Ion Trap Mass Spectrometry for theCharacterization of N-Methyl-1-(3,4-methylene-dioxyphenyl)-2-butanamine and N-Ethyl-3,4-methylenedioxyamphetamine, Two WidelyDistributed Street Drugs

Luciano Garofano1, Massimo Santoro1, Paolo Patri1, Federico Guidugli2, Tiziano Bollani2,Donata Favretto3 and Pietro Traldi 3*1Sottocentro Carabinieri Investigazioni Scientifiche, Parma, Italy2Thermoquest Italia, Strada Rivoltana, Rodano, Milano, Italy3CNR, Area della Ricerca, Corso Stati Uniti 4, Padova, Italy

The potential of ion trap mass spectrometry has been evaluated for the characterization and distinction oftwo isomeric amphetamines drugs, namely N-methyl-1-(3,4-methylenedioxyphenyl)-2-butanamine and N-ethyl-3,4-methylenedioxyamphetamine. Whereas the electron impact spectra of the two molecules lackspecificity, collisional experiments on the ionic species atm/z72 allows unequivocal distinction between thetwo isomers. Analogous results are achieved by positive ion chemical ionization and collisional experimentson the protonated molecules. All the different approaches have been successfully applied to the gaschromatography/mass spectrometry analysis of a tablet of illicit drug.# 1998 John Wiley & Sons, Ltd.

Received 17 March 1998; Revised 20 April 1998; Accepted 21 April 1998

The market for street drugs is, unfortunately, in a continuousexpansion and, in the past 35 years, a wide variety of illicitdrugs has appeared. Consequently, the rapid development ofaffordable analytical methods to characterize the structuresof these new molecules becomes important for publichealth.

In the investigation on drugs of abuse, chromatographicand immunobiological assays do not exhibit in some cases asufficient specificity to characterize isomeric compoundsand to identify new active molecules.

These shortcomings certainly hold for amphetamines.Many of these molecules contain the basic amphetamine (1-phenyl-2-aminopropane) skeleton to which various func-tional or structural groups have been added. These newchemical substances show slight modifications in themolecular structure of the parent compound. It is commonpractice for clandestine laboratory chemists to plan newsimple synthetic strategies (e.g. adding a methylenedioxybridge to the aromatic ring of the amphetamine, exploitingalkylation to obtain a series of homologues, or modifyingthe length and the branching of side chains) in order toovercome legislation of different countries, based on thetime between the moment a new drug is illegally marketedand the moment the new molecule becomes acontrolledsubstance.

The most widely distributed derivative of this class ofcompounds is methylenedioxymetamphetamine (MDMA).This synthetic substance, known under the street name‘ecstasy’ or ‘adam’, is representative of the so-called‘designer drugs’ that exhibit stimulating effects (typically

amphetaminic) and hallucinogenic effects (typical ofmescaline).1,2

During the last two years, a new molecule, N-methyl-1-(3,4-methylenedioxyphenyl)-2-butanamine (MBDB), hasappeared on the Italian market, providing the same effectsas its isomer, N-ethyl-3,4-methylenedioxyamphetamine(methylenedioxyethylamphetamine, MDEA), already undercontrol by Italian law.

MBDB andMDEA aredifficult to distinguish.They areisomers,havethesamemolecularmass,solubility andshowsimilar electronimpact(EI)-inducedfragmentation patterns.In fact the EI mass spectrum of MBDB is practicallysuperimposable on those of MDEA and other isomericamphetamines, so that EI massspectrometry can not besuccessfully employed for its identification.1,3 Only tandemmass spectrometric experiments (MS/MS),4 performedusing a triple quadrupole instrument on the fragmentionsat m/z 72, can lead to a clear distinction of MBDB vs.MDEA5–7 without the useof derivatization techniques.

*Correspondenceto: P. Traldi, CNR, Area della Ricerca,CorsoStatiUniti 4, Padova,Italy.

CCC 0951–4198/98/120779–04$17.50 # 1998JohnWiley & Sons,Ltd.

RAPID COMMUNICATIONS IN MASS SPECTROMETRYRapid Commun.MassSpectrom.12, 779–782(1998)

It mustbeemphasizedthat,in thelastfew years,differentanalytical approaches havebeenwidely employed provingtheir power in the field of amphetamine derivatives. Inparticular, methodsbasedon GC/MS8–16 of derivatizedamphetamines(eitherunderEI or chemicalionization[CI]conditions), as well as on HPLC/MS,17,18 have beendeveloped.The developmentof analytical procedures ableto distinguish the two title compounds by low costinstrumentation is clearly of considerableinterest,due totheir possible widespreaduse.

Recently, the appearance of ion trap based GC/MSinstruments has made MS/MS techniques (and highlyeffective chemical ionization) more easily affordable. Inthe present paper we wish to report and discuss someexperimental approaches, based on mass spectrometricstudies performedusing an ion trap, which allow an un-equivocal characterization of MBDB and MDEA mole-cules.

EXPERIME NTAL

All mass spectrometric measurements were performedusing an ion trap massspectrometer GCQTM (Finnigan,SanJose, CA, USA) combined with a gaschromatographGC8000 TopTM (Carlo Erba Instruments, Rodano, MI,Italy), underEI or positive ion chemical ionization (PICI)conditions. Collisional experiments were performed byapplication of a supplementary RF field of appropriatevoltage (tickle voltage) to the endcaps of the ion trap atqz = 0.224. Isolation of precursor ions was performed atqz = 0.83. Typical valuesof excitation voltage and tickletimewerein therange50–1800mV and15ms,respectively.For PICI experiments,CH4 wasusedasthereactant gasatapressureof 8� 10ÿ5 Torr (1 Torr = 133.3Pa).

The gas chromatographic conditions were as follows:column DB5-MS (J & W Scientific, Folsom, CA, USA)(30m� 0.32mm i.d., 0.25mm film thickness); temperatureprogram: 100°C for 1 min, ramp to 210°C at 20°C/min,ramp to 310°C at 10°C/min; injector temperature250°C;transfer line temperature300°C.

RESULTS AND DISCUSSION

TheEI massspectraof MDEA andMBDB, obtained using aquadrupole filt er mass spectrometer, have already beendiscussed1,3 and the inadequacy of the method for theirstructural characterization hasbeenemphasized.

Analogous results are achieved using the ion trapanalyzer. The EI spectra of the two compounds arepractically identical but, asmay be seenin Fig. 1(a), thereare some minor differences(in the relative abundancesofthe fragment ions at m/z135 and in the scarcelyabundant(3%) fragment at m/z 178, which is detected for MBDBonly). Such differences can not be considered significantfrom the analytical point of view, in particular when theanalytesmust bedetectedin a chromatographicrun andthemass spectraof the compoundsof interest show interfer-encesfrom co-chromatographingsubstances.

In the literature it has been proposed that collisionexperimentsperformedon the EI-inducedfragment ion atm/z72 represent theonly methodto obtain a differentiationbetween thetwo isomers,basedon thedetection of productionscharacteristicof thestructuresof thetwo isobaricions.Theseresults7 wereobtainedusing a triple stagequadrupolemass analyzer with a collision energy of 22eV.

Theion trap19 is known to beahighly valuabledeviceforMS/MS experiments, but themechanismof energy deposi-tion on the preselected species is different from thatoperatingin multi-stage ion beamanalyzers. In the lattercasea quite wide internal energy distribution of the pre-cursorions is obtained,while in ion trap conditionsa ‘stepby step’ energy deposition operates, which generallyfavoursdecomposition processes with lower critical ener-gies.20 However, aswill benotedin thetwo spectrareportedin Fig. 1(b), a clear differentiation is obtained by ion trapMS/MSbetween theEI-generatedfragment ionsatm/z72ofMDEA andMBDB. In the caseof MDEA essentially onlyoneproduct ion is detectedatm/z44,while for MBDB ionicspeciesat m/z 57, 44, and 30 are observed.A possiblerationalefor thesedifferentbehaviors is reportedin Scheme1. The ethylene lossfrom the ion at m/z72, leadingto thespeciesat m/z44, is a processcommonto bothcompoundseventhough it probably leadsto productionswith differentstructures. The m/z 72 ions of the N-methyl derivative(MBDB) showadditional collisionally induced fragmenta-tion processes, consisting of C3H6 and CH3

� lossesaccording to Scheme1. The latter process is an exceptionto the evenelectron rule21 and can be rationalized by theexistenceof a diradical intermediate,analogous to thatalreadyproposed by Budzikiewicz andBold.22

By varying the collision energy, further differentiationcanbeachievedwith respect to theformation of the ionsatm/z44 from theprecursorsatm/z72.Thebreakdowncurvesrelatedto these species, reported in Fig. 2 show that the

Figure 1. (a) GC/MS chromatogramobtainedfrom an illicit tabletunderEI conditions,with the ion trap operatingin the normal scanmode.(b) GC/MS chromatogramobtainedfrom the sametabletwiththe ion trapsetto monitor thespeciesgeneratedby CID of the ionsatm/z72(b1 = total ion current,b2 = reconstructedion chromatogramform/z44, b3 = reconstructedion chromatogramfor m/z30).

Rapid Commun.MassSpectrom.12, 779–782(1998) # 1998JohnWiley & Sons,Ltd.

780 ION TRAP MS FOR MDEA AND MBDB

formation of an ion at m/z 44 requires a collision energylower for MDEA than for MBDB, indicating that for theformer isomer the activation energy of the process[C4H10N]� → [C2H6N]� is lower than for the latter. Thisresult is consistentwith themechanismreported in Scheme1.TheN�–Cbond,whosecleavageis involvedin thelossofC2H4 for MDEA, is surely weaker than the C–C bondinvolvedin theanalogousprocessfor MBDB. Alternatively,the transient diradical structure for the ions at m/z 72originating from MDEA andMBDB canbeconsideredalsofor the formation of the ionic speciesat m/z44. In suchastructure, one can assumethat the reactivity would bedifferentfor thetwo isomersandcouldexplain theobserveddifferent behaviors.

From the above reported data obtained by ion trapmethodology, aswell as from the literaturedataobtained7

by triple stage quadrupole systems, it appears that adifferentiation between MDEA andMBDB canbeachievedby collision experiments on the abundant EI-generatedfragment ion at m/z 72. Thus MS/MS experiments are

indicated in order to characterize the two isomericcompounds.

It was considered useful to undertake some chemicalionization23 experimentson thetwo compounds, in ordertoevaluatethepotentialof this approachfor thecharacteriza-tion of MBDB and MDEA. The PICI(CH4) spectraof thetwo compoundsarereportedin Fig. 3(a). Theybothexhibitabundant [M � H]� speciesatm/z208(which is responsiblefor thebasepeakof thespectrumin thecaseof MBDB), butdifferences between the two isomersareclearly evident. Inparticular, such differences are related to the relativeabundancesof the ionic speciesat m/z163 and177.Whiletheformerrepresentsthebasepeakfor MDEA andexhibitsa relative abundanceof only 10% for MBDB, the latter isdetectableonly for MBDB. This behaviorcanbeexplainedby cleavageof the C–N bond, activated by protonationonthe nitrogen atom, as shown in Scheme2. In the samescheme, theformation of theion at m/z135,presentin bothCI spectra and to which both a tropylium-like or abenzylium-like structurecan be assigned, is also reported.It mustbe emphasizedthat theseions arenot collisionallyproduced from ions at m/z 163 and 177. Hence, byPICI(CH4) a cleardifferentiation between the two isomerscan be obtained. From the analytical point of view thisrepresentsa significant result, allowing identification ofMDEA andMBDB by simple GC/MSinstrumentswithoutthe needfor MS/MS devices.Nonetheless,the differencespresent in the CI spectraare further enhancedby MS/MSexperimentsperformedon PICI-induced[M � H]� species,asmay be seenin Fig. 3(b).

The methodsdescribed abovehavebeenapplied to the

Scheme1.

Figure 2. Breakdowncurvesof theionsatm/z44obtainedby collisionof the EI-generatedion at m/z72 from MDEA (O) andMBDB (&).

Figure 3. (a) GC/MS chromatogramobtainedfrom an illicit tabletunderPICI(CH4) conditions,with the ion trapoperatingin thenormalscan mode. (b) GC/MS chromatogramobtained under PICI(CH4)conditionswith the ion trap set to monitor the speciesgeneratedbycollision of MH� ionsat m/z208.

# 1998JohnWiley & Sons,Ltd. Rapid Commun.MassSpectrom.12, 779–782(1998)

ION TRAP MS FOR MDEA AND MBDB 781

GC/MS analysisof a tabletavailable on the il licit market.Figure 1(a) reportsthe chromatogramobtained in full scanmode; peaks1 and2 leadto themassspectrareported in thesame figure. The presencein bothcasesof anabundant ionat m/z 72 suggests their amphetamine nature,but on thebasisof theEI spectranostructural assignmentcanbedone.Onthecontrary,whentheion trapis setto selectthespeciesat m/z72 andto performcollision experimentson this ion,the unequivocal structural characterization shown in Fig.1(b) canbe achieved.

The same characterization canbeobtained by PICI(CH4)experimentsaswell asby further MS/MS experimentsonthe MH� species, asshown in Fig. 3(a) and(b).

In conclusion,by using anion trapmassspectrometerthecharacterization of MDEA and MBDB can be easily

achievedby the different methodologies availableon theinstrument, i.e. either by MS/MS experiments on the EI-generatedfragment ionsatm/z72,or by chemical ionizationusingCH4 andMS/MS of PICI-generatedMH� ionsof thetwo isomers.

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Scheme2.

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782 ION TRAP MS FOR MDEA AND MBDB