Mass spectral studies on vinylic degradation products of sulfur mustards under gas chromatography/mass spectrometry conditions

Article abstract of DOI:10.1255/ejms.1398

Sulfur mustards are a class of vesicant chemical warfare agents that rapidly degrade in environmental samples. The most feasible degradation products of sulfur mustards are chloroethyl vinylic compounds and divinylic compounds, which are formed by the elimination of one and two HCl molecules from sulfur mustards, respectively. The detection and characterization of these degradation products in environmental samples are an important proof for the verifcation of sulfur mustard usage. In this study, we synthesized a set of sulfur mustard degradation products, i.e., divinylic compounds (1-7) and chloroethyl vinylic compounds (8-14), and characterized using gas chromatography/mass spectrometry (GC/MS) under electron ionization (EI) and chemical ionization (CI) (methane) conditions. The EI mass spectra of the studied compounds mainly included the fragment ions that resulted from homolytic cleavages with or without hydrogen migrations. The divinylic compounds (1-7) showed [M - SH]⁺ ions, whereas the chloroethylvinyl compounds (8-14) showed [M - Cl]⁺ and [M - CH₂CH₂Cl]⁺ ions. Methane/CI mass spectra showed [M + H]⁺ ions and provided molecular weight information. The GC retention index (RI) values were also calculated for the studied compounds. The EI and CI mass spectral data together with RI values are extremely useful for off-site analysis for the verifcation of the chemical weapons convention and also to participate in offcial Organization for the Prohibition of Chemical Weapons profciency tests.

Full text of DOI:10.1255/ejms.1398

L.S. Sachin et al., Eur. J. Mass Spectrom. 21, 791–800 (2015)
791
Received: 18 October 2015
n
Revised: 30 November 2015 n Accepted: 2 December 2015 n Publication: 15 December 2015
EUROPEAN
JOURNAL
OF
MASS
SPECTROMETRY
Mass spectral studies on vinylic degradation
products of sulfur mustards under gas
chromatography/mass spectrometry
conditions
L. Sai Sachin, R. Karthikraj, K. Kalyan Kumar, T. Sony, N. Prasada Raju and S. Prabhakar
National Centre for Mass Spectrometry, CSIR-Indian Institute of Chemical Technology, Hyderabad- 500 007, Telangana, India.
E-mail: prabhakar@iict.res.in
Sulfur mustards are a class of vesicant chemical warfare agents that rapidly degrade in environmental samples. The most feasible
degradation products of sulfur mustards are chloroethyl vinylic compounds and divinylic compounds, which are formed by the elimina-
tion of one and two HCl molecules from sulfur mustards, respectively. The detection and characterization of these degradation prod-
ucts in environmental samples are an important proof for the verification of sulfur mustard usage. In this study, we synthesized a set
of sulfur mustard degradation products, i.e., divinylic compounds (1–7) and chloroethyl vinylic compounds (8–14), and characterized
using gas chromatography/mass spectrometry (GC/MS) under electron ionization (EI) and chemical ionization (CI) (methane) condi-
tions. The EI mass spectra of the studied compounds mainly included the fragment ions that resulted from homolytic cleavages with
or without hydrogen migrations. The divinylic compounds (1–7) showed [M – SH]+ ions, whereas the chloroethylvinyl compounds (8–14)
showed [M – Cl]+ and [M – CH2CH2Cl]+ ions. Methane/CI mass spectra showed [M + H]+ ions and provided molecular weight information.
The GC retention index (RI) values were also calculated for the studied compounds. The EI and CI mass spectral data together with RI
values are extremely useful for off-site analysis for the verification of the chemical weapons convention and also to participate in official
Organization for the Prohibition of Chemical Weapons proficiency tests.
Keywords: sulfur mustards, vinylic degradation products, GC/MS, homolytic cleavages, GC-RI values
Introduction
Chemical warfare agents (CWAs) are highly toxic chemicals
that kill, injure or incapacitate human beings.1,2 The CWAs
are also a threat to the animals, plants and environment as
they can easily spread in the environmental matrices like
soil, water and other organic matter. The Chemical Weapons
Convention (CWC) was created to eliminate the risk of this
Chemical Weapons (OPCW), which is an intergovernmental
organization located in The Hague, The Netherlands. There
is also a verification program for the usage of toxic chemicals
and their precursors as listed in Schedules 1, 2 and 3 of the
CWC. The CWAs are highly reactive and undergo degradation in
the environmental matrices,5 and most of the resulting degra-
entire category of weapons of mass destruction by prohib- dation products are non-scheduled chemicals as per CWC.
iting the development, production, acquisition, stockpiling, The OPCW, however, listed possible degradation products of
retention, transfer or use of chemical weapons.3,4 The CWC
is administrated by the Organization for the Prohibition of
CWAs as non-scheduled reportable chemicals in one of their
instructions in the official OPCW Proficiency Test Program, and
ISSN: 1469-0667
doi: 10.1255/ejms.1398
© IM Publications LLP 2015
All rights reserved

792
Mass Spectral Studies on Vinylic Degradation Products of Sulfur Mustards
named as “Additional Non-Scheduled Reportable Chemicals
(NSRC)”. Detection of the degradation products of suspicious
compounds in any area provides a hint on the alleged usage of
the parent CWAs. Hence, detection and identification of CWAs
and their degradation products in environmental samples
are crucial for the CWC verification process. For verification
purposes, the OPCW uses both on-site and off-site analysis
of suspected environmental samples. The OPCW uses its
worldwide designated laboratories for the off-site analysis.
The designation status of the laboratories depends on the
performance of the laboratory in the official OPCW proficiency
tests (PTs) conducted twice a year.6
Scheme 1. Degradation of sulfur mustards to form divinyl (1–7)
and chloroethyl vinyl compounds (8–14). The chemical names
of compounds 1–14 are given in Table 3.
Among CWAs, the sulfur mustards (Schedule 1.A.04
etc.]. However, when the EI mass spectrum of a target analyte
chemicals of CWC), commonly known as blistering agents, is not present in the databases, an EI mass spectrum of a
are volatile organic compounds and mainly known to cause reference chemical is needed for identification. The GC/MS
blisters on the skin. They cause severe damage to the eyes, with a selected ion monitoring mode was also applied for
respiratory system and internal organs. Several articles have
reported on the reactivity and the effect of sulfur mustards
characterization of CWAs and their degradation products.23
Out of 17 possible vinylic degradation products from the
on various biological components. For example, bis(2-chloro- group of sulfur mustards (Schedule 1.A.04 chemicals of CWC),
ethyl) sulfide, commonly known as sulfur mustard or mustard
gas, reacts with a large number of biological molecules, such
only four degradation products of bis(2-chloroethyl) sulfide
were reported in the literature. These were identified as
as DNA nucleotides, permanently alkylates them and even- divinyl sulfide, 2-chloroethyl vinyl sulfide, 1,2-bis(vinylthio)
tually causes cell death.7–9 The sulfur mustard also reacts
with proteins containing free carboxylic group present in the
blood and forms esters.10–12 Besides this, the sulfur mustards
present in the environmental matrices degrade into vinylic
products by a series of elimination reactions, such as the
removal of one or two HCl molecules. The OPCW has included
the vinylic degradation products of sulfur mustards in the
NSRC list. Thus, the detection of all possible degradation
products of sulfur mustards in environmental matrices is
important for the verification process.
ethane and (2-chloroethylthio)ethyl vinyl sulfide.24,25 Only
the EI mass spectra of divinyl sulfide and 1,2-bis(vinylthio)
ethane are available in the Wiley 9/NIST 11 library.261,5-
bis(divinylthio)-n-pentane, the degradation product of one of
the sulfur mustards, was spiked in a water sample of 34th
official OPCW PT. The participating laboratories synthesized
1,5-bis(divinylthio)-n-pentane to confirm its presence in the
given water sample. Hence, it is important to synthesize the
possible vinylic degradation products of sulfur mustards and
develop a GC/MS method for a separation and identifica-
tion that enable an easy identification in future verification
processes. In the present study, we synthesized a series of
chloroethyl vinylic and divinylic sulfur mustard degradation
products (Scheme 1) and characterized their identities by
using GC/EIMS and GC/chemical ionization mass spectrom-
etry (GC/CIMS). We also included the degradation products
of bis(2-chloroethyl) disulfide, which in turn a degradation
The CWAs and their degradation products may exist at a low
level in environmental samples such that it can be masked
by background or matrix-associated chemicals. There are
numerous sample preparation methods and analytical
methods in the literature to extract and detect the CWAs and
their degradation products in environmental samples. The
most popular analytical techniques include nuclear magnetic
resonance spectroscopy, Fourier transform infrared spectros- product of bis(2-chloroethyl) sulfide in this study.25
copy and mass spectrometry (MS).13,14 The chromatographic
techniques [gas chromatography (GC) or high performance
liquid chromatography (HPLC)] with element-specific detec-
Experimental
tors and/or a mass spectrometry (MS) detector15 are routinely
Materials
used for the analysis of CWAs. The gas chromatography/elec-
tron ionization mass spectrometry (GC/EIMS)16–22 technique
has been widely used for the detection and identification of
All the compounds (1–14) were synthesized from the hydroxy
intermediates as shown in Scheme 2. Bis(2-hydroxyethyl)
many scheduled compounds and their degradation prod- sulfide and bis(2-hydroxyethyl) disulfide were commercially
ucts, with or without prior derivatization. GC/EIMS is very available (Sigma-Aldrich, Steinheim, Germany), and other
popular because of its high sensitivity and the EI mass spec- hydroxy intermediates were synthesized using a known proce-
trum obtained for each component separated in GC provides
structure-indicative fragment ions. It is easy to identify target
compounds by searching their EI mass spectra with that in EI
mass spectral databases [OPCW Central Analytical Database
(OCAD), Validation Group Working Database (VGWD), National
Institute of Standard and Technology (NIST), Wiley Registry
dure.27 Phosphorous trichloride (PCl3), 1,8-diazabicyclo[5.4.0]
undec-7-ene (DBU) and the HPLC grade solvents used in
the present study were purchased from S.D. Fine-Chem Ltd
(Mumbai, India). The hydroxy intermediate compounds were
treated with PCl3 overnight to form the corresponding sulfur
mustards. Then cold water was added to the reaction mixture,

L.S. Sachin et al., Eur. J. Mass Spectrom. 21, 791–800 (2015)
793
Results and discussion
All the degradation products of the sulfur mustards (1–14)
under study were analyzed by GC/MS under EI and CI condi-
tions. All the components in each reaction mixture were well
separated in the GC/MS analysis, and thus the EI/CI mass
spectra obtained for the target compounds 1–14 were pure
without any interfering peaks from the impurities/by-prod-
ucts. The GC retention times of homologues series gradually
increased as the spacer chain length increased in each set of
compounds (divinylic, 1–7 and chloroethyl vinylic, 8–14). GC/RI
values of the studied compounds are discussed at the end of
this manuscript.
Scheme 2. Synthetic scheme for divinyl compounds (1–7) and
chloroethyl vinyl compounds (8–14).
GC/EIMS
The EI mass spectra of the compounds 1–7 and 8–14 are
summarizedinTables1and2, respectively. TheEImassspectra
of 1,5-bis(vinylthio)-n-pentane (7) and 1-(2-chloroethylthio)-
5-vinylthio-n-pentane (14) are given in Figure 1 and those
of 1,3-bis(vinylthio)-n-propane (5) and 1-(2-chloroethylthio)-
3-vinylthio-n-propane (12) are given in Figures S1 and S2
(see the supplementary information) as examples. GC/EI
high-resolution mass spectral data for structure-indicative
fragment ions are summarized in Table S1. The presence of
the one sulfur or two sulfur atoms with or without chlorine
was clearly reflected in the isotopic patterns of the detected
molecular ion and/or fragment ions.
keeping the flask on the ice bath, and the mustard was
extracted into dichloromethane (DCM). The DCM extract was
dried over anhydrous Na2SO4 and concentrated to 1mL. The
mustard in DCM was then treated with excess DBU at room
temperature and kept overnight. The reaction flask was kept
at 0°C and saturated aqueous ammonium chloride added. The
DCM layer was separated and dried over anhydrous Na2SO4;
the products in DCM were then subjected to GC/MS analysis.
GC/MS analysis
The GC/EIMS analyses were performed using an Agilent 6890
gas chromatography (Agilent Technologies, Palo Alto, CA,
USA) equipped with an Agilent 5973N mass-selective detector
(a single quadrupole instrument) and an Agilent HP-5MS
capillary column of 30m length, 250µm inner diameter and
0.25 µm film thickness was used. The column oven was
programmed initially from 50°C with a 2min holdup time to
the final temperature of 280°C with a 10°C min–1 ramp and the
final temperature holdup time was 5min. Helium was used as
EI fragmentation of divinylic compounds
(1–7)
Molecular ion (M+•) peaks were dominant in the EI mass
spectra of the lower homologous compounds (1, 2 and 3,
73–100%); however, in the case of the higher homologous
compounds the M+• peaks were either absent (4, 6 and 7) or
of low abundance (5). The EI mass spectra of 1 and 2 were
simple and their fragmentation patterns were different when
the carrier gas in a constant flow mode at a flow rate of 1.0mL compared to those of 3–7. The EI mass spectrum of 1 matched
min–1. The inlet and GC/MS interface temperatures were kept well with that available in the Wiley/NIST library,26 and showed
at 200°C and 280°C, respectively. The samples were intro- the [M – H]+ ion (as the base peak). The compounds 1 and 2
duced in splitless injection mode. The temperatures of the EI possessed two vinyl groups, but their EI mass spectra showed
source and quadrupole analyzer were kept at 230°C and 150°C, [M – CH3]+ and [M – SH]+ ions; these ions must be formed from
respectively. Similar experimental conditions were used for
GC/CIMS experiment using methane as the reagent gas with
an electron energy of 220 eV. The mass spectrometer was
scanned from m/z29 to m/z600 and from m/z60 to m/z600 for
EI and CI, respectively. The GC total ion chromatogram of each
reaction mixture showed well separated and abundant peaks
corresponding to the divinyl and chloroethyl vinyl degradation
products of sulfur mustards.
the molecular ions involving intramolecular rearrangements
and hydrogen migration. The spectra of 1 and 2 also included
common fragment ions at m/z45, 57, 58 and 59 corresponding
to [HCS]+, [C2HS]+, [C2H2S]+• and [C2H3S]+, respectively. The
homolytic cleavage of the C–S bond in 1 afforded the dominant
fragment ion at m/z59, whereas the corresponding fragment
ions caused by homolytic cleavage of the C–S bonds (m/z59
and m/z91) were of low abundance in 2. The spectrum of 2
showed the structure-indicative fragment ions at m/z90, 64,
The EI high resolution mass spectra were recorded using a
JEOL GC-AccuTOF (Tokyo, Japan), a time-of-flight mass spec- 72 and 46, corresponding to [M – C2H4]+•, [S2]+•, [M – CH2S]+•
trometer equipped with an Agilent 7890A gas chromatograph. and [CH2S]+•, respectively.
The GC and MS conditions were similar to those described
The EI mass spectra of 3–7 showed a set of fragment ions
above. The instrument resolution was 8000 (full-width at half- caused by homolytic cleavages that provide their structure
maximum) and perfluorokerosene was used as the internal
reference compound. The mass errors were mostly 5ppm.
information. The homolytic cleavage fragment ions possible in
3–7 are summarized in Scheme 3; they included the fragment

794
Mass Spectral Studies on Vinylic Degradation Products of Sulfur Mustards
Table 1. EI mass spectra of divinylic compounds (1–7).
Compound
number
Molecular
weight
Ions (relative abundance, %)
1
2
3
86
118
132
39(4), 41(4), 45(34), 46(2), 47(2), 53(6), 57(13), 58(33), 59(47), 60(13), 71(6), 85(100), 86(73), 87(8),
88(3).
29(1), 39(4), 45(25), 46(3), 47( ), 57(8), 58(8), 59(7), 60(1), 64(9) 71(4) 72(11), 73(4), 85(18), 90(64),
91(3), 92(2), 103(29), 104(2), 105(1), 118(100), 119(6), 120(8).
39(14), 45(36), 47(1), 53(2), 58(4), 59(9), 60(1), 65(2), 67(3), 69(6),
71(45), 72(20), 73(2), 76(5), 85(13), 86(1), 99(2), 103(76),
104(51), 105(26), 131(7), 132(100), 133(8),134(6).
4
5
6
7
146
160
174
188
39(2), 41(4), 45(76), 46(4), 47(13), 53(15), 54(1), 57(7), 58(37), 59(62), 60(7),61(7), 63(1), 71(2),
73(28), 74(1), 75(1), 84(3), 85(67), 86(19), 87(100), 88(5), 89(4), 91(5), 99(1), 97(2), 105(3), 112(15),
113(3), 118(63), 119(5), 120(5).
39(22), 41(45), 45(92), 46(10), 47(20), 53(5), 54(3), 55(4), 57(6) 58(31), 59(62), 60(11), 61(11), 65(6),
67(58), 69(3), 71(6), 72(5) 73(48), 74(6), 85(100), 86(31), 87(40), 91(6), 99(171), 100(39) 101(23),
105(3), 113(14), 119(20), 120(1), 127(14), 132(3), 133(8), 160(9), 161(1) 162(1).
29(8), 39(8), 41(8), 43(3), 45(52), 46(4), 47(12), 53(7), 54(2), 55(38), 57(1), 58(17), 59(30), 60(11),
61(7), 65(1), 67(3), 69(3), 73(77), 74(3),75(4), 79(3), 81(10), 80(2), 85(30), 86(100), 87(26), 88(5),
89(2), 99(2), 100(1), 101(1), 113(1), 114(2), 115(47), 120(12), 141(2), 147(1).
29(3), 39(11), 41(57), 45(55), 46(4), 47(13), 53(7), 55(8), 57(2), 58(16), 59(32), 60(13), 61(9), 65(4),
67(25), 68(15), 69(49), 73(64), 74(1), 75(6), 85(32), 86(100), 87(40), 88(6), 89(2), 95(5), 99(9),
100(10), 101(23), 113(4), 115(5), 120(4), 127(1), 128(2), 129(26) 155(6).
Table 2. EI mass spectra of chloroethyl vinyl compounds (8–14).
Compound
number
Molecular
weight
Ion (relative abundance, %)
8
122
154
168
45(51), 46(3), 47(8), 49(2), 53(2), 57(7), 58(25), 59(35), 60(58), 61(5) 62(3), 63(6), 65(2), 73(100),
74(4), 75(4),85(2), 87(6),94(2), 122(66) 123(4), 124(23), 125(1), 126(1).
9
55(<1), 58(11), 63(42), 64(30), 65(12), 78(11), 79(4), 91(26) 92(43) 96(100), 97(3), 98(12), 99(2),
105(10), 109(3), 111(1), 119(4), 128(3) 154(41), 155(2), 156(17), 157(1).
10
39(2), 41(3), 45(79), 46(14), 47(20), 48(1), 49(11), 51(4), 53(6), 57(7) 58(33), 59(52), 60(17), 61(3),
62(1), 63(10), 64(2), 65(4), 69(1), 73(65) 74(4), 75(3), 80(2), 81(3), 85(10), 86(2), 87(26), 91(8),
95(10), 97(4) 99(<1), 105(3), 108(19), 109(100), 110(11), 111(37), 113(2), 119(46) 120(2), 121(4),
133(36), 134(3), 135(4), 168(32), 169(2), 170(13).
11
12
182
196
29(1), 35(1), 39(1), 41(2), 45(46), 46(6), 47(11), 53(4), 57(4), 58(22) 59(35), 60(17), 61(27), 63(30),
64(3), 65(10), 73(34), 85(11), 86(3), 87(19) 91(9), 95(8), 109(12), 111(5), 113(<1), 119(10), 120(3),
122(23), 123(100) 124(13), 125(36), 146(1), 147(7), 182(23), 183(2), 184(9).
29(<1), 39(8), 41(23), 45(35), 46(7), 47(12), 49(1), 53(3), 55(1), 58(11) 59(22) ,60(6) ,61(10) ,63(14)
,65(6), 66(3), 67(7), 69(2), 71(3), 72(2) 73(35), 74(12), 85(26), 86(5), 87(24), 91(11), 95(1), 99(6),
100(6), 101(7) 103(1), 105(7), 106(4), 107(3), 109(6), 111(2), 113(1), 118(4), 119(2) 120(1), 123(1),
127(1), 133(100), 134(8), 135(7), 137(1), 161(1), 169(1) 196(34), 197(3), 198(14).
13
14
210
224
29(10), 39(12), 41(12), 45(61), 46(11), 47(25), 53(12), 54(6), 55(66), 58(18), 59(38), 60(25), 61(14),
63(29), 65(10), 67(5), 73(64), 74(4), 75(6), 79(4), 80(3), 81(9), 85(30), 86(37), 87(54), 88(18), 89(7),
95(1) ,99(2), 101(21), 105(6), 109(76), 110(3), 111(28), 113(31), 115(100), 116(8), 117(4), 122(2),
123(3), 135(3), 137(<1), 141(<1), 147(49), 148(5), 149(5), 151(31), 152(3), 153(26), 175(1) 183(1),
210(13), 211(1), 212(5).
29(5), 39(16), 41(12), 45(46), 46(8), 47(21), 53(8), 55(16), 58(14), 59(34), 60(17), 61(17), 63(23),
65(11), 67(44), 68(39), 69(100), 73(53), 74(6), 75(8), 85(21), 86(34), 87(34), 88(4), 94(3), 95(7),
99(15), 100(11), 101(54), 102(20), 102(2), 103(5), 109(51), 111(19), 113(5), 115(7), 123(1), 127(1),
128(3), 129(70), 130(6), 131(4), 137(<1), 151(1) 155(2), 161(18), 165(31), 167(11), 197(<1), 189(2),
224(13), 225(2), 226(6).

L.S. Sachin et al., Eur. J. Mass Spectrom. 21, 791–800 (2015)
795
Figure 1. EI mass spectra of (a) compound 7 and (b) compound 14.
ions caused by a cleavage, b cleavage and homolytic cleav- consistently observed in the high mass region of the spectra of
ages of C–S and C–S bonds. The C–S cleavage referred to
3–7, but found to be of low abundance. The homolytic cleavage
of the (H2)C–S bond resulted in both the expected fragment
ions, of which one fragment constantly appeared at m/z59 (S–
CH=CH2+•), while the second fragment ion shifted by +14u as
the spacer –CH2– length increased from one to five (appeared
at m/z73, 87, 101, 115 and 129 in compounds 3, 4, 5, 6 and 7,
respectively). The S–CH2 cleavage with hydrogen migration
that resulted in the fragment ion at m/z60 (SC2H4+•) was also
observed in the spectra. Mostly, the fragment ions formed as a
result of C–S cleavages were dominant over those formed from
C–S cleavages. Similarly, the fragment ions resulted by a and
b cleavages also appeared as dominant ions in the low mass
region of the spectra of 3–7. These a and b cleavage fragment
ions were similar to those observed for long-chain aliphatic
compounds and bis(alkylmercapto)alkanes.29 Further, losses
of the H• radical and H2 from the homolytic cleavage frag-
ment ions discussed above were also observed in the spectra.
For example, the ion m/z 87 was always accompanied with
m/z86 and m/z85, and m/z59 appeared along with m/z58 and
the vinylic cleavage that resulted in [M – C2H3]+ ion by the
•
loss of vinyl radical (C2H3 ) from M+•. The [M – C2H3]+ ion was
Scheme 3. Possible homolytic cleavage fragment ions in
compounds 3–7.

796
Mass Spectral Studies on Vinylic Degradation Products of Sulfur Mustards
the simultaneous loss of two S–CH=CH2 groups with a proton
migration from the spacer alkyl chain to one of the S–CH=CH2
groups. Alternatively, these ions could also be formed by the
consecutive loss of CH2=CH–S and CH2=CH–SH from molec-
ular ion. Shuttleworth29 reported the formation of similar
olefin-type ions [CnH2n–1]+ in the case of bis(alkylmercapto)
alkanes by the loss of RSH and RS. from their molecular ions.
As in compounds 1 and 2, the EI spectra of the other divinyl
compounds (3–7) also showed the [M – SH]+ ion. This ion could
be formed through an intramolecular rearrangement involving
proton migration(s) to yield a cyclic thiophene ring with the
alkyl chain on the sulfur. Gills et al.30 reported that only the
lower homologues of compounds like methylvinyl sulfide
and methylvinyl sulfoxide showed the rearrangement ions
Scheme 4. General fragmentation pattern for compounds 3–7
and 10–14.
m/z57. This type of subsequent hydrogen radical loss is well
known in the cyclic disulfide compounds.28 The EI spectrum
of 3 showed a fragment ion at m/z39 corresponding to [C3H3]+
ion. This ion gradually shifted by +14 u as the spacer chain
length gradually increased from two to five in compounds 4 to
[M – SH]+ and [M – H2S]+ where corresponding fragment ion
attained a stable structure. Whereas, in the present case, all
the homologues divinyl compounds (1–7) consistently showed
the [M – SH]+ ion in considerable abundance (2–18%); this
suggests that the presence of the two vinyl groups in 1–7 could
7 (the ion appeared at m/z53, 67, 81 and 95 in the spectra of 4, stabilize the [M – SH]+ ion better than that obtained from the
5, 6 and 7, respectively). High-resolution mass spectrometry
(HRMS) data of all these ions suggested that they all belong
to an unsaturated hydrocarbon type of fragment ions with
the general formula [CnH2n–3]+. We propose these ions were
formed from the [M – (SCH=CH2)]+ ion by the loss of a H2S
molecule. The cyclic thioalkanes are known to show the loss of
H2S from their molecular ions; a similar type of intermediate
structure could be proposed for [M – (SCH=CH2)]+ to explain
the further loss of H2S from it.
above alkyl vinyl sulfides. Besides [M – SH]+, the spectrum of
4 included the [M – H2S]+• ion.
EI fragmentation of chloroethyl vinyl
compounds (8–14)
EI mass spectra of all the chloroethyl vinyl compounds (8–14)
showed significant M+• ions (13–100%; Table 2). Compounds
8–14 possessed an S-vinyl group at one end, but their EI
spectra did not show the anticipated [M – SH]+ ions. Similarly,
compounds 8–14 had one chloroethyl group at another end,
and even then the expected [M – HCl]+ ions were absent in their
EI spectra. The [M – Cl]+, [M – (CH2Cl)]+ and [M – (CH2CH2Cl)]+
The spectra of 5, 6 and 7 showed another fragment ion at
m/z41, m/z55 and m/z69, respectively; HRMS data suggested
that these ions corresponded to carbonations of saturated
hydrocarbons with the generic formula [CnH2n–1]+ (Scheme 4). ions were commonly observed in the spectra of 8 and 9. Apart
In fact, these fragment ions provided information about the
spacer chain lengths in 5–7. A similar type of ion was expected
in the spectrum of 3 at m/z27, but this ion was not visible in
the spectrum as the mass spectrometer was scanned from
m/z29 to m/z600 to avoid nitrogen-peak interference. These
ions might have formed from the respective molecular ions by
from these, the spectrum of 8 included the [M – C2H3S]+
(m/z 63), [M – C2H3Cl]+ (m/z 60) and the fragment ions corre-
sponding to C2H3S+ (m/z 59), C2H2S+ (m/z 58), CH3S+ (m/z 47)
and CHS+ (m/z45). The spectrum of 9 showed additional peaks
corresponding to [M – C2H2]+ (m/z 128), [M – CHS]+ (m/z 109),
[M – SC2H2]+ (m/z96; the base peak), [M – CHCH2Cl]+ (m/z92)
Scheme 5. Possible homolytic cleavage fragment ions in compounds 10–14.

L.S. Sachin et al., Eur. J. Mass Spectrom. 21, 791–800 (2015)
797
and [M – C3H5Cl]+ (m/z78) ions. The fragment ions at m/z58, as substituents in 10–14. The homolytic cleavage fragment
+•
m/z63 and m/z64 corresponding to C2H2S+, C2H4Cl+ and S2
respectively, also appeared in the spectrum of 9.
,
ions retaining charge on the vinyl group containing fragments
appeared at m/z59, 73, 87, 101, 115 and 129 according to the
spacer chain length. Similarly, the homolytic cleavage frag-
ment ions appeared at m/z95, 109, 123, 137, 151 and 165 when
the charge is retained on the chloroethyl group containing
fragments. The [M – CH2CH2Cl]+ ion was found to be dominant
in 10–14. The [H2C=S–CH2CH2Cl]+ ion (m/z 109) was consist-
ently observed in 10–14; however, the other expected homo-
lytic cleavage fragment ion, [M – CH2Cl]+, was absent (except
in 10).
Further loss of H2S from the homolytic cleavage fragments
ions of 10–14 (retaining the charge on vinyl group containing
fragments) were also observed in the spectra and confirmed
by the HRMS data (Table S1). This suggested that the resulting
fragment ions attained an alkenyl cation type structure
(Scheme 4). The [M – Cl]+ ions also showed further loss of H2S,
but they were of low abundance. Besides these, fragment ions
due to further loss of the H• radical or H2 from the homolytic
The EI fragmentation patterns of 10–14 are similar to those
observed for 3–7 (Scheme 4). The fragment ions caused by
homolytic cleavages were dominant in the spectra of 10–14
and they include more fragment ions when compared to 3–7
because of the asymmetric substitution on sulfur atoms in
10–14 (one end S-vinyl group and another side S-chloroethyl
group). The m/z values of the homolytic cleavage fragment
ions depended on which side of the fragment retains the
charge. The possible homolytic cleavage fragment ions from
10–14 are summarized in Scheme 5, where the first m/z
value was the fragment ion retaining the charge that was
on the vinyl group containing the fragment and the second
m/z value represented the fragment ion retaining the charge
on the chloroethyl group-containing fragment. The presence
of the [M – C2H3]+, [M – Cl]+ and [M – SC2H3]+ ions provided
the information on presence of both vinyl group and chlorine
a)
b)
Figure 2. Methane/CI mass spectra of (a) compound 7 and (b) compound 14.

798
Mass Spectral Studies on Vinylic Degradation Products of Sulfur Mustards
Table 3. GC-RI values for the studied compounds (1–14) along with the RI values of the parent sulfur mustards (OPCW libraries).
Divinyl compounds
Compounda
RI value
Chloroethyl vinyl compounds
Sulfur mustards
Compound
Compoundb
RI value
906
RI value
1178d
1401e
1569d
1703d
1811d
1
2
3
4
5
631
1090
1146
1172
1288
8
Bis(2-chloroethyl) sulfide
9
1125
Bis(2-chloroethyl) disulfidec
Bis(2-chloroethylthio)methane
1,2-Bis(2-chloroethylthio)ethane
10
11
12
1311
1440
1543
1,3-Bis(2-chloroethylthio)-n-
propane
6
7
1407
1516
13
14
1663
1775
1,4-Bis(2-chloroethylthio)-n-butane
1,5-Bis(2-chloroethylthio)-n-pentane
1933d
2045d
aDivinyl sulfide (1), divinyl disulfide (2), bis(vinylthio)methane (3), 1,2-bis(vinylthio) ethane (4), 1,3-bis(vinylthio)-n-propane (5), 1,4-bis(vinylthio)-n-butane (6),
1,5-bis(vinylthio)-n-pentane (7).
b2-Chloroethyl vinyl sulfide (8), 2-chloroethyl vinyl disulfide (9), 1-(2-chloroethylthio)-1-vinylthiomethane (10), 1-(2-chloroethylthio)-2-vinylthioethane (11),
1-(2-chloroethylthio)-3-vinylthio-n-propane (12), 1-(2-chloroethylthio)-4-vinylthio-n-butane (13), 1-(2-chloroethylthio)-5-vinylthio-n-pentane (14).
cBis(2-chloroethyl) disulfide does not belong to the sulfur mustard group; it is a degradation product of bis(2-chloroethyl) sulfide.
dOCAD, v17.
eVGWD 2015.
cleavage fragments appeared in the spectra at m/z73, 87, 101, the reagent gas, met the CI criteria of the PTs. The methane/
115 and 129.
The specific fragment ions at m/z 41, m/z 55 and m/z 69, [M + H]+ ion. The spectrum of 2 showed, additionally, the [M]+•,
which were observed from 5–7 in accordance with the spacer
[MH – CH3]+, [MH – C2H4]+ and [MH – SC2H5]+ ions. The spectra
CI spectrum of 1 showed [M]+• and [M – H]+ in addition to the
chain length, were also observed in the spectra of 12, 13 and 14, of 3–7 also showed a few fragment ions (m/z69 in 3, m/z87
respectively. The HRMS data supported these as being carbo- and m/z105 in 4, m/z119, m/z101 and m/z75 in 5, m/z115 in
cations of saturated hydrocarbons with the generic formula
[CnH2n–1]+. These ions might have formed from the respective
molecular ions (12, 13 or 14) by the simultaneous loss of the
S–CH=CH2 and S–CH2CH2Cl groups with a proton migration
from the spacer chain. Alternatively, the above ions could also
be formed by the consecutive loss of either [CH2=CH–S and
CH3CH2Cl] or [CH2=CH–SH and CH2CH2Cl] from the respective
molecular ion.
6 and m/z115 in 7). The methane/CI spectrum of 5 is shown
in Figure S1. The spectra of 8 and 9 showed [M]+•, [MH – HCl]+
and [MH – SC2H4]+ ions. The methane/CI spectra of 10–14
showed [MH – SC2H4]+, [MH – HCl]+ and [MH – (CH3CH2Cl)]+
ions, in addition to a few homolytic cleavage fragment ions
as found in the respective EI spectra (the spectrum of 12
is shown in Figure S2). For example, the CI spectrum of 7
shows the homolytic cleavage fragment ions at m/z129, 101,
86 and 75 and that of 14 shows the ions at m/z129, 109 and
101 (Figure 2).
GC/CIMS
The GC/CIMS was routinely used as a secondary technique
together with the GC/EIMS technique (the primary technique)
by the participants during the official OPCW PTs. Hence, it was
important to study the CI data of target molecules. Initial CI
experiments were performed using isobutane as the reagent
gas. The isobutane/CI spectra of all the compounds showed
GC/RI values
The GC/RI values were calculated for all the compounds
under study (1–14) by Van den Dool’s formula28 using standard
n-alkane hydrocarbons (Table 3). The GC/RI values of 1–14
were also compared with the parent mustard/dichloro
abundant [M + H]+ ions with a low abundance of fragment ions. compound, whose RI values are available in the OCAD data-
The isobutane/CI mass spectrum of 7 is given in Figure S3 as
an example. Thus, the GC/CIMS analysis using isobutane as
the reagent gas was good enough to confirm the molecular
weight of the compounds under study. With a view to checking
the behavior of the compounds under study using methane as
the regent gas, we also performed the GC/CIMS analysis using
methane as the reagent gas.
base and the same are included in Table 3. The GC/RI values
of divinylic degradation products are lower than those of chlo-
roethyl vinyl products, which are in turn lower than those of
the parent mustards. The EIMS and CIMS data together with
RI values can be used for screening the degradation products
under study.
The methane/CI spectra of 1–14 also showed abundant
[M + H]+ ions (20–100%), except 4, with an abundance just
above 10%. For the official OPCW PTs, it was required that the
peak that provided the molecular weight information must
be ≥10%. Thus, the CI spectra of 1–14, even with methane as
Conclusions
Unambiguous identification of CWAs and their degradation
products is very important for CWC verification (on-site or

L.S. Sachin et al., Eur. J. Mass Spectrom. 21, 791–800 (2015)
799
off-site analysis) as well as for the participation of official
OPCW PTs. A number of degradation products are possible
for the CWC scheduled chemicals, but analytical data are
available in the literature for only a few degradation products.
In this study, we present the mass spectral identification of
a set of degradation products (chloroethylvinyl and divinylic
compounds) of sulfur mustards. The degradation products
were successfully synthesized and well separated from the
by-products in GC before analyzing them by EIMS and CIMS.
The EI-HRMS data were used to support the proposed struc-
ture of the fragment ions. The EI fragmentation of the degra-
dation products under study (1–14) was found to be mainly
due to homolytic cleavages with or without hydrogen migra-
tions. All the divinyl compounds showed [M – SH]+ ions, while
the chloroethyl vinyl compounds showed selective homolytic
cleavage fragment ions retaining chlorine. The EI fragmenta-
tion of the compounds under study makes it easy to identify
and characterize the degradation products of sulfur mustards.
The CI mass spectra recorded with isobutane or methane as
the reagent gas provided molecular weight information. The
GC/RI values were also calculated for the compounds under
study that could be used for the unambiguous identification
together with GC/MS data.
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Acknowledgments
TheauthorsthanktheDirector, CouncilofScientific&Industrial
Research (CSIR) Indian Institute of Chemical Technology, for
the facilities and encouragement, and CSIR, New Delhi, for
financial support (AARF project, CSC-402). The authors thank
CSIR, New Delhi (R.K.), and UGC, New Delhi (L.S.S. and T.S.)
for the award of senior/junior research fellowships.
Supplementary data
Supplementary data associated with this article can be found
in the online version at http://dx.doi.org/10.1255/ejms.1398.
12. B.R. Capacio, J.R. Smith, R.J. Lawarence, B.L. Boyd,
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“Gas chromatographic–mass spectrometric analysis
of sulfur mustard plasma protein adducts: validation
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