Analysis of Residues
Laboratory Analysis of Debris and
Other 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
Laboratory Analysis of Debris and
Other 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
Laboratory Analysis of Debris and
Other 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
Laboratory Analysis of Debris and
Other 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
Laboratory Analysis of Debris and
Other 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
Laboratory Analysis of Debris and
Other 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
Laboratory Analysis of Debris and
Other 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
Laboratory Analysis of Debris and
Other 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
Classification of Ignitable Liquids
Laboratory Analysis of Debris and
Other 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