Following the Scent: Development of 

Canine Training Aids Guided by Measurements

Bill MacCrehan, Stephanie Moore, Michele Schantz

Chemical Sciences Division, NIST
Why do we care?

• Canines are sensitive, selective, 

 mobile detectors 

• Outperform portable instruments

• Canine evidence challenged effectively in court

• Lit et al “Handler beliefs affect scent detection 

dog outcomes”

• Supreme Court currently questioning canine 

evidence in two cases
What can be done?

• Follow consensus training/certification “best 

practice” guidelines 

• Need a uniform, validated set of training/testing 

materials with well characterized properties

• Costs of real controlled substances = high

• Costs of non-hazardous training aids = low
How did we start?

A “snapshot” in time of the volatile content using SPME
Identical TATP Experiments Sampled with 

Fiber 1 (Solid Line) and Fiber 2 (Dotted Line)

0.0E+00

4.0E+08

8.0E+08

1.2E+09

1.6E+09

2.0E+09

0 10 20 30 40

Time (hrs)

TATP Peak Area

Characterizing Odor Release as a 

Function of Time with SPME

0.4% TATP on PRP-1

TATP on filter paper

Vapor-time profile for TATP materials (1.4 mg) 

using direct, automated SPME

Repeat Experiment

Moore, S., MacCrehan, W., Schantz, M., Evaluation of vapor profiles of explosives over time using ATASS (Automated 

Training Aid Simulation using SPME). Forensic Science International 212 (1-3); 90-95 (2011).
Characterizing volatiles in explosives as a function of time

. 

SPME with Externally-Sampled Internal Standard (SPME-ESIS)

Measure A/E ratio = Area Analyte/Area ESIS
0.0

0.2

0.4

0.6

0.8

0 20 40 60

A/E Ratio

Hours

C-4 M

C-4 G

Dynamic, 

asymmetric sampling

ESIS: 1-Oct 6 s

Analyte: 2-EH 5 min

SPME-ESIS of C-4 Explosive for

2-EH (plastic explosive odorant)

2-EH
Odorant laden particles

Permeation Devices

Particle/vapor delivery 

- via fine particles loaded with 

odorant(s) 

- trapped in the nose (not the 

lungs) and heated to 39 oC

Permeation tube/bag delivery (COMPS) 

- vapor release by diffusion through container

Training Aid Odor-Delivery Systems

Odorant infused polymer Odorant(s) infused (3 ways) into PDMS

- polydimethylsiloxane (PDMS), easily cast 

- clear, like firm Jello
0.0

0.2

0.4

0.6

0.8

0 20 40 60

A/E Ratio

Vapor Concentration ( g/mL)

Hours

1 % 2-EH on C silica 18

1 % 2-EH infused PDMS

0.1

0.0

0.2

0.3

Dynamic, symmetric sampling 6 s

ESIS: 1-Oct; Analyte: 2-EH

SPME-ESIS of Training Aids for

2-EH (plastic explosive odorant)
Dynamic, 

asymmetric sampling

ESIS: 13C3-TATP 30 s

Analyte: TATP 10 min

SPME-ESIS of 

Training Aids for TATP

2,4-DNT too!
Infusing Vapor Components into PDMS

• Direct vapor infusion

from complex hazardous

substances, i.e., 3 types 

of Semtex - no a priori

knowledge of 

composition required, 

i.e., marijuana

• Direct addition of vapor compound(s) to uncured polymer

• Absorbtion from solution of vapor compound

 Renders hazardous substances safe to handle

LCUV
controlled-release

holes

“infused” polymer

Controlled-release vapor canister

Infused PDMS as a Canine Training Aid
Conclusions

• Canine detection is highly useful for a wide range of mobile 

detection needs provided accuracy can be validated

• Important role for ‘best practices’ consensus standards

• Metrology can support development of technology for 

canine training aid development 

The Department of Homeland Security 

Science and Technology Directorate 

funded the production of the work 

presented in this material under 

HSHQDC-10-00297 with NIST.