Analysis of Residues

1. Analysis of Residues

2. Laboratory Analysis of Debris andOther Samples 1. Preparation of Liquid Samples: • Liquid samples are simply drawn into a special syringe and injected into a gas chromatograph (GC) 2. Preparation of Fire Debris samples: • There are four commonly used methods to separate or concentrate any ignitable liquids from fire debris samples: heated headspace, steam distillation, carbon strip or tube absorption, and solvent wash

3. Laboratory Analysis of Debris andOther Samples i. Heated Headspace: • The paint can containing the fire debris is punctured with a nail, the hole covered with tape, and the can incubated for 1+ hours at 70-80 °C • After removing the can from the oven, the headspace vapor is quickly sampled with a gas-tight syringe and immediately injected into a GC • Advantages: simple with minimal handling • Disadvantages: not for trace amounts of ignitable liquid residues

4. Laboratory Analysis of Debris andOther Samples ii. Steam Distillation: • Debris is placed into a flask and either water or ethylene glycol added • The flask is attached to a distillation apparatus and brought to a boil • The condensate is collected, and if any ignitable fluids are present, it will separate into a second discernible liquid phase • Disadvantages: time-consuming and risk of contamination

5. Laboratory Analysis of Debris andOther Samples iii. Carbon Strip or Tube Absorption: • Uses activated carbon to absorb hydrocarbon vapors • A strip is suspended above the debris & the can is heated to vaporize the residues • Hydrocarbons are removed from the strip by a solvent wash, which can be analyzed directly by GC • A very sensitive technique

6. Laboratory Analysis of Debris andOther Samples iv. Solvent Wash: • Fire debris is placed into a flask, solvent added, mixed and allowed to sit for a period of time • The solvent is separated from the debris, then analyzed as with the other approaches • Works best for high boiling point ignitable liquids that cannot be easily vaporized

7. Laboratory Analysis of Debris andOther Samples 3. Laboratory Examination of Prepared Samples: • Gas chromatography separates mixtures of compounds by a partitioning process between a mobile and a stationary phase • Ignitable fluids such as gasoline produce a very complex pattern of peaks

8. Laboratory Analysis of Debris andOther Samples • Different ignitable liquids will produce very different GC patterns • A library of patterns is obtained from known standards of all possible accelerants • With fire debris samples, many of the most volatile components tend to be lost • The GC chromatograms can be compared to give an indication of the type of accelerant used, but the GC should not be considered an identification technique

9. Laboratory Analysis of Debris andOther Samples • Individual peaks from the GC can be identified using a mass spectrometer (MS) • As compounds reach the end of the GC column, they pass into the MS • The MS bombards the compounds with high energy electrons, fragmenting the compounds and yielding a mass spectrum that can be used to identify the compound

10. Classification of Ignitable Liquids

11. Laboratory Analysis of Debris andOther Samples • Comparison specimens are samples of the surface or substratum on which ignitable liquid residues might be present • Natural and synthetic materials may contain volatile compounds that produce GC peaks when heated or extracted • Specimens should be collected from unburnt areas of the fire scene