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ExploringApplicabilityofDirectAnalysisinRealTime
withMassSpectrometry(DART-MS)toIdentifyHomemadeExplosiveResiduesPost-Blast
by
ChelseaElizabethBlack
AthesissubmittedtotheFacultyofGraduateandPostdoctoralAffairsinpartialfulfillmentoftherequirementsforthedegreeof
MasterofScienceIn
Chemistry
CarletonUniversityOttawa,Ontario
©2019ChelseaElizabethBlack
1
AbstractApplication of Direct-Analysis-in-Real-Time (DART) ionization with mass spectrometry
(DART-MS) to identify explosives from post-blast residues is presented. Explosives of
interest represent real current threatsencountered in criminal investigations inNorth
America and Europe: homemade organic peroxides, binary explosives and smokeless
powder.Aseriesof simulated improvisedexplosivedevices (IEDs)weremanufactured
usingtriacetonetriperoxide(TATP),hexamethylenetriperoxidediamine(HMTD),methyl
ethylketoneperoxide(MEKP),homemadebinaryexplosives(composedofafuel-oxidizer)
andsingleanddouble-basesmokelesspowders.EachIEDwasconfiguredtoyieldbomb
fragmentsrepresentativeofactualmaterialsrecoveredfrombombinginvestigations.The
goal of this study was to demonstrate the validity of DART-MS for identification of
homemade explosives using real world samples (i.e. not laboratory simulations) and
develop a quality assured method for use in accredited forensic laboratory settings.
Smokelesspowderwasofspecificinterestasthereiscurrentlynoreportedmethodto
identify nitrocellulose (NC) post-blast, unless unconsumed material is recovered.
Therefore, this study aimed to demonstrate the validity of DART-MS to characterize
thermalbreakdownproductsofNC.Allrecoveredfragmentswereanalyzeddirectlyand
in directly (i.e. cotton swabs and solvent extraction methods) using full scan high
resolutionmassspectrometry (HRMS).Thisworkdemonstrates the forensicvalidityof
DART-MStoproviderapidandqualityassuredidentificationofexplosiveresiduesfrom
realpost-blastIEDfragments.
2
Acknowledgements
TomysupervisorsDr.NigelHearnsandDr.JeffreySmith,Iwouldliketothankyou
bothfortheopportunitytoworkonthisprojectwithyouboth.Yourvision,supportand
guidancethroughoutourworkingyearstogetherwasparamountinthesuccessofthis
project.Jeff,Itrulyappreciatetheamazingopportunitiesyouhavegivenme.Forallthe
advice,supportandencouragement,Iamtrulythankful.Havingcometoyourofficein
bothmomentsofexcitementandstress,youalwaysknewexactlywhatIneededtohear
tofurthermotivatemeorhelpmegetthroughanystrugglesIwasexperiencing.Nigel,I
amforevergratefulfortheexperienceIhavehadworkingonthisprojectwithyou.The
developmentofmyknowledgeandskillsareadirectresultofthepatienceandtimeyou
havetakenteachingwhenmeaboutforensicscience,explosives,experimentaldesign,
professionalismandthelistgoeson.Thankyouforadvocatingforthisresearchwithinthe
labandtheorganization.Yourcontinuous,never-endingsupporthasmadethisthemost
rewardingandmemorableworkingexperienceofmylife.Thank-you!
To my friends and family – I would like to thank you all for your continuous
encouragementandsupportduringthecompletionofmyMasters.Dad,withtheturning
of each school year, and yes I know there have beenmany, your support has never
wavered.Asaparentchaperoneonpublicschoolfieldtrips,afaninthestandsofmany
sportsgamesandcomingtoOttawatositinasaspecialguestatmydefence-youhave
never missed any special moment in my educational career, big or small. Your
understandingandappreciationformyloveofschoolhasallowedmetopursueanyand
everydreamIhaveeverhad.Yourkindwords,immenseloveandthoughtfuladvicehas
3
helpedmereacheachdestinationinthepaththathasledmetotheendofgradschool.
Youaretrulymygreatestconfidant.Mom,havingsharedyourinnatelovefor learning
withme,Ihaveyoutothankformydriveanddeterminationtoobtainsuchafulsome
education.RyanandCourtney,youhavebeenthegreatestrole-modelsalittlesistercould
ask for. Your hard-work, determination, and commitment to your professions while
maintainingimportantrelationshipsandfriendshipsissomethingItrulyadmireinbothof
you. Thank you so much for always cheering me on, providing sound advice and
encouragingmetonevergiveup!TotheMacDonaldfamily,Icanneverthankyouenough
for includingme in your extremely loving and supportive family. Finally, tomy girls –
Christine,Stephanie,Annah,JillianandKylie.Ourfriendshipmeanstheworldtome.Iam
so thankful for all the memories made and your never-ending support and
encouragement.
BeingamemberoftheSmithLabhasbeensuchapleasure.Participatingingroup
meetings,celebratingtheholidaysatourepicChristmaspartiesandsharingaglassof
beer(ciderformeofcourseJ)attheendoftheweekwillforeverbesomeofmyfondest
memories of my time at Carleton University. To all Smith labmembers, current and
alumni,Iwanttothankyoufortheknowledge,experienceandadviceyouhaveshared
withmeduringmytimeinthelab.Karl,ourabilitytonaturallyseguefromexperiment
troubleshootingtoourlatestFridaynightadventureswithourfriendsandfamilieswill
neverbelostuponme.OurfriendshipisextremelyimportanttomeandIlookforwardto
continuousupdatesandcatchingupwhenyoucometovisitinKingston!
4
ToallthemembersoftheDepartmentofChemistryatCarletonUniversity,Ithank
you for your support, knowledge, ideas and friendships and the many learning and
teachingopportunitiesprovidedtomebyTApositionsandvolunteeropportunities.
To all the members of the Trace Evidence section of the Forensic Laboratory
Services and the RCMP at large; I thank you for your support, access to resources,
knowledgeandpatienceasInavigatedmywaythroughthisresearchstudy. Youhave
beensowelcoming,encouragingandsupportive.
5
TableofContentsAbstract...................................................................................................................................................................1
Acknowledgements.................................................................................................................................................2
ListofTables............................................................................................................................................................6
ListofFigures..........................................................................................................................................................7
ListofSchemes......................................................................................................................................................12
ListofAbbreviations..............................................................................................................................................13
Foreword...............................................................................................................................................................15
1.Introduction......................................................................................................................................................18
1.1.Explosives...................................................................................................................................................18
1.1.1.Homemadeexplosives.......................................................................................................................20
1.2.ExplosiveAnalysis......................................................................................................................................29
1.2.1.IonMobilitySpectrometry(IMS)........................................................................................................29
1.2.2.ChromatographyMethods.................................................................................................................30
1.2.3.MassSpectrometry(MS)....................................................................................................................35
2.MaterialsandMethods.....................................................................................................................................45
2.1.Consumables,ReagentsandStandardReferenceMaterials.....................................................................46
2.2.IEDConstruction,DetonationandFragmentCollection............................................................................47
2.3.ReferenceMaterialSamplePreparation...................................................................................................49
2.3.1.FuelandOxidizer................................................................................................................................49
2.3.2.OctanitrateCellobioseSynthesisandSamplePreparation................................................................49
2.3.3.SmokelessPowder.............................................................................................................................50
2.4.Post-BlastExtractPreparation...................................................................................................................50
2.5.DART-MSAnalysis......................................................................................................................................51
3.ResultsandDiscussion......................................................................................................................................52
3.1DART-MSParameterOptimization.............................................................................................................52
3.2.AnalysisofFragments................................................................................................................................53
3.2.1.OrganicPeroxideExplosives...............................................................................................................61
3.2.2.BinaryExplosives................................................................................................................................74
3.2.3.SmokelessPowders............................................................................................................................90
4.Conclusion.........................................................................................................................................................96
5.FutureWork......................................................................................................................................................97
References.............................................................................................................................................................98
Appendix1:SupplementaryInformation............................................................................................................102
6
ListofTablesTable1.Examplesofproductsthatsourcecomponentsforbinaryexplosives............................24
Table2.TypeandamountofexplosiveusedasmainchargeforeachIED...................................48
Table3.LODsobservedforexplosivesofinterestmeasuredusingin-housemethodandQuickStripcomparedtoliteraturevalues.............................................................................52
Table4.DepictionoftheOPBEidentifiedviaDART-MSdirectanalysisofamultitudeofdifferentpost-blastfragmentscomparedtoin-direct.........................................................................62
Table5.CharacteristicionsofHMTDpresentuponanalysisofresiduescollectedviaswabsdifferentiatedbysubstrate...................................................................................................71
Table6.Listofmassformulaefortheionscharacteristicofnitratedsugarthermalbreakdownproducts,withassociatedmassshift(amu)..........................................................................93
7
ListofFiguresFigure1.Triacetonetriperoxide(TATP)........................................................................................21
Figure2.Hexamethylenetriperoxide(HMTD)..............................................................................22
Figure3.Methylethylketone(MEKP)..........................................................................................22
Figure4.Fully-nitratednitrocellulose...........................................................................................26
Figure5.Nitroglycerin...................................................................................................................27
Figure6.Diphenylamine...............................................................................................................27
Figure7.Ethylcentralite...............................................................................................................27
Figure8.Schematicdiagramofanionmobilityspectrometer(IMS)............................................29
Figure9.Schematicdiagramoftheinstrumentationusedtoseparateanalytesofamixtureviahigh-performanceliquidchromatography(HPLC)................................................................31
Figure10.Schematicdiagramoftheinstrumentationusedtoseparatevolatilecomponentsinamixtureviagaschromatography(GC)...................................................................................32
Figure11.Schematicdiagramoftheinstrumentationusedforsimultaneousseparationofanionsandcationsinsolutionviaionchromatography(IC).............................................................33
Figure12.SchematicdiagramofDARTsource..............................................................................39
Figure13.ImagesofthedifferentorientationsoftheDARTsourcewithrespecttotheMSinterface:(a)surfacedesorptionmodeand(b)transmissionmode.....................................42
Figure14.SchematicdiagramofthedesignandengineeringoftheQ-Exactivehybridmassspectrometer.........................................................................................................................44
Figure15.Fragmentscollectedpost-blastfromthedetonationofdevicesutilizinghomemadeexplosivesasthemaincharge(IED#1-14)............................................................................47
Figure16.IonsobservedviaoperationoftheQExactiveinpositivefullscanmode,withouttheDARTsourceturnedon.Totalioncount103.........................................................................54
Figure17.EndogenousDART-MSions.Totalioncount104-105..................................................54
Figure18.Analysisofanunusedcottonswabinpositivemodeusingfullscan.Totalioncount104.........................................................................................................................................55
Figure19.AnunusedQuickStripanalyzedinpositivemodeusingfullscan.Totalioncount103-105.........................................................................................................................................55
8
Figure20.WaterdepositedontoaQuickStrip,analyzedinpositivemodeusingfullscan.Totalioncount104–105................................................................................................................56
Figure21.MethanoldepositedontoaQuickStrip,analyzedinpositivemodeusingfullscan.Totalioncount104–106................................................................................................................56
Figure22.AcetonedepositedontoaQuickStrip,analyzedinpositivemodeusingfullscan.Totalioncount104–106................................................................................................................57
Figure23.AcetonitriledepositedontoaQuickStrip,analzyedinpositivemodeusingfullscan.Totalioncount104–106.......................................................................................................57
Figure24.AnalysisofdichloromethanedepositedontoaQuickStrip,inpositivemodeusingfullscan,tobeusedforsolventassociatedionsubtraction.Totalioncount104–106..............58
Figure25.AnalysisofhexanedepositedontoaQuickStrip,inpositivemodeusingfullscan.Totalioncount104–105................................................................................................................58
Figure26.Positivemode,fullscanhigh-resolutionmassspectrumforTATPanalyzedfromcertifiedreferencestandard.IonscharacteristicofTATPhavebeenboldedandlabelled...63
Figure27.Positivemode,fullscanhigh-resolutionmassspectrumforTATPupondirectanalysisoffragmentfromIED#2.IonscharacteristicofTATPhavebeenboldedandlabelled.........64
Figure28.Positivemode,fullscanhigh-resolutionmassspectrumforTATPanalyzedfromaswabusedtocollectpost-blastresiduesfromIED#2fragments.IonscharacteristicofTATPhavebeenboldedandlabelled.............................................................................................64
Figure29.Fullscanhigh-resolutionmassspectrumforHMTDanalyzedfromcertifiedreference.IonscharacteristicofHMTDhavebeenboldedandlabelled................................................65
Figure30.Fullscanhigh-resolutionmassspectrumdepictingidentificationofHMTDfromdirectanalysisofafragmentcollectedpost-blastfromIED#3.IonscharacteristicofHMTDhavebeenboldedandlabelled......................................................................................................66
Figure31.Fullscanhigh-resolutionmassspectrumdepictingidentificationofHMTDuponanalysisofaswabusedtocollectpost-blastresiduesfromIED#3fragments.IonscharacteristicofHMTDhavebeenboldedandlabelled.......................................................66
Figure32.Positivemode,fullscanhigh-resolutionmassspectrumforMEKPanalyzedfromthecrudesynthesizedproduct.IonscharacteristicofMEKPhavebeenboldedandlabelled...68
Figure33.Positivemode,fullscanhigh-resolutionmassspectrumdepictingidentificationofMEKPfromdirectanalysisoffragmentcollectedpost-blastfromIED#5.IonscharacteristicofMEKPhavebeenboldedandlabelled...............................................................................69
9
Figure34.Positivemode,fullscanhigh-resolutionmassspectrumdepictingidentificationofMEKPuponanalysisofaswabusedtocollectedpost-blastresiduesfromIED#5fragments.IonscharacteristicofMEKPhavebeenboldedandlabelled................................................69
Figure35.Fromlefttoright-cottonswab,paperswab,modifiedpaperswab...........................71
Figure36.Fullscanhigh-resolutionmassspectradepictingidentificationofHMTDuponcollectionofpost-blastresiduesfromIED#5usingdryandsolventdampenedswabs.......73
Figure37.Fullscanhigh-resolutionmassspectrumofglucosedissolvedinwaterasareferencematerial.Collectedinpositivemode.....................................................................................76
Figure38.Fullscanhigh-resolutionmassspectrumofsucrosedissolvedinwater,usedasareferencematerial.Collectedinpositivemode....................................................................76
Figure39.Fullscanhigh-resolutionmassspectrumofTANGdissolvedinwater,usedasareferencematerial.Collectedinpositivemode....................................................................77
Figure40.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#11metalsubstratefragment.Collectedinpositivemode...................................................................77
Figure41.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#11plasticsubstratefragment.Collectedinpositivemode...................................................................78
Figure42.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#11rubbersubstratefragment.Collectedinpositivemode...................................................................78
Figure43.Fullscanhigh-resolutionmassspectrumofdextrinreferencematerialdissolvedinwater.Collectedinpositivemode.........................................................................................79
Figure44.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#12plasticsubstratefragment.Collectedinpositivemode...................................................................79
Figure45.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#12metalsubstratefragment.Collectedinpositivemode...................................................................80
Figure46.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#12rubbersubstratefragment.Collectedinpositivemode...................................................................80
10
Figure47Fullscanhigh-resolutionmassspectrumofanautomotivegrease,usedasareferencematerial.Collectedinpositivemode.....................................................................................83
Figure48.Fullscanhigh-resolutionmassspectrumdepictingidentificationofautomotivegreasefrompost-blastresiduesextractedwithhexanefromIED#10metalsubstratefragment.Collectedinpositivemode....................................................................................................83
Figure49.Fullscanhigh-resolutionmassspectrumdepictingidentificationofautomotivegreasefrompost-blastresiduesextractedwithhexanefromIED#10plasticsubstratefragment.Collectedinpositivemode....................................................................................................84
Figure50.Fullscanhigh-resolutionmassspectrumdepictingidentificationofautomotivegreasefrompost-blastresiduesextractedwithhexanefromIED#10rubbersubstratefragment.Collectedinpositivemode....................................................................................................84
Figure51.Negativemode,fullscanhighresolutionmassspectrumuponoperationoftheDART-MS,depictingtheendogenousions.Totalioncount106......................................................86
Figure52.AnalysisofwaterdepositedontoaQuickStrip,innegativemodeusingfullscan.Totalioncount106.........................................................................................................................87
Figure53.Negativemode,fullscanhigh-resolutionmassspectrumforammoniumnitrateanalyzedasareferencematerial..........................................................................................87
Figure54.Negativemode,fullscanhigh-resolutionmassspectrumforacommerciallyavailablestumpremover(commercialsourceofKNO3),analyzedasareferencematerial................88
Figure55.IdentificationofKNO3innegativemodeviafullscanhighresolutionDART-MSanalysisofpost-blastresiduesextractedfrommetalsubstratefragmentsfromIED#10withwater................................................................................................................................................88
Figure56.IdentificationofKNO3innegativemodeviahigh-resolutionDART-MSanalysisofpost-blastresiduesextractedfromplasticsubstratefragmentsfromIED#10withwater...........89
Figure57.IdentificationofKNO3innegativemodeviafullscanhigh-resolutionDART-MSanalysisofpost-blastresiduesextractedfromrubbersubstratefragmentsfromIED#10withwater................................................................................................................................................89
Figure58.Determinationofionscharacteristicofthethermalbreakdownproducts.................92
Figure59.Relativesolubilityofresiduescontainingthermalbreakdownproducts.....................94
Figure60.Positivemode,fullscan:high-resolutionmassspectrafordiesel,analyzedasareferencematerial...............................................................................................................102
Figure61.Positivemode,fullscan:high-resolutionmassspectraforlampoil,analyzedasareferencematerial...............................................................................................................102
11
Figure62.Positivemode,fullscan:high-resolutionmassspectraforVaseline,analyzedasareferencematerial...............................................................................................................103
Figure63.Positivemode,fullscan:high-resolutionmassspectraforwax,analyzedasareferencematerial...............................................................................................................103
12
ListofSchemesScheme1.Reactionschemefortheelectronicorvibronicproductionofmetastablespecies(M*)
frominertgas(M)occurringinthesourceviaaseriesofelectrodes...................................38
Scheme2.Reactionschemestoproducesecondaryionizingspecies(ionizedwaterclusters)inpositivemodeviareactionofmetastablespeciesproducedbytheDARTsourcewithatmosphericreagents............................................................................................................40
Scheme3.Reactionschemestoproduceionizedanalytespecies(S+•)inpositivemodeviareactionofsecondaryionizedspeciesandanalytemoleculespresentedtothesourceregion....................................................................................................................................40
Scheme4.Reactionschemesforproductionofnegativeionizedanalytespecies(S-)via...........41
13
ListofAbbreviations ACN=Acetonitrile
AN=AmmoniumNitrate
Ar=Argon
DART=DirectAnalysisinRealTime
DART-MS=DARTcoupledMassSpectrometry
DPA=Diphenylamine
EC=EthylCentralite
EIC=ExtractedIonChromatogram
FTIR=Fourier-TransformInfraredSpectroscopy
FLS=ForensicLaboratoryServices
FWHM=Full-WidthHalf-Maximum
GC=Gaschromatography
He=Helium
He*=Excited-stateHelium
HRMS=High-resolutionmassspectrometry
HME=HomemadeExplosives
HMTD=HexamethyleneTriperoxide
HPLC=High-PerformanceLiquidChromatography
IC=Ionchromatography
IED=ImprovisedExplosiveDevices
14
IMS=IonMobilitySpectrometry
LOD=LimitofDetection
LRMS=Low-resolutionmassspectrometry
MEKP=MethylEthylKetonePeroxide
MeOH=Methanol
MS=MassSpectrometry
N2=Dinitrogengas
NC=Nitrocellulose
NG=Nitroglycerin
ONCB=OctanitrateCellobiose
OPBE=Organicperoxide-basedexplosives
PETN=PentaerythritolTetranitrate
RCMP=RoyalCanadianMountedPolice
TATP=TriacetoneTriperoxide
Th=Thomsons
TIC=TotalIonChromatogram
TLC=ThinLayerChromatography
TPOF=TechnicalandProtectiveOperationsFacility
15
Foreword
Forensic science is the application of science to law and is a subject of great
fascinationtothepublicatlargeasoftenportrayedinmainstreamentertainmentmedia
andHollywoodcinematographicmovies.1Entertainmentmediaforpublicconsumption
oftenportraysadistortedorembellishedviewofactivitiesinvolvedwithforensicscience.
The truth about advantages and limitations, policies and regulations are often
misrepresented.InCanada,forensicscienceservicesaredeliveredbyscientistswhowork
atalllevelsofgovernment,includingfederal,provincialandmunicipal.Medicalcoroners
areeithermunicipallyorprovinciallyregulated.Forensicanalysisservicesrequestedby
municipal and provincial police agencies are funded by the provincial government in
OntarioandQuébecandareperformedbyscientistsattheCentreofForensicSciencein
TorontoforOntarioortheLaboratoiredesciencesjudiciairesetdemédecinelégaledu
QuébecinQuébec,respectively.1TheRoyalCanadianMountedPolice(RCMP)Forensic
LaboratoryServices(FLS)deliversforensicanalysisservicestoallpoliceagenciesoutside
ofQuébecandOntario,andforallfederalpolicingactivities inallprovincesacrossthe
country.1
Manystreamsofscience(e.g.biology,psychology,toxicologyandchemistry)are
utilized considerably to assist in criminal investigations. 2 Locard’s exchange principle
states thatwhen twoobjects come intocontact there isalwaysa transferofmaterial
between them, even if only at the microscopic level. The consequence of Locard’s
exchange principle in forensic science is that any action made by an individual in
commissionofacrimeleadstotheproductionofevidence.Thepowerofsuchevidence
16
lies in the ability to detect, identify and understand the information provided for
capturing the individual or re-creating the circumstances of the crime committed. 2
Chemicalanalysesprovidespolicewithanswers to investigationalquestions toensure
valid identification and source attribution of evidence found at the scene of a crime.
Explosive materials represent a serious hazard as they can be illicitly used for mass
destructionandinjuryordeath.Detectionandidentificationofexplosivesthusremain
critical to ensure public safety, infrastructure security, and bolster counter-terrorism
readiness. After an explosion, recovering and analyzing bomb fragments can provide
importantforensiclinksfortheensuinginvestigation,especiallyincaseswherethereare
no biological traces (i.e. DNA) found at the scene. The substrate, size, and degree of
burningofthefragmentscollectedpost-blastcanprovidenecessaryinformationforthe
re-constructionof theexplosivedevice.Post-blast residueswillyieldunconsumedand
combustionproducts3fromtheoriginalenergeticmaterial,whichprovidesthenecessary
informationtoidentifythetypeandthesourceoftheexplosivefillerusedinthedevice.
Variousfieldandlaboratorytechniquesareavailablefordetectionofexplosives,
bothpre-andpost-blast.4Ionmobilityspectrometry(IMS)remainsapopulartechnique
forrapidfielddetectionofawidevarietyofexplosivesandisextensivelyusedforpre-
screeningpeopleandobjectsat securitycheckpointsas theyareeasilyprogrammable
making them user friendly for front line staff. 5 Matrix interference arising from
environmentalcontaminantsorothercongenerscanaffectthediscriminatingpowerof
IMSandtestresultsarelargelyusedforpresumptivepurposesonly.6,7Furthermore,the
complexity of post-blast samples necessitates a multiplexed analytical scheme to
17
uniquelycharacterizethevariousorganicandinorganiccomponentsofexplosiveresidues
apart from matrix interference. 8 Therefore, much attention is devoted to
chromatography and mass spectrometry 9, 10 because the requisite sensitivity and
selectivityiswellestablishedandaccepted8incourtsoflaw.However,thesemethods
remainstationary,laboratorybased,andwaittimesforresultscanbelengthyiflaborious
sampleprocessing is required;allofwhichcanresult in frustratingdelaysat theearly
stagesofaninvestigation.
Recent research on explosive detection has begun to focus on ambient mass
spectrometry(MS)asitprovidesmechanismsforrapiddetectionandidentificationthat
doesnotrequirecomplexsamplepreparation.11Primarytechnologiesprovidingambient
MScapabilitiesincludedesorptionelectrosprayionization(DESI)anddirectanalysisinreal
time(DART);bothambientionizationsourcesweredevelopedintheearly2000s.11By
eliminatingtheconstraintssufferedbycommonionizationsourcessuchaselectrospray
ionization (ESI) and matrix assisted laser desorption/ionization (MALDI), ambient
ionizationsourcesprovidecapabilitiestoanalyzesamplesurfacesdirectlyinstitutingrapid
andhigh-throughputsamplingregimes.Inorganicandorganicexplosivematerialshave
both been identified and quantified using ambient ionization techniques. 12, 13, 14
However, literature lacks inprovingtheapplicabilityof thesetechniquestobeableto
identifyexplosivematerialsfromgenuinepost-blastfragments.
18
1.Introduction
1.1.ExplosivesExplosivesareenergeticmaterials thatupon ignitionundergorapidexothermic
decomposition to instantaneously release high pressure gas, heat and light. 15
Decomposition is predominately driven towards the production of more
thermodynamicallystableproducts,namelyCO2,N2andH2O.Thekineticstabilityofan
explosive is affected by conventional reactivity trends based on structure and bond
strength.Theweakoxygen-oxygenbondinperoxideexplosivesandthenitratespecific
carbon-oxygen bond in nitrated organic explosives increases reactivity leading to
productionof kinetically stableproducts. 16 In the caseofperoxides, instabilityof the
peroxidebond (-O-O-) isattributed inpart to theelectron repulsionbetween the two
electron-richoxygenatoms.16Thedegreeofkineticstabilityofanyexplosivewilllargely
determineignitionsensitivity.
Themechanismofanexplosionisinfactarapidcombustionreaction,whereinthe
oxidizerdecomposestosupplyoxygentosupportcombustionofthefuel.Ifthemixture
issufficientlysensitivetoshock,however,itwilldetonateinsteadofsimplyburn.17High
order explosives detonate creating a supersonic explosive shock front that travels at
velocitiesgreaterthan1000m•s-1.18Loworderexplosivesdeflagratebysurfaceburning
thatoccursatspeedslessthan1000m•s-1.18Explosivesextremelysensitivetoenergetic
stimuli are classified as primary explosives; often used as an initiator for larger less
sensitivemaincharges.Secondaryexplosivesarerelativelylesssensitivetoshock;often
used as themain charge as they are safer to handle, transport and store. 18 Tertiary
19
explosives are relatively insensitive requiring initiation by larger amounts of primary
and/orsecondaryexplosives,suchasso-calledboosters.18
To date, the number and varieties of different explosive materials has grown
immenselyalongwithmanydifferentapplications.Differenttypesofexplosivescanbe
categorized using a variety of classification schemes, depending on the property or
measurement of interest, including use, chemical composition, energetics, or blast
properties.Explosivesofsignificantconcernare thoseaccessible foruse incriminalor
terroristactivity.InaCanadiancontext,commercially-availablefirearmpropellantsand
consumer fireworks are commonly used as explosive fillers for IEDs, but homemade
explosives(HME)areanever-increasingthreatduetoeaseoffabricationusingreagents
sourcedfromcommonhouseholdchemicals.HMEincludeanyexplosivematerialthathas
beenalteredbeyonditsintendeduse,hasbeencreatedbycombiningproductstogether
orhasbeensynthesizedfromreadilyavailablereagents.19
Afterabombing, rapid sourceattributionof theexplosive fillerusedashaving
beeneitheracommercialorHMEproductcanprovidekeyforensiclinksfortheensuing
investigation.Equallyas important,early identificationofexplosive tracescanprovide
pivotal investigative forensic intelligence to help prevent a tragedy from occurring.
Therefore, delivering quality assured answers to front-line personnel with faster
turnaround times motivates improvement of the methods used for explosive trace
detection.Manydifferentanalyticalschemeshavebeendevelopedtoachievethisgoal.
20
1.1.1.Homemadeexplosives
1.1.1.1.PeroxideExplosivesOrganic peroxides are highly reactive compounds containing oxygen-oxygen
bonds.Theelectronrepulsionexperiencedbythelonepairofbothoxygenatomsinthe
peroxidebonddecreases theenergy required tobreak thebond. 20Organicperoxide-
basedexplosives(OPBE)requirenoconfinementtodetonateandproducehigh-pressure
shockwavestravelingatspeedsbetween4500-5500m•s-1,classifyingthemashigh-order
explosives.21Withrespecttosensitivity,OPBEareclassifiedasprimaryexplosivesdueto
extremesensitivitytoanyenergeticstimuli.21Thesematerialsposesignificantconcern
asthesynthesisusesreadilyavailableandcommonhouseholdproductsrequiringvery
basicknowledgeortraining.22UponsynthesisanduseasexplosivefillerinanIED,OPBEs
cause considerable damage and harm, as unfortunately demonstrated by several
domestic and international terrorist attacks in recent years. 23, 24 The detection and
identificationofOPBEsremainsacriticaloperationinensuringpublicsafety.
Triacetone triperoxide (TATP), hexamethylene triperoxide (HMTD) and methyl
ethyl ketone peroxide (MEKP) OPBE are the most common clandestine OPBEs
encounteredincriminal investigationsandforensic laboratories(Figure1-3).TATPand
HMTD are very sensitive to impact, heat and friction and find no legitimate use as
commercialorindustrialmanufacturedexplosives.25MEKPisslightlylesssensitiveand
hasfounduseindilutesolutionsasapolymerizationcatalystincommercialmanufacture
ofpolyesterandacrylicresins.26
21
The reagents required to synthesize OPBEs are commercially available and
syntheticmethodsareavailablefrommanyillicitinternetsources,suchaschatroomsor
other forms of social media. 22 Synthesis of OPBE occurs via step-wise insertion
mechanisticsteps. 26Ifan insertionstepproducesastableproduct the finalyieldmay
containmixturesof linearorcyclicdimer, trimerand tetramer forms;observed in the
synthesisofTATPandMEKP.26Thetrimeracetoneperoxide(i.e.TATP)isproducedasthe
mostabundantproduct,comparedtoamixtureofoligomersproducedinthesynthesis
of MEKP. 26 Purification of these synthetic products requires difficult and resource-
intensivemethodsresultingintheuseofimpureproductsinIEDs.Thehomemadenature,
limited solubility, lack of UV absorbance or fluorescence moieties and sensitivity to
mechanicalstresscreatesmanyanalyticalchallengesforthedetectionandidentification
ofOBPE.
Figure1.Triacetonetriperoxide(TATP).
22
Figure2.Hexamethylenetriperoxide(HMTD).
Figure3.Methylethylketone(MEKP).
23
1.1.1.2.BinaryExplosives Binaryexplosivesaremixturesconsistingoftwocomponentsblendedtogether,
namely: a combustible fuel and strong oxidizer. Separately, neither component is
explosive,butuponmixingtogetherinthecorrectratiotheresultingblendwillbehaveas
anexplosiveuponshockwithsufficient force.Upon ignitionofbinaryexplosiveshigh-
pressure shock waves traveling at speeds between 2500-4500 m•s-1 are produced
classifying them as high-order explosives. 27 With respect to sensitivity, most binary
explosives are classified as tertiary explosives as they require significant energy for
initiationandaresafetohandle,transportandstore.Mostcommerciallymanufactured
explosivesintendedforuseinmining,quarryingandblastingareabaseduponabinary
explosive formulation, albeit other different additives are regularly included (e.g.
emulsifiers,plasticizers,binders,etc).27Stringentregulatoryrequirementsstipulatethat
commercial explosives must be secured in licensed magazines to limit unauthorized
access and prevent theft. Consequently, clandestine fabrication of homemade binary
explosivemixtureshasbecomeanattractivealternativeforcriminalactivity,becausethe
oxidizer and fuel components can be sourced from commercial household products.
Many petroleum-based products can be used as the fuel source. Sugar-based food
products,suchasstarchorconfectionarysugar,canalsobeusedasasuitablecombustible
fuel source. Commercial fertilizers, compression-type instant cold packs and stump
removersareall sourcesofsuitablestrongoxidizers.Bysimplymixingorblendingthe
correctcombinationofcombustiblefuelwithastrongoxidizerabinaryexplosivecanbe
prepared.
24
Table1.Examplesofproductsthatsourcecomponentsforbinaryexplosives.
FuelPrecursors OxidizerPrecursorsComponent Source Component Source
Petroleumbased
DieselAutomotiveGrease
ParaffinWaxLampOilVaseline
PotassiumChlorate Textiles,matches,pyrotechnics
PotassiumPerchlorate
Airbaginitiator,pyrotechnics
Carbohydratebased
StarchSucroseFlour
AmmoniumNitrateFertilizers,Coldpacks,
ExplodingtargetsPotassiumNitrate StumpRemover
CurrentaccreditedmethodsutilizedbytheRCMPfordetectionandidentification
of binary explosives from recovered from post-blast residues include gas
chromatography-mass spectrometry (GCMS), ion chromatography-mass spectrometry
(ICMS) and Fourier-transfer infrared spectroscopy (FTIR). Chromatography methods
combinedwithmassspectrometryarewellsuitedtoseparatethedifferentcomponents
of binary explosives and identify each component in isolation. The specific choice of
whichtechniqueisusedwilldependonthechemicalcompositionandphaseoftheactual
binaryexplosiveexamined(e.g.ICMSforwater-solublesalts,GCMSforvolatileorganics).
With the identification of both components, the overall energetic mixture can be
exposed.
25
1.1.1.3.SmokelessPowderProducts Modernsmokelesspowdersarethepropellantsusedinsmallfirearmammunition.
28 Ignition of the propellant the energy released, via formation of gaseous products,
resultsintheejectionofthebulletfromthechamberofagun.28Smokelesspowdersare
largely produced and used in the assembly of self-packed ammunition. However,
smokelesspowdercanalsobeprocuredforillicituseinIEDs.28,29Theseproductsproduce
negligible smoke when ignited and burned as they are largely composed of organic
explosives that produce only CO2 and H2O gaseous products upon combustion. In
contrast, other propellants, such as black powder, mainly produce solid, non-volatile
productsuponcombustionthusproducingairborneblacksootvisibleassmoke.
Nitrocellulose(NC)isthebaseorganicexplosiveusedtomanufacturesmokeless
powders (Figure4).However,nitroglycerine (NG) canalsobeused in certain typesof
smokeless powders to increase the output energy (Figure 5). Single-base smokeless
powdercontainsNConlyanddouble-baseproductscontainingNCandNG.Adouble-base
smokelesspowdermaycontainbetween10-50%NGcontentbyweightdependingonthe
productused.BecauseNGcandetonateithasthepotentialtoshatterafirearm.NCis
obtained from nitration of cellulose; nitration is an exothermic esterification reaction
wherebyvariouspendanthydroxylgroupsarenitratedbuttheb(1-4)linkagesbetween
monomerunitsinthecellulosechainarenotbroken.30Eachglucosemonomercontains
three potential hydroxyl groups that can be nitrated. The degree of total nitration
dependson thecellulosesourceand the reactionconditions. 30NCcanbenitrated to
different,varyingdegreesandthefinalextentofnitrationcanaffectthecommercialuse
oftheNCprepared.Highly-nitratedNCisconsideredtohaveanitrogencontentofatleast
26
14%byweightandistheformusedinsmokelesspowders.30LessernitratedNCisused
to fabricate cigarette paper and party streamers. Stabilizers, plasticizers and surface
coatings are used in different smokeless powders tomodify or improve performance
characteristicsandprolongshelflifeofthefinalpropellantpowder.Acommonexample
isdiphenylamine(DPA)whichisaweakbaseaddedtosmokelesspowderstoneutralize
theslightly,naturallyacidicNCandpreventspontaneousdecompositionovertime(Figure
6).28,29Anothercommonexampleisethylcentralite(EC)whichisabothaplasticizerand
flameretardanttoraiseignitiontemperatureandslowtheburningrateofthepropellant
powder(Figure7).28,29
Figure4.Fullynitratednitrocellulose.
27
Figure5.Nitroglycerin.
Figure6.Diphenylamine.
Figure7.Ethylcentralite
28
Methods to characterize NG, NC and the various additives from smokeless
powdershavebeendeveloped.31-35However,currentmethodstoidentifynitrocellulose
relyuponrecoveryofanintactpropellantgrainfromwhichthevariousconstituents(NC,
NG, additives) can be extracted and characterized. No method has been previously
reportedtoidentifynitrocellulosepostblastbasedonitsthermal-degradationproducts
in the absenceof a recoverable intact grain for analysis. Identificationof the thermal
breakdown products of nitrocellulose remains challenging due to absence of a
characteristicreferencematerial.
29
1.2.ExplosiveAnalysis
1.2.1.IonMobilitySpectrometry(IMS) Ion mobility spectrometry (IMS) is a commonly used technique to screen for
contraband at border security checkpoints, including concealed drugs and explosives.
Detectionofillicitmaterialsoccursbyobservingcharacteristicmobilityofionsconverted
fromsamplevaporsinaweakelectricfield.36MostIMSinstrumentationisengineeredto
includefourmainsub-components:anionsource,aniongate,adrifttubeandadetector
(Figure8).36Uponionizationofsamplevaporsinthesource,theiongateelectronically
ejectsionsintothedrifttubewherebyanelectricfieldisapplied.12Asionsexperience
theelectricfieldtheymovetowardsthedetector,whichinmostdevicesisaFaradaycup.
36Uponcollisionalneutralizationatthedetector,currentflowiscollectedasameasurable
signal.36Amobilityspectrumisproduced,plottingioncurrentagainstdrifttime.Based
solely on a specimen’s drift time, detection and identification of illicit materials is
achievable.
Figure8.Schematicdiagramofanionmobilityspectrometer(IMS).
30
Ionmobilityisonepreferredmethodusedtoscreenforexplosiveresiduesasitis
relativelyinexpensive,easytouseandprovidescapabilityforrapidanalysisthatisfield
deployable,allwhilemaintaininghighsensitivity.36However,duetosinglemechanism
discrimination(i.e.drifttime)lossofsensitivityandselectivityduetomatrixinterference
arising from environmental contaminants and other congeners remains a significant
critiqueofIMStechnology.Therefore,withrespecttoidentificationanddetectionthese
methodslargelyremainpresumptivetests.Duetothecomplexityofpost-blastsamples
multiplexedanalyticalschemesarerequiredtouniquelycharacterizethevariousorganic
andinorganiccomponentsofexplosiveresiduesapartfrommatrixinterference.37
1.2.2.ChromatographyMethods Many forensic laboratories are equipped with severeal chromatographic
instrumentation as they remain the gold-standard techniques for separation,
identification and quantification of compounds in a mixture. 38 All chromatography
methodsincludeamobileandstationaryphase.Physicalseparationofamixtureisbased
ondifferentpartitioningfactorsofcomponentsinthemixturebetweenthemobileand
stationary phases. 38 Factors such as adsorption, affinity, polarity and size affect
separation processes. 38 Many different detectors are coupled to chromatography
instrumentationprovidingidentificationmechanismsbasedonstructure,mass,charge,
volatility and polarity. Separation techniques are included in many forensic practices
because forensically-relevant samples often contain many unknown compounds in a
complexmixture.Inclusionofchromatographymethodsprovidesensitiveandselective
detection,identificationandquantificationofforensicallyrelevantcompounds,suchas
31
explosives. Therefore, much attention has been invested in using chromatography
methodsforexplosiveanalysis.9,10
High-performanceliquidchromatography(HPLC),gas-chromatography(GC)and
ion chromatography (IC) are themost common chromatographymethods utilized for
explosiveanalysis.39 HPLC employs a closed, pressurized column containing a solid
phase(Figure9).Athigh-pressuresthemobilephaseispassedthroughacolumncarrying
components to be separated. 38 Separation occurs via differences in analyte relative
affinityforthemobileandstationaryphases.Thepolarityoftheanalytesdictatesrelative
affinityformobileandstationaryphasesprovidingamechanismforphysicalseparation
ofthecomponents.38Samplemixturesareinitiallyloadedontothecolumnviaaffinityfor
thestationaryphase.38Uponaswitchinpolarityofthemobilephase,analytesaredriven
backtothemobilephaseandelutefromthecolumn.38HPLCisadesirableseparation
and identification technique for explosive analysis due to itswell-respected accuracy,
efficiency and reproducibility. Methods can be set up in a highly automated fashion
allowingforhigh-throughputanalysesofawidevarietyofsamples.
Figure9.Schematicdiagramoftheinstrumentationusedtoseparateanalytesofa
mixtureviahigh-performanceliquidchromatography(HPLC).
32
Methods involving GC are used in explosive analysis for detection and
identification of volatile compounds. GC columns contain a liquid stationary phase
adsorbedontoaninertsolid.Themobilephaseisusuallycomposedofinertcarriergases
(e.g.heliumornitrogengas).Volatileanalytesenter thegaseousmobilephaseandas
they pass through the column, depending on relative affinity for the mobile phase,
separationoccurs (Figure10). 14As a simple,multi-faceted, rapid andhighly sensitive
method, GC has proven its ruggedness and robustness while providing appreciable
sensitivityandselectivityrequiredforexplosiveanalysis.33-35
Figure10.Schematicdiagramoftheinstrumentationusedtoseparatevolatilecomponentsinamixtureviagaschromatography(GC).
33
Due to thewidevarietyofexplosivematerialsposingsignificant threats toour
safetyandsecurity, capabilitiesofouranalyticalmethods todetectand identify them
continuetobechallenged.11Whilemanyexplosivesareorganiccompoundsamenableto
HPLC and GC methods, inorganic explosive classes are not compatible. Ion
chromatographyisthepreferredseparationtechniqueformanyexplosive-relatedionic
species such as ionic salt oxidizers used in binary explosivemixtures (Figure 11). 40, 41
Basedonelectrostaticinteractionsbetweenmobileandstationaryphases,separationof
ionicspeciesoccurs.ChangesinpH,concentrationofionsaltsandionicstrengthofthe
bufferedmobilephaseareusedtoeluteionsfromthecolumn.38Bothanion-exchange
and cation-exchange columns are available. IC is a commonly used, quality assured
methodforanalysisofinorganicexplosives.
Figure11.Schematicdiagramoftheinstrumentationusedforsimultaneousseparation
ofanionsandcationsinsolutionviaionchromatography(IC).
34
Chromatographymethodsremainprimarydetectionandidentificationmethods
forexplosiveanalysis.However,thestationaryandlaboratorybaseddesignandrequired
laborious sample preparation creates lengthy wait times for results. Associated
frustratingdelayscausedatearlystagesofaninvestigation,duetolimitationsassociated
withchromatographymethods,motivatesadaptation,innovationandvalidationofnew
methodsandtechniques.Ambient-ionizationmassspectrometrymethods,suchasDART-
MS,havebecomelucrativemethodsfordetectionandidentificationofexplosivesasthey
are simple, facile and rapid methods that still maintain robustness, reproducibility,
sensitivityand selectivity required for court. 11, 42-47 Furthermore,due to compatibility
withlow-resolutionmobilemassspectrometersthereispotentialformobilityfromthe
labtothecrimescene.11TheapplicabilityofDART-MSfordetectionofmanydifferent
nitro, nitrosamine and nitroaromatic explosives has been studied excessively due to
prolific use of these explosives in IED. 48 However, adaptability to combat the more
contemporaryforensicchallengesassociatedwithdetectionofhomemadeexplosivehas
yettobeexplored.
35
1.2.3.MassSpectrometry(MS) Since invention intheearly1900s,massspectrometry(MS)remainsoneofthe
mostpowerfulanalyticaltoolsavailable.Predominantlyusedforstudyandrecognitionof
matter by filtering substances based on mass-to-charge ratio (m/z). 49 Versatile
applications of mass spectrometers results in inclusion of these instruments in
laboratories of many scientific disciplines all around the world. 50 With continuous
innovation, adaptation, andmodificationsMSmethods continue to prove robustness,
sensitivityandselectivity.
Thefundamentalconceptsandengineeringofmassspectrometershasremained
constant since invention. As described, characterization of an analyte via MS is
accomplishedbyionization,filtrationanddetectionofgaseousanalytespeciesbasedon
the m/z. 50 Instrumental configurations of mass spectrometers include four main
components: vacuumsystems,an ionization source,amass filterandadetector. Ions
producedinthesourceareacceleratedintoanelectricfieldwherebyseparationbased
onm/ztakesplace(i.e.massfilter).Compoundswithslightlydifferentmassesresultin
variable m/z and unique trajectories through the mass filter providing a robust
mechanism for differentiation. As ions reach the detector the electrical response is
plotted against m/z to create a mass spectrum exposing identity and abundance of
speciespresentinthesample.17Vacuumsystemsareincorporatedtoreducelikelihood
andfrequencyofioncollisionsresultinginpotentialchargetransfersultimatelyhindering
thepathofionsfromsourcetodetector.50
36
CompatibilityofananalytewithMSmethodsdependsonitscapabilitytotransfer
to the gaseous phase and become ionized. To facilitate this required transformation,
manyionizationsourceshavebeendeveloped.Innovationhasledtomanymodifications
andadaptationsproducingalonglistofionizationsourceswithcompatibilitytoawide
variety of analytes such as: small molecules, inorganic compounds, large organic
compounds and biomolecules. Ionization sources can produce ions with negative or
positive charges. Historically, ionization sources have been located inside the mass
spectrometerundervacuumbuttodatemanyambientionizationsourceshavebecome
available.51Ionizationsourcesarepredominantlyclassifiedbyvacuumrequirements,but
also are classified by the strength of the ionization. Hard-ionization sources describe
ionizationofamoleculebyproducingfragmentionsfromparentanalyte.Soft-ionization
mechanismspredominantlyproduceionizedparentionswithlittletonoproductionof
fragmentions.
Productionofionsinthesourcemigratethroughthemassfiltertothedetector.
Manyfiltersareavailableandingeneral,manipulateanestablishedelectromagneticfield
tocontrolthesuccessfultrajectoryofanionfromthesourcetothedetector.Massfilters
aredifferentiatedbyshape,size,andmaterialofthecomponents;ultimatelyleadingto
differences in resolution andmass limits. Low-resolutionmass spectrometers (LRMS)
measurem/zbywholenumbermassesofatoms;high-resolution(HRMS)instrumentation
provides superior mass accuracy by measuring the exact mass of each atom to the
thousandth decimal place. 51 HRMS instrumentation becomes extremely useful when
37
masses of many analytes are similar as it has the power to resolve and uniquely
characterizesimilarmasscompounds.51
Detectionofionsoccursbyconvertingtheelectricalresponse,createdwhenan
ion reaches the detector, into representable and readable signals. Many different
detectors are on the market today. Examples of commonly used detectors include
photoplates, photomultipler tubes, Faradaydetectors, electron-multipliers and image-
currentdetectors.
In most cases, post-blast explosive analysis relies solely on detection and
identificationofresiduesfromanyunconsumedexplosivesfoundpost-blast.However,
thedestructivenatureofanexplosion(heat,pressure,oxidationandpyrolysis)creates
considerablechallengesasanyundetonatedmaterialtypicallyoccursinsmallamounts
andisspreadovermanyfragmentsacrosslargeareasofland.Therefore,qualityassured
methods and techniques are required for success. MS remains one of the most
predominant methods used for explosive analysis from trace quantities of residues
collectedpost-blast.
38
1.2.3.1.DirectAnalysisinRealTime(DART)IonizationDART, an ambient soft-ionization technique, was designed and engineered by
Codyetal.in2005.50Afteradecadefrominitialrelease,DARTsourceshavefoundtheir
wayintomanyfood,environmental,healthandindustryrelatedlaboratories.DARThas
foundspecificapplicationinfoodanalysis,chemicalidentificationandcharacterization,
pesticidedevelopmentanddetection,drugdevelopmentandscreeningandforensics.42-
47, 54-55 Particularly with respect to forensic analysis, DART-MS has proven to be a
powerfullyreliabletechniqueforexplosiveanalysis.42-47
Operating in ambientenvironmentswithout samplepreparation requirements,
DARTprovidescapabilitytoionizeliquid,solidandgaseoussamplesintheirnativeform.
49 Ionizationofanalytemolecules thermally-desorbedfromsamplesurfacesoccursvia
production and resulting reactions with metastable species produced by the source.
Heatedinertgasessuchashelium(He),argon(Ar)ordinitrogengas(N2)enterthesource
andpass througha seriesof electrodesproducingmetastable species suchas excited
statehelium(He*)(Scheme1).Uponexitingthesource,adrystreamofexcitedgaspasses
throughafinalelectrodedirectingionstotheMS,removinganychargedmoleculesto
preventundesiredionrecombinationandcontrollingthepolaritymode(i.e.positivevs.
negativemode)(Figure12).53
M+energy=M*
Scheme1.Reactionschemefortheelectronicorvibronicproductionofmetastablespecies(M*)frominertgas(M)occurringinthesourceviaaseriesofelectrodes.
39
Figure12.SchematicdiagramofDARTsource.
Mechanismsresponsibleforproducingionizedanalytemoleculesaredictatedby
theinertcarriergasused.HeandN2arethemostcommonwiththeformerreportedto
be most effective. 53 Metastable species exiting the source react with atmospheric
moleculestoproducereagentions.UponreactionbetweenHe*andatmosphericspecies,
ionizedreagentmoleculesareproducedviaPenningionization.19Ionizedwaterclusters,
the primary reagent ion produced, are responsible for consecutive ionization of
thermally-desorbedanalytemolecules.53Applicabilityofthisionizationsourceislimited
tomoleculeswithmassrangesfromm/z50-1200asmanycompoundsoverm/z1200lack
requiredvolatility. 53Exactmechanismsforproductionof thesereactivespecies isnot
clear however further investigation has led to a few proposals. 49 Protonation,
deprotonation, direct charge transfer and adduct ion formation are key mechanisms
responsible for production of positively charged analyte molecules (Scheme 2, 3).
Negativelychargedanalytemoleculesareproducedbyflippingthepotentialontheend
gridelectrodetonegativepotentials.ElectronsproducedbyPenningionizationundergo
electroncapturewithatmosphericmolecules inthereactivezonebetweenthesource
andtheMS(Scheme4).49
40
(a) M*+N2àM+N2+•+e-
(b) M*+H2OàM+H2O+•+e-
(c) N2
+•+N2+N2(3rdbody)àN4+•+N2(3rdbody)
N4+•+H2Oà2N2+H2O+•
(d) H2O+•+H2OàH3O++OH•
H3O++nH2Oà[nH2O+H]+
Scheme2.Reactionschemestoproducesecondaryionizingspecies(ionizedwaterclusters)inpositivemodeviareactionofmetastablespeciesproducedbytheDART
sourcewithatmosphericreagents.
S+[nH2O+H]+à[S+H]++nH2O
S+N4+•àS+•+2N2
S+O2+•àS+•+O2
S+NO+àS+•+NO
S+[NH4]+à[S+NH4]+
Scheme3.Reactionschemestoproduceionizedanalytespecies(S+•)inpositivemodeviareactionofsecondaryionizedspeciesandanalytemoleculespresentedtothesource
region.
41
O2+e-àO2-•
S+O2-•àS-•+O2
S+e-àS-•
SX+e-àS-+X•
SHà[S]-+H+
Scheme4.Reactionschemesforproductionofnegativeionizedanalytespecies(S-)via
In summary, operation in positive mode predominantly produces protonated
analytemoleculesandinnegativemodeproducesdeprotonatedmolecules.49Depending
on theanalytemolecule,other ionized speciesmaybe favorable (i.e. ammoniumand
chloride adducts). Coupling to amass spectrometer, analysis in eithermode provides
relativelysimplemassspectra.
Tofacilitatethetransitionofionsfromtheambientionizationreactionzonetothe
massspectrometerunderhighvacuum,aninterfacehousingskimmerorificewithslight
potentialdifferencesbetweenthemisinstalledonthefrontend.53Thesecomponentsof
theinterfaceareresponsibleforremovingneutralcontaminationsanddirectingionized
species into theMS.A roughpumpconnectedto the interfaceand isusedto remove
neutralcontamination.
42
Operation of DART-MS can occur in surface desorptionmode or transmission
modesimplybymanipulatingorientationofthesourcewithrespecttotheMS-interface.
Set at 45° (Figure 13 (a)) surface desorption of analytemolecules occurs providing a
simple, easy to usemethod for direct analysis. Set at 0°, (Figure 13 (b)) transmission
analysisofsamples ispossibleprovidingmechanismsforanalysisof liquidsorsamples
foundonporousmaterials.Commerciallyavailableconsumablesupportmechanismsare
availableforanalysisofsolidandliquidsamples.Bysimplyplacingthesamplesontoretro
fitted supports, which are set into a mechanical rail (Figure 16. (b)), a reproducible
mechanismtomovethesamplesintoandoutofthereactionzonebetweentheDARTand
theMSisprovided.
Figure13.ImagesofthedifferentorientationsoftheDARTsourcewithrespecttotheMSinterface:(a)surfacedesorptionmodeand(b)transmissionmode.
(a) (b)
43
1.2.3.2.Q-ExactiveMassSpectrometer As previously described, the mass analyzer is a key component of a mass
spectrometerasitprovidescapabilitytofilterandselectivelydetectspecieswithspecific
m/z.LRMS includemassanalyzerssuchasquadrupolesand linear iontrapswhichcan
detectionsbasedonnominalm/z.HRMSdemonstratesitspowerofofferingaccuracy,
sensitivity and selectivity simply by providing m/z measurements to the thousandth
decimal place. 52 Instrumental platforms available include Fourier-transform (FT) ion
cyclotronresonance(ICR),time-of-flight(TOF)andOrbitrapmassanalyzers(Figure14).52
UsingHRMSforexplosiveanalysisprovidescapabilityfordetectionandidentificationof
explosives from complex sample matrix with the sensitivity, selectivity, and accuracy
requiredbythecourtsoflaw.
By combining the Orbitrap and quadrupole instrumentation, the hybrid
technology coined the Q-Exactive was released in 2011. 56 Since original design and
engineering theQ-Exactiveencompassesaquadrupole,C-trap,High-energyCollisional
Dissociation (HCD)celland theOrbitrapmassanalyzer. 56Selectivityofdesired ions is
offeredbymanipulatingtheelectromagneticfieldestablishedbetweenthequadruples.
57Ionsthatdonothavethespecificm/z,migrateirregularlythroughthefield,crashing
intotherodsorthesidesofthemassanalyzeranddonotreachthedetector.57TheC-
trapcollectsionsintopacketspriortoinjectionintotheHCDortheOrbitrap.Withinthe
HCDcell,fragmentationofionsoccurswhenanincreaseinthekineticenergyoftheions
results in collisions with neutral molecules. Due to a conversion of kinetic energy to
internalenergyuponcollision,bondsbreakandfragmentsareproduced.58FromtheHCD
cell, newly produced fragments are sent back into the C-trap for re-focusing and
44
subsequentlyinjectedintotheOrbitrapforthefinalmassanalysisandproductionofthe
massspectrum.58TheOrbitrapmassanalyzerisanelectrostaticdevicethatconsistsofa
central,spindle-shapedelectrodethationsoscillatearound.59Bydetectingaxialmotion
around the inner electrode the signal produced is Fourier-transformed yielding high
resolutionmassspectra.24-27OperationoftheQ-Exactiveinfullscanmodedoesnotutilize
theHCDcell.Simplyswitchingoperationmodestotheallionfragmentation(AIF)mode
providesthecapabilityforMS/MSanalysis.
Theouterelectrodeissplitupsymmetricallyservingasasensorsurroundingthe
centralelectrode.56Detectionoftheionsoccursviaimagecurrentdetectionwherebythe
encapsulatingouterelectrodesmapsthecurrentinducedbyaxialmotionofionsaround
thecentralcylindricalelectrode.56Thedatacollectedbythesensorsisconvertedtom/z
byFouriertransformation.
Figure14.SchematicdiagramofthedesignandengineeringoftheQ-Exactivehybridmassspectrometer.
45
Duetothecomplexsamplematrixcreatedwhenablastoccurs,itisimportantto
demonstrate and verify the capability of ambientMS techniques to identify explosive
residuesfrompost-blastsampleswithappropriatesensitivityandselectivityrequiredby
courtsoflaw.Thescopeofthisthesiscomprisesanexplorationintotheapplicabilityof
DART-MS to characterize typical homemade explosives (HME) used in simulated
improvisedexplosivedevices(IEDs).
46
2.MaterialsandMethods
2.1.Consumables,ReagentsandStandardReferenceMaterialsAll consumables, reagents and solvents purchasedwere used as received.ACS
gradeorbetteracetone(>99.7%,CaledonLaboratoriesLtd.,Georgetown,ON),methanol
(>99.8%,CaledonLaboratoriesLtd.,Georgetown,ON)andacetonitrile(≥99.9%,Sigma-
Aldrich,Oakville,ON)wereusedassolvents;hydrogenperoxide(50wt.%,Sigma-Aldrich,
Oakville, ON), sulfuric acid (95.0 -98.0%, Caledon Laboratories Ltd, Georgetown, ON),
citricacid(≥99.5%,Sigma-Aldrich,Oakville,ON),nitricacid,anhydrideaceticacid,D(+)-
cellobiose,hexamethylenetetramine(≥99.9%,Sigma-Aldrich,Oakville,ON),andmethyl
ethyl ketone (ACP Chemicals Inc., Montreal, Quebec) were used as HME synthesis
reagents; diesel, Vaseline, lamp oil, wax, grease, sugar, dextrin, and stump remover
(collectively purchased locally), ammonium nitrate, potassium perchlorate, potassium
chlorate were all used as either the fuel or oxidizer source for homemade binary
explosives;BlueDotsinglebasesmokelesspowderandGreenDotdoublebasesmokeless
powder commercial explosive products were used as purchased; certified explosive
standardswerepurchasedassolutions(0.1mg·mL-1 ineithermethanoloracetonitrile)
fromChromatographicSpecialtiesInc.(Brockville,ON).
47
2.2.IEDConstruction,DetonationandFragmentCollectionMultiple IEDs were assembled to yield a variety of post-blast fragments
characteristicofmaterialscommonlyrecoveredpost-blastandreceivedatourlaboratory
analysis,suchas:cellphones,wires,batteries,nuts,bolts,metalswitches,andmechanical
timers(Figure15).Forsafetyreasons,thecontainerusedforeachIEDwasathin-walled
aluminumcan.EachIEDwasconfiguredwithamaincharge(Table2)andfiredusinga
commercialelectricblastingcap(approximately1gPETN).TATP,HMTD,MEKPandall
binaryexplosiveswerepreparedbyaqualifiedchemist,inaccordancewithstandardbest
practicesand incompliancewithCanadianExplosivesRegulations(SOR/2013-211)and
characterized before use to demonstrate fit for purpose. The MEKP prepared was
confirmedbyLCMSanalysistocontainthelineardimer,trimerandtetramerasthemajor
constituents, and the cyclic trimer as aminor constituent. 27 Bluedot single-base and
GreenDotdouble-basesmokelesspowderwereplacedinindividualvials,aspurchased.
Figure15.Fragmentscollectedpost-blastfromthedetonationofdevicesutilizinghomemadeexplosivesasthemaincharge(IED#1-14).
48
Tolimitthespreadofdebrisandergonomicallyfacilitatefragmentcollection,each
IEDwasenclosedbycinderblocksbeforedetonation.EachindividualIEDwasremotely
detonatedusingacommandwireatRoyalCanadianMountedPolice(RCMP)Technical
andProtectiveOperationsFacility(TPOF)inOttawa,ON,byaqualifiedRCMPExplosive
Disposal technician. Conventional contamination-prevention protocols were followed
consistent-withactualcrimescenepractices,andallfragmentscollectedfromeachIED
sealedintonylon-linedevidencebagspriortotransportandduringstorage.
Table2.TypeandamountofexplosiveusedasmainchargeforeachIED.
IED# MainCharge Amount(g)1 TATP 402 TATP 53 HMTD 34 HMTD 5
5 MEKP 56 Perchlorate+Vaseline 107 AN(prills)+Diesel 10
8 AN(ground)+Wax 109 Chlorate+lampoil 1010 KNO3+grease 10
11 Chlorate+sugar 10
12 KNO3+dextrin 1013 Singlebase 20
14 Doublebase 20
49
2.3.ReferenceMaterialSamplePreparation
2.3.1.FuelandOxidizer The commercially available petroleum-based fuels used in the binarymixtures
were obtained and analyzed unmodified. Carbohydrate-based fuel products used to
prepare the binarymixtures were obtained and reference samples were prepared in
deionizedwater.Referencesamplesoftheoxidizersusedinthedeviceswereprepared
indeionizedwater.
2.3.2.OctanitrateCellobioseSynthesisandSamplePreparationOctanitrate cellobiose was synthesized and used as a reference material for
nitrocellulose.b-cellobiosewaschosenasthestartingmaterialbecauseitcontainsthe
same1-4-b-linkageasobserved innitrocellulose.Nitrationofb-cellobiosevia reaction
with anhydride acetic acid and fuming nitric acid produced the desired b-cellobiose
octanitrate(ONCB).Thefinalproductwasfiltered,usingawateraspirator,andwashed
multipletimeswithsodiumbicarbonatetoneutralizeanyresidualacid.Characterization
ofthefinalproductwasdonebyFTIRandmatchedliteraturevalues.
Approximately5mgONCBwasdissolvedin5mLacetone,methanol,acetonitrile,
water and dichloromethane. Additional samples of approximately the same mass of
ONCBwereplacedinglassPetridishesandexposedtoabutaneflamefromabarbeque
lighter.DuetotheenergeticpropertiesofONCB,thewhitepowder-productburnedtoa
stickysyruplikeresidue.TheresiduesweresubsequentlycollectedfromthePetridishes
using 5 mL acetone, methanol, acetonitrile, water and dichloromethane. No further
purification,filtrationorpre-concentrationwasconducted.
50
2.3.3.SmokelessPowderSamplesofapproximately10mgsingle-baseanddouble-basesmokelesspowders
were prepared similarly to the preparation methods for ONCB. Samples of both
smokelesspowdersweredissolvedindividuallyin5mLacetone,methanol,acetonitrile,
water and dichloromethane. In addition, samples were ignited and the remaining
residueswerecollectedfromthePetridishesusing5mLacetone,methanol,acetonitrile,
wateranddichloromethane.Nofurtherpurification,filtrationorpre-concentrationwas
conducted.
2.4.Post-BlastExtractPreparation Solventextractsofresiduesfrompost-blastfragmentsisanidealsamplingmethod
forobjectstoolargeorirregularlyshapedfromblastdamage;whichmaybeunsuitable
to be shipped to the laboratory and/or analyzed directly in the DART sample region.
Residuesfromthepost-blastfragmentsforthebinaryexplosiveswerecollectedbyrinsing
thefragmentswithhexane(petroleumbasedfuels)orwater(sugarbasedfuels).Residues
were collected from fragments from the smokeless powder device using acetone.
Nitrogengaswasusedasamechanismtopre-concentratetheextractswhenrequired.
Nopre-concentrationoffiltrationoftheextractswasincluded.
51
2.5.DART-MSAnalysisDatacollectedinpositiveandnegativemodewasdonewithanIonSense®DART
SVP 100 source coupled to a ThermoFisher Scientific Q Exactive™ (Orbitrap) mass
spectrometer(ThermofisherScientific,Waltham,MA).TheDARTsourcewaskeptat250°
Cand350Vgridvoltage.MSscan rangeofm/z50–700,witha resolutionof70000
FWHM. Thermo Scientific XCalibur software was used for data collection and
QualBrowsersoftwareforqualitativedatainterpretation.Fullscanacquisitionwasused
andnodopantwas added to promote adduct formation. Sampleswereprobedusing
three different DART configurations; direct analysis, analysis of swabs and extracts.
Fragmentswereanalyzeddirectlybyplacingtheminthesamplingregionforanalysisat
45°,whereasswabsandextractswereanalyzedat0°.Rectangularcottonswabs(4x4cm,
SmithsDetection,Mississauga,ON)wereused towipe fragments, andwere collected
eitherdryormoistenedwithasinglesolvent:acetone,methanoloracetonitrile.Swabs
with residue sub-sampled from fragmentswere thenanalyzedbyplacing them in the
samplingregion.ExtractsweredepositedontoanIonSenseQuickstrip(consumablecard
withstainlesssteelmeshwells),placed intoacardholdersittingonamechanical rail,
responsibleformovingthesamplestoandfromthesamplingregion.
52
3.ResultsandDiscussion
3.1DART-MSParameterOptimizationPrior tochallengingtheapplicationofDART-MSto identifyHMEresiduespost-
blast, a bench level method was validated in the laboratory. Target explosives were
analyzedinreplicateusingaQuickStripcardwhilesystematicallyvaryingDARTandMS
settings to ensure reproducibility and robustness of detection. Parameters optimized
included temperature of the DART probe, distance between the DART and MS and
resolution of the Orbitrap. Limit of detection (LOD) was evaluated to determine the
lowestquantityofexplosivesresultinginobservationofthreeormorecharacteristicions
with ≥ 3:1 signal-to-noise ratio (3σ). The LODsmeasured (Table 3) were found to be
comparabletoreportedvalues.44OncesatisfiedwiththeDART-MSparametersandthe
methoddesign,theapplicabilitytodetectexplosiveresiduesfromthepost-blastbomb
fragmentsandidentifythevarietyHMEusedinthedeviceswasinvestigated.
Table3.LODsobservedforexplosivesofinterestmeasuredusingin-housemethodandQuickStripcomparedtoliteraturevalues.
Explosives MeasuredLOD(ng) Reported45LOD(ng)TNT 0.01 0.25HMX 0.10 10RDX 0.01 0.50PETN 0.10 5Tetryl 0.10 1NG 1 5
2,4-DNT 10 0.502,6-DNT 10 0.50EGDN 100 100HMTD 1 -TATP 100 -MEKP 100 -
53
3.2.AnalysisofFragmentsDue to the design and capability of the DART-MS method, multiple sampling
regimes (e.g. direct, in-direct and extracts) were evaluated to determine efficacy of
residue recovery. Each sampling method revealed the HME used, however different
recoveryefficiencieswereexposed.Asidefromminordifferencesinrelativeabundance
ofions,sample-to-sample,themassspectraandcorrespondingfragmentationpatterns
forallexplosiveswereinhighagreementwiththereferencematerials.
As expected without pre-concentration or sample clean-up prior to analysis,
background ions were commonly observed in the DART-MS spectra. Spectra were
collected prior, during and after each sample analysis to monitor cleanliness of the
instrument and to identifybackground ionsendogenous to theDARTor the sampling
technique(i.e.swabbingoruseofQuickstrip)(Figure16-19).Analysisofbothpolarand
organic solvents deposited on theQuickStrip produced spectrawith total ions counts
ranging from 104 – 106 (Figure 20 and 25). To facilitate elimination of the solvent
contribution,solventblankswereincludedintheanalysisalongwithextractedsamples.
54
Figure16.IonsobservedviaoperationoftheQExactiveinpositivefullscanmode,
withouttheDARTsourceturnedon.Totalioncount103.
Figure17.EndogenousDART-MSions.Totalioncount104-105.
55
Figure18.Analysisofanunusedcottonswabinpositivemodeusingfullscan.
Totalioncount104
Figure19.AnunusedQuickStripanalyzedinpositivemodeusingfullscan.
Totalioncount103-105.
56
Figure20.WaterdepositedontoaQuickStrip,analyzedinpositivemodeusingfullscan.Totalioncount104–105.
Figure21.MethanoldepositedontoaQuickStrip,analyzedinpositivemodeusingfull
scan.Totalioncount104–106.
57
Figure22.AcetonedepositedontoaQuickStrip,analyzedinpositivemodeusingfull
scan.Totalioncount104–106.
Figure23.AcetonitriledepositedontoaQuickStrip,analzyedinpositivemodeusingfull
scan.Totalioncount104–106.
58
Figure24.AnalysisofdichloromethanedepositedontoaQuickStrip,inpositivemodeusingfullscan,tobeusedforsolventassociatedionsubtraction.Totalioncount104–
106.
Figure25.AnalysisofhexanedepositedontoaQuickStrip,inpositivemodeusingfullscan.Totalioncount104–105.
59
DetectionandidentificationoftheHMEusedforeachIEDwasobtainedbydirect
analysis of at least one fragment recovered from each device. In real casework it is
commontonotdetectexplosiveresiduefromeverybombfragmentduetotheunequal
geospatialdistributionofresidueswhichisadirectresultoftheunpredictablenatureof
anexplosiveblast.62Thephysicalsizeofthefragmentsfoundvariedfromsmall(e.g.SIM
card~0.25 cm2) to large (e.g.D-cell battery ~17.25 cm2),whichmeans fragments can
retaindifferentquantitiesof residue.The interactionareaof theDARTprobewill not
instantly desorb all residue from surfaces, which will limit the amount of material
transmittedtotheMSinletperscan.Moreover,manyofthefragmentsfromeachdevice
wereinstorageforatleastfour(4+)monthspriortoanalysis,whichisnotanuncommon
time-frame with actual investigations. Thus, some extent of residue loss from the
fragment surface(s) via degradation can be expected. 59-61 Recovery efficiencies with
longerexposuretimesofpost-blastIEDfragmentstoairorweatherwasnotquantified,
butwillbegivenfurtherconsiderationinfuturework.
In-directanalysiswasdonetoevaluatecompatibilityoftheDART-MSmethodwith
using swabs. Swabs are ideal to sub-sample objects too large to be shipped to the
laboratory or irregularly shaped fragments unsuitable for direct analysis. Analyzing a
fragmentdirectlymayalsocontributetohigherbackgroundintheMSifthesubstrateof
thefragmentitselfcanbedesorbedandionizedbytheDART,makingswabsanattractive
alternative.Inaddition,swabbingissuitedtoaccumulatemoreresiduefordesorptionby
theDARTprobeandtransmissiontotheMSinletperscan,whichwillenhancerecovery
and detection. Efforts tomaximize residue collection using swabs included evaluating
60
commercially available swabs manufactured with different substrates as well as
comparingcollectionefficiencyandeffectivenesswhenusingdryorsolvent-dampened
swabs.
Solventextractionwasconvenienttorecoverresiduefromafragmentwhendirect
analysiswasnotsuitable.Liquidextractscanbefilteredand/orpre-concentrationasa
mechanism to improve detection. Common best practices for forensic sampling of
explosives residues recommend either acetone or methanol be used as the solvent.
Acetone, methanol (MeOH), water, acetonitrile (ACN), dichloromethane (DCM), and
hexanewere evaluated as solvents to extract post-blast residueswhileminimally co-
extractingenvironmentalcongeners.Onedrawbackofusingpolarorganicsolventsisthe
potential for co-extraction of other substances and contaminants from the
substrate/bombfragment.Ingeneral,organicsolventsunselectivelyextractanyorganic
substancespresentfromaspecimen.
Substrate ionization canoccurwith plastics 64 and textiles 65, 66whichwill also
contributeunwanted spectral background. Fragments representingdifferentmaterials
recoveredpost-blast(e.g.plastic,metal,rubber,etc.)werethussurveyedtodetermine
possible spectral contribution from the different substrates themselves. No explicit
variationwasobservedbetweendifferentfragmentstoindicateanyonesubstratewas
preferentially ionizedoveranother, indicatingthebackgroundionsobservedcouldnot
bedistinguishedfromsubstrateorenvironmentalcontaminationwhenrecoveredfrom
the ground. Fortunately, this is probative for our verification purposes, because real
specimens from post-blast debris are expected to be dirty from environmental
61
contaminationandunwanted substances areoftenobserved in thematrixof forensic
samples.TovisuallyenhancewherethetargetHMEsweredetectedinthetotalDART-MS
desorptionprofileobservedforeachfragment,extractedionchromatograms(EIC)were
found particularly useful to visually isolate regions of interest. High mass accuracy
permittedassuredreliableidentificationofallHME.
3.2.1.OrganicPeroxideExplosivesTATP and HMTD are the most common OPBE encountered in case work at
Canadianforensiclaboratories.MEKPislesscommon,butiseasilypreparedanalogousto
TATPorHMTDanditremainsaprioritytoensurestandardmethodscandetectMEKP
post-blast aswell. Via both direct and in-direct samplingmethods, DART-MS analysis
revealedtheOPBEusedfromatleastonefragmentrecoveredfromeachdevice(Table
4).Analysisofswabswasgenerallyfoundtobemoreeffectivethanbydirectanalysisof
fragments, except for MEKP, which proved the most challenging peroxide HME to
sufficientlydetectpost-blast(Table4).
62
Table4.DepictionoftheOPBEidentifiedviaDART-MSdirectanalysisofamultitudeofdifferentpost-blastfragmentscomparedtoin-direct.
DIRECT SWAB TATP HMTD MEKP TATP HMTD MEKPPlasticsheathedelectricalwire
Hardplasticsubstrate Cellphonebody
9Vbattery Dcellbattery
Cellphonebattery Washer
IEDcontainer Nail
Substratenotfoundpost-blast 3-6characteristicions 2characteristicions 0-1characteristicions
TATPwaspositivelyidentifiedastheexplosiveusedinIED#1and2viadirectand
in-directanalysisofthepost-blastfragments(Figure27and28).Identificationwasoffered
byobservingthefollowingionsidentifiedascharacteristicviaanalysisofTATPcertified
reference material (Figure 26); ammoniated TATP molecular ion (m/z 240.1436
[M+NH4]+),mono-acetoneperoxide(m/z74.0364[M/3]+)andprotonatedfragmentsfrom
theparenttrimerm/z75.4406[C3H6O2+H]+,89.0597[C4H9O2]+and91.0390[C3H6O3+
H]+. The base peak observed for TATP from analysis-to-analysis was either the m/z
91.0390 fragment or m/z 240.1436 [M+NH4]+. Characteristic ions for TATP were
consistently detected with an abundance of 105 – 107 counts and with spectral
backgroundionstypicallybetween103–104counts.TheamountofTATPusedinIED#1
versus#2wasdeliberatelychosenas it replicatedpastcaseworkscenariosexamined.
63
QuantitiesofTATPrangingfrom101–103gramscale(i.e.smallandlargescale)havebeen
encounteredincriminalinvestigations,wherelargeramountsweremanufacturedtobe
usedasdemolitioncharge(s)21andsmalleramountsforconcealmentinvictim-operated
IEDs.22ThesimilarabundanceofionsobservedforTATPdetectedfrombothIED#1and
#2isindicativethatsufficientresiduewasretainedoncertainfragmentsfromIED#2to
be detected in similar quantity to that recovered from IED #1. The maximum signal
responsefortheMSis108counts,whichindicatestheionsdetectedforTATPfromeither
device did not saturate the detector. Retaining sufficient TATP for detectionwas not
unexpected because all fragments were collected soon after detonation and well-
preserved in air-tight evidence collection bags to optimize the opportunity for HME
residuerecovery.
Figure26.Positivemode,fullscanhigh-resolutionmassspectrumforTATPanalyzedfromcertifiedreferencestandard.IonscharacteristicofTATPhavebeenboldedand
labelled.
64
Figure27.Positivemode,fullscanhigh-resolutionmassspectrumforTATPupondirectanalysisoffragmentfromIED#2.IonscharacteristicofTATPhavebeenboldedand
labelled.
Figure28.Positivemode,fullscanhigh-resolutionmassspectrumforTATPanalyzedfromaswabusedtocollectpost-blastresiduesfromIED#2fragments.Ions
characteristicofTATPhavebeenboldedandlabelled.
65
HMTD was identified as the main charge for IED #3 via observation of
characteristicionsidentifiedinanalysisofHMTDcertifiedreferencematerial(Figures29-
31);protonatedmolecularion(m/z209.0768[M+H]+)andcommonlyobservedfragments
9, 42m/z 88.0394 [M-C3H6NO4]+, 145.06081 [M-CH2O3 + H]+, 179.0663 [M-CH2O + H]+,
191.0664 [M-H-O]+ and224.0878 [M–H2+NH4]+. Themajor ionobserved forHMTD
analysis-to-analysiswaseitherthem/z145.06077or224.0878fragments.Characteristic
ionsforHMTDwereconsistentlydetectedwithanabsoluteabundancerangingfrom105
–106andwithbackground ions remainingbetween103–104 counts.Thequantityof
HMTDselectedforIED#3agreeswithpastcaseworkexamples,whereHMTDhasbeen
encounteredasfillerusedforhomemadedetonators.Anionwithm/z207.0979wasnot
reproduciblyobserved,consistentwithpreviousreports.9,63
Figure29.Fullscanhigh-resolutionmassspectrumforHMTDanalyzedfromcertifiedreference.IonscharacteristicofHMTDhavebeenboldedandlabelled.
66
Figure30.Fullscanhigh-resolutionmassspectrumdepictingidentificationofHMTDfromdirectanalysisofafragmentcollectedpost-blastfromIED#3.Ionscharacteristicof
HMTDhavebeenboldedandlabelled.
Figure31.Fullscanhigh-resolutionmassspectrumdepictingidentificationofHMTDuponanalysisofaswabusedtocollectpost-blastresiduesfromIED#3fragments.Ions
characteristicofHMTDhavebeenboldedandlabelled.
67
Whensynthesizedandleftunseparatedbychromatography,MEKPisamixtureof
monomeric, dimeric, trimeric (linear and cyclic) and higher oligomeric species. 39 For
realism,wepreparedMEKPandonlyisolatedfromunreactedreagents,butdidnotpurify
further before use. DART-MS analysis of our MEKP reference material yielded four
characteristic ions (Figure 32); ammoniated linear trimer (m/z 316.1965 [C12H26O8 +
NH4]+),ammoniatedlineartetramer(m/z404.2488[C16H34O10+NH4]+),andmonomeric
fragments m/z 77.0233 [C2H5O3]+ and 89.0597 [C4H9O2]+. Characteristic ions were
detectedwithanabsoluteabundanceof105–106andspectralbackgroundionsremained
between 103 – 104 counts. The ion observed at m/z 316.1965 is best calculated as
corresponding to a linear trimer adductwith ammonium [C12H26O8 +NH4]+ and not a
monomer adduct as previously reported. 43 Parent ions attributable to either the
monomerordimerspecieswerenotobserved.ThedesorptionprofileobservedforMEKP
byDART-MSwasbroadandtherelativeratiosofionsobservedchangedfrombeginning
toend. Initially, the lowermass fragmentsm/z77.0233and89.0597weredominantly
favouredatthebeginningofthescan,buttransitionedtopredominantlythehighermass
ions316.1965andm/z404.2488towardstheend.Thefragmentionsm/z77.0233and
89.0597arecommontoboththemonomeranddimer,suggestingapseudo-distillation
profileisoccurring,wherethelighterMEKPmonomeranddimerspeciesaredesorbed
and ionizedbefore theheavieroligomers, but theparent ionswere simplynot stable
enough to be observed.When the averageMS is plotted over all scans in the broad
desorptionprofile, themajor parent ionsobserved fromanalysis-to-analysiswere the
ammoniumadductofeitherthetrimer(m/z316.1965)ortetramer(m/z404.2488).We
68
didnotelucidatefurtherifthemonomerordimerparentionsmaybepresent,because
detectionofthefourionsobservedissufficientforidentificationofMEKPinapost-blast
residue.MEKPwasidentifiedasthemainchargeforIED#5asthesamecharacteristicions
identifiedinanalysisofthecrudeMEKPproductwereobservedinthespectraobtained
fromanalysisofdirectandin-directsamplingtechniques(Figure33and34).MEKPwas
themostchallengingperoxideHMEtodetectpost-blast(Table3).
Figure32.Positivemode,fullscanhigh-resolutionmassspectrumforMEKPanalyzedfromthecrudesynthesizedproduct.IonscharacteristicofMEKPhavebeenboldedand
labelled.
69
Figure33.Positivemode,fullscanhigh-resolutionmassspectrumdepicting
identificationofMEKPfromdirectanalysisoffragmentcollectedpost-blastfromIED#5.IonscharacteristicofMEKPhavebeenboldedandlabelled.
Figure34.Positivemode,fullscanhigh-resolutionmassspectrumdepicting
identificationofMEKPuponanalysisofaswabusedtocollectedpost-blastresiduesfromIED#5fragments.IonscharacteristicofMEKPhavebeenboldedandlabelled.
70
Both direct and in-direct analysis of the post-blast fragments permitted
identificationofeachOPBEused.In-directanalysisusingswabbingprovidedamechanism
to sample large or irregular objects not amenable to direct analysis. Swabbing also
enhancesrecoverybyaccumulatingmoreresidueonasmallersurfacearea.Therefore,
furtheroptimizationwascompletedtodeterminethemostsuitableswabsubstrateand
comparerecoverywithdryandsolvent-dampenedswabs.
Post-blast fragments from IED#3wereused for thisoptimizationwork. Swabs
madeofcotton,Teflonandpapermodifiedwithathinadhesivecoatingweretestedto
determinetheirrespectiverecoveryefficiencies(Figure35).Cottonswabsarereported
tobeaneffectiveresourceforcollectingsamplesof forensic interests. 65Collectionof
residues using cotton swabs resulted in positive identification of the explosive used
(HMTD) (Table 5) and cotton was therefore chosen as the preferred swab material.
Detectionofexplosivespresentonaswabviaanalysisintransmissionmoderequiresthe
active ionizinggas streamtopass through thematerialand interactwith the residues
present.Comparedtothemodifiedpaperswabs,cottonswabsaresufficientlyporousto
facilitatedesorptionandionizationforMSdetection.Usingcottonswabsisinagreement
with best practice for forensic sample collection as cotton swabs are regularly
recommendedtofront-linestaffmembersandinvestigatorsforsamplecollection
71
Table5.CharacteristicionsofHMTDpresentuponanalysisofresiduescollectedviaswabsdifferentiatedbysubstrate.
M–H2+NH4]
+224.0878
[M+H]+
209.07681[M-C3H6NO4]
+88.0394
[M-CH2O3+H]+
145.0608[M-CH2O+H]
+179.0663
Cotton Teflon
Modifiedpaper
Ionpresent Ionabsent
Figure35.Fromlefttoright-cottonswab,paperswab,modifiedpaperswab.
Analysis of dry versuswet swabswas conducted to evaluate any difference in
effectiverecoveryofresidueswhenusing(ornotusing)solvents.Analysisofdryswabs
collected from, afforded identificationofHMTD (top, Figure36).DART-MSanalysis of
swabswettedwithacetone,acetonitrileormethanolresultedinpositiveidentificationof
HMTDfromIED#5container(Figure36).Wettingaswabwithasolventpriortoswabbing
can enhance explosive residue recovery 9, but solvents will also co-dissolve other
substancespresentfromenvironmentalcontaminationorthesubstrateitself.Clean-up
proceduresforswabextractspriortoanalysiscanbeused.9Dryswabbing,however,will
72
not dissolve any substances or the substrate, reducing unwanted sample matrix and
fewer background ions to clutter the MS spectrum (Figure 36). Dry swabbing can
eliminateextractionorclean-up,andwasfoundeffectiveforexplosiveresiduerecovery.
Whenanalyzingdryandwetswabscollectedfromthepost-blastcontainerofIED#3,we
observed an additional predominant ionm/z 207.0614 (Figure 35) not apparent from
directanalysis(Figure29).Thisdaughterionisbestcalculatedas[C6H11N2O6]+whichisin
agreementwithstructuralassignmentasthedialdehydederivativeprotonatedinsteadof
ammoniated,i.e.[M–H2+H]+.Theappearanceofionm/z207.0614post-blastbutnot
apparent from the referencematerial can be associatedwith degradation from blast
effects(heat,pressure).Tothebestofourknowledge,ionm/z207.0614hasnotbeen
previouslyreportedfrompreviousLCMSstudies.10,62
73
Figure36.Fullscanhigh-resolutionmassspectradepictingidentificationofHMTDuponcollectionofpost-blastresiduesfromIED#5usingdryandsolventdampenedswabs.
74
3.2.2.BinaryExplosives Homemadebinaryexplosiveswereincludedinthisstudybecausetheindividual
components (i.e. fuel and oxidizer) can be easily sourced from common commercial
productsandposeasignificantthreatforfabricatingIEDs.Detectionofbinaryexplosives
products post-blast poses challenges because the different chemical nature between
fuels and oxidizers necessitates different analytical tools. Many of the commercial
products containing the precursor chemicals have complexmatrices arising from the
additionofdifferentstabilizers, fragrancesandpreservatives.UsingDART-MS,thefuel
and oxidizer can be detected separately by switching between positive or negative
polarity.ExamplesofcommoncommercialsourcesofHMEprecursorfuelsandoxidizers
arelistedinTable1.
Currently,theRCMPdoesnothaveavalidmethodforcharacterizationofsugar-
basedfuelspost-blast.TheuseofDART-MStodetectsugar-basedfuelswasthusexplored
asapotentialsolutiontothiscapabilitygap.Avarietyofdifferentcommerciallyavailable
carbohydrate-based or sugar-containing products are suitable as fuel sources,making
identificationofanysourcechallenging.ThemainchargeofIEDs#11and12wasbinary
explosive prepared using a carbohydrate-based fuels (TANG ® juicemix and dextrin).
TANG® isa food-gradesourceof sucrose,which is themain ingredient.Sucrose is the
dimerglucoseandfructosemonomerslinkedviaa(1,2)glycosidiclinkages.Dextrinisa
complexcarbohydratepolymercomposedofhighlycross-linkedglucoseunits.DART-MS
analysisofsucrose,TANGanddextrinindilutesolutionsverifiedeachcarbohydratefuel
was identifiable (Figures38,39and43).Becauseglucose isabasemonomer ineither
carbohydrate,analysisofeithersucroseordextrinresultedinasimilarMSspectrumand
75
fragmentation pattern, including common ions that can be used to identify each fuel
whencomparedtoaglucosereferencematerial.61DART-MSanalysisofglucoseyields
the following characteristic ions (Figure 37); ammoniated glucose ion (m/z 198.0973
[C6H12O6+NH4]+)andfragmentionsviathelossofwater(m/z180.0867[C6H12O6+NH4–
H2O]+,m/z163.0601[C6H12O6+NH4–NH3–H2O]+,m/z145.0496[C6H12O6+NH4–NH3–
2H2O]+andm/z 123.0390 [C6H12O6+ NH4 – NH3 – 3H2O]+). 60 Characteristic ionswere
detectedwithanabsoluteabundanceof105–106andspectralbackgroundionsremained
between103–104counts.
Ablendedproductofasugar-derivedfuelandastrongoxidizerisanexampleof
high-brisanceexplosive.Consequently,manyoftheIEDfragmentsrecoveredpost-blast
weresmall(e.g.SIMcard~0.25cm2)renderingrecoveryofresiduefordetectionbyDART-
MSdifficult.Co-extractionofmultiplefragmentsofsimilarmaterialstogetherafforded
detectionofacarbohydratebasedfuelinIED#11and12viaDART-MSanalysis(Figures
40-42and44-46).Thisisacommonsamplingmethodusedintheforensicanalysisofpost-
blast explosives. Similar DART-MS spectrum of both sucrose and dextrin prevents
identificationofthecommercialproductsourcepost-blast.Becausemostcarbohydrate-
basedfuelsarenon-volatileresiduelossbyevaporationisnotaconcern.Sugar-derived
fuelresiduesareexpectedtopersistandbedetectableifanalyzedatalatertime,which
isanalogouswiththeexpectationfortheinorganicresiduesoftheoxidizersaltsusedin
thesamebinaryexplosivemixtures.
76
Figure37.Fullscanhigh-resolutionmassspectrumofglucosedissolvedinwaterasareferencematerial.Collectedinpositivemode.
Figure38.Fullscanhigh-resolutionmassspectrumofsucrosedissolvedinwater,usedasareferencematerial.Collectedinpositivemode.
77
Figure39.Fullscanhigh-resolutionmassspectrumofTANGdissolvedinwater,usedasareferencematerial.Collectedinpositivemode.
Figure40.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#11metal
substratefragment.Collectedinpositivemode.
78
Figure41.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#11plastic
substratefragment.Collectedinpositivemode.
Figure42.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#11rubber
substratefragment.Collectedinpositivemode.
79
Figure43.Fullscanhigh-resolutionmassspectrumofdextrinreferencematerialdissolvedinwater.Collectedinpositivemode.
Figure44.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#12plastic
substratefragment.Collectedinpositivemode.
80
Figure45.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#12metal
substratefragment.Collectedinpositivemode.
Figure46.Fullscanhigh-resolutionmassspectrumdepictingidentificationofaglucosecontainingproductfrompost-blastresiduesextractedwithwaterfromIED#12rubber
substratefragment.Collectedinpositivemode.
81
Currently,GC-MSisthequalityassuredmethodusedbytheRCMPfortheanalysis
ofpetroleum-derivedfuelsinbinaryexplosives.However,DART-MSprovidesasuitable
andrapidalternative.Avarietyofcommonpetroleum-derivedproductsencounteredin
binaryexplosivesweresurveyed(Table1)andeachfuelexhibitsadifferent,distinctive
profile(Figures47,60-63).Itwasbeyondthescopeofthisworktoanalyzeallthedifferent
typesofpetroleum-derivedfuelsthatcouldpotentiallybeusedtomakeabinaryHME.
Eachfuelanalyzedwasdilutedinhexane,whichisasolventcommonlyusedtoextract
petroleum-derived fuels from explosives. Analysis of neat hexane assisted in the
background subtraction of any solvent associated ions (Figure 25). Identification of
automotivegreasepost-blastwasinvestigatedbyanalyzingfragmentsfromIED#10.
Automotive greases are manufactured by blending many different substances
together (e.g. lubricants, thickener, additives,preservatives),which togetheraffordsa
complexmixture.Analysisofatypicalautomotivelubricatinggrease(Figure47)exhibited
ahigh-abundancepatternof lowmass ions in them/z rangeof100-250anda lower-
abundancehydrocarbonprofileinthem/zrangeof300-450.Analysisofhexaneextracts
from the post-blast fragments (e.g. metal, plastic and rubber substrate fragments)
resulted in observation of three predominant ions (m/z 149.0237, 279.1589, and
391.2844) (Figure 48-50). EICs depicted observation of these ions in the DART-MS
spectrumoftheunusedautomotivegrease,whichwasanalyzedasareferencematerial.
However,theionsobservedpost-blastwerenotasabundantlyobservedfortheunused
grease.Thisisnotunexpected,astheblasteffects(heat,pressure)areknowntochange
thecompositionofpetroleum-derivedfuels,asiscommonlyobservedinignitableliquid
82
analysis.63Thebestpracticetoidentifythecombustionresidueofapetroleum-derived
fuelistocomparewithasuitablyweatheredorignitedreferencematerial;thescopeof
whichwasbeyondthispresentstudy.Regardless,thedetectionofionspost-blastthatare
identifiablycommonwiththeunusedgreaseindicatesthatapetroleum-derivedgrease
fuelcanbeidentifiedpost-blast.
Combustion is expected to consume some (or all) of the components of the
grease. Pyrolysis and other irreversible oxidation side-reactions are also expected to
occurduringtheexplosion.66Consequently,aweatheredsampleofgreaseisexpectedto
affordamorerepresentativematerialforcomparisonandidentificationofagreasepost-
blast,whichisthecommontechniqueusedinfire-debrisinterpretationofignitableliquids
after an arson fire. 66 Weathering grease samples is not a straightforward task. The
preparation of suitably weathered petroleum-derived fuels as reference samples for
comparisonwithresidueanalysisoffuel-productsusedindevices#6-10byDART-MSwill
bethesubjectoffuturework.
83
Figure47Fullscanhigh-resolutionmassspectrumofanautomotivegrease,usedasareferencematerial.Collectedinpositivemode.
Figure48.Fullscanhigh-resolutionmassspectrumdepictingidentificationofautomotivegreasefrompost-blastresiduesextractedwithhexanefromIED#10metal
substratefragment.Collectedinpositivemode.
84
Figure49.Fullscanhigh-resolutionmassspectrumdepictingidentificationof
automotivegreasefrompost-blastresiduesextractedwithhexanefromIED#10plasticsubstratefragment.Collectedinpositivemode.
Figure50.Fullscanhigh-resolutionmassspectrumdepictingidentificationof
automotivegreasefrompost-blastresiduesextractedwithhexanefromIED#10rubbersubstratefragment.Collectedinpositivemode.
85
Identificationoftheoxidizercomponentofthebinaryexplosivesmixturesusing
DART-MSwas also studied. Table 1 lists commonexamples of inorganic salts used as
oxidizersintheproductionofhomemadebinaryexplosives.DART-MSanalysisofthese
exemplarycommercialsourcesofoxidizerswasperformedinnegativemode.Instrument
andsolventblankswereincludedtomonitorcleanlinessoftheinstrumentandtoidentify
background ions endogenous to the DART itself (Figure 51 and 52). Analysis of the
commercialsourcesofoxidizerswasincludedtodeterminedetectioncapabilityforthe
realsubstancesthatareusedtomakeHME.Ammoniumnitratesourcedfrominstantcold
compressionpacks,wasidentifiedbytheobservingthenitrateion(m/z61.9867[NO3]-)
anditsadductwithnitricacid(m/z124.9819[HNO3+NO3]-).Potassiumnitratesourced
from commercial stump remover, was identified by observing the nitrate ion (m/z
61.9867[NO3]-).Anotherionwasalsoreproduciblyobservedatm/z121.9819([C7H5O2]-)
whichisattributabletoanorganicadditivepresentintheproduct.Detectionofnitrate
inorganic salts was in agreement with expectation because of their sufficient vapour
pressure at room temperature. 12 Upon analysis of aqueous extracts collected from
fragmentsrecoveredforIED#10post-blast,thesamecharacteristicionsobservedwere
observedidentifyingtheoxidizercomponentofthebinaryHME.Analysisofthefragments
fromtheremainingdevices(#7,8and12)willbecompletedinfuturework.
86
AnalysisofperchloratesandchloratesviaDART-MSprovedtobechallenging,in
agreement with other reported studies. 67 The low vapour pressure of chlorates and
perchlorates has been cited as the cause for poor ability to detect, which poses a
challenge to thermal desorption required for the DART ionization process. 67 Upon
analysisofchlorateandperchloratesaltswith theDARTprobe temperatureof250°C,
whichisstandardforanalysisofexplosives,detectionofperchloratesandchlorateswas
notobserved.NoionscharacteristicofperchlorateorchloratewereobservedinanyEICs
generatedfromanalysisofthebinaryexplosiveresidues.Increasingthetemperatureof
the DART ionizing gas has been reported as ineffective to recover either chlorate or
perchlorate.67FurthermethodoptimizationtouseDART-MStodetecteitherchlorateor
perchloratesaltsfrompost-blastbinaryexplosiveresidueswasnotperformedwithinthe
scopeofthisstudypresented,butwillbeexploredwithfuturework.
Figure51.Negativemode,fullscanhighresolutionmassspectrumuponoperationof
theDART-MS,depictingtheendogenousions.Totalioncount106.
87
Figure52.AnalysisofwaterdepositedontoaQuickStrip,innegativemodeusingfull
scan.Totalioncount106.
Figure53.Negativemode,fullscanhigh-resolutionmassspectrumforammonium
nitrateanalyzedasareferencematerial.
88
Figure54.Negativemode,fullscanhigh-resolutionmassspectrumforacommercially
availablestumpremover(commercialsourceofKNO3),analyzedasareferencematerial.
Figure55.IdentificationofKNO3innegativemodeviafullscanhighresolutionDART-MSanalysisofpost-blastresiduesextractedfrommetalsubstratefragmentsfromIED#10
withwater.
89
Figure56.IdentificationofKNO3innegativemodeviahigh-resolutionDART-MSanalysisofpost-blastresiduesextractedfromplasticsubstratefragmentsfromIED#10with
water.
Figure57.IdentificationofKNO3innegativemodeviafullscanhigh-resolutionDART-MSanalysisofpost-blastresiduesextractedfromrubbersubstratefragmentsfromIED#10
withwater.
90
3.2.3.SmokelessPowders
Asblasteffects(heatandpressure)canchangethecompositionofacompound,
ignitionofNCisexpectedtoresultinthermalbreakdowntooligomersofvaryinglength
and degree of nitration. Characterization of these thermal breakdown products is
challengingasreferencematerialsdonotexist.Commercialsourcesofmonomerordimer
nitratedsugarproductsarenotavailablemotivatingthesynthesisofareferencematerial
in-house.Successfulsynthesisofb-cellobioseoctanitrate(ONCB)affordedareference
material structurally similar to potential breakdown products from the thermal
degradationofNC.
Initial analysis of ONCB and unconsumed grains of single and double based
smokelesspowderresultedindissimilarspectra.Ionscharacteristicoftheadditivesand
preservatives included in smokelesspowder (e.g.DPAandEC)dominated the spectra
obtained upon analysis of both single and double base products unconsumed.
PredominantionsobserveduponanalysisofONCBwereabsentinthespectraobtained
viaanalysisofthesmokelesspowder.ComparisonofONCBandresiduescollectedfrom
the ignited smokeless powder also did not warrant similar spectra. New ions were
observed in the spectra from analysis of the ignited smokeless powders but were
dissimilarfromthepredominantionsintheONCB.TheseresultssuggestedthattheONCB
inpureformmaynotbeacomparablematerialforthecharacterizationofNCthermal
breakdownproducts.
91
ComparisonofignitedONCBandsmokelesspowderwascompletedtodetermine
if the ignited product was a more suitable reference material than unburned ONCB.
Analysis of extracted ONCB and smokeless powder residues with acetonitrile was
completed. After subtracting the spectral contributions from acetonitrile (Figure 23),
similar ions in the m/z range of 300-500 were observed upon analysis of ONCB and
smokelesspowderresidues.Proposedcharacteristicionsareasfollows;m/z323.0718,
341.0822,491.0744,508.0643,and536.0597.Ionabundancewashighlyvariableacross
analyses of all samples. The highly complex sample matrix created by burning the
productsresultedinmassspectrawithionsobservedfromm/z50–500atcountsof106
-107.Subtractionofspectralcontributionfromthesolventreducedioncountsbyonlya
signalmagnitude (107 to 106) further emphasizing complexity of the ignited samples.
Figure58depictshowEICswereusedtoconfirmthattheproposedcharacteristicionsare
notattributedtoanysamplecomponentotherthannitratedsugarthermalbreakdown
products. The ions used to produce the EICs are indicated on the left of the figure.
DescriptorsofthesamplesplacedineachwellonaQuickstriparelabelledalongthetop.
ThelongblackboxwithgreycirclesoverlaidontheEICdepictstheQuickstripcardthat
blank, control and extract sampleswere deposited onto. The firstwell contained the
extraction solvent; included to facilitate background subtractions. Blank wells were
analyzedbetweeneachsampletofacilitatesubtractionofionsendogenoustotheDART-
MSandmonitorinstrumentcleanliness.AnalysisofTNTservedasanegativecontrolas
the thermal breakdown products would not be present in the TNT sample and their
structurewouldnotbesimilartothatofTNT.Theignitedresiduesweredepositedonto
92
wellsfive,sevenandnine.ObservationofthecharacteristicionsintheEICforallthree
samples confirms detection and identification of similar thermal breakdown products
betweenignitedONCB,SBandDBsmokelesspowders.Absenceofthecharacteristicions
in the wells associated with the instrument background, solvent, and TNT further
confirmsassociationtothenitratedsugarthermalbreakdownproducts.Characterization
of the thermal breakdown products is supported by identification of common
characteristic ions in both the reference sample (ignited ONCB) and the consumed
smokelesspowders.
Figure58.Determinationofionscharacteristicofthethermalbreakdownproducts.
93
Mass analysis of each ion was used for structure determination based on
acceptable mass shift (± 0.003 amu) with respect to high-resolution accurate mass
measurements (Table 6). MS/MS analysis may provide further clarification on the
structureofthethermalbreakdownproductsbyproducingfragmentsthatcanbeused
toelucidatefunctionalgroupsandstereochemistry,andshallbeexploredinfuturework.
Table6.Listofmassformulaefortheionscharacteristicofnitratedsugarthermalbreakdownproducts,withassociatedmassshift(amu).
m/z MassFormulae Massshift(amu)
323.0718C9H9O5N9 -0.486
C10H15O10N2 -0.491
341.0822C9H11O6N9 -0.611
C10H17O11N2 -0.616
491.0744C13H15O13N8 -1.129
C26H11O7N4 -0.616
508.0643C12H14O14N9 -1.112
C26H12O8N4 -0.605
536.0597C13H14O15N4 -0.907
C27H12O9N4 -0.399
Solubility of the thermal breakdown products was explored using a series of
solvents commonly used in accepted forensic practices (acetone, MeOH, water,
acetonitrile,DCMandhexane).ChangesinobservationofionsintheEICswasusedasa
measurementofsolubility.Thethermalbreakdownproductsareassumedtoberelatively
polar if they retain thepolarnitrategroups.Solventsofvaryingpolaritywereused to
confirm this hypothesis. Figure 59 depicts a combination of the EICs obtained from
analysis of ONCB, SB and DB residues extracted with six different solvents. Wells
highlighted by the red box indicates samples extracted with hexane. Absence of all
94
characteristic ions upon analysis of hexane extract confirms the thermal breakdown
products are not soluble in a non-polar solvent. Wells highlighted in the purple box
indicatesamplesextractedusingDCM.Characteristicionswereobserveduponanalysis
of ignited ONCB but not smokeless powders confirming many species with slightly
differentpolaritycouldbepresent.Yellow,greenandorangeboxesindicateextraction
withacetone,ACNandMeOH,respectively.Asthesearerelativelypolarsolvents,with
retentionofthenitrategroupsuponthermaldegradation,itisnotsurprisingthatresidues
were soluble in these polar solvents. The blue box depicts extractionwithwater and
absenceofcharacteristicionsconfirmstheyarenotsolubleinwater.
Figure59.Relativesolubilityofresiduescontainingthermalbreakdownproducts.
95
SynthesisofareferencematerialsuchasONCBwasessentialfordetectionand
identificationofNCthermalbreakdownproducts.IgnitionofONCBaffordedproduction
of residuesalike thoseproducedupon the ignitionof a smokelesspowder. Successful
detection and identification of similar ions upon analysis of ignited products provides
mechanisms for characterization of thermal breakdown products. Post-blast
identification of NC would remain impossible without detection and identification of
characteristicthermalbreakdownproducts.
FuturegoalsincludeusingtheignitedONCBasareferencematerialandDART-MS
to fully characterize smokeless powders from post-blast residues when used in IED.
Therefore, it is imperative to test applicability of this novelworkwith real post-blast
fragments.Thesetestswillbecarriedoutinfutureworktoensurethatcharacteristicions
observeduponburningtheproductsareidentifieduponanalysisofpost-blastresidues.
Toensureefficientextractionpost-blastresiduesshouldbeextractedwithACN.
96
4.ConclusionDARTcoupledwithhigh-resolutionMSwasdemonstratedasasuitableanalytical
techniqueapplicableforforensicidentificationofhomemadeexplosivefrompost-blast
residuesrecoveredfromIEDfragmentsrepresentativeofitemsandsubstratescommonly
recoveredfromgenuinebombinginvestigations.Explosivesofintereststudiedincluded
organicperoxides (triacetonetriperoxide,hexamethylenetriperoxideandmethylethyl
ketone peroxide), binary explosives (fuel and oxidizer mixtures) and commercial
smokelesspowders(bothsingle-anddouble-base).Eachexplosivewascharacterizedby
comparing questioned mass spectra with known reference materials to identify ions
characteristic of the target explosive. DART-MS was also successfully used to
characterization the thermal breakdownproducts of nitrocellulose (i.e. nitrated sugar
derivatives)whichcanbeusedtoidentifyasmokelesspowderpost-blastintheabsence
ofrecoveringanintactgrain.
DART-MSwasverifiedtoidentifyHMEresiduesbydirectanalysisofthepost-blast
IEDfragmentsthemselvesandbyindirectanalysisofsub-samplescollectedusingdryor
wetswabswithsolvents.Drycottonswabswere foundeffective forexplosive residue
recovery and yielded the least co-extracted environmental background. Since dry
swabbing is also a commonplace sampling techniqueused at security check-points to
detect concealed explosives or residues,we suggestDART-MS is compatible for rapid
forensicdetectionoftraceexplosivesinscreeningapplications.
97
5.FutureWork The residues studied in this project were not subjected to weathering or
degradationeffectswhich are commonlyobserved in forensic samples collected from
crime scenes as this was beyond the scope of the study. Post-blast fragments were
collected andpackaged in sealable nylon-evidence bags immediately after detonation
unlike realistic scenarios where many safety precautions are taken before front-line
memberscanenterablastscenetocollectevidence.Exposuretoenvironmentalfactors,
suchasprecipitation,temperatureschangesorsunlight(e.g.UV)canaffectthelifetime
and recoverability of explosive residues post-blast. The potential for sample loss or
contaminationofevidence(e.g.sourcedbyexposuretoweather)couldbestudiedinthe
futuretofurtherreplicaterealisticscenarios.Delayedcollectionofthefragmentsintime
increments representative of realistic scenarios is oneway to study exposure effects.
Simulatingchangesintemperaturebyexposingthefragmentstoheat(e.g.placinginan
oven with temperature set to represent realistic Canadian summer heat) is another
mechanisminwhichmeasuringtheeffectsofweatheringcouldbestudied.
Furthermore,duetothehomemadenatureofOPBEandbinarymixturesdifferent
precursor sources and synthesis methods can contribute to changes in the residues
collectedpost-blast.Additionalanalysisofpost-blastresiduesfromdetonationofdevices
that containproducts synthesizedwithdifferentprecursors (i.e. lowerwt%hydrogen
peroxide,differentacidcatalysts,andadditionalcommercialfuelandoxidizersources)
wouldfurtherdepicttherobustcapabilityofDART-MSasan identificationmethodfor
homemadeexplosives.
98
References[1] TheGlobalPracticeofForensicScience,editedbyDouglasH.Ubelaker,John
Wiley&Sons,Incorporated,2014.
[2] R.W.Byard,H.James,J.Berketa,K.Heath.JForensicSci(2016)61:545-547.
[3] N.Abdul-Karim,C.S.Blackman,P.P.Gill,E.M.M.Wingstedt,B.A.P.Reif.RSCAdv.
4(2014)54354–54371.
[4] J.S.Caygill,F.Davis,SP.J.Higson.Talanta(2012)88:14-29.
[5] EicemanGA,KarpasZ.Ionmobilityspectrometry,2ndrev.edn.BocaRotan,FL:
TaylorandFrancis,2005.
[6] G.W.Cook,P.T.LaPuma,G.L.Hook,B.A.Eckenrode.JournalofForensicScience
(2010)55:1582-1591.
[7] C.L.Crawford,H.H.Hill,Jr.AnalyticaChimicaActa(2013)795:36-43.
[8] Beveridge,ForensicInvestigationsofExplosions,CRCPressTaylor&Francis
Group,India,2012.
[9] D.DeTata,P.Collins,A.McKinley.ForensicScienceInternational(2013)233:63-
74.
[10] X.Xu,M.Koeberg,C.-J.Kuijpers,E.Kok.ScienceandJustice(2014)54:3-21.
[11] T.P.ForbesandE.Sisco.Analyst(2018)143:1948-1969.
[12] J.Pavlov,A.B.Attygalle.Anal.Chem.(2013)85:278−282.
[13] E.Sisco,J.Dake,C.Bridge.For.Sci.Int.(2013)232:160–168.
[14] T.P.Forbes,E.Sisco,M.Staymates,G.Gillen.Anal.Methods(2017)9:4988-
4996.
[15] Kubota,PropellantsandExplosives:ThermochemicalAspectsofCombustion,2nd
ed.,Wiley–VCH,Germany,2007.
[16] J.C.Oxley,J.L.Smith,J.Huang,W.Luo.J.ForensicSci(2009)54:1029–1033.
[17] L.R.RothsteinandR.Petersen.PropellantsandExplosives(1979)4:50-60.
[18] M.VaullerinandA.Espagnacq.Proppelants,ExplosivesandPyrotechnics.(1998)
23:237-239.
[19] N.Hagan,I.Goldberg,A.Graichen,A.St.Jean,C.Wu,D.Lawrence,P.Demirev.J.
Am.Soc.MassSpectrom.(2017)28:1531-1539.
99
[20] R.D.Bach,P.Y.Ayala,H.B.Schlegel.J.Am.Chem.Soc.(1996)118:12758-12765.
[21] Agrawal,J.P.;Hodgson,R.D.OrganicChemistryofExplosives(2007).
[22] J.Pachman,R.Matyas.ForensicScienceInternational(2011)207:212–214.
[23] R.vs.BRIDGES,Dane.OntarioCourtofJustice;Ottawa:2012-2013.
[24] R.vs.AMSEL,Guido.ProvincialCourtofManitoba;Winnipeg:2017–2018.
[25] F.SRomolo,L.Cassioli,S.Grossi,G.Cinelli,M.V.Russo.ForensicSci.Int.(2013)
224:96–100.
[26] N.A.Milas,A.Golubovic.J.A.C.S.(1959)81:5824-5826.
[27] A.Miyake,K.Takahara,T.Ogawa,Y.Ogata,Y.WadaandH.Arai.Jour.ofLoss
PreventioninthePro.Ind.(2001)14:533-538.
[28] R.M.Heramb,B.R.McCord.For.Sci.Comms.(2002)4.
[29] R.Gonzalez-Mendez,C.A.Mayhew.J.Am.Soc.MassSpectrom.(2017)30:1531-
1539.
[30] C.Christodoulatos,T.Su,A.Koutsospyros.WaterEnvironRes.(2001)27:185-
191
[31] E.Goudsmits,G.Sharples,J.W.Birkett.TrACTrendsAnal.Chem.(2015)74:46–
57
[32] R.V.Taudte,A.Beavis,L.Blanes,N.Cole,P.Doble,C.Roux.Biomed.Res.Int.
(2014)16:16.
[33] M.Joshi,K.Rigsby,J.R.Almirall.ForensicSci.Int.(2011)208:29–36
[34] M.Mach,A.Pallos,P.Jones.J.ForensicSci.(1978)23:433–445
[35] A.Zeichner,B.Eldar,B.Glattstein,A.Koffman,T.Tamiri,D.MullerJ.Forensic
Sci.(2003)48:961–972
[36] R.Ewing.Talanta54(2001)515–529.
[37] Beveridge,ForensicInvestigationsofExplosions,CRCPressTaylor&Francis
Group,India,2012.
[38] O.Coskun,NorthClinIstanb.(2016)3:156–160.
[39] D.S.Moore,J.V.Goodpaster.AnalBioanalChem(2009)395:245–246
[40] BarronandE.Gilchrist,AnalyticaChimicaActa(2014)806:27-54.
[41] E.Gilchrist,N.Smith,L.Barron,Analyst(2012)137.
100
[42] J.M.Nilles,T.R.Connell,S.T.Stokes.PropellantsExplos.Pyrotech.(2010)35:
446-451.
[43] K.Clemons,J.Dake,E.Sisco,G.F.VerbecIV.ForensicSci.Int.(2013)231:98-101.
[44] L.Frederick,T.Joseph,B.D.Muselman,A.B.ScienceandJustice(2016)56:321-
328.
[45] F.Rowell,J.Seviour,A.Y.Lim,C.G.Elumbaring-Salazar,J.Loke,J.Ma.Forensic
SciInt(2012)221:84-91.
[46] J.R.Swider.JournalofForensicSciences(2013)58:1601-1606.
[47] E.Sisco,J.Dake,C.Bridge.ForensicSci.Int.(2013)232:160-168.
[48] F.Rowell,J.Seviour,A.Y.Lim,C.G.Elumbaring-Salazar,J.Loke,J.Ma.Forensic
Sci.Int.(2012)221:84-91.
[49] Dong,DirectAnalysisinRealTimeMassSpectrometry,Wiley–VCH,Germany,
2018.
[50] D.C.Harrisetal,in“QuantitativeChemicalAnalysis.”7thedition.W.H.Freeman
andCompany.NY.USA.2007.
[51] M.Huang,C.Yuan,S.Cheng,Y.Cho,J.Shiea.Annu.Rev.Anal.Chem.(2010)
3:43–65.
[52] A.G.MarshallandC.L.Hendrickson.Annu.Rev.Anal.Chem.(2008)1:579–99.
[53] Cody,R.B.;Laramée,J.;Nilles,J.M.Anal.Chem.(2005)77:2297-2302.
[54] E.S.Chernetsova,G.E.Morlock.MassSpectrometryReviews(2011)30:875-
883.
[55] J.M.Nilles,T.R.Connell,H.D.Durst.AnalChem(2009)81:6744-6749.
[56] Michalski,A.etal.Mol.Cell.Proteomics(2011)9.
[57] Brunnee,C.Int.J.MassSpectrom.IonProc(1987)76:125-237.
[58] J.V.Olsen,B.Macek,O.Lange,A.Makarov,S,Horning,M,Mann.Nature
Methods(2007)4:709-712.
[59] Hardman,M.,andMakarov,A.A.Anal.Chem.(2003)75:1699–1705.
[60] J.C.Oxley,J.L.Smith,K.Shinde,J.Moran.Propellants,Explos.,Pyrotech.(2005)
30:127-130.
[61] L.E.DeGreet,M.M.Cerreta,C.J.Katille.ForensicChem.(2017)4:41-50.
101
[62] T.A.Ong,T.Mendum,G.Geurtsen,J.Kelley,A.Ostrinskaya,R.Kunz.Anal.Chem.
(2017)89:6482-6490.
[63] N.Abdul-Karim,R.Morgan,R.Binions,T.Temple,K.Harrison.J.ForensicSci.
(2013)58:365-371.
[64] D.S.Saang’onyo,D.L.Smith.RapidCommun.MassSpectrom.(2012)26:385–
391.
[65] R.J.Brownlow,K.E.Dagnall,C.E.Ames.J.ForensicSci.(2012)57:713-717.
[66] E.Stauffer,J.DolanandR.Newman.FireDebrisAnalysis,Elsevier,2008.
[67] T.P.Forbes,E.Sisco,M.Staymates.Anal.Chem.(2018)90:6419-6425.
102
Appendix1:SupplementaryInformation
Figure60.Positivemode,fullscan:high-resolutionmassspectrafordiesel,analyzedasareferencematerial
Figure61.Positivemode,fullscan:high-resolutionmassspectraforlampoil,analyzed
asareferencematerial
103
Figure62.Positivemode,fullscan:high-resolutionmassspectraforVaseline,analyzedasareferencematerial
Figure63.Positivemode,fullscan:high-resolutionmassspectraforwax,analyzedasareferencematerial
top related