Figure 1—Detailed Methods

Lab Preparation

Preparation of Charred Samples

1. Pine wood should be cut into small pieces approximately 3 cm long and 1 cm wide. A piece of craft board which is ¼″ thick by 3″ wide and 3′ long easily yields enough wood pieces for several large lab sections.
2. About ten pieces of the finely divided pine wood should then be placed into four different 125 mL Erlenmeyer flasks.
3. Using a disposable Pasteur Pipette, deliver 10 mL of accelerant to its corresponding flask. Enough accelerant should be added so that the wood chips are able to soak up the accelerant, but accelerants (particularly gasoline) should not be added in great excess. After adding accelerant, stopper each flask with rubber septa.
4. Leave the wood chips to soak for 2–6 hours.
5. After the wood chips have soaked for several hours, pour the excess accelerants out of each Erlenmeyer flask, and discard the excess accelerant in the appropriate waste container.
6. Either in a hood, or outdoors, place the wood chips on a large watch glass and ignite the chips with a match. Take care not to drop the match in the wood chips and allow it to burn with the chips.
7. After the chips are mostly charred, extinguish the fire by blowing out the flame, and allow the chips to stop smoking. Immediately after the wood chips have stopped smoking, take small pieces of the chips and place them in a small labeled container.

Preparation of Clothing Swatch

1. Soak the clothing in the accelerant of your choice and allow it to dry. Place inside a labeled vial as unknown #4.

Preparation of Standards

1. Using a disposable Pasteur pipette, add 10-20 mL of each standard accelerant into labeled vials and secure lid.

Materials

1. Samples of gasoline, isopropyl alcohol, Ronsonol lighter fluid, and Lamplight lamp oil were purchased from local vendors and used as received. Pine wood was obtained from a local vendor and cut into small pieces according to specifications listed above.
2. A 100 micro Liter airtight syringe, with a Teflon tip plunger, from Agilent Technologies (no. 5183-2058).

Running the Experiment

An HP mass detector 5973 and HP GC system 6890 was used in this experiment. The autosampler was removed to allow for manual injections.

GC-MS Settings

Running Samples

1. Amber vials containing standard accelerants should be placed in a 100°C hot water bath and allowed to warm for five minutes.
2. After the vial has been warmed, students should use the static headspace analysis technique to collect 100 μL of gas just above the liquid surface of the accelerant using an air tight 100 μL syringe.
3. The vapor should then be injected into GC-MS. In the case of manual injection, the student should take care to hold the plunger of the syringe down for one minute after the sample has been injected. This is necessary because the high vapor pressure of some accelerants will cause the gaseous analyte to escape if not forced onto the GC column.
4. Allow the GC-MS to complete run.
5. Between samples, students should continually aspirate the syringe to ensure that previous accelerant vapor does not contaminate successive standard runs.
6. After the chromatograms for the standard accelerants have been collected, students should collect chromatograms for the four unknowns, repeating steps 2–6 after warming each unknown vial in a 100°C warm water bath for five minutes.
7. Software integrated with the GC-MS allows for total ion current chromatograms to be analyzed almost immediately after the mass spectra are stored in the computer. Once a peak is obtained it is possible to pull up the mass spectra at any retention time on the chromatogram. A library search can then be performed against that mass spectrum to give insight as to the chemical composition of the injected sample.

Hazards

1. Caution must be used when handling flammable accelerants. It is especially important to remove all excess accelerant from wood chips before ignition.
2. Proper eyewear, gloves, and a lab coat should be worn while in lab.