Chiral gas chromatography as a tool for investigations into illicitly manufactured methylamphetamine

Article abstract of DOI:10.1002/chir.20957

The aim of this study was to develop a chiral gas chromatographic method for the separation of compounds likely to be found in the EMDE synthesis of methylamphetamine, a heavily abused stimulant drug. Here we describe the separation of the enantiomers of

Full text of DOI:10.1002/chir.20957

CHIRALITY 23:519–522 (2011)
Chiral Gas Chromatography as a Tool for Investigations into
Illicitly Manufactured Methylamphetamine
1
2
2
CALUM MORRISON,1 FRANK J SMITH, TOMASZ TOMASZEWSKI, KAROLINA STAWIARSKA, AND MAREK BIZIUK2
*
1School of Science, University of the West of Scotland, Paisley, United Kingdom
2Chemical Faculty, Gdansk University of Technology, Gdansk, Poland
ABSTRACT
The aim of this study was to develop a chiral gas chromatographic method for
the separation of compounds likely to be found in the EMDE synthesis of methylamphetamine,
a heavily abused stimulant drug. Here we describe the separation of the enantiomers of ephe-
drine, pseudoephedrine, chlorinated intermediates and methylamphetamine using fluorinated
acid anhydrides as chemical derivatization reagents prior to gas chromatographic analysis on a
2,3-di-O-methyl-6-t-butyl silyl-b-cyclodextrin stationary phase (CHIRALDEXTM B-DM). Separa-
tion of the enantiomers of pseudoephedrine, methylamphetamine and chloro-intermediates was
achieved using PFPA derivatization, and enantiomers of ephedrine using TFAA derivatization,
in run times of less than 40 minutes. The use of HFBA as a derivatization reagent for this set of
C
VV
analytes is also discussed. Chirality 23:519–522, 2011.
2011 Wiley-Liss, Inc.
KEY WORDS: Methylamphetamine, EMDE synthesis, chiral GC, cyclodextrin
INTRODUCTION
mobile-phase additives in capillary electrophoresis (CE).9,11 In
addition, the formation of diastereoisomers and subsequent
analysis using a nonchiral gas chromatographic column has
been attempted successfully.12
Methylamphetamine is a stimulant-type drug based on the
phenethylamine structure and was reclassified in January
2007 in the United Kingdom from Class B to A within the Mis-
use of Drugs Act 1971. Here, we refer to the N-methylamphet-
amine substance. The terminology associated with this sub-
stance can be confusing with methylamphetamine used in this
legislation and in the literature, with other commonly used
terms such as methamphetamine, N,a-dimethylphenylethyl-
amine, (2S)-N-methyl-1-phenyl-propan-2-amine, and deoxye-
phedrine particularly in the case of the (2)-(R)-enantiomer.
The Chemical Abstract Service (CAS) registry number for
methylamphetamine is 537-46-2. The drug is a major problem
throughout the world particularly in East and Southeast Asia
and the United States, which accounts for 40 and 56%, respec-
tively, of the seized material worldwide in 2007.1 The prob-
lems associated with methylamphetamine use have been well
documented in the media, and a general summary can be
found in the US Drug Enforcement Administration web-
pages.2 Recent concerns have been reported involving the
exposure of children3,4 and the general population5 to methyl-
amphetamine and chemicals found in clandestine laboratories.
In the United States, differences in penalty exist between
the two enantiomers, with Federal Sentencing Guidelines
imposing greater penalties on seizures containing >80% of
the (1)-(S)-methylamphetamine. Therefore, in the United
States, chiral analysis is required and usually carried out by
the formation of a diastereoisomeric N-trifluoroacetyl-L-prolyl
derivative followed by achiral gas chromatography.6 The rea-
son for differences in sentencing is due to the greater activity
of the (1)-(S)-enantiomer as a central nervous system stimu-
lant, whereas the (2)-(R)-enantiomer shows greater periph-
eral activity and indeed has been used in nonprescription
decongestants.7 A recent review covers the pharmacology
of methylamphetamine, including some stereochemical
considerations.8
In terms of drug profiling studies applied to methylam-
phetamine, these studies have recently focused on isotope
ratio mass spectrometry,13 organic impurity characteriza-
tion,14 chiral analysis using reversed-phase CE with highly
sulfated g-cyclodextrin as chiral selector,15 achiral gas
chromatography–mass spectrometry with electron impact and
chemical ionization,16 and achiral gas chromatography–mass
spectrometry using a-methoxy-a-(trifluoromethyl)phenylacetyl
chloride for the formation of diastereoisomeric derivatives.17
Many less common synthetic routes for the illicit manufac-
ture of methylamphetamine exist,15 but the three most com-
monly encountered routes are Nagai (nonmetal reduction
using hydriodic acid/red phosphorus), Birch reduction (dis-
solving metal reduction with liquid ammonia and lithium
or sodium), and Emde (chlorination with thionyl chloride fol-
lowed by hydrogenation over palladium).18 These routes are
illustrated in Figure 1.
Published investigations into the chlorination of the ephe-
drine enantiomers in the Emde route showed complete rever-
sal of configuration at C-1 forming chloropseudoephedrine
enantiomers, implying an SN2 mechanism. Therefore, the
predicted product for chlorination of (2)-(1R,2S)-ephedrine is
the (1)-(1S,2S)-chloropseudoephedrine intermediate and for
(1)-(1S,2R)-ephedrine is the (2)-(1R,2R)-chloropseudoephe-
drine. However, the chlorination of pseudoephedrine enan-
tiomers does not follow SN2 completely, and in fact, a mixture
of 40% chloroephedrine: 60% chloropseudoephedrine enan-
Contract grant sponsor: Royal Society of Chemistry.
*Correspondence to: Calum Morrison, School of Science, University of the
West of Scotland, Paisley, United Kingdom. E-mail: calum.morrison@uws.
ac.uk
Received for publication 30 October 2009; Accepted 20 January 2011
DOI: 10.1002/chir.20957
Published online 19 April 2011 in Wiley Online Library
(wileyonlinelibrary.com).
There have been several reports of stereospecific separa-
tion of methylamphetamine using chiral stationary phases in
liquid chromatography and gas chromatography9,10 and
C
VV
2011 Wiley-Liss, Inc.

520
MORRISON ET AL.
was identical for all derivatizing reagents, with minor modifications for
HFBA (described in Results and Discussion section):
1. Addition of 50 ll of methanol solution to vial.
2. Evaporation to dryness at 508C under a stream of nitrogen, removing
from heat at point of dryness.
3. Addition of 50 ll derivatizing reagent followed by 50 ll of ethyl ace-
tate and heated for 15 min at 508C.
4. Evaporation to dryness at 508C under a stream of nitrogen.
5. Addition of 50 ll of ethyl acetate prior to chromatographic analysis.
Nitrogen was supplied by a generator (model UHPN 3001; Domnick
Hunter, Gateshead, UK).
Summary of Preparation of Chloro Intermediates
The chlorination step of the Emde synthesis was carried out with
minor modifications to the method outlined in the clandestine guide
authored by Uncle Fester.22 The 1H NMR spectral data were compared
with literature values and indicative with chloroephedrine/chloropseu-
doephedrine having been formed.19,20 Additionally, infrared analysis of
the intermediates showed the absence of the OH band and the presence
of CꢀꢀCl signal, indicating chlorination had taken place. Furthermore,
1H NMR investigation is required to differentiate chloroephedrine and
chloropseudoephedrine in the synthesized samples.
The general synthetic method is as follows: (1)-(1S,2S)-pseudoephe-
drine (5.02 g, 0.030 mol) was dissolved in 10 ml chloroform and added
to a mixture of 10 ml thionyl chloride and 10 ml chloroform. The reac-
tion was heated in a water bath at a temperature of 70–758C for a period
of 5 h. The reaction mixture was then cooled in an ice bath followed by
the addition of 100 ml diethyl ether. The crystals formed were filtered
under vacuum, washed with acetone, weighed as a crude product, and
recrystallized from methanol.
Fig. 1. Common synthetic routes to methylamphetamine.
tiomers is suggested, implying a mixture of SN2 and SNi
(retention of configuration).19,20
A chiral profile may therefore be used to determine the
source of starting material and provide links to street batches.
For example, (2)-(1R,2S)-ephedrine and (1)-(1S,2S)-pseudoe-
phedrine have been identified as important components
derived from the Ephedra plant (Ephedraceae family).21
The identification of the chlorinated intermediates would
indicate the use of the Emde synthesis, rather than other
routes such as the Birch reduction and Nagai methods.
The method was applied to all other stereoisomers of ephedrine
hydrochloride and pseudoephedrine using similar mole ratios between
reactants.
MATERIALS AND METHODS
Chemicals
RESULTS AND DISCUSSION
Methanol, ethyl acetate, chloroform, diethyl ether, and thionyl chloride
were supplied by Fisher Scientific (Loughborough, UK). Trifluoroacetic
anhydride (TFAA), pentafluoropropanoic anhydride (PFPA), and hepta-
fluorobutyric anhydride (HFBA) were purchased from Sigma-Aldrich
(Poole, UK).
(1)-(1S,2R)-Ephedrine hydrochloride [24221-86-1], (2)-(1R,2S)-ephe-
drine hydrochloride [50-98-6], (1)-(1S,2S)-pseudoephedrine [90-82-4],
(2)-(1R,2R)-pseudoephedrine [321-97-1], (1)-(S)-methamphetamine
hydrochloride [51-57-0], and (2)-(R)-deoxyephedrine [33817-09-3] were
purchased from Sigma-Aldrich.
The analytical approach involved evaluation and develop-
ment of various chromatographic conditions for enantiomer
separations of ephedrine, pseudoephedrine, methylamphet-
amine, and the chlorinated intermediates, chloroephedrine
and chloropseudoephedrine, from the Emde synthetic route.
An important consideration was provision of a chromato-
graphic system that can separate all analytes and therefore
quickly provide additional useful information for analysts
involved in drug profiling studies.
The chromatographic column used for the separations was
a derivatized b-cyclodextrin (2,3-di-O-methyl-6-t-butyl silyl).
Chromatography
Enantiomeric separations were performed on a HP5890 gas chromato-
graph with FID detector connected to an Agilent 3396 series 3 integra-
tor. The chromatographic column used was an Astec CHIRALDEXTM
B-DM capillary column (30 m 3 0.25 mm 3 0.12 lm film thickness)
supplied by Supelco (Bellefonte, PA). Helium (CP Grade) was used as a
carrier gas and was supplied by BOC Gases Europe (Guildford, UK).
The flow of carrier gas was 1 ml/min, with constant flow conditions
being observed throughout. The temperature programs were as follows:
•
PFP derivatives: Initial temperature of 1158C for 28 min followed by
temperature gradient of 58C/min for 5 min to a final temperature of
1508C, which was held for a further 5 min, giving a total run time of
40 min.
•
•
TFA derivatives of ephedrine: Isothermal temperature at 1108C.
The injector and detector temperatures were set at 2008C.
Derivatization Procedure
Stock solutions of single enantiomers were prepared in methanol at
Fig. 2. Separation of enantiomers after PFPA derivatization.
concentrations of approximately 1 mg/ml. The derivatization procedure
Chirality DOI 10.1002/chir

CHIRAL ANALYSIS OF METHYLAMPHETAMINE
TABLE 1. Retention time data from Figures 2 and 4
521
Enantiomer
Rt
Rt0
k0
(2)-(R)-Methylamphetamine PFP
(1)-(S)-Methylamphetamine PFP
(1)-(1S,2S)-Pseudoephedrine PFP
(2)-(1R,2R)-Pseudoephedrine PFP
Chloro-intermediate PFP
Chloro-intermediate PFP
(2)-(1R,2S)-Ephedrine TFA
(1)-(1S,2R)-Ephedrine TFA
23.93
24.61
26.25
26.72
38.39
38.66
22.13
22.57
2.47
2.47
2.47
2.47
2.47
2.47
2.18
2.18
8.69
8.96
9.63
9.82
14.54
14.65
9.15
9.35
Rt and Rt0 are retention times in minutes of analyte and nonretained com-
pound. k0 is the retention factor.
Chemical Derivatization
Chemical derivatization was investigated using fluorinated
acetylating reagents, TFAA, PFPA, and HFBA, as a means
of reducing polarity/basicity of analytes and improving enan-
tiomeric separations. The derivatizing reagents were added
prior to the addition of ethyl acetate to maximize reaction
with the analytes.
Pentafluoropropionyl derivatives of pseudoephedrine and
methylamphetamine separated well as shown in Figure 2.
However, poor resolution was noted with ephedrine, even
after decreases in column temperature, as illustrated in
Figure 3. This is also the first eluting enantiomeric pair, and
therefore, further decreases in temperature were not consid-
ered. The trifluoroacetyl derivatives of ephedrine showed
good resolution at 1108C, as shown in Figure 4; however,
peak coelution was noted for methylamphetamine and pseu-
doephedrine at this temperature. By reducing the tempera-
ture to 1008C, a separation of all six enantiomers was pro-
vided, but retention times were long and peak shapes poor.
Therefore, for samples containing ephedrine and pseudoephe-
drine, two separate derivatization procedures are required,
with TFAA derivatization recommended for ephedrine enan-
tiomers only. Retention time data along with separation fac-
tors and resolutions are listed in Tables 1 and 2 for the penta-
fluoropropionyl (PFP) and trifluoroacetyl (TFA) derivatives.
The chloro intermediate of ephedrine/pseudoephedrine
showed enantiomer resolution for TFA and PFP derivatives,
but distinguishing chloroephedrine from chloropseudoephe-
drine has not been accomplished at present. Future investi-
gations will focus on the NMR analysis of the samples for
chloroephedrine and chloropseudoephedrine intermediate
content and determine if both intermediates are present as
predicted.19,20
Fig. 3. Effect of temperature on the separation of ephedrine after PFPA
derivatization.
Compound classes separated on this phase include aliphatic,
olefinic, and aromatic enantiomers, with examples including
selegiline (tertiary amine) and ibuprofen (carboxylic acid)
enantiomers.23 The desired blocking effect of surface silanols
from the 6-t-butyl silyl groups on the cyclodextrin was not
sufficient for the compounds of interest in this investigation,
that is, secondary amine (methylamphetamine) and secon-
dary amine/alcohol (ephedrine and pseudoephedrine), and
therefore, a derivatization procedure using fluorinated acid
anhydrides was used.
When HFBA was used as a derivatizing reagent, partial
resolution of pseudoephedrine and chloro intermediate could
be achieved with single peaks observed for ephedrine and
methylamphetamine under the same conditions (isothermal
temperature 1308C). Additionally, oily residues of heptafluor-
TABLE 2. Separation factors and resolution of PFP and
TFA derivatives
Analyte
a
Rs
Pseudoephedrine PFP
Methylamphetamine PFP
Chloro-intermediate PFP
Ephedrine TFA
1.02
1.04
1.01
1.02
0.94
1.51
0.90
1.23
Fig. 4. Separation of ephedrine after TFAA derivatization.
Chirality DOI 10.1002/chir

522
MORRISON ET AL.
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Further steps are therefore required before chromatography,
for example, addition of larger volumes/repeated additions
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Internal Standards
Internal standards were not used in this study as the focus
here was on the ratios of enantiomers. However, should
quantification of methylamphetamine be required, for exam-
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CONCLUSION
The gas chromatographic analysis of the optical isomers of
important compounds found within the Emde synthesis of
methylamphetamine, including the starting materials and
intermediates, can be achieved using readily available deriva-
tizing reagents in combination with a chiral stationary phase.
The derivatization procedure is quick and simple. In parti-
cular, the enantiomers of pseudoephedrine, methylamphet-
amine, and chlorinated intermediates can be separated in a
run time of approximately 40 min, using PFPA as a derivatiz-
ing reagent. A separate derivatization procedure with trifluoro-
acetic anhydride is required for the separation of ephedrine
enantiomers. HFBA requires a more labor-intensive derivati-
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The identification of chlorinated intermediates within
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ACKNOWLEDGMENTS
The authors thank Mr. C. McGinness, University of the West
of Scotland, for technical assistance, and Dr. David Adam,
School of Chemistry, University of Glasgow, for NMR analysis.
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Chirality DOI 10.1002/chir