Library Dissertation Showcase

Comparison of charcoal and MonotrapTM probes for the pre-concentration of petrol prior to gas chromatography-mass spectrometry

  • Year of Publication:
  • 2018

Ignitable liquids such as petrol can be used as accelerants to initiate or accelerate a fire, especially in arson attacks. Therefore, their detection and identification help in fire investigations. Sensitive analytical techniques are required to analyse ignitable liquids from fire debris due to the minimal amount of traces left of them at a fire scene. ASTM standards E1412 and E1618 recommend isolating ignitable liquids from fire debris by passive headspace analysis and the use of charcoal as an adsorption package. Then, the desorption of any ignitable liquids from the charcoal using carbon disulphide, and subsequent analysis using gas chromatography – mass spectrometry (GC-MS). An alternate method for the isolation of ignitable liquids from fire debris involves commercial, disk type adsorption packages called Monotraps. These recently developed Monotraps are made from an ODS silane monolithic material modified with activated charcoal. This study investigates the influence of optimisation of adsorption temperature and adsorption time for both charcoal probes and Monotrap probes on their efficiency to detect petrol: 18 hours at 40°C for charcoal probes and 90 minutes at 30°C for Monotrap probes. To compare their performance to detect petrol, for both adsorption packages, the precision, efficiency and limit of detection (LOD) were evaluated: the Monotrap probes had an LOD at 2 μL of petrol per litre of headspace compared to charcoal probes which had a lower limit of detection at < 0.5 μL of petrol per litre of headspace. The charcoal probes also had greater signal-to-noise ratios for most petrol components. When using the probes’ respective optimised conditions, the charcoal probes show a significantly better efficiency at determining petrol components by GC-MS when compared to Monotrap probes. With a 99.7% confidence interval, statistical analysis shows that there is a significant difference between results for charcoal probes and Monotrap probes. Therefore, based on their overall performance, the use of Monotraps as a sampling technique for the determination of petrol by GCMS is not recommended.

Keywords: Petrol, Monotraps, Activated Charcoal, GC-MS, Passive Headspace.

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