A selective turn-on fluorescent sensor for sulfur mustard simulants

Article abstract of DOI:10.1021/ja401845e

A fluorescent turn-on sensor for the selective and sensitive detection of sulfur mustard simulants in water that uses a metal-ion indicator displacement assay (IDA) has been devised. In this IDA approach, a sulfur mustard simulant (the analyte) is allowed to react with a dithiol (1) to form a podand (2). This podand has a strong affinity to bind with Cd²⁺ and displaces an indicator (4-methylesculetin, ME) from a Cd²⁺-indicator complex (8) to give a turn-on of fluorescence. The detection is rapid and highly selective, as we did not observe any interference from other electrophiles, even from the oxygen analogue of the mustard simulant. The protocol was successfully used for the detection of the simulant present on surfaces and in soil samples.

Full text of DOI:10.1021/ja401845e

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Article
A Selective Turn-on Fluorescent Sensor for Sulfur Mustard Simulants
Vinod Kumar, and Eric Van Anslyn
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja401845e • Publication Date (Web): 01 Apr 2013
Downloaded from http://pubs.acs.org on April 3, 2013
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Journal of the American Chemical Society
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A Selective Turn-on Fluorescent Sensor for Sulfur Mustard Simulants
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Vinod Kumar† and Eric V. Anslyn*
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Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712, United States.
ABSTRACT: A fluorescent turnꢀon sensor has been devised for the selective and sensitive detection of sulfur mustard simulants in
water using a metalꢀion indicator displacement assay (IDA). In this IDA approach, a sulfur mustard simulant (the analyte) is
allowed to react with a dithiol (1) to form a podand (2). This podand has strong affinity to bind with Cd2+, and displaces an indicaꢀ
tor (methyl esculatin, ME) from a Cd2+ ionꢀindicator complex (8) to give a turnꢀon of fluorescence. The detection was rapid, and
highly selective, as we did not observe any interference from other electrophiles, even from the Oꢀanalog of the mustard simulant.
The protocol was successfully used for the detection of the simulant present on surfaces and in soil samples.
spectrometry, flame photometry, mass spectrometry,
photoacoustic infrared spectroscopy, electrochemistry, and
detection kits and tickets which use a variety of chemical
reactions.5 Standoff detectors use infrared remote sensing
techniques from a significant distance. Apart from these,
methods based on conventional analytical techniques,6 molecꢀ
ularly imprinted polymers,7 immunochemical8, quartz crystal
microbalance9, and platinum(II) pincer complexes,10 have also
been developed.11
INTRODUCTION
Sulfur mustard (SM), also called mustard gas/HD (Figure
1), has been frequently used on a large scale against military
and civilian targets since the beginning of the 20th century,
causing millions of casualties.1 In a biological setting it
gradually reacts with water and releases HCl producing painful
blisters on skin and causes damage to eyes, lungs, and
sometimes leads to death. The toxicity of SM also lies, in part,
to its ability to alkylate the guanine nucleotide in DNA.2 In the
long run, it causes carcinogenic and mutagenic effects.3
Furthermore, there is no treatment, nor antidote, that can arrest
the basic cause of mustard gas injury. Owing to its ease of
preparation as compared to other chemical warfare agents, the
use of this agent by terrorist groups or rogue nations represents
a serious threat to human kind and homeland security.
Therefore, there is a significant interest in the development of
sensors and detection systems for this chemical.
The prime reason that efficient optical detection systems for
sulfur mustard do not exist, as compared to nerve agents, lies
in the different electrophilicity of SM. The general mechanism
to detect nerve agents is a nucleophilic attack of the probe
molecule on the electrophilic agent to form a phosphate ester
(Figure 2). The resultant phosphate ester responds in three
ways to generate a detectable optical signal (chromogenic and/
or fluorogenic), either by the suppression of a photoꢀinduced
electron transfer (PET) from the nitrogen atom to the fluoroꢀ
phore (Figure 2A) or by Internal Charge Transfer (ICT) (Figꢀ
ure 2B) or by an intramolecular cyclization also resulting in a
suppression of PET (Figure 2C).4
Cl
Cl
Cl
Cl
Cl
S
O
S
Sulfur mustard
(SM)
Bis(2ꢀchloroethyl)ether 2ꢀChloroethyl ethyl sulfide
(BCEE)
(CEES, a SM mimics)
(B)
(A)
F
P
CN
F
Cl
O
O
N
P
O
O
P
2ꢀChloroethyl ethyl ether
(CEEE)
O
OEt
O
Sarin
Tabun
Soman
Cl
P
OEt
N
P
EtO
O
O
S
OEt
(C)
Vx
Diethyl chlorophosphate
(DEP)
CN
F
Cl
Me
EtO
P
O
O
P
O
O
OEt
O
Diethyl cyanophosphate
(DECP, a tabun mimic)
Acetyl chloride
(strong electrophile)
Diisopropyl fluorophosphate
(DFP, a sarin and soman mimic)
Figure 1.Various chemical warfare agents and their mimics
.
Figure 2. Three strategies for detecting phosphoryl nerve agents.
(A) Phosphorylation of an amine participating in PET quenching
turns on fluorescence. (B) Chromogenic and/ or fluorogenic
detection via Internal Charge Transfer (ICT) (C) Phosphorylation
of a hydroxyl proximal to an amine leads to cyclization and
restoration of fluorescence.
Unlike nerve agents (Figure 1),4 colorimetric or fluorescence
detection methods for sulfur mustard are nearly nonexistent.
The detection protocols for sulfur mustard can be divided into
two general categories: point and standoff. The methods which
use point detectors work on the principle of ionꢀmobility
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In contrast, being a simple primary alkyl halide, SM is not a with real SM we anticipate a macrocycle. Consequently, the
1
2
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8
particularly good electrophile. However, in the presence of an
ionizing solvent, its electrophilicity is greatly enhanced due to
the formation of threeꢀmembered cationic sulphonium
heterocycles.12 The sulphonium heterocycle alkylates DNA,
and is reactive toward water (Eq. 1). The limited optical detecꢀ
tion technique, and the unique reactivity of SM, invoked our
analyte has been incorporated into the receptor. Separately, a
metalꢀindicator complex is prepared by selecting a metal
having good affinity for sulfur. The indicator, when bound to
the metal, is nonꢀfluorescent. The two components: analyteꢀ
bound receptor and metal ionꢀindicator complex are mixed
together. The receptor binds the metal and displaces the
indicator from the complex. Thus, the indicator regains
fluorescence, and the intensity can be correlated to the quantity
of the SM.
interest to develop a rapid, selective,
sensitive, and practiꢀ
cal chromogenic and/or fluorogenic chemical sensor for sulfur
mustard.
9
Eq. 1
Eq. 2 shows dithiol 1, and its reaction with CEES to form a
sulfurꢀbased podand (2). The carboxylic acid in 1 was
incorporated to increase the water solubility of this
nucleophilic dithiol. The resulting podand was anticipated to
be an excellent receptor for cadmium in water.15 Moreover, the
plan was to perform the reaction presented in Eq. 2 in hot waꢀ
ter at pH 9, which will hydrolyze other more reactive electroꢀ
philes, such as acetyl chloride and the phosphoryl nerve agents
(Figure 1), thus avoiding interference by these species. Furꢀ
thermore, any poorly electrophilic interferents, that are simply
primary halides and cannot form reactive cyclic systems, such
as bis(2ꢀchloroethyl) ether (BCCE), will not react with 1 as
quickly as SM.
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Nu/DNA
Nu/DNA
R
Cl
R
R
S
Cl
S
S
R = H, Cl Nu = Nucleophile
In our study, we chose 2ꢀchloroethyl ethyl sulfide (CEES)
as a sulfur mustard simulant, which is known as “half
mustard”. CEES has the relevant chemical properties of the
real agent without its associated toxicological properties. The
LD50 values for SM are 2.4 mg/kg (rats) and 8.1 to 9.7 mg/kg
(mice) for oral exposure. For skin exposure, these are found to
be 3.4 mg/kg (rats) and 19.3 mg/kg (mice).13 CEES was
introduced in World War I and is considered to have a
relatively high LD50, of 252 mg/kg (rat oral).14
Eq. 2
O
COOH
RESULTS AND DISCUSSION
Design Criteria
O
COOH
SH
Designing a fluorescent detection method for mustard gas is
challenging for two reasons. First, SM does not have any
traditional molecular recognition sites, such as hydrogen bond
donor or acceptor groups. Second, there are no highly
electrophilic sites, such as nerve agents possess, until the SM
is placed in an ionizing solvent. Furthermore, because the
other chemical warfare agents are more electrophilic, they
would be expected to react faster with any nucleophile, and
therefore the possibility of interference or confusion when
differentiating SM from these warfare agents is expected
(Figure 1). With these issues in mind, we designed a strategy
to selectively target the threeꢀmembered cationic sulphonium
heterocycle, while not signaling more electrophilic agents, nor
less active electrophiles. As discussed below, the plan was to
deactivate the more electrophilic species by using high pH, yet
use an nucleophile that is not reactive enough to target lesser
electrophilic species. In this manner we planned to make a
method that would only give a positive signal in the presence
of SM.
S
S
S
S
CEES
SH
1
2
Podand
Another aspect of our strategy is the recognition that the
metal ligating ability of dithiol 1 would also lead to a
displacement of an indicator from a thiophilic metal. In fact, 1
could equally or even better enhance fluorescence by stripping
any indicator from Cd2+. To overcome this problem, the detecꢀ
tion of SM will necessarily involve a process of capping any
unreacted 1 prior to addition of the test solution containing
CEES to the metalꢀindicator complex (see below)
Synthesis
The synthesis of dithiol 1 was completed in five steps
(Scheme 1).
Scheme 1. Synthesis of dithiol 1 from 5-hydroxyisophthalic
acid
A schematic of the basic strategy is shown in Figure 3. The
target analyte reacts with a dithiol to give a receptor. With
CEES the receptor would be an open chain (a podand), while
OH
OH
OH
MeOH, H2SO
Reflux, 8h
HO
OH
4 MeO
OMe
LiAlH4
THF, reflux, 3h
HO
OH
4
5
3
O
O
O
O
BrCH2COOMe
K2CO3, ACN, 6h
COOH
O
COOH
O
O
COOMe
OH
1) Thiourea, EtOH, r.t., 20 h
2) NaOH (aq), reflux, 4 h
3) HCl
30% HBr in AcOH,
HO
rt, 48 h
Br
Br
HS
SH
7
6
1
The esterification of 5ꢀhydroxyisophthalic acid (3) with methꢀ
anol in presence of H2SO4 afforded 5ꢀhydroxyisophthalic acid
dimethylester (4).16a Reduction of this with lithium aluminum
hydride gave 5ꢀhydroxybenzeneꢀ1,3ꢀdimethanol (5).16b The
Figure 3. Schematic presentation of an approach for the detection
of mustard gas.
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o
performed at 25 C in aqueous solution at pH 9, using sodium
reaction of 5 with methyl bromoacetate in presence of K2CO3
1
2
3
4
5
6
7
8
bicarbonate–sodium carbonate buffer.
resulted in the formation of methyl 2ꢀ[3,5ꢀbis(hydroxymethyl)
phenoxy]acetate (6) which on reaction with 30% HBr in acetic
acid gave 2ꢀ[3,5ꢀbis(bromomethyl)phenoxy]acetic acid (7).
The reaction of 7 with thiourea, followed by a base hydrolysis,
and then treatment with acid, afforded 2ꢀ(3,5ꢀ
bis(mercaptomethyl) phenoxy)acetic acid (1). The synthetic
procedures for the entire step are given in Supporting Inforꢀ
mation, Pages Sꢀ2–Sꢀ3.
Fluorescent titrations of 1 with Complex 8.
Compound 1 itself at pH 9, as well as podant 2, should strip
Cd2+ from a complex of ME and Cd(II) (8). This was
confirmed by fluorescence spectroscopy. In this control
experiment, a solution of 1 (buffered at pH 9 using sodium
bicarbonate–sodium carbonate) was used to titrate a solution
of 8, resulting in a Cd2+ ionꢀdithiol complex 9, yielding
displacement of ME (Eq.4). Thus, the indicator regains its
fluorescence (Figure 5).
9
Formation of Metal:Indicator Complex (8).
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6,7ꢀDihydroxyꢀ4ꢀmethyl coumarin, also known as
methylesculatin (ME), was used as an indicator. It binds with
metals through its catechol moiety17, resulting in the
quenching of its fluorescence.18 Three heavy metals, Ag+,
Hg2+, and Cd2+, were screened for the ability to both form a
stable complex with thioether based receptor 2 and for
quenching of ME. Cd2+ was found suitable for nearly complete
quenching (Eq. 3). For example, fluorescence titrations were
performed at 25 oC in an aqueous solution of ME, where
increasing the Cd2+ concentration leads to a decrease of
indicator emission band at 460 nm, as shown in Figure 4.
Eq. 4
Eq. 3
Me
Me
HO
O
Water
Cd2+
L .
n Cd
pH = 9
HO
O
O
1200000
(a)
O
O
O
ME
1100000
8
1000000
900000
800000
700000
600000
500000
400000
300000
200000
100000
0
1800000
(a)
1600000
1400000
1200000
1000000
800000
600000
400000
200000
0
400
450
500
550
600
Wavelegnth (nm)
400
425
450
475
500
525
550
575
600
1000000
Wavelegnth (nm)
(b)
900000
800000
700000
600000
500000
400000
300000
200000
100000
0
0
ꢀ200000
ꢀ400000
ꢀ600000
ꢀ800000
ꢀ1000000
ꢀ1200000
ꢀ1400000
ꢀ1600000
(b)
0
0.01
0.02
0.03
0.04
0.05
0.06
1 (mM)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Figure 5. (a) Fluorescence titration of a solution of Cd2+ ionꢀ
indicator complex 8 (containing Cd(NO3)2 at 64.4 ꢁM and
indicator at 26 ꢁM) with 1 (1.02 mM. All experiments were
performed at 25 oC in aqueous solution, pH 9, using sodium
bicarbonate–sodium carbonate buffer. (b)Isotherm showing
increase in fluorescence intensity with added 1 at 460 nm.
Equiv. of Cd2+
Figure 4. (a) Drop in the fluorescence intensity of ME at 51.5 ꢁM
at 460 nm in the presence of increasing amounts of
Cd(NO3)2.4H2O (titrant was 0.415 mM). Excitation wavelength
378 nm. (b) Isotherm showing decrease in fluorescence intensity
of ME solution with added Cd(NO3)2. All experiments were
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Page 4 of 8
oC to a give podand 2. The formation of 2 was confirmed by
Capping of Dithiol 1
1
2
3
4
5
6
7
8
mass spectrometry (Supporting Information, Page Sꢀ8, Figure
S3). Initially this reaction was carried out using 2.1
equivalents of CEES (8.3 mM), and therefore all thiols of 1
were converted to thioesters, and hence capping with 10 was
not necessary, as shown by a fluorescence titration (Supportꢀ
ing Information, Page Sꢀ6, Figure S1). This solution was tiꢀ
trated into complex 8, and the resulting emission spectra reꢀ
veals the displacement of ME from 8, as the fluorescence is
restored (Figure 7). The four sulfur atoms in 2 thus bind with
Cd2+ stronger than Cd2+ binds with a catechol moiety of ME,
thereby resulting in 12 (Eq. 6).
Before moving to the detection of CEES, we developed a
process to cap 1, thereby rendering it inactive to strip Cd2+ ion
from 8. The capping agent should meet two critaria. First, it
should react with 1 very quickly under ambient conditions
without reacting with water at pH 9. Second, the capping agent
should withdraw electrons from the sulfur atoms such that the
product will not ligate Cd2+ ion. With these considerations, we
studied various capping agents, such as 1ꢀfluoroꢀ2,4ꢀ
dinitrobenzene, 1ꢀ(bromomethyl)ꢀ4ꢀnitrobenzene, phenyl
isothiocyanate, and 2,4ꢀdifluorobenzaldehyde. In some cases,
we observed the capping of 1 with little change to the
fluorescence intensity of 8 upon addition of the capped
product of 1. However, none were quite optimal. However,
upon the use of the wellꢀknown chemistry of thiolꢀalkyne
addition,19 in which a thiol conjugate adds to an activated
alkyne to form an alkenyl sulfide, we achieved success. In the
product of this reaction, the sulfur lone pair is inconjugation
with the resulting α,βꢀunsaturated ketone, thus dramatically
lowering the availablity for coordination with metal ions. To
acheive this, we mixed 2.2 equivalents of 4ꢀphenylꢀ3ꢀbutynꢀ2ꢀ
9
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Eq. 6
o
one (10) (8.6 mM) with 1 (4.09 mM) at 80 C to form adduct
11, which occurs in less than a minute (Eq. 5). The formation
of 11 was confirmed by mass spectrometry on the crude
reaction mixture (Supporting Information, Page Sꢀ7, Figure
S2). Figure 6 shows that complex 8 with 1 gives a large enꢀ
hancement in fluorescence intensity, however, after addition of
10 there was a negligible change. The intensity is nearly idenꢀ
tical to that of complex 8. As a result, we used cappedꢀthiol 11
as a deactivating strategy due to its minimal ability to bind
with Cd2+ ion.
900000
(a)
Eq. 5
800000
700000
600000
500000
400000
300000
200000
100000
0
1200000
400
450
500
550
600
1000000
Wavelegnth (nm)
___
___
___
1 without capping agent and 8
800000
1 with capping agent and 8
700000
600000
500000
400000
300000
200000
100000
0
only 8
600000
400000
200000
0
(b)
400
450
500
Wavelegnth (nm)
550
600
Figure 6. Fluorescence spectra of Cd2+ ionꢀindicator complex 8
(containing Cd(NO3)2 at 64.4 ꢁM and indicator at 26 ꢁM) and a
solution of 1 (2.04 mM) capped with 10 (4.3 mM). All
experiments were performed at 25 C in aqueous solution, pH 9,
using sodium bicarbonate–sodium carbonate buffer.
0
0.25 0.5 0.75
1
1.25 1.5 1.75
2
2.25 2.5
o
CEES (mM)
Figure 7. (a) Fluorescence titration of a solution of Cd2+ ionꢀ
indicator complex 8 (containing Cd(NO3)2 at 64.4 ꢁM and
indicator at 26 ꢁM) with in-situ generated podand 2 (from CEES
Detection of Mustard Simulant.
To execute our approach, CEES (8.5 mM) was allow to
react with 1 (4.09 mM) in water at pH 9 for one minute at 80
o
at 4.5 mM). All experiments were performed at 25 C in aqueous
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solution, pH 9, using sodium bicarbonate–sodium carbonate. (b)
faces and soil for as long as several weeks following deployꢀ
Isotherm showing increase in fluorescence intensity of the Cd2+
ionꢀindicator solution with added podand solution.
ment.21 For the development of a practical detection system, it
becomes mandatory to detect SM on surfaces and in soil samꢀ
ples. As now described, using our detection system we sucꢀ
cessfully demonstrated the presence of CEES on surfaces and
in a soil samples.
1
2
3
4
5
6
7
8
Interferences Studies.
To test the selectivity of our strategy, we first examined
interference of a closely and structurely similar oxygen analog
of sulfur mustard, i.e bisꢀ(2ꢀchloroethyl ether) (CEEE) as well
as other electrophilic reagents: acetyl chloride and nerve
agents mimics such as diethyl chlorophosphate (DCP).
Reactions of 2.2 equivalants of CEEE, acetyl chloride, and
800000
(a)
700000
600000
500000
400000
300000
200000
100000
0
9
o
10
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DCP with 1 (4.09 mM) were carried at 80 C for one minute,
o
followed by capping with 10 at 80 C for another minute.
Subsequently, fluorescence was determined by addition of
these solutions into complex 8. No enchancement of
fluorescence after interaction of any the solutions was
observed (Figure 8). This may be attibuted to the fact that
chlorine in CEEE is not as reactive as compared to that in
CEES,20 while acetyl chloride and DECP hydrolyze under
these condition faster than reaction with 8.
400
450
500
550
600
Wavelegnth (nm)
900000
_____with CEES
(b)
760000
800000
_____with CEEE
_____with Acetyl chloride
700000
660000
560000
460000
360000
260000
160000
_____with DEP
600000
_____only 8
760000
500000
660000
560000
460000
360000
260000
160000
400000
300000
200000
100000
0
y = 266594x + 166333
R² = 0.9983
0
0.20.40.60.8
1 1.21.41.61.8 2 2.22.4
Equiv. of CEES
400
450
500
550
600
0
0.2 0.4 0.6 0.8
1
1.2 1.4 1.6 1.8
2 2.2 2.4 2.6 2.8
Wavelegnth (nm)
Equiv. of CEES
Figure 8. Fluorescence of solutions of
Cd(NO3)2.4H2O at 64.4 ꢁM and indicator at 26 ꢁM) with 1
(containing CEEE at 0.97 mM). All experiments were performed
at 25 C in aqueous solution, pH 9, using sodium bicarbonate–
8
(containing
Figure 9. (a) Titration of a solution of Cd2+ ionꢀindicator complex
(metal concentration 64.4 ꢁM and indicatorconcentration 26 ꢁM)
with increasing concentration of CEES (0.2 mM in each addition)
in water at pH 9 All experiments were performed at 25 oC in
aqueous solution, pH 9, using sodium bicarbonate – sodium
carbonate. (b) Isotherm showing increase in fluorescent intensity
of 8 with added podand 2.
o
sodium carbonate as buffer.
Calibration Curve and Sensitivity.
We next investigated the sensitivity of the detection system.
Incrementally increasing concentrations of CEES were added
to 1 (4.09 mM) using reaction condition as described above.
After capping (vide sufra), the resulting solution was added to
8, and the emission spectra were recorded at 460 nm. The
intensity of fluorescence increased linearly as a function of
CEES concentration from zero equivalents up to 2.2
equivalents (Figure 9). However, above 2.2 equivalents of
CEES a plateau is obtained. Using the line below 2.2 equivaꢀ
lents as a calibration curve, the concentration of two unknown
samples of CEES (as prepared independently by the group
members) was determined. A coincidental perfect agreement
was found for one sample, while another sample gave 10%
error (Supporting Information, Page Sꢀ9, Figure S4).
CEES (8 ꢁL), in form of drop, was placed on a glass
surface and allowed to sit for one minute. The liquid was then
wiped up with filter paper. This paper was extracted with
DCM. After evaporation of the DCM, the residue was treated
o
with 1 at 80 C for a minute, and then residue of 1 (if at all
unreacted) was capped with 10. This solution was added to 8
as described above. Figure 10a shows a large turnꢀon of fluoꢀ
rescence as compared to the same treatment of paper without
wiping a drop of CEES. To determine the presence of the anaꢀ
lyte in soil, 2 gm of dirt was spiked using a solution of CEES
(10 ꢁL) in diethyl ether (2 mL). The solvent was evaporated to
dryness and this soil sample was mixed with an aqueous soluꢀ
tion of 1 followed by the capping process. Addition of this
solution to complex 8 gave a large enhancement in fluoresꢀ
cence (Figure 10b), as compared to when there is no CEES in
soil (Supporting Information, Page Sꢀ9, Figure S5).
Analytical Applications.
Mustard gas is often delivered by aerial spraying, rockets,
bombs, or artillery shells. Unfortunately, it is known to be
persistent in the environment, i.e. it can remain active on surꢀ
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Scheme 2. Schematic presentation of proposed reaction between
mustard gas and 1
(a)
900000
800000
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600000
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400000
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200000
100000
0
1
2
3
4
5
6
7
8
_____8 with CEES
_____only 8
9
ASSOCIATED CONTENT
*Supporting Information
10
11
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60
400
450
500
Wavelegnth (nm)
550
600
Experimental details and mass. This material is available free of
charge via the Internet at http://pubs.acs.org.
(b)
800000
700000
600000
500000
400000
300000
200000
100000
0
AUTHOR INFORMATION
_____8 with CEES
_____only 8
Corresponding Author
*anslyn@austin.utexas.edu
Present Addresses
† Process Technology Development Division, Defence R&D Esꢀ
tablishment, Jhansi Road, Gwalior 474002, India
ACKNOWLEDGMENT
We thank the Office of Naval Research (N00014ꢀ09ꢀ1ꢀ1087) and
the Welch Foundation (Fꢀ1151), and Department of Science and
Technology, India and Defense Research and Development
Organization, India for financial support. We also thank Dr. Sanꢀ
mitra Barman and Mr. Erik Hernandez for preparing the unꢀ
known samples of CEES.
400
450
500
Wavelegnth (nm)
550
600
Figure 10. Fluorescence titration of Cd2+ ionꢀindicator complex
solution (containing Cd(NO3)2 at 64.4 ꢁM and indicator at 26 ꢁM)
with CEES detected (a) on surface, (b) in a soil sample. All
experiments were performed at 25 C in aqueous solution, pH 9,
usingsodium bicarbonate–sodium carbonate as buffer.
o
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In conclusion, we report the first fluorescence sensing
method for sulfur mustard in water. The method is rapid,
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advantage of the reactivity of threeꢀmembered cationic sulꢀ
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In a realꢀlife SM assay, our strategy would likely create a
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wise, all the essential aspects of the analysis are expected to
remain the same.
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