Odor detection has become a focused
area of research because of its importance
to the forensic, law enforcement,
and legal communities. Despite
the abundance of methods for the
detection of these characteristic
chemical odors, the use of trained
canines as biological detectors remains
widely accepted. Thus, detector dog
response is one of the major applications
involved in odor detection studies,
both to determine the chemical
signature of individual odors to which
the canines are actually alerting, and
to discover if there is a common element
within different items to support
the use of contraband mimics.
Previous research has demonstrated
that a compilation of chemical odors
can be detected in individual contraband
samples, including several
common odors as well as uncommon
odors.1,2 Current commercially available
pseudo aids contain different
amounts of either the actual explosive/narcotic or the chemical compound
of suspected interest by canine detectors.
The main chemical compound
in a substance is not always the dominant
volatile compound due to the
low vapor pressure or limited olfactory
receptor response.3 In addition, it has
been shown that only specific odors
are used by canines to detect the various
forms of contraband.
Narcotics detection
Detector dog teams are trained to
detect most commonly found illicit
narcotic substances (i.e., marijuana,
heroin, cocaine, and methamphetamines).
It has been shown that canines respond to volatile organic
compounds (VOCs) in the headspace
above the drug instead of the
parent compound itself. One case
in which this has been proven is for
cocaine. Field tests have shown that
the trained law enforcement detector
dogs respond to the compound methyl
benzoate.3–5 This implies that methyl
benzoate must be the dominant odor
chemical signature for cocaine.
The headspace above marijuana has
been repeatedly sampled and shown to
possess a complex array of organic compounds.
This list includes α-pinene;
β-pinene; myrcene; limonene; and, in
many cases, β-caryophyllene. These
compounds have been shown to dominate
the headspace of marijuana samples
(upwards of 85%6–8). In a similar
manner, it has been conjectured that
acetic acid is the dominant odor compound
in heroin samples.
Explosives detection
Classification by chemical groups
is a common method, especially for
research purposes. This is done by
classifying explosives into one of the following five groups: organic nitrates
(which include aliphatic nitro and
aromatic nitro), nitrate esters, nitramines,
acid salts, and peroxides.1,2
As with drugs, canines respond to
VOCs in the headspace above explosives
instead of the parent compound
itself. An example is single-based
smokeless powder, in which the main
compound is nitrocellulose, an involatile
compound. However, certain
common odors, including 2,4-dinitrotoluene
(2,4-DNT), 2,6-dinitrotoluene
(2,6-DNT), and diphenylamine
(DPA—a stabilizer), and uncommon
odors, such as ethyl centralite (a stabilizer),
have been found to be present
in these smokeless powders.1,2,9,10 The
compound identified as the canine
active odor for single-based smokeless
powders is 2,4-DNT.
Methodology
All solvents were purchased from
Fisher Scientific (Pittsburgh, PA).
The compounds used to create the
field samples were purchased from
Sigma-Aldrich (St. Louis, MO).
A 70-μm StableFlex Carbowax®/divinylbenzene (CW/DVB) solid-phase
microextraction
(SPME) fiber
was purchased from Supelco (Bellefonte,
PA). The samples were presented
using Sigma Pseudo scent
cages. The commercial narcotic
pseudo scents were Sigma Pseudo
Narcotic scents. Nonhazardous
explosives for security training and
testing (NESTT) samples utilizing
the silica form were purchased from
Ray Allen Manufacturing Co. (Colorado
Springs, CO). Headspace vials
(40 mL) fitted with phenolic plastic
caps and a PTFE/silicon septum were
purchased from Supelco. Sterile 5.1 ×
5.1 cm gauze sponges were obtained
from IMCO (Independent Medical
Co-op, Inc., Daytona Beach, FL).
The GC-MS analysis was performed
on an Agilent 6890 series with HP
5973 quadrupole mass spectrometer
(Agilent Technologies, Wilmington,
DE). An HP5 30 m × 0.25 mm
capillary column (Agilent) with
25 μm film thickness and a helium
flow rate of 1 mL/min was used. The
injection port was held at 235 °C
with 5-min SPME desorption. The
MS temperature was 230 °C. The
oven program began with a 40 °C
hold for 5 min, followed by a 10
°C/min ramp to 290 °C, and ending
with a 1-min hold at 290 °C. A
1.2-min solvent delay was used. Two
standard solutions were made for
each compound at 100 ppm and 50
ppm with dichloromethane.
For the Sigma Pseudo scents, 5 g
was weighed and heat-sealed within
3-mm low-density polyethylene
(LDPE) bags. Two spiked gauzes
were prepared (mixture A and
mixture B) comprised of 50 μL
each of five compounds: α-pinene,
β-pinene, myrcene, limonene, and
β-caryophyllene. Both types of
samples were placed in the Sigma
Pseudo scent cages on site for testing.
For the NESTT canine field
trials odor delivery system, 5 g of
each sample contained within an
open vial was placed inside a sterile
quart can.
For the dissipation study, 50 μL of a
compound (each in turn) was spiked
onto a single piece of gauze. The mass
of the gauze was recorded prior to
spiking and immediately afterward.
The mass was then recorded over a
period of 30 min at 0.5-min, 1-min,
and 5-min intervals. The process
was repeated in triplicate. Statistical
analysis was performed, and the results
were plotted.
Results
Table 1 - Field testing of heroin mimics
Field experiments were conducted
with certified law enforcement drug
detector dogs. The scent cages were
arranged in a line such that each sample
was approximately 1 m apart. Each
detector dog team was allowed to walk
the line and sample the odor emanating
from each cage. The handlers were
not informed of the contents of each
sample prior to the run. In addition to
the two samples, blank gauze sealed in
a 3-mm LDPE bag was included as a
negative control. As shown in Table
1, no canine alerted to the 5-g sample
of the Sigma Pseudo Heroin scent.
Canine 112 showed interest in the
sample. Only one canine alerted (8%)
to the acetic acid sample.
Table 2 - Field testing of marijuana mimics
A similar setup was used for the marijuana
pseudo sampling. Each detector
dog team was allowed to walk the
line and sample the odor emanating
from each cage. In addition to
the target odors, empty scent cages,
blank gauze sealed in a 3-mm LDPE
bag, and a dichloromethane sample
were included as negative controls.
The results of the marijuana pseudo
testing are shown in Table 2. None
of the detection teams alerted to the
Sigma Pseudo Marijuana scent. The
mixtures were composed of previously
reported headspace components
of marijuana samples. None of the
canines alerted to either of the mixed
spikes. In addition, no false positives
can be reported.