Meena Swaminathan
Jordan Clarke
Kelsey Dewitte
Kelsey Wilkerson
Experiment: Fire Debris Analysis Using Passive Headspace and GCMS
23/04/2015
Experimental
A clean quart lined paint can that has been prepared by baking at 80 °C for at least
16 hours to remove any adsorbed volatile compounds was selected and two pieces
of KimWipes were placed inside. 5 μL of unknown 14; an ignitable liquid was added
and closed immediately to prevent further evaporation and contamination. A paper
clip was bent to a hook shape and attached to a piece of dental floss. Then the
activated charcoal strip (ACS) was removed from the package and cut in half and put
on the paper clip. Then the can was opened and the paper clip with the ACS was
quickly put inside with it hanging inside by leaving the dental floss outside. It was
made sure that the paper clip was not touching the KimWipe or too high up. Then
the can was shut tightly, labeled with initials, and baked at 80 °C for an hour in the
oven. A method blank, with no liquid added was also prepared with similar
procedures and baked together with the unknown.
While the can was heating, standards were prepared by adding 30 μL to known 11;
the designated ignitable liquid in 1.5 mL of carbon disulfide to a GC vial. This
procedure was done under the hood, as carbon disulfide is toxic. The vials were then
labeled properly. A total of 15 known standards were prepared by each individual.
Once the cans were baked for an hour, it was removed from the oven and allowed to
cool for a few minutes, so it would be easier to handle. The lid was the removed and
ACS was removed from the can and quickly rolled and put in a vial insert. This was
done using forceps. The vial insert was then added to a GC vial and, under the hood,
enough carbon disulfide was added to cover the entire roll, and the vial was capped
and labeled properly.
The vials were then placed in the GCMS instrument. A sequence as a group was set
up with solvent blank in between samples, fire debris standard mix, method blank,
standards liquid samples, and unknown samples accordingly. The fire debris
standard mix was prepared ahead by the TA’s by adding 100 μL of E1618 mix to 150
μL of carbon disulfide in a GC vial with glass insert. Then the sequence was run. The
parameters of the instrument are shown below in Table 1.
Table 1: GCMS Parameters
Oven Temp and time
Ramps
Run Time
Inlet mode
Inlet initial temp & pressure
Split ratio
Split flow
Total flow
Gas Type
Column Type
Column max. temp
Column Length
Column diameter
Injector Volume
Solvent Delay
Initial temp: 60 °C & Initial time: 2.00 min
Rate: 10.00
Final Temp: 300 °C
26.00 min
Split
250 °C & 8.19 psi
20:1
19.9 mL/min
23.8 mL/min
He
Restek Rxi-5ms DB5
350 °C
30.0 m
250 μm
1.00 μL
3.0 min
Results and Discussion
The total ion chromatogram and extracted ion chromatogram of unknown 14 is
attached to the back of this report, and are labeled accordingly. From the
chromatograms it can be seen that the carbon range is between around C4 to C10;
and this would be considered a light product. Looking at unknown 14’s total and
extracted ion chromatograms and comparing them with the 15 known total and
extracted ion chromatograms; it seemed that unknown 14 was the most similar to
known 11; which was Klean strip, a lacquer thinner. This would mean that unknown
14 would be an oxygenated product under the ASTM E1618 classification. The
major peaks of unknown 14 chromatogram are clearly defined and spaced. The
abundance for the chromatograms for the peaks is different; thus the peak sizes are
smaller in unknown 14 than in known 11. However, upon closely comparing the
extracted ion chromatogram, the retention times of the peaks in the alkanes,
beginning of the aromatics and cycloalkane/alkene are similar. For example, in
unknown 14 in the alkanes, the retention times are around a little after 4.00, a little
before 6.00, about 7.50, and a little before 10.0. This matches the retention times in
known 11 alkanes. Also in aromatics there are two peaks beside each other around
3.00 and a little after in unknown 14, and this is the same in known 11.
Unknown 14 was first identified to be similar to known 2, which was America’s
Original Drygas Brand, a fuel injection and carb cleaner. This was due to the fact that
the total ion chromatogram looked similar. However, upon looking closely the peaks
in known 2’s total ion chromatogram had more “hash and trash,” and there were not
much single distinct peaks, and the overall shape was different. Also the extracted
ion chromatogram was different as well. Thus, in the end it was excluded as a
possibility.
Conclusions
Fire debris analysis using passive headspace, with activated charcoal strips, and
GCMS analysis was performed on an unknown liquid, unknown 14. Known
standards were also prepared and analysed by GCMS. The total ion chromatograms
and extracted ion chromatograms of unknown 14 and known were compared, and
known 11, which was Klean strip, a lacquer thinner. Unknown 14 had a carbon
range of around C4 to C10, which indicated that unknown 14 was a light product. Also
the peaks were clearly defined and spaced; there were higher than the baseline and
not really connected to the baseline. From this and extracted ion chromatogram,
unknown 14 was classified to be an oxygenated product under the ASTM E1618
classification. This information matched as known 11 was also a light oxygenated
product. Thus, it was concluded that unknown 14 was most probably known 11, the
Klean strip, a lacquer thinner.