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Headspace SPME → GC-MS Workflow

Run the Headspace SPME → GC-MS Workflow Fullscreen

About This MicroSim

After a suspicious fire, investigators want to know whether an accelerant (gasoline, lighter fluid, kerosene) was used. The challenge is that accelerants are volatile — they evaporate quickly and are present only in trace amounts in the charred debris. The standard laboratory answer is headspace solid-phase microextraction (SPME) feeding a GC-MS.

This MicroSim walks through the five-station pipeline:

  1. Debris Collection — debris sealed in an airtight metal can at the scene
  2. Sealed Can (Headspace) — gentle warming drives accelerant vapors into the air space above the debris
  3. SPME Extraction — a coated fiber adsorbs the vapors with no solvent
  4. GC-MS Injection — the fiber is desorbed onto the GC column; the MS identifies each compound
  5. Chromatogram — the peak pattern is matched to a reference accelerant

How to Use It

  1. Click each station to read its purpose and why that step matters.
  2. Watch the Sealed Can station: orange vapor molecules rise from the debris into the headspace, and the saturation bar fills as vapor accumulates. Press Replay Vapor to restart the animation.
  3. In the Chromatogram, click any peak to reveal its compound name and retention time.
  4. Read the Reference Match panel — the questioned sample's peak pattern is matched against a reference accelerant standard.
  5. Use the Accelerant selector to switch between Gasoline, Lighter Fluid, and Kerosene and watch the whole peak pattern change.

What You Can Learn

  • Explain each stage of the SPME-to-GC-MS workflow and how the physical procedure connects to the analytical output.
  • Explain why sealing and warming the can concentrates volatile accelerant vapors so a solvent-free fiber can sample them.
  • Interpret a chromatogram by its pattern of peaks — a tight aromatic cluster (gasoline), light n-alkanes (lighter fluid), or a heavy n-alkane series (kerosene).

You can embed this MicroSim on your own web page with this iframe:

<iframe src="https://dmccreary.github.io/forensic-science/sims/headspace-spme-workflow/main.html"
        width="100%" height="502" scrolling="no"></iframe>

Lesson Plan

Audience: High-school forensic science (grades 9–12) Time: 15–20 minutes Bloom level: Understand (L2) — explain.

Worked example. Click through all five stations in order and have students narrate the journey of a single accelerant molecule from the debris to a peak on the chromatogram. Then click the tallest peak and read its identity.

Guided questions:

  • Why is the debris sealed in an airtight can instead of a bag or open tray?
  • What does "headspace" mean, and why does warming the can help?
  • Switch from Gasoline to Kerosene. How does the peak pattern change, and what does that tell you about the kinds of molecules in each accelerant?

Extension. SPME uses no solvent. Why is a solvent-free extraction an advantage when you are trying to detect a tiny amount of accelerant?

References

Specification

This MicroSim was generated from a specification in Chapter 10: Fire Investigation, Arson, and Explosives.

Design note: the chromatograms are schematic — each accelerant is drawn as a sum of Gaussian peaks from a representative peak table (retention time, compound, relative height). The patterns capture the real character of each accelerant class (gasoline's aromatic cluster, lighter fluid's light alkanes, kerosene's heavy n-alkane series) but are illustrative, not instrument data.