chromatographic separation
of the compounds, an ion source provides the ionization step and is followed
by component ion separation in the first quadrupole, which acts as a mass
filter. In the typical GC/MS experiment, detection of the ions would follow
this step to end the experiment. In a triple-quadrupole MS/MS experiment,
a second quadrupole acts as a collision chamber to produce collisional
induced dissociation (CID) of the selected ions. The third quadrupole, also
a mass analyzer, can resolve the resulting daughter ions produced in the
collision chamber and detect the ions. MS/MS can be coupled to gas or liquid
chromatography systems.

© 2004 by CRC Press LLC