In the Laboratory
An Economical Method for Static Headspace Enrichment for Arson Analysis Bjorn Olesen Department of Chemistry, Southeast Missouri State University, Cape Girardeau, Missouri 63701
[email protected] Arson is a serious crime and causes billions of dollars in physical loss each year. Many lives are lost as a result of arson. Accelerants are often used to start arson fires; thus, identification of the accelerants may aid in determining whether the fire was arson and who set the fire. Arson accelerants are grouped by different classes (Table 1) (1). An exact identification of the accelerant or accelerants is rarely possible because of the great number of substances that fall into each class. Also, arson samples do not give an exact match with known standards owing to sample aging, evaporation, and combustion. However, it is possible to assign an arson sample to its class. Headspace analysis is commonly used for detection of arson accelerants (2-5). This Journal has previously published five articles on the subject. Three of these analyses (6-8) require relatively large samples, one (9) deals with simplex optimization of headspace-enrichment conditions, and one (10) uses negative pressure dynamic headspace concentration for sampling. This experiment was designed to give upper-level undergraduate or beginning graduate students a real-life introduction to arson analysis by requiring them to generate their own arson library, extract accelerants from burned samples, and identify the accelerants in several unknown arson samples by using critical thinking skills. Static headspace analysis is routinely accomplished using carbon strips supplied by Albrayco Laboratories, Cromwell, CT. The cost of these strips is about $3.00 per sample if a whole strip is used per analysis. To reduce the cost of the analysis, a Sears carbon filter costing 1.5¢ per sample has been successfully substituted for the Albrayco strip. This experiment demonstrates the effectiveness of the Sears carbon filters in isolating volatile organic components from arson samples and compares the results with those obtained using the Albrayco strips. The Experiment Two samples were prepared for each accelerant by adding several drops of accelerant to a 1 cm 2 cm substrate such as wood, paper, or carpet. The accelerant and substrate were ignited and allowed to burn long enough to char the substrate. The fire was extinguished by smothering it with a watch glass, and the samples were sealed in vials for later analysis. For headspace enrichment, small pieces of the previously ignited sample were placed in 50 mL headspace vials. In separate vials, one-half of an Albrayco strip and a 1 cm 2 cm Sears filter were suspended on a wire above the sample. Each vial was capped with a Vicar septum, sealed, and placed in an oven at 80 °C. 314
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After 1 h, the samples were removed from the oven and remained sealed overnight at room temperature. The next day, the carbon membranes were removed and placed in gas chromatography (GC) sample vials. Approximately 1 mL of carbon disulfide was added to each vial and 0.2 μL samples were analyzed on a DB-1 column using a flame ionization detector. Background samples of burned substrate minus accelerant, neat standards, and neat samples of the carbon filters were analyzed in the same manner. Hazards Kerosene is a flammable liquid that is harmful if swallowed or inhaled. It causes irritation to skin, eyes, and the respiratory tract. It also affects the central nervous system. Other potential accelerants would have similar general properties. Carbon disulfide is a flammable liquid and the vapor may cause a flash fire. It may be fatal if swallowed or inhaled and is harmful if absorbed through the skin. It affects the central and peripheral nervous system, the cardiovascular system, liver, and kidneys. It is a developmental and reproductive hazard. Consult the MSDS for specific accelerants used. Results Students readily classify their unknown ignited accelerants on various substrates. The Albrayco strip and the Sears filter are comparable in their ability to detect the accelerants. The chromatograms for pure kerosene standards are shown in Figure 1. Visual inspection of these chromatograms shows that the Albrayco strip and the Sears filter give nearly identical results. The variability of retention times can be accounted for by manual injections and by manually starting the recording integrator. The major peaks in both chromatograms have the same relative intensities, and close inspection of the chromatograms shows the two to be virtually identical with respect to the retention times and relative intensities for the minor peaks. The gas chromatograms from ignited student unknown kerosene samples analyzed on pine are shown in Figure 2. The retention times of the major peaks in both are close and the relative intensities of the major peaks are nearly identical in both chromatograms. The sample analyzed using the Sears filter shows an enlarged peak at 23.254 min that is not present in pinewood alone, but is present at a lower intensity in the sample analyzed with the Albrayco strip. This peak does not interfere with the assignment of this sample as a class 4 accelerant.
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Vol. 87 No. 3 March 2010 pubs.acs.org/jchemeduc r 2010 American Chemical Society and Division of Chemical Education, Inc. 10.1021/ed800078b Published on Web 02/09/2010
In the Laboratory Table 1. Arson Accelerant Classes Class 1: Light petroleum distillates
Hydrocarbon Content C4-C8
Examples Petroleum ethers, lighter fluid, naphtha
2: Gasolines
Gasoline, gasohol, camp stove fuels
3: Medium petroleum distillates
C4-C10
Paint thinner, mineral spirits, charcoal lighter fluid
4: Kerosenea
C8-C16
#1 Fuel oil, jet fuel, insect spray, charcoal lighter fluid
5: Heavy petroleum distillates
C10-C23
#2 Fuel oil, diesel
0: Unclassified a
Alcohols, toluene, xylene, lacquer thinner, isoparaffinnic hydrocarbons
Kerosene is sometimes classified with heavy petroleum distillates.
unknowns. Cost per analysis using the Sears filter is 1.5¢ compared with $1.50 for the Albrayco strip. Thus, the Sears filters provide an economical way to do static headspace enhancement for arson analysis. Acknowledgment Figure 1. Kerosene standard analyzed with a (left) Albrayco strip and (right) Sears filter.
Figure 2. Ignited kerosene unknown sample on pine analyzed with a (left) Albrayco strip and (right) Sears filter.
Conclusion Students are successful in classifying the unknown arson accelerants. They are exposed to a real-life application of chemistry in forensic science. The students gain valuable critical thinking skills by generating their own arson library. The substitution of the Sears carbon filter for the Albrayco carbon strips readily allows for the classification of arson accelerants. The Sears carbon filter gives GC traces that are similar to those obtained with the Albrayco carbon strips. Retention times on both carbon sources are similar. Ignited samples closely resemble pure standards in both retention time and relative peak intensities, thus, allowing for the correct classification of
r 2010 American Chemical Society and Division of Chemical Education, Inc.
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The chromatograms were run by Sheena Arink, Caleb Buis, Angela Hirtzel, and Greg Woods. Literature Cited 1. Excerpts from The Pocket Guide to Accelerant Evidence Collection; http://www.interfire.org/res_file/aec_20ig.asp (accessed Dec 2009). 2. Reeve, V.; Jeffery, J.; Weihs, D.; Jennings, W. J. Forensic Sci. 1986, 30, 479. 3. Tranthim-Fryer, D. J. J. Forensic Sci. 1990, 35, 271. 4. Brettell, T., SISWEB Application Note; http://www.sisweb.com/ reference/applnote/ap2-a.htm (accessed Dec 2009). 5. Pert, A. D.; Baron, M. G.; Birkett, J. W. J. Forensic Sci. 2006, 51, 1033. 6. Blackledge, R. D. J. Chem. Educ. 1974, 51, 549. 7. Elderd, D. M.; Kildahl, N. K.; Berka, L. H. J. Chem. Educ. 1996, 73, 675. 8. Sodeman, D. A.; Lillard, S. J. J. Chem. Educ. 2001, 78, 1228. 9. Warnke, M. M.; Erickson, A. E.; Smith, E. T. J. Chem. Educ. 2005, 82, 1082. 10. Anzivino, B.; Tilley, L. J.; Ingalls, L. R.; Hall, A. B.; Drugan, J. E. J. Chem. Educ. 2009, 86, 55.
Supporting Information Available Complete experimental conditions, sources of materials, and additional gas chromatograms. This material is available via the Internet at http://pubs.acs.org.
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