Page 253 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

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instrument parameters determined since that time may provide further
improvement. Thus, neither GC/MS nor GC/MS/MS could confirm some of
the weak K9 hits when a low odor medium petroleum distillate was present.
Although conducted with only one laboratory and one K9, this study
served as a check on where this method resides in sensitivity relative to the
K9. In this study, the GC/MS/MS method was easily able to detect ignitable
liquids that have a significant number of aromatic components, as expected,
and resulted in an improvement in the confirmation of the K9 hits over the
analysis conducted by GC/MS analysis on the same instrument.
Thus, GC/MS/MS is not too sensitive and does not appear to exceed the
capabilities of the K9. The moderate increase in sensitivity by GC/MS/MS is
due to the increase in specificity only and not in signal strength.

5.2.4.3 Disadvantages
The disadvantage of the target class approach is the somewhat lower sensi-
tivity than the target compound approach for one specific compound, as the
MS/MS acquisition parameters are more general and not optimized for any
specific compound. The analysis by MS/MS also does not allow for the review
of the general quantity or type of pyrolysates that may be present in the
sample. These pyrolysates have been purposefully filtered out as we program
the MS/MS parameters to focus as much on ignitable liquids as possible.
Similarly, an analysis by MS/MS does not allow the study of any unusual
matrix components that may be of interest or be incidental. As sometimes
is the case, the matrix profile may be useful to link samples to a location
within a case (e.g., a case file may contain samples 2, 3, and 6 that are all
carpet as found in the living room, and samples 1, 4, and 5 are wood from
the floor joist in the basement). This link can be shown by a study of the
polypropylene or wood pyrolysates to confirm the link of the sample to the
results in the GC/MS analysis.

5.2.4.4 Benefits
The primary objective is the detection and identification of ignitable liquids.
The advantage of a target class GC/MS/MS analysis is the greater specificity
realized by mixture identification through comparison by pattern recognition
of the reconstructed daughter ion chromatograms. GC/MS/MS is still more
sensitive than GC/MS and it has been proven in one study that GC/MS/MS
can lengthen the period of time that a residue of an ignitable liquid can be
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identified by 2 additional weeks. The more sensitive and specific analysis
by GC/MS/MS may also help the investigator. In theory, samples that contain
an ignitable liquid can still be proven positive at a greater distance from the
initial location of an ignitable liquid as it can detect more minute residues
of ignitable liquids and thus be more forgiving as to the sample location. It

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