RESEARCH FRONT

CSIRO PUBLISHINGFull Paper

Aust. J. Chem. 2010, 63, 30–37 www.publish.csiro.au/journals/ajc

Detection of Impurities in Organic Peroxide Explosivesfrom Precursor Chemicals

Andrew Partridge,A Stewart Walker,A and David ArmittB,C

ACentre of Expertise in Energetic Materials, School of Chemistry, Physics and Earth Sciences,Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia.

BDefence Science and Technology Organisation, PO Box 1500, Edinburgh, SA 5111, Australia.CCorresponding author. Email: david.armitt@dsto.defence.gov.au

Previous analyses of organic peroxide explosives have focussed on identification of the explosive itself, and were performedusing explosive samples synthesized from laboratory-grade precursors. In this work, analytical studies of precursorsobtained from retail outlets identified compounds that could be carried over into the explosives as impurities duringsynthesis. Forensic and intelligence information may be gained by the identification of possible precursor impuritiesin explosive samples. This hypothesis was tested using triacetone triperoxide and hexamethylene triperoxide diamineprepared from domestically available off-the-shelf precursors. Gas chromatography–mass spectrometry analysis showedthat compounds originating from such precursors could be detected in the organic peroxide samples at different stages intheir purification. Furthermore, some compounds could also be detected in the residues of samples that had been subjectedto thermal initiation.

Manuscript received: 9 September 2009.Manuscript accepted: 4 November 2009.

Introduction

Cyclic organic peroxides, such as triacetone triperoxide (TATP),diacetone diperoxide (DADP), and hexamethylene triperoxidediamine (HMTD), shown in Fig. 1, were first synthesized in thelate 1800s by German chemists,[1–3] who recognized their explo-sive properties. Owing to their high sensitivity to mechanicalshock, friction, heat and electrostatic discharge, and their poorstorage properties, these explosives have no military or com-mercial use. However, they have found increasing use amongterrorist groups and backyard enthusiasts as they are easily pre-pared from readily available precursors using procedures widelydistributed on the internet. This has led to a higher incidencein the encounters of peroxide explosives for law enforcementand emergency response personnel.[4,5] Recent examples of inci-dents in which organic peroxides were involved include theLondon transit system bombings in 2005[6] and the foiled plotto destroy trans-Atlantic airliners in 2006.[7]

As a result of the expanding use of organic peroxide explo-sives, the number of articles describing instrumental techniquesfor the detection and identification of trace amounts, both pre-and post-blast, has rapidly increased.[8–18] In most of the reportedstudies, the focus was on the detection of the actual organicperoxide explosives, which were manufactured from laboratory-grade precursors, not ingredients readily available to the generalpublic. As such, these explosives are not truly representative ofthe clandestine product likely to be experienced in the field.Hence, the analysis of commercially available precursors is war-ranted, to determine whether any impurities could be introducedinto organic peroxide explosives from these precursors duringsynthesis. Impurities may then serve as markers for the iden-tification of the starting materials and batches of explosives

OO

O O

OO

O

O O

OO

O

N NO

O

O O

TATP HMTD DADP

Fig. 1. Structures of organic peroxide explosives.

for evidence or intelligence purposes, in a similar manner tothat established for illicit drug analysis.[19–22] This approachis complementary to earlier work, in which the analysis ofTATP that had been contaminated with acid impurities identi-fied some differences in degradation products dependent on theacid present.[23] Furthermore, the detonation of TATP has beencalculated to be an entropic process that is not accompanied bya release of large amounts of heat.[24] Therefore, there appearsto be an increased opportunity for any associated impurities tosurvive the initiation of organic peroxide explosives.

The aims of this study were three-fold:

• The identification of non-active ingredients of some com-mon off-the-shelf (OTS) precursors that may be retained asimpurities in the final organic peroxide product,

• Gas chromatography–mass spectrometry (GC-MS) analysisof HMTD and TATP synthesized using the OTS precursors todetermine if the impurities were retained and can be detectedin the final explosive product, and

• GC-MS analysis of initiation products of the HMTD andTATP to determine if the impurities survived and weredetectable.

© CSIRO 2010 10.1071/CH09481 0004-9425/10/010030

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Detection of Impurities in Organic Peroxide Explosives 31

Table 1. NMR and IR data of unknown and three long-chain alkanes

Compound 1H [ppm] 13C [ppm] IR [cm−1]

Unknown impurity 1.25 (m), 0.88 (m) 31.9, 29.7, 29.4, 22.7, 14.1 2955, 2919, 2849, 1473, 1463, 1378, 730, 720Tricosane[26] 1.26 (m), 0.89 (m) 32.1, 29.8, 29.5, 22.8, 14.1 2955, 2918, 2873, 2814, 1474, 1465, 730, 720Tetracosane[26] 1.26 (m), 0.88 (m) 32.0, 29.8, 29.5, 22.8, 14.1 2954, 2917, 2872, 2850, 1471, 1463, 730, 718Pentacosane[26] Not in database 32.0, 29.8, 29.5, 22.8, 14.1 2955, 2918, 2873, 2850, 1474, 1463, 730, 720

Results and DiscussionAnalysis of OTS PrecursorsThe first part of this work was the identification of compoundsthat could persist through a typical organic peroxide synthesisand workup to remain in the final product as trace impurities.After consideration of the precursor chemicals required for thesynthesis of HMTD and TATP, it was decided to concentrate onOTS hexamine and H2O2 products for the screening of potentialimpurity compounds.

Four brands of OTS hexamine camping stove fuel tablets weresubjected to solubility testing in three solvents, H2O, acetone,and MeOH, to determine the best solvent for use in instrumen-tal analysis of both the precursor and the resulting HMTD. Aninsoluble impurity was observed in two brands of hexamine fueltablets that were dissolved in H2O and MeOH, with a higheramount being found in one brand. Initial examination of theimpurity using IR indicated the presence of CH3, CH2, andC–C groups only, suggesting that it may have been a type ofparaffin wax compound. The compound was poorly soluble in arange of common organic solvents; the best result was achievedby extended sonication in CHCl3. A peak at a retention timeof 14.99 min was observed in the GC-MS chromatogram of asample of hexamine (retention time 9.86 min), but could not bereproduced with further samples. The resulting mass spectrumcontained a series of fragment ions that were separated by 14 m/zunits, which provided further evidence that the impurity waslikely an alkane. National Institute of Standards and Technology(NIST) mass spectrum library[25] matches were best for alkanesof 21–25 carbon atoms in length. The recorded NMR and IRspectra were compared with reference spectra obtained from theSpectral Database for Organic Compounds[26] and tetracosaneshowed the best agreement with the spectra obtained for the hex-amine impurity (Table 1). An authentic sample was not availablefor direct comparison; hence no definitive identification of thesubstance could be achieved. The reference IR spectra of tri-,tetra-, and pentacosane are all similar to the observed spectrum,while integration of the 1H NMR peaks did not conclusivelydetermine the number of protons present in the compound. Theimpurity remained present during an entire mock synthesis ofHMTD (no hexamine present) and was trapped by the filter paperduring the simulated workup. As a result, it was concluded thatthe impurity would persist through a synthesis of HMTD.

H2O2 is commonly found in hair-bleaching products, whichalso contain several other chemicals. Potential candidates forimpurities in TATP and HMTD were identified from the ingre-dients listed on the side of the bottle of one brand of H2O2-basedhair-bleaching créme. A survey of other brands revealed simi-lar ingredient lists. Of the six ingredients, cetearyl alcohol andmethyl paraben appeared the most likely to persist through anorganic peroxide explosive synthesis. Cetearyl alcohol is a mix-ture of three compounds: 1-hexadecanol, 1-octadecanol, and1-dodecanol, with 1-hexadecanol and 1-octadecanol making

Table 2. Retention time data for reference and extract samples

Sample Retention time [min]

Reference Extract

Methyl paraben 11.852 11.7721-Hexadecanol 14.440 14.4321-Octadecanol 15.433 15.432

Table 3. Organic peroxide explosive workup and samplingHMTD, hexamethylene triperoxide diamine; TATP, triacetone triperoxide

Step Process HMTD TATP

1 No wash (filtration only) Yes Yes2 Step 1 + H2O wash Yes Yes3 Step 2 + dilute NaHCO3 solution wash Yes Yes4 Step 3 + MeOH wash Yes No

up the majority of the mixture. These compounds have poorsolubility in water and a lower density relative to water. Thissuggests they should remain present during synthesis and couldbe collected with the resulting explosive crystals. Authenticsamples of three of the candidate compounds 1-hexadecanol,1-octadecanol, and methyl paraben were obtained and analyzedby GC-MS to provide reference retention times and mass spectra.1-Hexadecanol, 1-octadecanol, and methyl paraben were suc-cessfully extracted from the bleaching créme matrix, followingdeactivation of the H2O2 with MnO2 (Table 2).

HMTD and TATP AnalysisThe second part of this study was to analyze HMTD andTATP that had been made from OTS products to confirm thatimpurities could be detected in the final products. Organicperoxide explosives samples were synthesized using OTS pre-cursors, containing other non-active components, by replacingone laboratory-grade reagent with either OTS hexamine or OTSH2O2. Samples of the products were taken at each stage ofthe workup to attempt to detect impurities originating from theprecursors (Table 3). Typical workup involves filtration of theprecipitated organic peroxide crystals, and sequential washingwith H2O, a dilute NaHCO3 solution, and MeOH. The MeOHwashing step was omitted for TATP, which has appreciablesolubility in this solvent.

HMTD crystals obtained from the OTS hexamine were simi-lar in appearance to HMTD synthesized using laboratory-gradereagents. No evidence for the presence of the unknown impu-rity, at any stage of purification, was observed by GC-MS. It was

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32 A. Partridge, S. Walker, and D. Armitt

0

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Average of 2.259 to 2.312 min.: 5.D (�)

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5873

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Spectrum 1ABP: 45.3 12.842 min, scan: 1280, 40:400, ion: 499 us, RIC: 1.760e�6, BC

45.3

44.4

88.0

43.4

56.3

50 100 150 200

m/z

73.0

89.1116.9

207.7

Fig. 2. Reference[31] (top) and observed (bottom) mass spectra for hexamethylene triperoxide diamine (HMTD).

believed that the impurity may not have sufficient volatility fordetection under the conditions used for organic peroxide explo-sive analysis. Of interest, however, was the presence of a peakat a retention time of 12.81 min, which displayed a shape sim-ilar to that observed for TATP. There are currently few articlesin the literature on the detection of HMTD by GC-MS,[27–29]

with deactivation of GC columns by HMTD resulting in broadasymmetrical peaks being reported.[30] Thus, direct compari-son of mass spectral data obtained under similar conditions wasdifficult. As a result, the observed mass spectrum (from an ion-trap mass spectrometer) was compared with one obtained on aquadrupole GC-MS instrument (J. Oxley, pers. comm.). Therewas good agreement between the spectra (Fig. 2), except for theabsence of the peak at m/z 176 and different peak intensities.These differences may be attributed to the different instruments

used to collect the spectra.[31] The reduced relative abundanceof the molecular ion in the observed spectrum indicates a higherdegree of fragmentation in the ion-trap instrument comparedwith the quadrupole instrument. The implication is that moreenergy is imparted to the analyte either during ionization or bycollisions within the ion trap, and could account for the loss ofthe m/z 176 ion, as it fragments more readily.

The appearance of the HMTD obtained from OTS H2O2 wassignificantly different to the HMTD synthesized using OTS hex-amine. The product retained the appearance of the bleachingcréme emulsion and it was difficult to determine if there wereany crystals of HMTD present. At each successive stage of theworkup, the product became progressively drier; however, it stillretained a significant amount of other material and the sam-ple that underwent total workup took on the appearance of a

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Detection of Impurities in Organic Peroxide Explosives 33

HMTD

1-Hexadecanol

Methylparaben

0

5 10 15

Minutes

20 25

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11.765 min

12.815 min

15.418 min

1-Octadecanol14.419 min

181017_027.SMS TIC

1-Hexadecanol

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5.887 min

TATP

17.803 min

12.295 min

11.412 min15.409 min

14.408 min

10.584 min

1-Octadecanol

080829_018.SMS TIC

Fig. 3. Total ion chromatograms of pre-initiation samples of (a) hexamethylene triperoxide diamine (HMTD), and(b) triacetone triperoxide (TATP), synthesized from off-the-shelf H2O2.

solid lump. The presence of HMTD, along with all three pre-cursor impurities from the hair bleach, was detected in eachsample, confirming the theory that these impurities could per-sist through the synthetic process. A typical chromatogram isshown in Fig. 3a.

TATP synthesized using OTS H2O2 also retained the appear-ance of the bleaching créme emulsion and got progressively drierwith each subsequent wash, although liquid was still present ineach sample. It was also difficult to observe if any crystals werepresent. TATP was detected in all samples, with a small amountof DADP also being detected in the no-wash sample at a retention

time of 1.99 min. Only two impurities were able to be iden-tified in the TATP samples, 1-hexadecanol and 1-octadecanol.The region of the chromatogram at the retention time for methylparaben was extremely cluttered (Fig. 3b), but an extracted ioncurrent chromatogram for m/z 152 and 121 (the major fragmentions for methyl paraben) did not reveal a peak at ∼11.7 min.This may be due to previous analysis of HMTD samples having adetrimental effect on the column.These results, however, demon-strate that the impurities present in an OTS H2O2 precursor canpersist through synthesis to remain present in the final explosiveproduct.

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34 A. Partridge, S. Walker, and D. Armitt

HMTD

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081024_021.SMS TIC

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5.527 min6.508 min

1-Octadecanol

081024_009.SMS TIC

Fig. 4. Total ion chromatograms of post-initiation samples of (a) hexamethylene triperoxide diamine (HMTD)synthesized from off-the-shelf (OTS) hexamine, (b) HMTD synthesized from OTS H2O2, and (c) triacetone triperoxide(TATP) synthesized from OTS H2O2 (part c is continued on next page).

Post-Initiation AnalysisAs components from the OTS precursors had been successfullydetected in HMTD and TATP products, the next phase of thestudy was to determine if they would survive the initiation ofthe explosives in detectable amounts. Explosives samples (5–10 mg) were subjected to initiation attempts in sealed 20-mLsolid phase microextraction (SPME) vials by the application ofa remotely controlled gas flame to the bottom of the exterior ofthe vials. TATP that had undergone all washing procedures wasin enough abundance for duplicate experiments. Residues were

extracted with MeCN (HMTD) or MeOH (TATP) and analyzedby GC-MS.

HMTD samples produced from OTS hexamine that hadundergone initiation did not contain the unknown impurity, asfor the pre-initiation samples. However, chromatograms of allsamples contained peaks at ∼0.9 min (Fig. 4a), which returneda NIST library match for formic acid, and this was subse-quently confirmed by comparison with an authentic sample offormic acid. Thermal decomposition of HMTD is known to gen-erate formaldehyde,[32,33] while ultraviolet and acid-catalyzed

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Detection of Impurities in Organic Peroxide Explosives 35

1-Hexadecanol

DADP

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14.711 min15.166 min

15.683 min16.020 min

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081024_045.SMS TIC

Fig. 4. (Continued)

decomposition gives hydrogen peroxide.[18,34] It is possible thatunder the conditions of initiation, formaldehyde is released,which reacts with H2O2 (or another oxidant, e.g. oxygen) to formformic acid. Intact HMTD was also detected in some samples.

After initiation, HMTD samples made using the hair-bleaching créme were found to still contain all three of theimpurities from the OTS H2O2. Of interest were numerous peaksof higher retention time than 1-octadecanol in the chromatogramof the no-wash sample (Fig. 4b). The mass spectra of thesepeaks have similar fragmentation patterns to the two alcoholimpurities. These peaks may arise from partial combustion orthermal cleavage of the precursor impurities followed by recom-bination of fragments during initiation. This is also seen in thewater-only wash sample, but to a much lesser degree, with onlyone peak following each alcohol impurity. The NaHCO3- andMeOH-wash samples contain large peaks at 0.9 min, indicatingthe decomposition of HMTD into formic acid as above.

Two impurities, 1-hexadecanol and 1-octadecanol, weredetected in very small quantities in the TATP NaHCO3-washsamples following initiation. Also present in the chromatogramsof these samples and the water-wash sample were numerouspeaks around the retention times of the alcohols (Fig. 4c).The mass spectra of these peaks resembled those of long-carbon-chain molecules. This result is similar to that of HMTDsynthesized from OTS H2O2 and may suggest that, although1-hexadecanol and 1-octadecanol survive initiation, another pro-cess occurs that produces new compounds. Further investigationinto the identities of these products is warranted.

Also of note was the relatively large amount ofTATP detected,even in samples that had been observed to initiate. It is thoughtthat sublimation of the highly volatileTATP to areas in the SPMEvials away from the gas flame caused an incomplete deflagration.Solid residues were noted on previously clean parts of the SPMEvials following heating.

Conclusions

A qualitative study into the persistence of non-active componentsfrom OTS precursors in the final products of organic peroxideexplosive synthesis was conducted in three parts.

OTS reagents, obtained from retail outlets, were analyzedto determine the likelihood of contamination of the product ifused to synthesize HMTD and TATP. One candidate for con-tamination was found in hexamine camping stove fuel tablets,but has not been conclusively identified to date. Three com-pounds (1-hexadecanol, 1-octadecanol, and methyl paraben)were identified as likely contaminants from H2O2 hair-bleachingcréme.

‘Clandestine’HMTD and TATP samples were prepared usingthe OTS reagents. Impurities emanating from the hair-bleachingcréme were observed in both HMTD and TATP samples byGC-MS, which indicates that their persistence throughout thesynthesis and workup process is possible. The impurity found inhexamine tablets was not detected in HMTD samples by GC-MS;however, this may be due to the insolubility and non-volatilityof the impurity, and other analytical techniques may be moreapplicable.

The clandestine organic peroxide explosives samples weresubjected to initiation and subsequent analysis by GC-MS. IntactTATP and HMTD were able to be detected along with precursorimpurities, indicating that the impurities are able to withstandinitiation. The presence of other compounds may also serveas markers for organic peroxide explosives prepared from OTSreagents following an explosion.

Thus, chemical characterization of the explosives HMTD andTATP may be performed both pre- and post-blast to potentiallyreveal the precursors used during manufacture. This is signifi-cant as it will provide information for forensic, law enforcementand Defence personnel in the fight against improvised explosivedevices and home-made explosives.

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36 A. Partridge, S. Walker, and D. Armitt

Table 4. Column settings for GC-MS analyses

Injection volume [µL] 1.0Initial temperature [◦C] 50Hold time [min] 2.0Intermediate temperature [◦C] 90Temperature ramp [◦C min−1] 10Hold time [min] 3.0Final temperature [◦C] 200Temperature ramp [◦C min−1] 20Hold time [min] 10.0Run time [min] 24.5Injector temperature [◦C] 120Carrier gas flow rate [mL min−1] 1.0Split ratio 30:1

Experimental

CAUTION: Organic peroxide explosives such as HMTD andTATP are highly sensitive to initiation by impact, friction, elec-trical discharge, and heating. Handling of these explosives wasperformed by trained and experienced staff within a specializedlaboratory using appropriate safety equipment and procedures.

ReagentsHexamine (≥90%, Aldrich), H2O2 (30% w/w in water, VLSISelectipur 31%, BASF Ludwigshafen), 1-hexadecanol (99%,Sigma–Aldrich), 1-octadecanol (99%, Sigma–Aldrich), methyl4-hydroxybenzoate (methyl paraben) (≥99%, Fluka), MnO2(technical grade, Ace Chemical Co.), MeCN (99%, Burdick &Jackson), MeOH (>99.5%, Sigma–Aldrich), CHCl3 (99.0–99.4%, Aldrich), and acetone (>99.5%, Ajax Chemicals) wereused as received. Four different brands of hexamine campingstove fuel tablets and one brand of hair-bleaching créme con-taining H2O2 were obtained from retail outlets and used withoutpurification. Reference samples of TATP, DADP, and HMTDwere synthesized from analytical-grade chemicals at the DefenceScience and Technology Organisation (DSTO) using establishedprocedures. ClandestineTATP and HMTD samples were synthe-sized at DSTO using procedures obtained from the internet bysubstituting one laboratory-grade reagent with an OTS reagent.

InstrumentsGC-MS analysis was performed on a Varian 4000 ion-trap GC-MS fitted with a Restek RTX®-5 SILMS (15 m × 0.25 mm ×0.25 µm; Bellefonte, PA, USA) and a CombiPal autosampler.Chromatographic column conditions are outlined in Table 4. Themass spectrometer was operated in internal electron ionizationmode (70 eV), with an emission current of 10 µA, multiplieroffset of 0V, scan range of m/z 40–400, and filament delay of0.75 min. The transfer line and ion trap temperatures were set at170◦C and 150◦C, respectively, to minimize thermal degradationof the analytes.

IR analysis was performed on a Thermo Electron Corp.Nicolet Avatar 370 DTGS Fourier-transform infrared (FT-IR)spectrometer (Thermo Fisher Scientific Inc., Waltham, MA,USA) in % transmittance mode. Samples were taken over ascan range of 4000–400 cm−1. Sample solutions were depositedonto a sodium chloride (NaCl) window and the solvent wasallowed to evaporate, or powdered samples were incorporatedinto potassium bromide (KBr) discs. NMR spectra were recordedon a Varian NMR spectrometer (Varian, Palo Alto, CA, USA)

Remotely operatedflame

Explosivesample

SPME vial

Fig. 5. Schematic diagram of initiation experiments. SPME, solid phasemicroextraction.

operating at 300 MHz (1H) or 75 MHz (13C) using CDCl3 as thesolvent and internal lock. Chemical shift values were recordedin ppm from internal tetramethylsilane.

Sample PreparationPrecursor AnalysisHexamine fuel tablets (2.0–18.9 g) were dissolved in MeOH,

with two brands leaving an insoluble white powdery residuefloating on the surface of the solvent, which was collected by fil-tration and dried. The residue was partially dissolved in CHCl3or CDCl3 by extended sonication for GC, GC-MS, and NMRanalysis. δH 1.25 (m), 0.88 (m). δC 31.9, 29.7, 29.4, 22.7, 14.1.νmax(KBr)/cm−1 2955, 2919, 2849, 1473, 1463, 1378, 730, 720.GC-MS Rt 14.995 min; m/z [%] 125 (7), 111 (36), 97 (87), 83(94), 69 (100), 55 (99), 41 (85).

The hair-bleaching créme was treated with solid MnO2 toremove the H2O2 before the extraction of its other componentsfor safety reasons. A small quantity of MnO2 was added tobleaching créme (40 mL) along with water (40 mL) to increasethe amount of aqueous phase. Once the generation of gas hadceased, the solution was carefully decanted into a separating fun-nel and extracted with ether (50 mL).The resulting organic phasewas collected and concentrated under vacuum. The residue wasrecrystallized from MeOH, then redissolved in MeOH beforebeing filtered. GC-MS standards of each of the possible impu-rities of interest (1-hexadecanol, 1-octadecanol, and methylparaben) were prepared as 10 ng µL−1 solutions in MeOH.

Organic Peroxide ExplosivesFollowing the synthesis of clandestine TATP and HMTD,

samples of each batch were taken at different stages of workup:no-wash, H2O wash, NaHCO3 wash, and MeOH wash (HMTDonly). TATP and HMTD samples for GC-MS analysis wereprepared as 1 µg µL−1 solutions in MeOH and MeCN, respec-tively. Reference samples of pure TATP and DADP of the sameconcentration were also prepared.

Post-Initiation AnalysisOrganic peroxide explosive samples (5–10 mg) in sealed

SPME vials were placed under a remotely operated Bunsenburner in a purposely built facility. Four samples underwent heat-ing with the gas flame each time. Samples were placed with theexplosive nearest the flame and the top of the vial facing awayfrom the flame (Fig. 5). The flame was operated for 10-s inter-vals and the samples were deemed to have initiated on visualobservation of a flash within the vial. Workup was undertaken

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Detection of Impurities in Organic Peroxide Explosives 37

by injecting 1 mL of the appropriate solvent (MeCN for HMTD,MeOH for TATP) through the top of the SPME vial, and rollingand agitating the vial for a period of 30 s to extract the residues.

AcknowledgementsOur appreciation goes to Professor Jimmie Oxley (University of RhodeIsland) for providing a mass spectrum of HMTD. The authors would liketo acknowledge the contributions of Mark Fitzgerald and Mark Champion(DSTO) to this body of work. A.P. would also like to thank the Centre ofExpertise in Energetic Materials for the provision of funding.

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