Patent Abstract:
the primary aspect of the controlled odor mimic permeation system is that it provides a field deployable instant and reproducible source of known amounts of target odors . this technology consists of a permeable polymer container , stored inside a non - permeable package . the design allows for the pre - equilibration of the target odors such that the outer surface of the inner package can saturate with odor during storage . removal of the inner item then provides an instant and reproducible source of known target vapor flux . we have successfully demonstrated this technology by placing the target odor chemicals within permeable membranes such as low density polyethylene which are then sealed within a non - permeable membranes such as metallized polyester . this design has multiple advantages including preventing cross contamination when storing multiple odor targets as well as being light - weight disposable , low unit cost potential , no external power / operating unit / machinery / hardware , simple to use and providing a known reproducible concentration of the target odors to the detector in the field . the applications of these comps include the whole range of biological and electronic detectors with examples such as explosives , drugs , human remains and live human scent .

Detailed Description:
explosive standards were obtained from cerilliant ( round rock , tex .) including epa method 8330 components ( nitrobenzene , 1 , 3 - dinitrobenzene , 1 , 3 , 5 - trinitrobenzene , 2 - nitrotoluene , 3 - nitrotoluene , 4 - nitrotoluene , 2 , 4 - dinitrotoluene , 2 , 6 - dinitrotoluene , 2 , 4 , 6 - trinitrotoluene , rdx , hmx and tetryl ) and edgn , trinitroglycerin and petn . explosive training aid samples were sampled from local and state law enforcement agencies , including miami dade police department bomb squad , florida international university police department k9 unit , palm beach county sheriff &# 39 ; s office bomb squad and k9 division , and florida highway patrol k9 division . nestt training aids were purchased from ray allen manufacturing company ( colorado springs , colo .). trinitroglycerin was in the form of a package of trinitroglycerin tablets ( 25 × 0 . 4 mg dose ). selected smokeless powders were purchased from a local outdoor & amp ; hunting store . smokeless powder samples were also donated from rifle patrons at a south florida gun range . headspace vials ( 4 ml and 10 ml ) fitted with phenolic plastic caps and a ptfe / silicon septum , solid phase microextraction fibres and fibre holders , abc autosampler vials ( 2 ml ) were purchased from supelco ( bellefonte pa .). steel quart and gallon sized paint cans were obtained from all american containers ( miami , fla .). metal electrical junction boxes , 4 ″× 4 ″× 2 ″ were purchased from a local hardware store . sterile cotton gauze , 2 ″× 2 ″, was purchased from independent medical co - op ( daytona beach , fla .). plastic heat seal bags were obtained in 1 . 5 , 2 . 0 , 3 . 0 and 4 . 0 mil low density polyethylene , 2 . 0 mil polypropylene , and cellophane chemistries . aluminised kapak bags were purchased separately from kapak ( st louis minn .). explosive samples ranging from 0 . 25 g to 1 . 0 g of explosive were placed inside 10 ml glass vials from supelco and capped with silica / ptfe septa . smokeless powder samples ranged from 2 . 0 g to 3 . 0 g were prepared in a similar fashion . the nestt aids were measured out to 3 . 0 g and again placed inside a 10 ml glass vial , and capped . for extractions performed at room temperature , the explosive samples were stored on the laboratory bench , and a clamp stand used to support the spme fibre holster above the vial . the spme holsters with the variation needle were set to 2 . 4 cm , which permitted approximately 2 cm of fibre to enter the headspace of the vial , preventing contact between the fibre and the sample . extractions performed at elevated or depressed temperatures were performed in hot water , or iced water baths respectively . the hot water bath was constructed from a beaker of water resting on a hot plate . a thermometer was used to monitor the bath temperature , and polystyrene beads placed on the surface of the water bath to minimalise evaporation . the water temperature was observed prior to introducing the explosives , to ensure that a steady temperature was achieved . the ice water bath was constructed from an insulated polystyrene foam container filled with ice and water . again a thermometer was used to monitor bath temperature . in both cases a clamp stand was used to support the thermometer , to hold the vial in the water bath , and to support the spme holster . the headspace of the sample was then extracted using the spme fibre . the fibre was inserted through the septum and exposed approximately 1 . 0 cm above the sample within the closed vial for the allotted time , prior to immediate gc analysis . the general volatiles spme - gc - ms method used a 70 um stableflex ™ carbowax ®/ divinylbenzene ( cw / dvb ) spme fibre from supelco ( bellefonte , pa .) to sample the headspace at ambient temperature with injections into a supelco ® spme liner at 235 ° c . the spme exposure time was optimized to 30 minutes for the high explosives and 15 hours for the low explosive powders . the gc - ms used was the agilent 6890 - 5973 combination running chemstation software . the column used was an hp5 30 m , 0 . 25 mm i . d ., 25 μm film thickness column also obtained from agilent . the injection port was held at 220 ° c ., with a 5 minute spme desorption . the oven program was a 40 ° c . hold for 5 minutes followed by a 10 ° c ./ minute ramp to 280 ° c ., with a 1 minute hold at 280 ° c . the carrier gas was helium at 1 . 0 ml / minute . the ms was operated in electron ionization ( ei ) full scan mode from 50 amu to 500 amu , with a 1 minute solvent delay . the explosive specific spme - gc - ecd method used a 100 um polydimethylsiloxane ( pdms ) spme fibre from supelco with an exposure time of 5 minutes with injections into a 1 mm restek ® deactivated liner at 235 ° c . the gc used was an agilent 5890 with ecd . the column employed was a 6 . 0 m 0 . 53 mm i . d ., 1 . 5 μm film thickness restek ( bellefonte , pa .) rtx ®- tnt column , a specialist column for explosives analysis . the injection port was held at 250 ° c . with a 1 second desorption . the oven program began with a 1 minute hold at 80 ° c ., followed by 10 ° c ./ minute ramp to 180 ° c . this was followed by a 30 ° c ./ minute ramp to 300 ° c . and finished with a 3 minute hold at 300 °. the carrier was helium at 15 ml / minute with a nitrogen 60 ml / minute makeup in the ecd . the detector was held at 330 ° c . with anode purge . having confirmed the multiple presences of certain suspected odor chemicals , field trials were arranged with local law enforcement agencies that were operating trained and certified explosives detection canines . the odor chemicals were prepared as acetonitrile solutions . the acetonitrile was obtained from fisher scientific ( pittsburgh , pa .) and the odor chemicals ordered from sigma aldrich ( milwaukee , wis .). solutions at 1000 and 100 , 000 ppm ( mg / l ) were prepared . 100 μl aliquots of the solutions cold then be used to apply 0 . 1 mg and 10 mg respectively , of the odor chemical to test substrates . the 100 μl of acetonitrile was shown to evaporate within 90 minutes leaving a residue of the odor compound . typical odor delivery substrates were 125 mm filter paper , or 5 . 1 cm × 5 . 1 cm gauze sponge heat sealed within a 2 mil low - density polyethylene ( ldpe ) bag . negative controls were applied , including the acetonitrile solvent and uncontaminated filter papers & amp ; gauze . the odor aids were presented to the canines in metal electrical boxes that had been previously cleaned with soap , then rinsed with water and baked at 200 ° c . overnight . the odor chemicals detected were then presented to the canines in an “ odor line - up ” of hide boxes . the electrical boxes were placed 1 . 5 m apart along a floor surface and presented to the canines . the detection canines would then walk the boxes , with the handlers ensuring that the canines detailed each box with a sniff directly above it . the handlers were not informed of the content of the electrical boxes , and there was no specific marking to indicate the contents . one box contained the suspected odor chemical , other boxes contained distracters or negative controls including the acetonitrile solvent . a positive control , usually actual explosive material provided by the police agency , was presented separately , also in a hide box . the order of the hides , to contain the blank / test odor / controls , was randomised to prevent assumption or guessing from the handlers . 45 certified police detection canines participated in this study , although actual numbers at each field test ranged from four to fourteen on any given day . each canine was assigned a three digit identification to assure anonymity in reporting the results . the complete range of nestt aids ( including the blank distracters ) were obtained and placed in the same metal hide boxes used in the field trials above . again , negative ( the blank distracter ) and positive ( real explosive ) controls were made available separately . having identified several chemicals as potential target odors for explosives detection canines , attention was focused towards developing a method of controlled delivery of the odor to the canines during training . initial compounds utilized were 2 , 4 - dinitrotoluene , reported as a vapour target for tnt explosive , and 2 - ethyl - 1 - hexanol , a target for c - 4 and other plasticized explosives . 10 % solutions of 2 , 4 - dinitrotoluene and 2 - ethyl - 1 - hexanol in acetonitrile were prepared , and 100 pt of the solutions spiked onto a 2 ″× 2 ″ sterile cotton gauze . the gauze was left to sit for 90 minutes to allow the acetonitrile solvent to evaporate to dryness . the gauze was then heat sealed inside 3 ″× 3 ″ plastic bags of different polymer chemistry , and monitored gravimetrically over time . the plotted results of mass loss over time allowed calculation of diffusion rates of the odor compounds through the plastic membranes . the controlled odor mimic permeation system ( comps ) tnt mimic was produced by diluting 2 , 4 - dinitrotoluene with 400 mesh silica powder to 5 % w / w . 5 . 0 g of 2 , 4 - dinitrotoluene was powdered in a mortar and pestle to reduce particle size and added to 95 g of silica . the powders were mixed in a large vessel using a magnetic stirrer bar for 1 hour . the resulting mixture was then weighed out into 25 g portions , which were packaged and heat sealed within 2 . 0 mil ldpe bags . the training aids made using the ldpe bags were then stored in a sealed paint can and transferred to the trainer for use in the field testing . all preparation was conducted wearing nitrile gloves to avoid human scent contamination of the aids . the odor compounds chosen for version 1 are listed in table 93 . 10 . 0 mg of each chemical was deposited on individual cotton gauze and sealed in permeable polymers for clean , controlled delivery . the cotton gauze aids were prepared in a similar fashion to the dissipation study in 0 . 10 % w / v solutions of the odor chemicals were prepared in acetonitrile . 100 μl of the solutions were then spiked onto sterile cotton gauze , and left to sit for 90 minutes to allow the solvent residue to evaporate . the blank control distracters were prepared using 100 μl of the acetonitrile solvent . for larger concentration of odor compounds , the amount of 10 % w / v solution was increased , and the evaporation time adjusted accordingly . for very large amounts , or for liquid odor compounds , the chemical cold be measured or weighed directly onto the gauze . the 3 . 0 mil lpde bags were used , to exploit the permeation of odor through the plastic which retaining a durability . the prepared aid was then stored and heat sealed within an aluminised kapak bag . all preparation was performed wearing nitrile gloves . optimisation of the fibres suitable for gas chromatography ( those stable to the high temperatures of the injection port ) was performed . from the recommended applications in table 13 it follows that those fibres suited for odors and flavours ( dvb / car on pdms ) and volatiles ( pdms and pdms / dvb ) may be best suited to the analysis of the chemical headspace of explosives , although all fibre chemistries were tested . the headspaces of tnt and c - 4 samples , were extracted in triplicate using the selection of fibres . the exposure time utilised was 15 minutes and the injection port temperature set to 235 ° c . the general volatiles method detailed in paragraph [ 0092 ] was used , such that the only variable observed was the specific fibre chemistries . table 15 and table 16 present the peak areas of the odor chemicals extracted for tnt ( 2 , 4 - dinitrotoluene and 2 , 4 , 6 - trinitrotoluene ) and c - 4 ( 2 - ethyl - 1 - hexanol and 2 , 3 - dimethyl - dinitrobutane ) respectively . the standard deviation between the triplicate extractions for each odor compound / spme chemistry is denoted by the error bars . it can be shown that whilst the pdms and pdms / dvb exhibited the most efficient extraction of the tnt odor compounds , the pdms was not so suited to the c - 4 headspace . conversely , the dvb / car / pdms and pa performed poorly for tnt odor yet gave large peaks for the c - 4 sample . certain fibre chemistries such as 7 um pdms and car / pdms did not extract certain odor compounds for c - 4 and tnt respectively . the cw / dvb performed well for both the tnt and c - 4 samples . additionally the reproducibility of the cw / dvb was observed to be better than that of the other fibres , denoted by the smaller deviation between samples . the cw / dvb was chosen as the best universal fibre for the gc - ms method . this study was in good agreement with a previous optimisation conducted during an earlier project , which concluded that cw / dvb and pdms were the best suited fibres for explosive headspace extraction , in laboratory and field environments respectively [ 46 ]. an additional benefit of the cw / dvb fibre chemistry is its short conditioning time of 30 minutes at 220 ° c ., compared with other fibres that can extend to 4 hours at 320 ° c . ( dvb / car / pdms ). headspace spme sampling involves a three - way equilibrium between the concentrations of the target analytes in the sample , the sample headspace , and the spme fibre surface . frequently the headspace collection is performed at non - equilibrium conditions , whereby the exposure time of the spme fibre is insufficient to achieve equilibrium , however detectable levels of analyte are observed . the concentration of analyte upon the fibre surface increases steadily , proportional to the length of exposure up to a certain maximum point ; at which point the concentration can then be seen to reduce before achieving equilibrium . headspace spme is also competitive , with headspace components vying for a limited space on the fibre surface . smaller , lighter volatiles absorb / adsorb fastest , with the larger , less volatiles compounds following at a slower rate . longer exposure times will thus favour the heavier analytes , whereas shorter exposures will favour lighter elements of the headspace . studies with tnt explosive revealed that maximum extraction was obtained after 120 minutes , after which analyte concentrations were observed to drop off . examination of the peak shapes during gc data analysis reveal peak tailing at longer exposure times , as a result of overloading or slower thermal desorption . it was chosen that an exposure time of 30 minutes was sufficient to provide useful headspace data for the explosive samples ; however longer exposures of 60 to 180 minutes cold be used for samples that did not exhibit abundant headspace chemistries . extractions of 18 hours were also considered for explosives with low vapour pressures , although overloading of the more volatile components was observed in such circumstances . the exposure temperature of the headspace extraction clearly has the potential to affect the profile and peak abundance of chemicals collected . a short study to confirm this expectation was performed using an inert tnt training aid from nestt . headspace samples were collected at 0 ° c ., 25 ° c ., 50 ° c ., 75 ° c . and 100 ° c ., using a cw / dvb fibre , with exposure times of 1 and 30 minutes . the gc - ms general volatiles method was used . as expected , the ratio of 2 , 4 - dnt / 2 , 4 , 6 - tnt was reduced as the less volatile 2 , 4 , 6 - trinitrotoluene was heated and volatilised , as visualised in table 18 and table 19 . with the exception of the 50 ° c . sample , which was indicative of the competitive extraction of heavier analytes over longer exposures , very little difference was noted in the ratios from the one and 30 minute samples . for the main study , the exposure temperature was set simply to room temperature , considered to be ˜ 20 ° c ., to achieve the realism of the average environment that an explosives detection canine might be working in . the injection port of the gas chromatograph is responsible for the thermal desorption of the analytes from the sme fibre . the operating range of the carbowax / divinylbenzene fibre is 200 ° c .- 250 ° c . with 30 minute exposures of c - 4 and tnt explosive at room temperature were compared in triplicate , at a range of injection port temperatures including 205 ° c ., 220 ° c ., 235 ° c . and 250 ° c . for the tnt samples , a difference in injection port temperature was noted , with an increase in 2 , 4 - dinitrotoluene peak areas as the injection port temperature increased from 205 ° c . to 235 ° c ., followed by a sharp drop in peak area at 250 ° c . it is proposed that the more efficient thermal desorption is countered by the thermal degradation before the analytes exit the separation column . there was very little difference in peak area for both the 2 - ethyl - 1 - hexanol and the 2 , 3 - dimethyl - 2 , 3 - dinitrobutane in the headspace of the c - 4 explosive , however the reproducibility of the peak areas for the 235 ° c . was significantly better than the other exposure temperatures . an injection port temperature of 235 ° c . was chosen as the optimal temperature for the spme - gc - ms method , balancing thermal desorption and thermal degradation . the analysis of the high explosives covered tnt and cast explosives , polymer bonded ( plastic ) explosives , and petn detonation cords . the cast explosives are commonly based around tnt and other aromatic nitrates whereas the plastic explosives generally involve the nitramine or nitrate ester explosives such as rdx and petn . three samples of tnt , plus one sample each of hdp - 1 sheet , composition b and a cast primer charge , used as canine training aids , were sampled from local law enforcement agencies , including miami dade police department ( mdpd ), palm beach sheriff &# 39 ; s office ( pbso ) and florida international university public safety ( fiu ). the odor headspaces , analyzed by spme - gc - ms , shown in table 22 , table 23 and table 24 were shown to contain the parent explosive 2 , 4 , 6 - trinitrotoluene in every sample , often in addition to 2 , 4 - dinitrotoluene ( 5 / 6 ), 2 , 6 - dinitrotoluene ( 3 / 6 ), 3 , 5 - dinitrotoluene ( 3 / 6 ) and 1 , 3 - dinitrobenzene ( 2 / 6 ) in several of the samples . the frequency of occurrence of the odor compounds is summarised in table 29 . incidentally , the cast primer was analyzed for content and shown to be tetratol , a combination of tnt and tetryl , but no tetryl was observed in the headspace . eight samples of polymer bonded explosive sampled from local and state agencies were also prepared for analysis ; two flex - x deta sheet samples , four composition 4 ( c - 4 ) samples , and one each of petn booster and tnt booster charges . following spme - gc - ms headspace analysis , no parent explosives , such as the rdx in the c - 4 or petn in the booster , were observed in the headspaces , as presented in table 25 , table 26 , table 27 and table 28 . 2 - ethyl - 1 - hexanol ( a common additive to plastic explosives ) was detected in five of the eight samples . other chemicals detected included the detection marker 2 , 3 - dimethyl - 2 , 3 - dinitrobutane or dmnb ( 6 / 8 ), and 2 - ethylhexanoic acid ( 2 / 8 ). cyclohexanone , phenol , acetic acid butyl ester , acetic acid 2 - ethylhexyl ester and citric acid tributylacetyl ester were all detected in one of the 8 samples , and as such were not considered common odors . cyclohexanone , a common recrystallisation solvent used in rdx synthesis , has been reported as a common headspace component of c - 4 in previous publications [ 47 ], but is more commonly observed in fresh samples of c - 4 than aged samples , due to its volatility . although labelled as tnt based booster , no tnt or other aromatic nitrates were detected in the headspace of the sample . the polymer bonded explosives were also analyzed using the spme - gc - ecd method to ensure that the parent explosives , if present in the headspace , were not being lost due to the gc - ms conditions . spme exposure was shortened to five seconds to prevent excessive overloading of the more sensitive detector . similar headspace signatures were seen employing spme - gc - edc . no parent explosives ( tnt , petn and rdx respectively ) were observed in the headspace of the tnt or petn booster , and the c - 4 or deta sheet samples , and similarly no 2 , 3 - dimethyl - 2 , 3 - dinitrobutane was detected in the headspace of the untagged deta sheet and c - 4 samples . no volatile organic chemicals were detected in the headspace of the petn detonation cords . even by increasing the spme exposure time to 18 hours did not result in a successful identification of any potential headspace component headspace analysis of the single based powders from hodgdon powder company , imr powder company and vihtavuori , revealed a headspace chemistry that was remarkably constant for each manufacturer ; however variance was observed between manufacturers . hodgdon and imr powder companies recently merged , which may explain the similarity between headspace components . results , presented in table 31 , table 32 , table 33 , and table 34 , reveal the common occurrence of diphenylamine in most single - based powders , in addition to the presence of either 2 , 4 - dinitrotoluene or ethyl centralite in high abundance in the headspace . the range of chemicals detected was in good agreement with a qualitative analysis recently published following an international inter - laboratory “ round - robin ” study [ 48 ]. sigma aldrich markets a “ pseudo - powder ” explosive training aid , and this was analysed in the same manner . the headspace of sigma &# 39 ; s pseudo aid was shown to contain only methyl isobutyl ketone , which was not observed in real powder samples . table 42 summarises the odor chemicals observed for the single based powders . the spme - gc - ms method did not reveal the presence of nitroglycerins in the headspace , but this was to be expected as a result of thermal degradation during the analysis . 2 , 4 - dinitrotoluene , 2 , 6 - dinitrotoluene and ethyl centralite were observed in the headspace of accurate arms powders , but not the other two brands analysed . 2 - nitrodiphenylamine was observed in both the hodgdon and vihtavuori powders , in addition to 4 - nitrodiphenylamine observed in hodgdon brand only . other compounds including 2 - nitrotoluene , 2 - nitrophenol and even 2 - ethyl - 1 - hexanol ( observed in most plasticized explosive headspaces ) were observed in selected powders . table 43 summarises the chemicals observed in the headspaces . nitroglycerins were observed in the headspace of double - based powders from all companies , when analysed by spme - gc - ecd . additionally , dinitrotoluenes were observed in the accurate arms powders , and nitrodiphenylamines were observed in the hodgdon and vihtavuori samples . the combination of spme - gc - ms and spme - gc - ecd provided complementary information with ethyl centralite and diphenylamine / nitrodiphenylamine seen as major components using ms detection whereas ecd highlighted the presence of nitroglycerins and nitrotoluenes . the most commonly observed headspace chemicals across all powders were 2 , 4 - dinitrotoluene , ethyl centralite and diphenylamine . additionally , trinitroglycerin was observed for the double - based powders . it follows that shared odor compounds between smokeless powders and high explosives exist ; namely the commonality of 2 , 4 - dinitrotoluene between the powders and tnt based explosives , and trinitroglycerin between the double - based powders and dynamites / water - gels . these results raise significant apprehension regarding the scientific soundness of the choice of smokeless powders used in training explosives detection canines . there is potential to use certain powder brands as odor sources for training on high explosives , however further research and a field trial including the training of explosive detection canines on smokeless powders only , are required before this hypothesis may be confirmed . conversely , the commonality of the odor between certain powders and high explosives may also present detection problems . if the smokeless powder chosen as a training aid is double - based , the canine is presented with an odor containing trinitroglycerin , which should already be learnt from dynamite . thus there is no new odor for the canine to imprint . should a single based powder containing 2 , 4 - dinitrotoluene be chosen , the commonality of the odor with tnt explosives will raise a similar problem . non explosive training aids are marketed for use in areas where the use of live explosives is not practical and to potentially provide more consistency in the odor chemicals used in training . the leading line of non - explosive training aids is the nestt ( non - hazardous explosives for security training and testing ) range from van aken international ( rancho cucamonga , calif .). purified explosives are diluted to 4 - 8 % by silica granules or petrolatum jelly . the complete range of nestt aids ( including the blank distracters ) were obtained and analyzed by spme - gc - ms and spme - gc - ecd . the spme - gc - ms method showed a large unresolved complex hydrocarbon mixture for the petrolatum jelly aids in table 44 , table 45 and table 46 , and only through selected ion monitoring at m / z = 210 cold the 2 , 4 , 6 - trinitrotoluene be detected in the tnt aid . no other parent explosives were detected in the petrolatum aids . table 47 gives the spme - gc - ecd headspace for the same nestt samples . the hydrocarbon background was not detected by the ecd , and resultantly , 1 , 3 - dinitrobenzene , 2 , 6 - dinitrotoluene and 2 , 4 - dinitrotoluene were also detected in the headspace of the tnt aid . again , no rdx or petn were detected using the ecd method in the headspaces of the respective aids . spme - gc - ms headspace analysis , shown in table 48 and table 49 , of the silica based aids gave a similar range of results to the petrolatum based aids . only the tnt aid contained the target explosive , 2 , 4 , 6 - trinitrotoluene , in addition to 2 , 4 - dinitrotoluene . although clear of the petrolatum background , a significant presence of siloxane compounds was present throughout the headspace samples , although it cold not be determined of this was from the silica training aid , the spme fibre or the column stationary phase . additionally , 2 , 4 - bis -( 1 , 1 - dimethylethyl )- phenol was observed in the blank , rdx and inorganic salt samples . the spme - gc - ecd method for the silica aids revealed the presence of 1 , 3 - dinitrobenzene , 2 , 6 - dinitrotoluene and 1 , 3 , 5 - trinitrobenzene in addition to the nitroaromatics observed in the spme - gc - ms headspace . table 50 also shows that the rdx aid did produce a small peak of the parent explosive , although given the vapour pressure of rdx , it is more likely that this was due to dusting of the silica matrix than a true vapour headspace . table 51 details the headspace components observed for the petrolatum and silica nestt aids . the common odor chemicals observed in the spme - gc headspace analysis of the high , low and pseudo explosives were presented individually , and combined , to previously trained and certified explosives detection canines . the hypothesis that stands is ; should a trained and certified explosives detection canine alert to a sample , believing that sample to be an explosive , then the chemical contained in that sample ( with the required controls in place ) may be considered an active explosive odor . a sample to which the canine does not alert may be considered an inactive odor , but it should be noted that an inactive odor might still have the potential to enhance an active odor &# 39 ; s potency . canine alerts to a container containing only one chemical odor believing there to be an explosive present chemicals to which the canines show no interest may still have the potential to enhance the odor signature when combined with active odors a canine “ alert ” is defined as a change in behaviour of the canine , recognised by the handler . for most explosives detection canines , this indicated by the dog sitting or lying down by the hide . a “ non - alert ” is when the canine is seen to sniff but walk away of his / her own accord to search another item . a canine “ interest ” fills the gap between alert and non alert , and is defined by the canines investigating but not alerting , such that the handler has to pull the dog off the item being searched , after dog has had sufficient time to alert / walk away . table 53 lists a field experiment comparing 100 ug of 2 , 4 , 6 - trinitrotoluene with 100 ug of 1 : 1 ( i . e . 2 × 50 ug ) 2 , 4 - dinitrotoluene + 2 , 4 , 6 - trinitrotoluene and also 100 ug of 1 : 1 : 1 ( 3 × 33 . 3 ug ) 1 , 3 - dinitrobenzene + 2 , 4 - dinitrotoluene + 2 , 4 , 6 - trinitrotoluene . the pure 2 , 4 , 6 - tnt reported 5 / 12 alerts , versus 2 / 12 for the binary mixture and 4 / 5 for the tertiary mixture . unlike 2 , 4 - dinitrotoluene which observed an increase in alert responses when combined with another nitrotoluene , the 2 , 4 , 6 - trinitrotoluene observed a decline . when factoring in the interest responses however , all mixtures reported higher overall canine response than the individual components . interestingly , 100 ug of pure tnt received fewer positive responses that 100 ug of commercial tnt , suggesting that a contaminant in the commercial product increased the ease of detection . a later study using 5 . 0 mg of 2 , 4 , 6 - trinitrotoluene reported 0 / 9 alerts ( table 54 ). 2 , 4 - dinitrotoluene , observed in tnt and cast explosives in addition to most smokeless powders , was tested at levels from 10 . 0 mg to 1 . 25 g . response to the odor chemical was varied across all concentrations , however better results were generally observed at the higher concentrations . 100 ug of 2 , 4 - dinitrotoluene was presented in the comparative study in table 53 with other nitroaromatics , reporting only 1 / 11 alerts but 5 / 11 interests . a 5 . 0 mg sample was offered in a following study but reported 0 / 9 alerts in a generally poor field test . 2 , 4 - dinitrotoluene was also tested with the low explosive odors , and 1 . 0 g was presented to several canines , reported in table 64 , which surprisingly also reported no positive responses . at the time of the field testing , the canines in question were known to be training regularly with an alleged tnt aid , which did not have the usual characteristic odor , which raises concern regarding the canines &# 39 ; capability towards tnt explosive at the time of the field work . later testing with 1 . 25 g of 2 , 4 - dinitrotoluene reported 7 / 10 alerts and 2 / 10 interests , described in table 91 during mimic aid testing , discussed supra under explosive mimic aids . other nitroaromatics tested included 2 - nitrotoluene and 1 , 3 - dinitrobenzene , the former observed in some smokeless powders in addition to its use as a tagging agent , and the latter observed in some cast explosive products . 2 - nitrotoluene was tested against the range of nitroaromatics in the field trial presented in table 54 , where 1 / 8 dogs alerted and 2 / 8 showed interest towards 2 - nitrotoluene , in preference over 1 , 3 - dinitrobenzene , 2 , 4 - dinitrotoluene and 2 , 4 , 6 - trinitrotoluene during the same test . in later studies , 0 . 5 μl of 2 - nitrotoluene elicited 2 / 10 alerts ( table 58 ) whilst 25 . 0 μl was 0 / 12 alerts and only 1 / 12 interests reported . 1 , 3 - dinitrobenzene was presented individually and in combination with 2 , 4 - dinitrotoluene and 2 , 4 , 6 - trinitrotoluene , presented in table 53 . 100 ug of 1 , 3 - dinitrobenzene reported 3 / 11 alerts and 1 / 11 interests , and whilst in a 1 : 1 : 1 combination with 2 , 4 - dinitrotoluene and 2 , 4 , 6 - trinitrotoluene , reported 4 / 11 alerts and 4 / 11 interests . a similar combination of 2 , 4 - dinitrotoluene and 2 , 4 , 6 - trinitrotoluene without the 1 , 3 - dinitrobenzene , reported 2 / 11 alerts and 6 / 11 interests . a later study of 1 , 3 - dinitrobenzene reported 0 / 9 responses to 5 . 0 mg ( table 54 ). 2 - ethyl - 1 - hexanol , present in the headspace of 5 / 8 plasticized explosives , in addition to occasional smokeless powders , was tested on several occasions . most success was observed at delivery levels of 5 . 0 mg which received 8 / 9 alerts and 1 / 9 interest , reported in table 57 . aids containing 0 . 5 μl 10 . 0 μl and 25 . 0 μl were also tested with 2 / 10 , 7 / 10 and 2 / 12 alerts respectively , and 0 / 2 , 3 / 10 , and 5 / 12 interest responses given in table 58 , table 59 and table 60 . clearly delivery levels around 5 . 0 mg / 10 . 0 μl elicit the best response from the canines , receiving an alert or interest from every canine . the 0 . 5 μl aid appeared to be below the level of detection for most canines ; whereas the 25 μl aid may have resulted in saturation of the odor , making it difficult for the canines to trace the aid to source . a detection level study was also performed for 2 - ethyl - 1 - hexanol , and whilst most dogs alerted to 1 - 10 mg of 2 - ethyl - 1 - hexanol , one dog did give an alert to 10 ng of the odor compound , seen in table 61 . present often only in fresh c - 4 , cyclohexanone was presented to the canines in various quantities . an early field test in table 52 , presented 1 . 0 g sealed inside an ldpe bottle , to which 2 / 6 canines alerted to and a further 2 / 6 showed interest . in later studies , significantly lower amounts were presented , sealed within the 2 . 0 mil ldpe bags . at 0 . 5 μl there were 0 / 10 alerts and the same result was observed for 10 . 0 μl , albeit one canine did give an interest , as indicated in table 58 and table 59 respectively . at 25 μl , 1 / 12 canines alerted and a further 2 / 12 showed interest in table 60 . a previous study , using canines trained under behavioural laboratory conditions with dilution olfactometry , indicated that cyclohexanone and 2 - ethyl - 1 - hexanol may be odor signature chemicals for c - 4 explosive [ 10 ]. the federal tagging agent 2 , 3 - dimethyl - 2 , 3 - dinitrobutane was not well received by the majority of the canine population tested . on three separate field trials , there was not one alert to the 2 , 3 - dimethyl - 2 , 3 - dinitrobutane source . in two separate tests , 5 . 0 mg was presented , with 2 / 11 interest and 0 / 9 interest reported in table 55 and table 57 respectively . on a different day , 100 . 0 ug was presented to the canines with only 1 / 7 interests reported in table 56 . nevertheless , 2 , 3 - dimethyl - 2 , 3 - dinitrobutane should be included in a training aid selection due to its sole application in the tagging of low vapour pressure explosives . whilst it is a common low explosive odor , 2 , 4 - dinitrotoluene was tested previously for the high explosives , and thus there was little benefit of testing it again by itself for the low explosives . trinitroglycerin , diphenylamine , ethyl centralite and 2 - nitrodiphenylamine were chosen for the activity testing based upon the headspace chemistries observed previously in smokeless powders . the canines were presented with a package of heart medication that contained trinitroglycerin . a bottle of 25 × 0 . 4 mg tablets was opened and presented to the canines as an additional item during the field trial in table 63 . 3 / 12 canines alerted and 3 / 12 gave an interested response to the medication that contained a total mass of 10 . 0 mg trinitroglycerin . as the most common low explosive odor , diphenylamine was included in some of the early “ screening ” field trials alongside the high explosives . the first trial used 100 ug of diphenylamine in table 56 , which warranted 1 / 7 alerts and 1 / 7 further interests . increasing the sample size to 5 . 0 mg in table 57 did not support a detection level theory , as the canines &# 39 ; responses dropped to 1 / 9 interests . following review of manufacturer &# 39 ; s safety data sheets , diphenylamine and 2 , 4 - dinitrotoluene were combined in a 1 : 5 w / w ratio to mimic hodgdon brand single based power , but this first mimic produced 0 / 10 responses , shown in table 62 . ethyl centralite was observed in both single and double based powders . a 5 . 0 mg sample shown in table 63 produced a 2 / 12 alert response and a further 1 / 12 interest . previously , an increased the sample size of 10 . 0 mg in table 64 did not reflect the success of the subsequent activity determination , with the canines responses at 0 / 6 alerts . given that ethyl centralite is present in smokeless powders at ˜ 1 - 3 %, the 1 . 0 g sample also presented in table 64 is representative of ˜ 35 - 100 g of powder explosive , however again there were 0 / 6 alerts . present only in select double based powders , 2 - nitrodiphenylamine is less commonly observed than either diphenylamine or ethyl centralite . in two field tests , presenting 5 . 0 mg and 10 . 0 mg of the chemical to the canines ; neither test resulted in any response from the canines . it is highly probable therefore , that either ( i ) 2 - dinitrodiphenylamine is too uncommon an odor to be chosen by the canines as an active odor , ( ii ) there are other more common odors such as 2 , 4 - dinitrotoluene and trinitroglycerin present in most powders that negate the requirement for the canines to ‘ learn ’ a new odor , or ( iii ) the canines used in this study had simply not been trained on any powder brands that contain 2 - nitrodiphenylamine . the wide variability of observed odor chemical signatures for smokeless powders and the variability in the smokeless powders used in the training of the canines tested may preclude the identification of active odor chemical ( s ) for low explosives . the complete range of nestt aids ( including the blank distracters ) were obtained and placed in the same metal hide boxes used in the field trials above . again , negative controls ( the blank distracter ) and positive controls ( real explosive ) were made available separately . the dogs had difficulty in locating the nestt aids in several separate tests . in early field work , the nestt silica tnt and rdx aids had been used as positive controls during tnt and plasticised explosive odor chemical studies , and so whilst they were run blind to the canines , the dog handlers did know the contents . in the true double blind studies that followed , listed in table 65 , no canines alerted to any of the nestt aids , although one individual did show interest in the nitrate and rdx aids . with the same population of canines as the silica aid tests above , the petrolatum based aids gave similarly poor results in table 66 and table 67 , with no positive alerts , and only one interest response towards the distractor and the rdx aid . a different sample set of canines in table 68 gave a more positive response to the tnt aid ( 2 / 4 ) and the rdx aid ( 1 / 4 alert and 1 / 4 interest ), however there were also alerts to the blank distractor ( 2 / 4 ) which negates any meaningful result from the field work . these results demonstrate a lack of consistency in the results when using nestt aids and that the mode of delivery may play an important role in the available odor of these aids . the results are not surprising , however , when comparing the odor signatures seen for the nestt aids and live explosive samples . for example , the c - 4 samples tested showed 2 - ethyl - 1 - hexanol as the dominant odor chemical while the only chemical seen in the nest rdx aid was rdx and only in the headspace of the silica aid . it is possible that canines trained to alert to the nestt aid may also locate the c - 4 samples containing rdx , using a different odor chemical which is present in a significantly lower quantity , and may have limited availability depending on the packaging of the explosive . the benefit of assigning each canine a particular identification number goes beyond providing anonymity to the canines and their handlers . in addition to producing statistical success rates on individual odors , the performance of the individual canines can also be tracked . data regarding the breed , age and length of service of the canines , in addition to their original training cold also be used to draw hypotheses and conclusions , and to establish trends for further confirmation . the tables list the canines &# 39 ; reference numbers against their responses to the training aids or odor chemicals as a fraction . the numerator lists the total number of alerts or interest , whilst the denominator reports the total number of hides . for example : a canine has been presented 2 , 4 - dinitroluene five times ; twice it has alerted , once it has shown interest and twice it gave no alert . its overall performance is reported as 3 / 5 or 60 . 0 %. the decision was made to report an interest as an alert , because an interest is indicative of the canine &# 39 ; s uncertainty regarding the odor ; an uncertainty in the explosives detection field which is preferable to err on the side of caution . the reflectance of the interest in the field work is to promote further study to determine a clear activity / inactivity resolution . the dogs were not regularly assessed on their ability to locate real explosive , given their certifications and current operational status . additionally , the performance of many of the canines was observed at regular training periods , during which must of the field work was conducted . there were certain times that a real explosive was a formal hide in a field test however , and these are the explosives listed in table 69 . the overall canine population &# 39 ; s performance on both the tnt and deta - sheet was 100 % ( 10 / 10 for each ) location of the training aid . the ability to locate detonation cord was also highly proficient at 83 . 3 % ( 10 / 12 ). the black powder response seems low at 75 . 0 % ( 3 / 4 ) but this is the result of only four canines , and should therefore be taken with a pinch of salt . the c - 4 / plastic explosives result was low at 62 . 5 % ( 14 / 23 ), originally raising serious concerns regarding the usability of the data . however a closer study of the training records not only explains this result but provides further useful observations . the low detection rate is explained by the choice of plastic explosives . the first run used traditional c - 4 explosive with a detection rate of 91 . 7 % ( 11 / 12 ), whereas the latter run used a rarer petn based plastic explosive . the petn explosive was chosen because it was uncommon , and the only plastic explosive analysed whose headspace did not contain 2 - ethyl - 1 - hexanol . unsurprisingly given the field data on the activity of 2 - ethyl - 1 - hexanol , the detection rate of the petn plastic explosive was only 27 . 3 % ( 3 / 11 ). whilst this raises concern regarding the detection capabilities towards the petn based plastic explosive , it does support the observed field data that 2 - ethyl - 1 - hexanol plays a significant role in the chemical odor of plasticized explosives . the far right column in each table gives the canines &# 39 ; responses to the blank and negative control containers . a high score here questions the individual canine &# 39 ; s ability in the field work , to distinguish explosive odors from background or control odors . across all canines and all field tests there was a 4 . 99 % ( 33 / 661 ) alert rate to negative or blank containers . this seemed high , but by examining the performance of individual canines , it was highlighted that canines 120 , 140 and 141 did not perform satisfactorily . canine 120 reported 20 / 28 false alerts , and canines 140 and 141 both reported 4 / 6 false alerts . this is tantamount to a 2 in 3 probability of alerting to an empty container or distracting odor . resultantly , the data from canines 120 , 140 and 140 were discounted from the overall statistical data regarding the activity of the odor compounds . removing those three canines from the statistics regarding false alerts , it was observed that the overall false alert rate dropped to 0 . 81 % ( 5 / 621 ), a much more acceptable figure . given the false alert rate of less than 1 . 00 %, there is a strong significance to the overall population &# 39 ; s performance on the field testing of odor compound activity . table 70 is split into three sections , detailing the odor chemicals detected in tnt & amp ; cast explosives , plasticized explosives and smokeless powders . ( 38 . 5 %), 2 , 4 - dinitroltoluene ( 46 . 2 %) and 2 , 4 , 6 - trinitrotoluene ( 50 . 0 %). the alerts to various members of the nitroaromatics family of molecules favoured the di - and tri - nitrotoluenes . from a biological perspective , considering the olfactory system as a target molecule / receptor site mechanism , one may question the difference in molecular shape of dinitrotoluene and trinitrotoluene in the lock and key model . accordingly , although 2 , 4 , 6 - trinitrotoluene did exhibit the highest alert / interest result , 2 , 4 - dinitrotoluene was a close second . its higher volatility and higher commonness amongst explosive products including smokeless powders , and the restricted nature of the parent 2 , 4 , 6 - trinitrotoluene explosive makes 2 , 4 - dinitrotoluene a viable odor for training aid design . the odors from plasticized explosives revealed a clear favourite amongst the canines tested for the active odor . there was an excellent response to 2 - ethyl - 1 - hexanol ( 74 . 4 %), whilst cyclohexanone ( 27 . 5 %) and 2 , 3 - dimethyl - 2 , 3 - dinitrotoluene ( 12 . 5 %) were less favoured . 2 - ethyl - 1 - hexanol was clearly shown to be the active odor of choice for the majority of the population tested . dogs 121 - 129 had just completed their initial training prior to field testing , imprinted on rdx in place of c - 4 explosive , and six were tested on 2 - ethyl - 1 - hexanol immediately after their first exposure to c - 4 during training . of the six dogs tested , 2 / 6 alerted and 2 / 6 gave an interest to the 2 - ethyl - 1 - hexanol . the role of experience , both of the handler and the canine , can also be shown . canines 108 , 109 and 118 were considered to be three of the most experienced teams . the combined blank negative result for these dogs was 0 / 142 , whilst the 2 - ethyl - 1 - hexanol result was a very promising 13 / 15 ( 86 . 7 %). the few canines that did not respond to the 2 - ethyl - 1 - hexanol did alert to the 2 , 3 - dimethyl - 2 , 3 - dinitrobutane instead , supporting the hypothesis that different canines may choose different odor chemicals from the same explosive sample . of course this may also be the result of a training effect , as it was observed that canines 101 - 133 were training on both tagged and un - tagged explosive , and in the absence of the 2 , 3 - dimethyl - 2 , 3 - dinitrobutane tag , and alternative volatile odor may need to be chosen . it was also noted that dogs imprinted on rdx before introduction to composition 4 , showed an increased response to cyclohexanone , which cold be a result of residual traces of the recrystalisation solvent on the rdx tablets used . the smokeless powder odors were less successful during field testing , than the tnt or plasticized explosives with limited alerts to ethyl centralite ( 14 . 0 %) and diphenylamine ( 35 . 0 %) and no positive responses to 2 - nitrodiphenylamine ( 0 . 0 %). given the variance of headspace compositions observed , as well as the common occurrence of 2 , 4 - dinitrotoluene and trinitroglycerin in many powders , there is a high probability that most of the smokeless powder “ odors ” may actually be those of high explosives instead . nevertheless , there are single based powders that do not contain 2 , 4 - dinitrotoluene , which will have an odor signature different to any high explosive , and training aids based upon diphenylamine / ethyl centralite must be considered . table 70 and table 71 conclude the data from the evaluation of the nestt training aids , both silica and petrolatum jelly based . the silica nestt distractor reported 0 . 00 % ( 0 / 10 ) alerts , whilst a 12 . 0 % ( 3 / 25 ) rate was observed for the petrolatum base . the canines &# 39 ; response to the silica nestt aids for the tnt , petn and rdx high explosives was 51 . 9 % ( 14 / 27 ), 43 . 8 % ( 7 / 16 ) and 0 . 00 % ( 0 / 10 ) respectively . the silica tnt aid was the most successfully tested aid , but with a positive response of only 51 . 9 %, this was still a low result for a product which is intended to simulate the odor or explosives for training purposes . the silica rdx aid was similarly successful . the petn aid did not report any alerts . the silica nestt aids for the nitrate and chlorate aids were poorly detected , with only 10 . 0 % ( 1 / 10 ) and 0 . 00 % ( 0 / 10 ) reported respectively . the petrolatum nestt aids for tnt , rdx , petn , nitrates and chlorates rated lower than the silica counterparts , at 8 . 00 % ( 2 / 25 ) and 12 . 0 % ( 3 / 25 ) for the tnt and rdx aids respectively , and 0 . 00 % ( 0 / 25 , 0 / 12 , and 0 / 12 ) for the petn , nitrate and chlorate aids . any significance of the alerts to the tnt and rdx aids is lost when the 12 . 0 % alert to the negative control distractor is considered . overall the nestt training aids faired very poorly , with the canines showing real difficulty in locating the explosive pseudo . unpublished data from the united states air force , and the working military dog ( wmd ) program has confirmed similar results to those reported here , with a significantly low population of canines trained on real explosive , capable of locating the nestt aids [ 49 ]. the wmd program has also trained canines on nestt and observed poor cross - over performances to the real explosive after the initial imprinting of odors using the nestt . acetonitrile was chosen as the optimal solvent to use as the delivery medium , based upon its suitability to dissolve every explosive . given the varying range of explosive chemistries , it is difficult to find one single solvent ; however acetonitrile is commonly reported as the best “ general purpose ” solvent for explosives , and most explosive standards when ordered , come in acetonitrile solution . acetone may also be used , but as it is a potential headspace component for tatp , and has been reported previously in smokeless powder headspace , it was not used in this study [ 50 ]. the volatility of acetonitrile was exploited to deliver precise amounts of odor compound . to permit this application it was first necessary to determine the length of time required to evaporate a known amount of acetonitrile . it was determined that 100 μl was a suitable amount , given that a 100 μl aliquot of a 10 % ( mass / volume ) solution would deliver precisely 10 . 0 mg of odor compound . four pieces of cotton gauze were taken and their mass monitored every 5 minutes over a two hour period . the control gauze , which was left unaltered , was observed to remain at a constant mass , whilst the three pieces which were spiked with 100 μl of acetonitrile showed a steady , liner decline in mass . after 90 minutes , it cold be shown that the mass of the cotton had returned to it original value before the application of acetonitrile , as seen in table 73 . accordingly it was determined that a 90 minute period should be sufficient to allow the 100 μl aliquot of acetonitrile delivery solvent to evaporate , leaving only the less volatile odor compound behind . after demonstrating the complete evaporation of 100 μl of acetonitrile within 90 minutes , the next step was to prepare 10 . 0 % w / v solutions of key odor components . 10 . 0 % solutions in 2 , 4 - dinitrotoluene , 2 - ethyl - 1 - hexanol , and ethyl centralite in acetonitrile were prepared , and 100 μl aliquots spiked onto cotton gauze . 2 , 4 - dinitrotoluene was chosen as the expected headspace component of cast explosives . for similar reasons 2 - ethyl - 1 - hexanol was chosen to represent plastic explosives following the successful field identification as a potential odor compound . ethyl centralite , a common stabiliser for smokeless powders was also chosen . the masses of the gauze pieces were monitored over time , and plotted in table 74 . it was observed that after 90 minutes , the remaining 0 . 010 g readings on the cotton were the respective odor compounds , whilst the blank acetonitrile solvent mass continued to reduce back to the baseline . it was therefore concluded that acetonitrile based delivery of the odor compounds was therefore a potential method to be used to produce training and field work aids based upon the odor chemicals . to protect the odor source ( cotton gauze ) from excessive contamination , it is preferable to have it sealed within some form of container . given the inertness , impermeability and fragile nature of glass , a plastic or polymer container would most probably prove the most cost effective and efficient . furthermore , by choosing the polymer chemistry and thickness , delivery of the odor compound may be controlled to a specific rate . using the same method of preparation from the evaporation study above , cotton gauze was spiked with 100 μl aliquots of 10 % solutions of 1 , 3 - dinitrobenzene , 2 , 4 - dinitrotoluene , and 2 , 6 - dinitrotoluene . at a later date , 250 μl aliquots of the diphenylamine and 2 , 3 - dimethyl - 2 , 3 - dinitrobutan solutions were also used to conduct this work for additional odors . reproducing the previous procedure for the solvent delivery experiments , the gauze was left to sit for 90 minutes ( 240 minutes for larger aliquots ) to evaporate the acetonitrile solvent to leave only the odor compounds . the gauze was then heat sealed into 2 . 0 mil low density polyethylene ( ldpe ) plastic bags and left in open containers . the masses of all training aids were monitored during the weathering process over a period ranging from two weeks for the more volatile components to six weeks for the less volatile compounds . the gradient of the best fit line gave the permeation rate in g / day , which was converted to pg / s for the aromatic nitrates , and ng / s for the more volatile odor compounds of c - 4 , due to their increased volatility . 1 , 3 - dinitrobenzene , chosen as an uncommon component of tnt headspaces , was observed to diffuse through the plastic container at a rate of 1 . 174 × 10 2 pg s − 1 , 2 , 6 - dinitrtoluene was also chosen , present both in certain tnt headspaces , but more commonly in the headspace of smokeless powders , due to its role as a deterrent and plasticizer . the permeation rate of 2 , 6 - dinitrotoluene was calculated to 1 . 556 × 10 2 pg s − 1 , similar to that of 1 , 3 - dinitrobenzene , somewhat expected due to the similar molecular chemistries and geometries . 2 , 4 - dinitrotoluene is the primary component of tnt headspace , in addition to a significant component of many smokeless powders . the permeation rate of 2 , 4 - dinitrotoluene was observed at 8 . 036 × 10 1 pg s − 1 , slightly less than that of 1 , 3 - dinitrobenzene or 2 , 6 - dinitrotoluene , which may be explained by the para - position of the second nitro group , making the molecule a little larger to pass through the pores of the ldpe container . diphenylamine , a common stabiliser for single based smokeless powder , and 2 , 3 - dimethyl - 2 , 3 - dinitrobutane , a federally mandated tagging agent for plasticized explosives are an order of magnitude more volatile than the dinitroaromatics , hence the larger sample size chosen for the permeation study . the diphenylamine was observed to permeate through the ldpe packaging at a rate of 3 . 23 × 10 3 pg s − 1 . the permeation within the sample set was not as uniform as observed for the nitroaromatics , as indicated by the spread of points on table 78 , however after one month the final readings are significantly closer together than halfway through the time period . 2 , 3 - dimethyl - 2 , 3 - dinitrobutane was chosen as a taggant due to its volatility and permeability , in addition to its exclusivity to the given application of tagging explosives . the permeation rate for 2 , 3 - dimethyl - 2 , 3 - dinitrobutane was determined to be 1 . 03 × 10 3 pg s − 1 through the ldpe packaging . 2 - ethyl - 1 - hexanol and cyclohexanone aids were also prepared , however owing to the significantly increased vapour pressure of the volatile compounds ; 1000 μl of each was spiked directly onto the gauze with no need for evaporation of the acetonitrile . again the gauze was sealed within 2 . 0 mil ldpe plastic bags . not surprisingly , the cyclohexanone was seen to evaporate from the ldpe container within a two week period . cyclohexanone is particularly volatile , and the observed loss at a rapid rate further correlates the observation that cyclohexanone is only observed in the headspace of very fresh c - 4 samples . the cyclohexanone was calculated to permeate through the ldpe at a rate of 9 , 745 × 10 2 ng s − 1 indicating very little “ trapping of the odor ” by the plastic membrane . 2 - ethyl - 1 - hexanol is less volatile than cyclohexanone but still several orders of magnitude more volatile than the 2 , 3 - dimethyl - 2 , 3 - dinitrobutane taggant or the dinitroaromatics . its permeation through the ldpe was determined at 4 . 36 × 10 1 ng s − 1 , falling between the very volatile cyclohexanone and the less volatile 2 , 3 - dimethyl - 2 , 3 - dinitrobutane , the two other components of the c - 4 headspaces observed . table 82 lists the rates of permeation through 2 . 0 mil ldpe , for the seven odor compounds tested . note the volatility of the c - 4 headspace components in comparison to the tnt headspace components . the permeation through a selection of alternative polymers was also conducted . polypropylene ( pp ), cellophane and aluminized kapak bags were also obtained in addition to the low density polyethylene . the ldpe bags were available in 1 . 5 , 2 . 0 , 3 . 0 and 4 . 0 mil thicknesses . 1 mil is defined as one thousandth of an inch . the polypropylene bags were also available in 2 . 0 mil thickness . the aluminized kapak bags feature the proprietary 2 . 5 mil three - layer polymer chemistry , with an aluminium foil layer sandwiched between other polymers . the kapak bags are particularly heat and cold resistant , and are more resistant to puncture than traditional plastic bags . the gauze was then heat sealed inside the assorted polymer bags and their masses collected over a period of 1 month . 250 μl aliquots of the 10 % acetonitrile solutions of 2 , 4 - dinitrotoluene , 2 , 3 - dimethyl - dinitrobutane , 2 - ethyl - 1 - hexanol , and diphenylamine were delivered onto gauze and set aside for the acetonitrile to evaporate , to leave a 25 . 0 mg residue of odor compounds . regardless of polymer chemistry , the 2 , 4 - dinitrotoluene was observed to permeate a steady rate . the different thicknesses of the ldpe ranging from 1 . 5 - 4 . 0 mil were observed to have little effect , with no noticeable difference in the rate of loss . the kapak and polypropylene bags did appear to have a marginally slower rate of permeation , although the mass was still observed to reduce gradually over time . a similar result was observed for the 2 , 3 - dimethyl - 2 , 3 - dinitrobutane samples , with no discernable difference between the rate of loss from the different polymers . there was a noticeable difference in the permeation rates for the diphenylamine samples . as expected , the ldpe polymers showed the greatest rate of loss of the odor compound , and furthermore the thinner membranes demonstrated a slightly increased rate over the thicker bags . as previously observed , the polypropylene and kapak bags were the most stable masses over time , with a reduced permeation rate observed when compared with the ldpe . as expected , the 2 - ethyl - 1 - hexanol samples exhibited the greatest variance in observed permeation rates . following from the ldpe study discussed previously , the loss of the 2 - ethyl - 1 - hexanol through the ldpe was swift , although it cold clearly be noted that the thickness of the ldpe packaging had an effect upon the rate of loss . the polypropylene and kapak produced a much slower rate of escape , whilst the cellophane fell somewhere in the middle between the ldpe bags and the polypropylene and kapak . a closer view of the first week of the 2 - ethyl - 1 - hexanol study clearly illustrates the different permeation rates of the various polymer chemistries and thicknesses . 1 . 5 mil ldpe had a significantly faster rate of loss than 4 . 0 mil ldpe . the cellophane in comparison shows a gradual loss of mass which continued over the following weeks . several of the cellophane bags were seen to increase in mass to begin with ; believed to be an effect of the humidity of the air resulting in moisture ingression and absorption . the kapak and polypropylene bags did show a very low rate of loss due to permeation . it was proposed that a double bag model should be tested for the explosive mimic aids , utilizing an inner ldpe bag containing the odor source , and a kapak outer bag with reduced permeability to restrict odor contamination of and from the aid . kapak was chosen over polypropylene due to its extreme temperature and puncture resistance . having successfully identified 2 - ethyl - 1 - hexanol as an active odor for plasticized explosives such as c - 4 and deta - sheet , it was chosen as the odor chemical to research the double bag training aid model . the 2 - ethyl - 1 - hexanol aids were prepared as in previous experiments , using 100 μl of the 10 % solution spiked onto the cotton gauze , which were then set aside for 90 minutes to allow the acetonitrile delivery solvent to evaporate . the gauze was then placed inside the 2 . 0 mil ldpe bag and heat sealed . that aid was then placed inside the 2 . 5 mil aluminised kapak bag , which was again heat sealed . it was hypothesised that the dual layer would prevent the odor of the training aid inside the bags from escaping , preventing contamination of the aid , or by the aid . removal of the outer bag would permit permeation through the ldpe to the surrounding environment . after preparation , the 2 - ethyl - 1 - hexanol aids were set aside for 3 weeks , after which the headspaces inside the inner and outer bags were sampled and compared by spme - gc - ms . the peak area of the 2 - ethyl - 1 - hexanol peaks are clearly the same for both the inner ldpe ( grey line ) and outer kapak ( black line ) bags , indicative of the permeable nature of the ldpe , allowing the 2 - ethyl - 1 - hexanol concentration to come to equilibrium between both bags . the mass of the double bag system was also monitored over the period of 3 weeks , and despite a slight mass loss at the beginning , believed to be a result of a little acetonitrile solvent residue , the mass of the total system remained constant , indicating that the outer kapak bag was capable of containing the volatile odor compound . the headspace analysis combined with the gravimetric analysis confirms the hypothetical model of the double bag training aid system ; the permeable inner ldpe bag that allows the odor compound to diffuse gradually , and the impermeable outer kapak bag that keeps the odor compound contained , preventing contamination of the aid , or contamination by the aid . the double bag model was ready for field application . this was tested by preparing two of the above double bags aids , and presenting both to the previously trained explosives detection canines . one aid would remain within the outer aluminised kapak , hopefully undetected , whilst the inner aid exposed should be easily located by the canines . the results from the field test of the double bag design were very encouraging . only one in ten dogs alerted to the 2 - ethyl - 1 - hexanol aid whilst it was still in the aluminised kapak bag , whereas seven out of ten dogs , alerted to the aid once it was removed from the outer packaging . the three dogs that did not alert to the 2 - ethyl - 1 - hexanol aid did give a good interest without resulting in a positive alert . the double bag design clearly has potential as a training aid mechanism , and the 2 - ethyl - 1 - hexanol aid as presented here is already extremely promising as a c - 4 mimic aid . the nestt aids use silica to “ dilute ” pure explosive to 5 - 8 % w / w . in particular the nestt tnt aid contains 8 % 2 , 4 , 6 - trinitrotoluene on silica . it follows that with 2 , 4 - dinitrotoluene more commonly observed than 2 , 4 , 6 - trininitrotoluene in the headspace of cast explosive , and additionally in the headspace of several smokeless powder brands , that it would be prudent to choose 2 , 4 - dinitrotoluene as a key odor to develop an aid around . additionally , the vapour pressure of 2 , 4 - dinitrotoluene is over 35 × that of 2 , 4 , 6 - trinitrotoluene , ensuring a more intense odor from an equivalent concentration . a concentration of 5 % w / w 2 , 4 - dinitrotoluene in silica was chosen , following the example of the nestt aids . the 5 % level is also close to what cold be expected of commercial tnt with an approximate impurity of the reaction precursor , 2 , 4 - dinitrotoluene . the aid was produced in large 500 g batches and measured out into 25 g samples which were bagged and heat sealed in 2 . 0 mil ldpe . a distractor was produced in similar fashion , without the addition of the 2 , 4 - dinitrotoluene . previously trained explosive detection canines were presented the comps tnt aids in the same manner as the field trials previously discussed . in general there was a good response to the mimic aids , with 7 / 10 dogs testing giving a positive alert to the aid and a further 1 / 10 showing interest but without the final alert . the two dogs who did not respond to this tnt aid were straight out of training , but no conclusions may be drawn regarding the effect this may have had on the two dogs , as one of the dogs who alerted was also from the same school . concerns arose regarding the bulk of the 25 g aids , and the problem of severe dusting if the ldpe bag was punctured . following the early success of the tnt aid , a second study was performed to investigate the possibility of training new dogs on the tnt aid , and seeing if they were capable of finding real tnt , i . e . crossing over to the real explosive after imprinting only on the comps mimic . contact was made with a handler based in the florida keys , who as a private trainer welcomed the idea of using non - controlled stimulants as the odor source . the trainer was given an extensive supply of the 25 g comps tnt aids , in addition to a supply of the 25 g distractors to proof the canines off the silica / ldpe odor . after 6 weeks of training , the trainer met with the florida international university public safety canine unit to determine the ability of the canines to cross over . an item search of 10 boxes was lined up , containing the comps distractor and comps tnt aid , in addition to an equivalent weight of real tnt . the results were less than promising , with none of the 3 new dogs trained capable of locating the real tnt , although one dog did give an interest . furthermore , the three dogs had difficulty in locating the tnt , with only one dog alert to the aid and one other showing an interest . in contrast , the fiu dog located both the comps tnt aid and the real tnt with little difficulty . subsequently , discussion of this outcome with several other trainers in the south florida area highlighted the original trainer &# 39 ; s inexperience in training detection canines , a fact that was not presented at the time of experimental design . the trainer &# 39 ; s area of expertise was in dog training for house pets , and although well read on the subject , his experience in detection canines was little more than 3 months as a handler before retiring from police duty . it was later determined that the trainer was keen to begin training detection canines and viewed the trial mimic aids as a method of obtaining training aids without the need for atf . this was deemed a miscommunication between the trainer and the author , rather than an intentional misrepresentation , and no further training on the tnt aids was planned with this trainer . although the silica model of the tnt aid was successful in early field trials , the biggest complaint and concern was regarding the silica dust . the thin plastic membrane of the 2 . 0 mil ldpe was relatively weak to puncture , and the heat seal whilst strong enough for modest handling cold not be guaranteed to remain intact if abused or treated roughly . several of the tnt aids began to dust soon after repeated use , and the potential for contamination through the deposition of the silica , in addition to the health concerns of inhaled silica dust , led to the need for an alternative to the fine silica powder . although larger grain silica may have been used , this would have closely resembled the nestt aids , besides which , success with the cotton gauze as a medium for the odor compounds in the permeation studies suggested the use of the cotton in place of the silica , removing the dust concerns , and making the aids much more compact and cost effective . returning to the successful double bag design in the early stages of the mimic aid project , the odor compounds observed in the headspace analyses of the explosives were used to prepare 10 mg aids ; the odor compound deposited onto the cotton gauze using the acetonitrile delivery method . 2 , 4 - dinitrtoluene and 2 - ethyl - 1 - hexanol were chosen again due to their success in previous studies . the tagging agent 2 , 3 - dimethyl - 2 , 3 - dinitrobutane was also chosen due to its recurrence in plasticized explosives . smokeless powder odors , ethyl centralite , diphenylamine and 2 - nitrodiphenyl amine were chosen for screening through the design process , as an individual odor for smokeless powders had not been determined , and due to the heterogeneity of the headspace analyses , it was unlikely that a single compound would be observed as the active odor . 10 % solutions of the six odor compounds were prepared in acetonitrile , and a seventh blank solution of acetonitrile was prepared simultaneous using the same solvent and measurement devices . 100 μl aliquots of the six solutions were delivered onto cotton gauze , and the process repeated 12 times . the blank aids were prepared with 100 μl aliquots of the acetonitrile , to prepare 72 distractors . each piece of gauze was allowed to weather for the predetermined 90 minutes , before placement inside 2 . 0 mil ldpe bags and heat sealing . the individual odors were prepared at different times on clean bench paper to prevent any cross contamination . the aids were intended to be shipped to participating canine agencies throughout the united states , and this was possible because not one of the aids contained a department of transport ( dot ) controlled explosive substance for delivery purposes . comps kits were prepared containing one of each odor compound and six distractors . the individual aids were not labelled for their contents , the field testing being run blind . each odor compound was twinned with a distractor and labelled a through f , and 1 or 2 . the six distractor / aid combinations were designed to be run during normal weekly training . complete kits were mailed to the six canine teams funded under the nfstc project grant , in addition to florida highway patrol and city of miami police . the agencies were asked to place and aid combination out during testing and report which of the two aids , if either , their teams alerted too . the results were collected and compiled . with the exception of two dogs ( 140 & amp ; 141 ), the distractors were not detected by the canines . a misunderstanding of the instructions enclosed with the training aids may well account for the positive alerts on the distractors , as both canines were from the same agency . the high frequency off occurrence of the dogs &# 39 ; false alerts to the distractors , means that these two dogs were excluded from the percentages calculated in the table . it is often observed that handlers will try to second guess their canines if they have expectation of a result , which is not duplicated by their canine . with the exception of the two dogs mentioned above , the results were encouraging and revealing . the 2 - ethyl - 1 - hexanol remained the most successful aid , with a 50 % positive response and a 33 % interest in the aid . comparing the 2 - ethyl - 1 - hexanol and the 2 , 3 - dimethyl - 2 , 3 - dinitrobutane aids , it is interesting to note that the canines which did not alert to the 2 - ethyl - 1 - hexanol did alert to the 2 , 3 - dimethyl - 2 , 3 - dinitrobutane . these two compound represent the two common odors of plasticized explosives , and here it is observed that whilst most dogs choose one of the two odors , there are dogs that choose the other of the two odors . the revised version two of these aids should benefit from combining the two compounds onto a single piece of gauze , making one c - 4 mimic containing both odor compounds . the 2 , 4 - dinitrotoluene aid was not as successful as previously observed , although is probably due to detection level complications . this aid contained only 10 . 0 mg in contrast to the previous silica design which contained 1 . 25 g in each aid . increasing the content of the 2 , 4 - dinitrotoluene aid for version two should prove more effective . the results for the smokeless powder odor compounds were less successful , however canines from different agencies did give alerts to the ethyl centralite and diphenylamine aids . the next round of aids should try combining the ethyl centralite and diphenylamine into a single aid . the 2 - nitrodiphenylamine was not carried forward to the revised aids , do the poor response to the aid in this first round . following the results of the first round of testing , the cotton gauze model of the training aids was revised for new odor compounds , presented in table 95 . the amount of 2 , 4 - dinitrotoluene in the tnt stimulant was increased from 10 mg to 0 . 2 g , however there was no response from the seven canines tested . the c - 4 mimic combined 0 . 02 g of 2 - ethyl - 1 - hexanol and 0 . 1 g of 2 , 3 - dimethyl - 2 , 3 - dinitrobutane , however only 2 / 7 canines gave an interested response . the improved smokeless powder mimic , containing 0 . 1 g each of ethyl centralite and diphenylamine reported the most promising results , with 1 / 7 ( 14 . 3 %) alerts and 3 / 7 interests . the same response was observed for the positive control ; 75 g of hodgdon clays ( double based ) smokeless powder . a further optimisation of the c - 4 mimic was conducted , comparing four different versions , as detailed in table 96 . each mimic contained 10 μl of 2 - ethyl - 1 - hexanol , followed by a possible combination of 10 μl of cyclohexanone and / or 10 μl of 2 , 3 - dimethyl - 2 , 3 - dinitrobutane . given the previous of success of 10 μl 2 - ethyl - 1 - hexanol aids , the field test was highly disappointing , with only 1 / 4 canines showing an interest in the 2 - ethyl - 1 - hexanol aid . no response was observed for the combined odor aids . alarmingly , no positive responses were observed for the positive control ; 75 g of black powder . given the poor responses of the canines towards the real explosive positive controls , the reduced number of canines now attending the field test , and the distance involved in travelling to each test , it was decided to cease the field testing until the quality of canines used cold be improved or a more convenient source of canines from a local agency cold be accessed . the bureau of alcohol , tobacco , firearms & amp ; explosives ( atf ) is the united states &# 39 ; federal agency responsible for the control and regulation of all weapons and explosive materials within the us . the atf has trained over 300 explosive detection canines , providing them both to domestic agencies and international law enforcement too [ 51 ]. in the absence of a national , standardised certification program for explosive detection canines , the atf has proposed the use of their odor recognition proficiency standard ( ort ), which involves 3 lines of 10 one gallon paint cans . within each gallon can is a quart sized can which may contain the explosive aid or distracting odor . the ort involves ten explosive odors , five distracting odors and fifteen blank cans , from which the canines must achieve a 100 % correct response on the ten explosive odors , and no more than two incorrect responses on the distractors / blanks . the atf has designated which explosives are to comprise the ten chosen for the ort , as listed in table 97 . there are six mandatory explosives ; black powder , dynamite , petn , rdx , tnt and double based smokeless powder . the remaining four explosives are chosen from a list of “ elective ” explosives , which includes ; binary charges , black powder substitutes , blasting agents , cast boosters , composition b , emulsions , improvised explosives based around nitrates , chlorates or perchlorates , photoflash & amp ; pyrotechnics , plastic explosives , semtex , slurries , single based smokeless powder , tetryl and water gels . at first glance this seems an extensive if not exhaustive list of explosive products , however , several of the elective explosives are duplicated in name . many of the elective charges therefore have the likelihood of duplicating each other and / or the mandatory charges , and there is a significant potential for the choice of ten explosives to completely overlook certain explosive combinations . most blasting agents are binary in nature , and water gel , emulsion and slurry are three names often used to describe the same explosive product . similarly cast boosters may include composition b and / or tetryl . table 98 lists several different formulations of cast primer , notably each one contains tnt , often in addition to other high explosives also on the atf mandatory list , and thus the use of those cast explosives would only duplicate odors at the expense of others . in response to this , the atf includes the following statement / disclaimer in their communication [ 52 ]; “ some explosives are available in a variety of chemical formulations . . . . it is imperative that the manufacturer &# 39 ; s product literature [ including msds ] be reviewed to ensure that the specific explosives content of each test sample used is known .” resultantly , although the atf has prescribed the recommended explosive groups , the individual responsibility of choosing the correct explosives to use falls upon the individual agencies , relying upon the knowledge of the master trainer to choose wisely . scientifically , it is more meaningful to give a list of specific explosive products to use , given knowledge of the explosive contents . table 99 details ten explosive products ( shaded ) that cover the majority of explosive odors , both individually and in combination . the results of this study suggest that multiple smokeless powders should be included into a complete training regime . further classification of the single and double - based smokeless powders suggests the rotation of powders from various manufacturers , including hodgdon , imr and vihtavuori lapua . additional studies should allow for the grouping of the most important powders to be included in training . results from this study indicate that single - based vihtavuori powders should be included in regular training , due to the observation that they have a relatively unique headspace including not containing dinitrotoluene in their headspace . the remaining explosives ( non - shaded ) may also be included as additional non - essential training material for variability . although hmx and tetryl are not included in the ten mandatory explosives suggested , there is no record of those explosives being used in commercial or military products without the presence of tnt or another explosive . it is not wise to use a combination explosive such as composition b , in place of two separate target odors such as tnt and rdx . given that tnt has a vapour pressure three orders of magnitude greater than rdx , it his highly probable that the canine will only imprint upon the tnt , leaving them vulnerable to explosives containing only rdx . in the interests of maintaining accurate and concise scientifically sound records , it is vital to be able not only to record the explosives trained on , but the odor chemicals to which the canines have been presented . it is therefore recommended that initial imprinting and regular training should provide the odors individually , particularly with the less volatile nitramine explosives . the national forensic science technology centre ( nfstc )/ international forensic research institute ( ifri ) certification provides canine agencies with an impartial , scientifically sound certification of the canine handler team . the certification is overseen by two evaluators , one an nfstc / ifri approved trainer , the other a scientist from ifri . the certification is conducted in line with the best practice procedures developed at the 3 rd national detector dog conference [ 53 ]. the certification requires a result & gt ; 90 % correct responses , with no more than 1 missed hide . there is a minimum requirement of 10 hides . generally the certification will involve 2 - 5 vehicles , 2 - 5 rooms and a luggage line - up of at least 10 items . at least 1 of each of the vehicle and room hides should be blank ( negative ). following several field certifications of canine and explosive and narcotic detection teams , the report sheet was updated with regard to several concerns . a sample of the new form is included in appendix iv . it allows for only one form to be completed , with space for both evaluators . the personal information is clearer and more self explanatory for the handler to complete . in addition to the alert and no alert boxes from previous forms , the addition of a correct , yes / no option allows for the explicit reporting of correct positive , correct negative , false positive and false negative results . this in turn allows simple numerical addition of correct and incorrect responses , providing a percentage result for the final pass / fail result . the revised nfstc / ifri certification form was further modified , whilst maintaining the same format , as a record sheet for daily maintenance training . these results raise concerns regarding the scientific soundness of the choice of explosive samples used in training explosives detection canines . these results indicate that dogs may not need to be trained on as many plasticized explosives as typically employed in canine training programs ( some have comparable headspace odor signatures such as those observed for c4 , flex x deta sheet and tnt booster tested in this study ). in addition , dogs trained on certain smokeless powders may not need to train on cast explosives such as tetratol and tnt as they both contain abundant amounts of one of the active odor signature chemicals , 2 , 4 - dnt . significant odor differences have been observed between smokeless powder brands and types , suggesting that the canines should be trained on multiple smokeless powders . accordingly , it is the responsibility of the trainer to choose a selection of powders , both double based and single based , from all manufacturers , to ensure the complete ability of the canine to locate all smokeless powders . whilst major headspace odor components such as diphenylamine and ethyl centralite in smokeless powders were not identified as individual active odor signature chemicals used by the dogs tested , they can still be useful in the calibration of instrumental techniques to improve detection . many of the vapour detectors currently used are targeted towards the less volatile parent explosives . utilising the odor chemicals observed would permit lower detection limits due to the increased volatility of the compounds . this study has identified several key odor chemicals which illicit positive responses from deployed explosives detection canines with 2 , 4 - dinitrotoluene and 2 - ethyl - 1 - hexanol identified as important odor chemicals for canine detection of cast and polymer based explosives respectively . these results support the hypothesis that most dogs use the most abundant chemicals available in the headspace to locate concealed explosives . for example , the detector dogs tested alerted to 2 - ethyl - 1 - hexanol found in the headspace of the plasticized explosives and explosive mimics tested but not the rdx observed in the headspace of the silica based rdx nestt aid . the results also suggest that dogs may use single dominant odor chemicals as a primary mechanism with the dogs tested alerting to 2 - ethyl - 1 - hexanol but not to the added marker dmnb although it was present in the majority of the canine training aids tested . these results also suggest that training dogs on the pure marker chemical dmnb and other single chemicals in low quantities may be advantageous in enhancing their performance . reliable non - hazardous training aids are needed for use in areas where live explosive aids are not practical and to provide more consistency in the odor chemicals released in training and in order to improve canine detection performance . in the present studies , nestt aids yielded inconsistent results with the deployed bomb dogs tested in this double - blind study , with most dogs not alerting to these materials under field operational conditions . these results also show that nestt aids have potentially undesirable matrix effects with a large hydrocarbon background observed for the petrolatum based aids and dusting with the silica based aids . additional field testing with commercially available pseudo scents and nestt aids should continue attempting to expand the number of teams and different agencies involved in the study . preliminary field tests with explosive odor mimics ( eom ) which provide controlled polymer permeation of active odor chemicals are promising with consistent alerts observed for target chemicals tested including 2 - ethyl - 1 - hexanol . continued study into refining the explosive odor mimics would prove highly beneficial prior to development of a commercial training product . the next stage in development of these eom training aids should involve the initial imprinting of the canines using these aids containing individual odor chemicals as well as combinations . this should be followed with testing with real explosives to determine the degree of generalisation / cross - over exhibited by the canines and the magnitude of individual versus multiple odor chemicals used by canines to locate explosives . moreover , training on low - volatility parent explosives such as purified rdx followed by threshold testing with actual explosive materials should be compared to the results observed for the high volatility headspace chemicals such as 2 - ethyl - 1 - hexanol . it would also be beneficial to imprint the canines on a selection of smokeless powders , chosen to mimic high explosives . the use of hodgdon 4350 and hodgdon clays cold provide suitable mimics for tnt and dynamites respectively . again , subsequent testing with real explosive materials should provide meaningful insight into odor generalisation of training aids . additionally , a more comprehensive screening of commercially available smokeless powders should be conducted with each placed into the optimal number of groupings to provide guidance for trainers to select the optimum number and brands of smokeless powder training aids . 1 collins english dictionary , 2003 , 6 th edition , harper collins , glasgow uk . 2 j . yinon & amp ; s . zitrin , modern methods and applications in analysis of explosives , john wiley & amp ; sons , chichister uk , 1993 . 3 r m heramb and b r mccord , forensic science communications , 2002 , vol 4 , no 2 . 4 containing the threat from illegal bombings : an integrated national strategy for marking , tagging , rendering inert , and licensing explosives and their precursors , national academy press , washington , d . c ., 384 pages , 6 × 9 , 1998 . 6 j . akhavan , the chemistry of explosives , royal society of chemistry , cambridge , uk , 1998 . 7 y . barnberger et al , proceedings of the third symposium on analysis and detection of explosives , 1989 , berghausen germany . 8 a . d . beveridge , forensic science review , 1992 , 4 ( 17 ) pp 18 . 9 t . tamiri & amp ; s . zitrin , journal of energetic materials , 1986 , 4 pp 215 . 10 m . williams et al , proceedings of spie , 1998 , 3575 pp 291 . 11 s . zitrin , journal of energetic materials , 1986 , 4 pp 199 . 12 j . m . f . douse , journal of chromatography , 1982 , 234 pp 415 . 13 s . a . peak , journal of forensic science , 1980 , 25 pp 679 . 14 b , glattstein & amp ; s . kraus , journal of energetic materials , 1986 , 4 pp 149 . 15 s . zitrin et al , proceedings of the 1 st international symposium on the analysis and detection of explosives ( isade ), 1983 , washington d . c ., usa . 16 k , yeager & amp ; m . hall , the detonator , 2005 , 32 ( 2 ) pp 60 - 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assisted detection , in alternatives for landmine detection , by j . macdonald , j . r . lockwood , j . mcfee , t . altshuler , t . broach , l . carin , r . harmon , c . rappaport , w . scott and r . weaver , 2003 , rand corporation , santa monica , calif ., pp . 285 - 299 . 38 j . j . bromenshenk et al , appendix s , alternatives for landmine detection , by j . macdonald , et al , 2003 , rand corporation , santa monica , calif ., pp . 273 - 283 . 40 s . sloan , k 9 case law , 3 rd national detector dog conference , may 2003 , north miami beach fla ., usa . 41 j . a . given , controlled substance training aids for dod , 3 rd national detector dog conference , may 2003 , north miami beach fla ., usa . 42 jehuda yinon , modern methods and applications in analysis of explosives , 1993 , wiley , new york . 43 black and smokeless powders : technologies for finding bombs and the bomb makers , national academy press , washington , d . c ., 1998 . 44 j . m . johnston and m . williams , enhanced canine explosive detection : odor generalization , unclassified final report for contract no . daad05 - 96 - d - 7019 , office of special technology , september 1999 . 45 z . penton , method development with solid phase microextraction , solid phase microextraction ; a practical guide , wercinski ed , 1999 , marcel dekker . 46 t . wan , analysis of explosive odor signatures and detector dog performance employing solid phase microextraction / gas chromatography ( spme / gc ) and controlled polymer permeation , 2002 fiu masters thesis . 47 m . williams et al , proceedings of spie , 1998 , 3575 , pp 291 - 301 . 48 w . a . maccrehan et al , journal of forensic science 2002 , 47 ( 5 ), pp 996 - 1001 . 49 w . burghardt , 4 th national detector dog conference , 2005 , auburn ala . 50 j . johnston et al , proceedings of spie , 1998 , 3392 pp 490 - 501 . 52 department of justice , odor recognition proficiency standard for explosives detection canines , atf draft publication , 2003 .