Case Number 28400 Burning Down the House: A Case Study in
Forensic Instrumental Analysis
Written by
Adam M. Boyd and Randolph K. Larsen III
Department of Chemistry and Biochemistry
St. Mary’s College of Maryland
As Dr. Marie Stanforth steered her cumbersome SUV into an unoccupied space at the
scene of the latest fire in upstate Michigan, she instantly recognized the address. It was
the current residence of her ex-husband. Yet, with the same calm and collected demeanor
with which she approached every crime scene she ever visited, Dr. Stanforth confidently
opened the door of her car and walked purposefully towards the extinguished blaze.
Her boots crunched through a thin layer of snow as she trudged toward the scene. The
record cold—the coldest morning to date that winter—gave rise to a light snow slowly
blanketing the entire state for the first time that year. Marie marveled at how snow
seemed to cover everything in a forgiving white veil. “Poor jerk,” she thought to herself
as she approached the smoldering blaze with her hands tucked in the pockets of her
heaviest parka. “I wonder where he’s going to live now.” Before she reached the scene,
however, she was met by her partner, Adley.
“So what happened?” she dryly asked Adley as she tried to maneuver closer to the
extinguished blaze.
“There was a fire,” Adley recounted. “There was a real bad fire.”
“Thanks for the update, partner,” Marie laughed as she put her hand on Adley’s shoulder.
“Let’s have a look,” she added as she tried to push her way past Adley’s outstretched
arms. “Last time I checked we still got paid poorly to dig through ashes and play around
with chemicals in a lab…. Why are you blocking me?”
“I think there is something you need to hear,” said Adley as he grabbed hold of Marie’s
arm.
“Look,” Marie retorted, as she looked down at her arm and then pried it loose from
Adley’s grasp, “I know what you’re going to say. One of the higher-ups is going to take
me off this case because Thomas and I officially broke it off a little over 13 months ago.
Given my emotional state, yada yada yada, I shouldn’t have anything to do with the
investigation—got it. I just feel bad that he’s going to have to find someplace else to live.
Can we go do our jobs now?”
“It’s different than that, Marie.”
“How is it different? Look, Ad, newsflash: that was a year ago. It was over with Thomas
about four days after it got started, so if you don’t mind I’d like to have a look at the
crime scene before we both freeze to death.” With that Marie pushed past her partner and
walked intently toward the roped off scene.
“Tom is dead,” Adley half muttered, forcing out the words as he choked on them. “I
didn’t know how to tell you. He died in the fire.”
Marie turned slowly around to look her partner in the eye. Her head cocked to the side as
her grey eyes appeared focused on something off in the distance. “He’s dead? Tom is
dead?”
“He couldn’t make it out in time. Fire squad found him face down on his mattress. It
looks like he tried to make his way out of his room, but the smoke was too dense. We
won’t know exactly what happened until we get the autopsy back from the coroner. Look,
Marie, you’re already off the case. Chief already came down here first thing this morning
to make sure everybody knew. At the moment, the only thing you can do is go down to
the station and talk to the police. They want to question you.”
“What are you saying?” Marie asked despondently, hoping for Adley to change his story.
“You know what I’m saying,” said Adley, his breath clouding up in front of his face as he
stared through her. “They want to question you about the fire. They think it was arson.
You’re a suspect.”
The final jab caught Marie off guard. Everything inside of her wanted to scream—her
impeccable service record would be stained by unfounded charges. Instead she looked
weakly at Adley and then trudged slowly back to her car.
When Marie arrived for questioning at the police station, she reiterated her pleas of
innocence. “We’re on the same team, remember? I’ve been putting away bad guys for ten
years, and now I’m a suspect? We all know it’s some sick kid out for kicks on a Friday
night, or our serial guy who’s already lit up half of Michigan. I didn’t like Tom, but I
wasn’t going to burn down his house. Check with the lab,” Marie said as she stood up
from the table. “I can promise you that the results are going to show that it was either an
accident or a hasty gasoline fire started by some amateur with emotional problems.”
The detective looked over some files and then looked up at Marie. “Look, the fact of the
matter is you’ve got a clearly defined motive and the intelligence necessary to pull off
something like this. The victim’s mother is downright convinced it was you. She says
you’ve just been biding your time before you took a chance at doing some damage. Either
way, the fire burned almost the entire house to the ground. So we either got one heck of
an accidental fire on our hands or somebody made sure that fire finished what it started.
We’re not ruling anyone out until we hear back from the lab.”
You are a principal forensic chemist for the FBI. It is your job to analyze charred samples
recovered from the crime scene and a clothing swatch obtained from Dr. Stanforth. You
will analyze the samples for accelerants and compare your findings to standards of
common propellants that are often used to start fires. You should devise a justified
methodology for performing a qualitative analysis of the samples. Based on your
findings, Adley and the fire investigators will be able to determine whether the fire was
the result of arson and if charges leveled against Marie are credible.
Based on a report provided to you by Adley, you must analyze one cloth sample
recovered from a glove found in Dr. Stanforth’s trunk and three charred samples
collected from the scene of the crime as follows:
SAFETY
This forensic investigation will involve the use of gasoline, charcoal lighter fluid,
Coleman lantern fuel, and isopropyl alcohol. Prior to lab look up the MSDSs for these
chemicals and report the safe handling and disposal in your pre-lab.
Pre-lab: Include the experiment name, the purpose of the experiment, the major
experimental steps used to achieve this purpose and a summary of the safety precautions
for dealing with gasoline, charcoal lighter fluid, Coleman lantern fuel, and isopropyl
alcohol. In addition, answer the following questions:
1. What is the legal definition of arson?
2. What types of evidence have been used to convict individuals of arson? How will
you be able to tell if arson has been committed?
3. What is the significance of the term “point of origin”?
Background section: Explain how mass spectrometers work.
Introduction to GC-MS
A typical GC-MS. An HP 5970 was used in this experiment. Although this GC-MS is shown with an auto
sampler, injections were performed manually, at the injection port shown.
In gas chromatography (GC), a sample is transported through a chromatography column
by a gas mobile phase, called the carrier gas. When a volatile or semi-volatile liquid
sample is injected into the heated injection port of the GC, the sample volatilizes into a
gas and is swept out of the injection port and through the column via the carrier gas.
Because the components of a mixture move through the column at different rates based
on their affinity to the column material, they are said to have different retention times.
These retention times can be used to help identify components of the sample.
Mass spectrometry (MS) is an analytical technique in which atoms or molecules from a
sample are ionized, separated according to their mass to charge ratio, and then recorded.
In mass spectrometry, molecules are bombarded with high energy electrons. When an
electron with a sufficient amount of energy collides with a sample molecule, it dislodges
an electron from the sample molecule and creates a molecular ion called a cation ion
radical. The cation radical is positively charged and has an odd number of electrons but
has basically the same mass as the uncharged parent compound because the mass of an
electron is negligible. The positively charged ions are then directed into an analyzer tube
surrounded by a magnet. Given that different fragments will be formed, and they will
have different sizes, particular types of cationic species will have characteristic mass-tocharge ratios (m/z). A mass spectrometer scans all the m/z values and gives a distribution
of positive ions, called a mass spectrum, which is characteristic of a certain compound.
The most intense peak in the mass spectrum is called the base peak and is assigned a
relative intensity of 100.
When these two methods are coupled together into the same machine, we perform gas
chromatography / mass spectrometry or GC-MS analysis. Gas chromatography is used to
separate a mixture and mass spectrometry is used to analyze it. If we can selectively
monitor specific ions we can easily measure one component, for example an accelerant,
in a complex chromatogram of poorly separated compounds.
Introduction to Headspace Analysis
To recover and identify accelerants from charred debris, forensic chemists typically use
either headspace analysis or steam distillation. In headspace analysis, a portion of the
matrix (which contains the analyte) is placed in a glass tube, which is covered with a
rubber septum. When the tube is heated, volatile residue present in the debris will
vaporize and will be enclosed in the air space above the sample in the tube. The vapor
can be removed with a syringe and subsequently analyzed by gas chromatography. There
are three different types of headspace analysis (Grob, 1995):



Static Headspace
o Sample is heated to increase vapor pressure of analyte and gaseous sample
collected with syringe and analyzed via gas chromatography
o (+) Detection limit: 5–10 microliters of petroleum accelerant in gallon can;
ease of application
Passive Headspace
o Accelerant vapors are diffused from sample onto an absorbent placed
inside the container of fire debris.
o Accelerants are desorbed with carbon disulfide
o SPME (Solid-Phase Microextraction) An alternative passive headspace
sampling technique for gasoline in fire debris. SPME is a simple,
solventless extraction procedure in which a phase coated fused silica fiber
is exposed to the headspace above the fire debris packaged in a closed
container. SPME has been able to detect .04 microliters of gasoline in a
quart can.
o (+) multiple samples can be taken from one sample matrix, Teflon strips
can be frozen for later analysis
o (-) carbon disulfide can interfere with FID (Flame Ionization Detector)
Dynamic Headspace
o Air or inert gas is passed over the sample (purge and trap technique if
sample is liquid) and adsorbed onto a substance such as activated carbon.
After the accelerant has been adsorbed onto the carbon, it is often
extracted with carbon disulfide. Thermal desorption is not practical
because of the high temperature needed to remove hydrocarbons from
charcoal (950°C). In one version of this technique, chemists purged a can
containing fire debris with heated nitrogen. The nitrogen then passed out a
hole in the lid of the container and through a Pasteur pipette packed with
activated charcoal. The accelerant was then desorped from the charcoal
with carbon disulfide and subjected to GC analysis.
o (+) more sensitive than static headspace, and not as cumbersome as
distillation methods
o (-) does not give good recoveries of high petroleum distillates, such as
diesel fuel
Exploration: 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. The conditions for the run have been set for
you.
5. While you are waiting for your turn on the instrument, access the following web
page: http://www.shsu.edu/%7Echm_tgc/sounds/GC-MS.mov and answer the
following questions:
1. What parts are there on a GC/MS?
2. What temperature is your oven heated to? (You may have to wait until it
is your turn on the instrument to answer this question.)
3. What parts (from #1) are in the oven?
4. What happens to your sample after it is shot in the instrument?
5. Why does your sample have to be ionized? (What does it mean to be
ionized?)
6. Is it possible to recover the sample you shot in at the beginning of the
instrument at the output of the instrument? What implications does this
have in forensic investigations?
7. How will you know what your sample is (identity)?
6. Between samples, students should continually aspirate the syringe to ensure that
previous accelerant vapor does not contaminate successive standard runs.
7. 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.
8. 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.
9. The chromatograms and mass spectra for the different samples that you and your
colleagues run will be distributed to the class.
In your lab report you should 1) determine if the fire was the result of arson, 2) determine
whether Dr. Stanforth can be ruled out as a potential suspect, and
3) justify and explain your conclusions.