Not with a bang: Canine training aids for explosives

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  • Published: Oct 3, 2011
  • Author: Steve Down
  • Channels: Gas Chromatography
thumbnail image: Not with a bang: Canine training aids for explosives

Sniffing studies

It is widely regarded that dogs remain the best instruments for detecting explosives, in spite of recent advances in sniffer devices and other volatile profiling aids. But it comes at a high cost, that of training the animals so that they can recognise an explosive when they encounter it.

As noted by a team of US government scientists, safety requirements place great demands on the training teams, as would be expected for work with explosives, but safer training aids have been designed using diluted explosives. One problem with these is to establish whether or not they present the same volatile profile to the dogs as the neat explosives.

An additional concern is the evolution of the profile over time. Typically, the training aids are placed in the field in various containers, along with distracters and blanks, and might remain there for several hours during the exercise. Being volatile, it is likely that some components will escape into the air, altering the profile and, potentially, incorrectly training the dogs.

The US scientists have addressed these concerns by devising a method for assessing the training aids and comparing their volatile profiles with those of real explosives. William MacCrehan, Stephanie Moore and Michele Schantz from the US National Institute of Standards and Technology at Gaithersburg, MD, dubbed their method Automated Training Aid Evaluation using SPME (ATASS).


ATASS was designed to monitor selected volatile components which are thought to be of interest in canine explosives detection and was demonstrated for three explosives: C-4, 2,4-dinitrotoluene (DNT) and triacetone triperoxide (TATP).

The dilute training aids were prepared by coating an octadecylsilica chromatographic support with 1% by mass of DNT or TATP and 0.1% of C-4. They were analysed in closed containers or in paint cans open to the atmosphere to simulate training conditions in the field. Experiments were performed at room temperature and at the canine basal temperature of 40°C.

The vapours from the training aids and the headspaces of the pure explosives were sampled at intervals by SPME using a polydimethyl siloxane fibre for subsequent analysis by GC/MS with electron ionisation. The conditions were optimised for each of the three explosives and the volatile components were identified from their mass spectra.

The profiles of selected components of the training aids and the neat explosives were monitored for up to 120 hours and visualised as peak area chromatograms.

Accurate explosive canine training aids

Two of the three training aids, TATP and DNT, behaved in a similar fashion to their neat explosive equivalents, producing comparable volatile profiles but the position was less clear for C-4.

For military grade DNT, headspace SPME and GC/MS of a solid sample revealed the presence of several isomers 2,6-, 2,5-, 2,4-, 2,3- and 3,4-DNT as well as 4-methyl-3-nitroaniline (MNA) in the vapour.

In the open system in vials in the lab, the major components detected were 2,4- and 2,6-DNT both for the military grade material and the 1% training sample, with minor amounts of other volatiles.

For both samples, the levels of 2,6-DNT fell slowly over time, becoming undetectable after 100 h for the military grade explosive and 25 h for the training material. For 2,4-DNT, concentrations equilibrated after 20 h in both materials then stayed constant over the next 95 h.

Similar behaviour was observed for TATP. The 1% canine sample contained fewer impurities than were detected in the parent solution in acetone provided by the Bureau of Alcohol, Tobacco, Firearms and Explosives but dynamic experiments using a vial in the lab revealed that only TATP itself remained after 2.4 h.

TATP was released in detectable quantities for up to 25 and 30 h for the TATP solution and the 1% samples, respectively, and the peak area chromatograms had a similar shape for both.

With military grade C-4, ATASS studies in an open vial detected 2,3-dimethyl-2,3-dinitrobutane (DMNB) and diethyl phthalate, the latter possibly added as a plasticiser to the explosive or being present as an impurity from long-term storage.

However, during studies of the 1% C-4 canine sample, no peaks were observed at room temperature but low amounts of the two detectable components were found at 40°C. Comparison of the peak areas of DMNB between samples revealed a high relative standard deviation of 5-35%. Overall, ATASS is not suitable under these conditions for C-4.

A successful field trial was also carried out for TATP, using samples stored in paint cans. Despite the lower signals compared with the lab studies, both samples produced detectable signals for TATP for up to 50 h and the profiles were markedly similar.

So, ATASS can help to design canine training aids with volatile profiles that mimic those of real explosives in the field, ensuring that the sniffer dogs are trained correctly.

Before the system can be put into practice, further experiments are required to produce training aids with optimum performance. In addition, the experimental conditions for SPME and GC/MS should be optimised to reduce the current variation in peak areas and intensities between different experiments.

These improvements will go a long way to ensuring that ATASS can be applied in a dynamic, quantitative manner for the production of accurate explosive-containing canine training aids.



The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.


Evolution of the volatile profile of canine training aids containing explosives has been studied by an SPME-GC/MS system devised by US government scientists, which should aid in the design of training aids that correctly mimic real explosives
Image: courtesy K9

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