Retention capabilities of different genera of wood for common ignitable liquids
Hayward, Adam Lewis
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The ability to extract ignitable liquids from wooden fire debris samples is an important aspect of arson investigation. A common method by which the ignitable liquids are extracted is heated passive headspace extraction, a process by which a sample is heated in a sealed container and any ignitable liquid residues present desorb from the sample and adsorb to an adsorbent present in the container. An activated charcoal strip is most often used as the adsorbent, and the recommended extraction procedure is to allow the sample to extract in an oven set at a temperature between 50 °C and 80 °C for an amount of time between 8 and 24 hours. The ignitable liquid residues can then be eluted from the adsorbent and analyzed by gas chromatography-mass spectrometry (GC-MS) to identify the type of ignitable liquid present within the sample as well as specific compounds within the ignitable liquid. The extraction procedure typically does not yield 100% of the original amount of ignitable liquid deposited on the sample. Some of the ignitable liquid residue loss can be attributed to any irreversible adsorption that occurs between the substrate and the ignitable liquid. This irreversible adsorption is not known to be a constant across different wood genera; however, the extent of irreversible adsorption may vary between differing genera of wood. The focuses of this thesis are to examine any trends in irreversible adsorption that occur in wooden substrates, to see which genera of wood presents the greatest retention of ignitable liquids, and to see if any correlation exists between the retention capabilities of a wood genus and its density. The densities were determined for a total of thirteen common wood genera, which were spiked with one of three ignitable liquids and then subjected to heated passive headspace extraction. A semi-quantitative approach was taken by comparing the abundance of specific compounds within an ignitable liquid extracted from a wood substrate to the abundance present in a diluted sample of the same ignitable liquid, allowing a comparison between different genera to be made. Ultimately, it was determined that different genera of wood do display different retention capabilities for the common ignitable liquids examined in this thesis, but there was no genus of wood which consistently demonstrated a greater retention for the ignitable liquids compared to the other genera, nor was there a genus of wood which consistently allowed for greater recovery of the ignitable liquids compared to the other genera.
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