Page 252 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

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high-mileage automobiles selected from a local wrecking yard. Although their
interiors had a distinct odor of a garage from oil, grease, etc., there were no
positive results by either GC/MS or GC/MS/MS prior to the test burns. Thus,
GC/MS/MS tests were not too sensitive. After the introduction of gasoline
or diesel fuel and the subsequent extinguishing of the blaze by firemen in
this training program, additional samples were taken. Some of the results of
the postburn samples by GC/MS were not determined to be positive. These
samples were reanalyzed by GC/MS/MS, yielding some positive results, yet
some samples were still negative. This again illustrated that GC/MS/MS was
more sensitive than GC/MS but not too sensitive, as some samples were
determined to be negative even though an ignitable liquid was known to be
present in the vicinity of the sample prior to the burn.
The objective in a “target class” type of GC/MS/MS analysis is not to
develop the most sensitive analysis but to further improve upon the specificity
of ASTM 1618-01 (GC/MS) by providing more diagnostic information and,
hopefully, to more closely compare it with the capabilities of the K9 (canine)
trained to locate ignitable liquid residues. As sensitivity is an important issue,
a study was conducted by this laboratory to make a cursory comparison of
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our GC/MS/MS method with the capabilities of a K9. This study used
samples of pinewood and polypropylene carpet that were spiked with gaso-
line and a low-odor medium petroleum distillate (MPD, paint thinner). Some
of these samples were spiked with these liquids and then burnt with a propane
torch to provide highly weathered samples. All samples that had a K9 hit in
this study were placed in a nylon evidence bag after the K9 inspection. The
bag was then put in an oven at 90˚C for 10 min and subsequently extracted
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by Solid Phase Micro-Extraction (SPME) using ASTM E-2154. The SPME
fiber was exposed to the headspace of the sample directly by poking a hole
into the bag with the SPME needle and then exposing the fiber for 10 min
prior to injection into the GC/MS/MS. Of particular interest were the samples
of pinewood. This was an aged 2¢¢ ¥ 4¢¢ pine stud where the spike of the
ignitable liquid did not absorb well into the pore structure. At the lowest
level of K9 sensitivity (very weak hit, K9 showing some interest) for the highly
weathered, low-odor MPD spiked onto pinewood, neither GC/MS nor
GC/MS/MS could confirm the K9 hit. It was surprising that the K9 still
responded, although weakly, to the residues of the MPD on the heavily
burned wood. This illustrated the extraordinary sensitivity of the K9. The
K9 had no false hits and thus exhibited a high level of specificity. More than
GC/MS, the GC/MS/MS target class, analysis appeared to resemble the K9
in terms of specificity and sensitivity. However, due to the heavy reliance on
the alkane class determination of this medium petroleum distillate that had
less aromatic content (MPD low odor variety), the GC/MS/MS could not
improve the standard GC/MS analysis conducted in this study in 2001. Newer

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