Luminol-Based Turn-On Fluorescent Sensor for Selective and Sensitive Detection of Sulfur Mustard at Ambient Temperature

Sensitive Detection of Sulfur Mustard at Ambient Temperature

Article

Luminol-Based Turn-On Fluorescent Sensor for Selective and

Virendra V. Singh, Vinod Kumar,* Utpal Biswas, Mannan Boopathi, Kumaran Ganesan,

and Arvind K. Gupta

Cite This: https://dx.doi.org/10.1021/acs.analchem.0c04464

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sı Supporting Information

ABSTRACT: We have explored a novel turn-on ﬂuorescence detection of sulfur

mustard (SM) at “room temperature”. The innovative protocol that uses the

combination of luminol and an ionic liquid in water exhibits ﬂuorescence

detection of SM within seconds. In this simple, fast, and low-cost chemosensing

method, luminol acts as the receptor as well as a signaling element, and the ionic

liquid (1-ethyl-3-methylimidazolium dicyanamide) provides the requisite and

polarizing medium to realize the detection at “room temperature”. Interestingly,

with a higher concentration of a probe (0.56 mM), SM sensing can be visualized

with the naked eye, leading to the formation of a ﬂuorescent green color within a

minute, thus expanding the application of the developed sensing technique for

chromo-ﬂuorogenic detection of SM. Excellent selectivity, sensitivity (LOD: 6

ppm), and chemosensing at ambient temperature make this methodology

completely ﬁeld-deployable.

INTRODUCTION

colorless, odorless, and highly persistent, which further

■

intensiﬁes the severity of these agents and also makes their

For the ﬁrst time, mustard gas or sulfur mustard (SM) (a blister

agent) was used during the World War (WW I) in 1917, killing

thousands of soldiers and civilians and making 1 million people

−8

detection very diﬃcult by human perception.

Therefore, a

simple, cost-eﬀective, ready-to-use, and rapid detection without

any sample pretreatment or the use of complex equipment is

highly desirable amidst the ongoing threat of terrorism).

−3

incapacitated.

Recent attacks of chemical warfare agents

(

CWAs) in Syria have claimed hundreds of lives, and this is

14−16

The commercially available devices/detectors

such as

the alarming wake-up call to the international community for

timely countermeasures by developing a rapid yet reliable

detection system for “detect to protect”. CWAs are perhaps one

of the most ruthless synthetic chemicals that can be dispersed as

a gas, liquid, or aerosol.

predominantly dangerous class of CWAs

be a threat despite controls imposed by the Chemical Weapon

Convention, which prohibits the production and use of these

lethal chemicals (Figure 1 ).

AP2C (a handheld detector), individual chemical agent

detectors, automatic chemical agent detection alarms, joint

chemical agent detectors, detector papers, and residual vapor

detection kits are based on either instrumentation techni-

−8

In particular, blister agents are a

17−19

−11

ques

or chemical methods. In general, the aforemen-

that continues to

tioned techniques suﬀer from at least one of the limitations such

as high cost, slow response, lack of speciﬁcity, poor sensitivity,

operational complexity, or nonportability. As a promising

12,13

Unfortunately, CWAs are

21−31

solution to this, various research groups

work on the

novel strategies for speciﬁc and on-site chromogenic and

ﬂuorogenic detection of mustard gas that oﬀers the unrivalled

merits of high selectivity and sensitivity, low cost, and

operational simplicity and satisfy many of the requirements for

on-site monitoring of CWAs. However, despite considerable

success with these methods, many remaining challenges must

Received: October 22, 2020

Accepted: December 1, 2020

Figure 1. Various CWAs: (a) blister agents and (b) nerve agents.

XXXX American Chemical Society

Anal. Chem. XXXX, XXX, XXX−XXX

Analytical Chemistry

Article

mixture was ﬁltered, and to this ﬁltrate, 0.27 g of sodium metal

was added and stirred for 1 h. The reaction mixture was

concentrated on a rotavapor, washed with diethyl ether (twice),

and dried to give the product. Yield: 72%, mp: >300 °C,

NMR (DMSO-d , 100 MHz): 119.1 ppm (Supporting

Information , S4).

Procedure for Fluorescence Titration Studies of LH2

with SM. A 2 mL solution of LH2 (14.1 μM) and 1-ethyl-3-

methylimidazolium dicyanamide ([emim][DCA]) (0.31 M) in

a bicarbonate-hydroxide buﬀer (0.05 M) was transferred to the

ﬂuorescence cuvette, and the initial ﬂuorescence was measured

(

λ : 392 nm, λ : 462 nm). The titration was performed by

ex em

adding successive 0.1 mM of aliquots of the SM solution (2.0

mM) to the cuvette and recording the spectrum after addition of

each aliquot. A saturation maximum was achieved with a total

concentration of 1.0 mM, as indicated by the binding isotherm

(

Figure 3). The response was fast; titration did not require any

waiting time.

Figure 2. Schematic presentation of SM detection using LH2 and

[

emim][DCA].

still be overcome for the more widespread incorporation of the

sensing ensemble. In most of the reported protocols, the process

to prepare a chemical probe is also quite lengthy; furthermore,

most of the techniques work at elevated temperatures, which

may not have practical signiﬁcance for the development of

chemosensor kits/devices, and thus, the ultimate goal is

defeated.

Chemical detection nowadays focuses on targeting the

electrophilic site of SM, which provides a fairly good detection

method. Utilizing this aspect, Anslyn and our group have come

out with an approach of a metal indicator displacement assay

32−34

and a squaraine or acridine-based chemidosimeter.

The

proof of concept was ﬁrst established with the SM simulant and

Figure 3. Fluorescence of LH2 (14.1 μM) in the presence of

35,36

[

emim][DCA] (0.31 M) to SM at a varied concentration (2.0 mM)

then implemented on real agents.

In both cases, a reaction

in a bicarbonate-hydroxide buﬀer (0.05 M) at pH 8.5 (λ_e_x392 nm);

took place at a higher temperature (60−80 °C) with the

additional use of an indicator. These drawbacks partly diminish

our aim of developing an “ideal chemosensor” for SM under ﬁeld

conditions. Regardless of our sincere eﬀorts, none of the

chemosensors could be utilized for on-ﬁeld detection because of

major restrictions such as the reaction at elevated temperature

and sensitivity. Consequently, we engaged our focus toward

developing a sensing system that can detect chemical agents,

inset: binding isotherm of LH2 with SM.

Procedure for SM Detection and Selectivity Studies.

To a solution containing LH2 (0.056 mM) and [emim][DCA]

(1.24 M) in a bicarbonate-hydroxide buﬀer at pH 8.5 was added

SM (0.8 mM) at 25 °C. The formation of strong sky blue (under

a handheld UV lamp at 365 nm) took place, which indicated the

presence of the analyte (Figure 4a). Similarly, the excess of

interferences (2.4 mM) such as sarin, tabun, VX, diethyl

chlorophosphate (DECP), acetyl chloride, bis (2-chloroethyl)

ether (BCEE), diethyl sulﬁde, and benzyl bromide was added to

the sensing solutions (prepared as above). In all cases, the

solution remained nonﬂuorescent.

especially outside dedicated or designated laboratories.

EXPERIMENTAL SECTION

■

Chemicals and Materials. All chemicals and reagents were

bought from Aldrich and Fisher Scientiﬁc and used without

further puriﬁcation. Fluorescence measurement spectra were

recorded on a Perkin Elmer, LS-55, UK, equipped with a quartz

cuvette (path length: 1 cm, at 25 °C). NMR spectra were

recorded on a Bruker 400 MHz spectrometer using

tetramethylsilane as an internal standard. Mass analysis was

performed on a Xevo TQD of Waters (USA).

For the ﬂuorescence titration studies, the response of the

solution containing LH2 (14.1 μM) and [emim][DCA] (0.31

M) in a bicarbonate-hydroxide buﬀer (0.05 M) at pH 8.5 at 25

°C was measured (λ : 392 nm). Upon the addition of 1.0 mM of

SM and 3.0 mM of each of the interferents (sarin, tabun, VX,

diethyl chlorophosphate (DECP), acetyl chloride, oxygen

mustard, diethyl sulﬁde, and benzyl bromide) to the above

sensing solutions, the emission spectra (λ_e_m462 nm) were

recorded in all cases. The ﬂuorescence proﬁle is shown in Figure

4b.

Synthesis of Sodium Dicyanamide. To a solution of 0.5 g

of cyanamide dissolved in dry ethanol, 0.27 g of sodium metal

was added and stirred at room temperature for 1.5 h to obtain a

white precipitate. Then, 1.26 g of cyanogen bromide was added

in small fractions, and a white precipitate disappeared

immediately. The reaction mixture was further stirred for 1.5

h. The color of the solution turned yellow with a precipitate,

which indicated the formation of sodium bromide. The reaction

Fluorescence Titrations for Determining the Calibra-

tion Curve and Limit of Detection. The ﬂuorescence

response of LH2 (14.1 μM) and [emim][DCA] (0.31 M)

Anal. Chem. XXXX, XXX, XXX−XXX

Analytical Chemistry

hydroxide buﬀer at pH 8.5. A ﬂuorescent green color was

Article

Figure 4. (a) Fluorescence response of LH2 (0.056 mM) in the presence of [emim][DCA] (1.24 M) with 0.8 mM of SM and 2.4 mM of each of the

interferents (vials from left to right): (i) LH2 only and LH2 with (ii) SM, (iii) sarin, (iv) tabun, (v) VX, (vi) DECP, (vii) acetyl chloride, (viii) BCEE,

(

ix) diethyl sulﬁde, and (x) benzyl bromide; (b) ﬂuorescence proﬁle of LH2 (14.1 μM) toward 1.0 mM of SM and 3.0 mM of each of the interferents

(

sarin, tabun, VX, DECP, acetyl chloride, oxygen mustard, diethyl sulﬁde, and benzyl bromide. Bicarbonate-hydroxide buﬀer (0.05 M) at pH 8.5 (λ_e_x:

92 nm, λ : 462 nm).

with various concentrations of SM starting from 0.1 to 1.4 mM

was measured (bicarbonate-hydroxide buﬀer, 0.05 M) in a

similar manner as described above. The magnitude of

ﬂuorescence intensity depends on the concentration of SM.

The intensity increases with a regular pattern and becomes a

plateau at 1.0 mM (Figure 5).

in the presence of [emim][DCA] (0.31 M) with various

concentrations of SM starting from 0.02 to 0.2 mM was

measured in a bicarbonate-hydroxide buﬀer (0.05 M) in a

similar manner as described above (Figure 6). From Figure 6,

LOD was determined to be 6 ppm.

Procedure for Chromogenic Detection of SM Using

LH2. SM (0.25 mM, 0.04 mg/mL) was allowed to react with

LH2 (0.56 mM) and [emim][DCA] (1.24 M) in a bicarbonate-

To determine the limit of detection (LOD) of the present

sensing protocol, the ﬂuorescence response of LH2 (14.1 μ M)

Figure 5. Fluorescence proﬁle of LH2 (14.1 μM) in the presence of

[

emim][DCA] (0.31 M) toward SM (0.1−1.0 mM); inset: calibration

Figure 6. Fluorescence proﬁle of LH2 (14.1 μM) in the presence of

[emim][DCA] (0.31 M) toward SM (0.02−0.2 mM). Inset: calibration

curve showing linearity with an R of 0.97. Bicarbonate-hydroxide

buﬀer at pH 8.5 (λ : 392 nm, λ : 462 nm).

curve showing the linearity with an R of 0.98.

Anal. Chem. XXXX, XXX, XXX−XXX

Analytical Chemistry

photographed (Figure 7 a).

Article

developed, which persisted for more than 48 h. The vial was

in 1.0 mL of MeOH) was placed onto the test strip to develop

the ﬂuorescence which is visible under UV light (Ex. 365 nm)

(

Figure 7d).

Safety Statement. CWAs are extremely toxic. They were

prepared in an Organization for the Prohibition of Chemical

Weapons-declared a schedule 1 facility. Recommended

operating procedures must be followed during their preparation

and uses. Proper protective gears and equipment should be used

while handling the agents for analytical research.

Figure 7. (a) Chromogenic response of LH2 (0.56 mM) with 0.25 mM,

.04 mg/mL (right) and with no SM (left) in 1.24 M of the IL; (b)

ﬂuorescence response (from left to right) of LH2 with the unspiked soil

sample, LH2 with the SM-spiked soil sample and vapor-phase detection

of SM; (c) detection of SM in wipes; (d) spot detection of SM on the

probe coated on paper test strips in UV light (Ex. 365 nm), control

RESULTS AND DISCUSSION

■

Design Criteria. Herein, we explored LH2 as a chemical

probe that also acts as a signal transducer, which in the presence

of an ionic liquid (IL) exhibits turn-on ﬂuorescence detection

with SM at room temperature. LH2 is well known to display

(

left) and SM (right).

8−41

chemiluminescence and ﬂuorescence properties.

Its

Procedure for On-Site Detection (Analytical Applica-

chemistry has intensely been investigated in analytical and

biochemical applications such as crime scene investigations and

the areas such as pharmaceutical, environmental, or life

tions). Procedure for Fluorescence Detection of SM in the Soil

Sample. 1.0 g of dry soil was mixed with SM (3 μL in 2 mL of

diethyl ether). This was allowed to stand for 20 min. The solvent

from the soil sample was evaporated by nitrogen blowdown. The

SM-spiked soil sample was extracted with dichloromethane

DCM) and ﬁltered, and the ﬁltrate was evaporated to dryness.

To this SM sample were added LH2 (0.056 mM) and

emim][DCA] (1.24 M) in a bicarbonate-hydroxide buﬀer.

42,43

sciences.

Under basic conditions, it displays two distinct

nucleophilic reactions. With softer and weaker bases (such as

pyridine), the main eﬀect of the alkaline species is the increase of

the nucleophilicity of the aniline moiety. On the other hand,

when harder bases are used (alkaline metal hydroxides or

hydrides), it abstracts protons majorly from more acidic enolic

(

[

The solution ﬂuoresces within a minute, which was photo-

graphed.

functionalities (Scheme 1).

The reactivity/toxicity of SM lies in its ability to alkylate

DNA, RNA, and protein molecules, thus leading to cytotoxicity,

Procedure for Fluorescence Detection of SM in the

Gaseous Phase. SM vapors were generated using gas generation

45−48

which results in cell death.

Its chemical reactivity is further

assembly, which were passed through a solution vial

containing LH2 (0.056 mM) and [emim][DCA] (1.24 M) in

a bicarbonate-hydroxide buﬀer. The solution ﬂuoresces within 2

min, which was photographed (Figure 7b).

aggravated in the presence of water or any ionizing solvent

because of the stabilization of the electrophilic three-membered

episulfonium ion (Figure 2). The factor that stabilized the

intermediate ion will enhance the rate of reaction, leading to the

lower reaction temperature. The task-speciﬁc ILs, particularly

Procedure for Fluorescence Detection of SM on the

Surface. The SM-contaminated wipe sample (Supporting

Information, S5) was placed into a test vial containing LH2

basic ILs such as ([emim][DCA]), will not only aﬀect the

reaction environment but also abstract a proton from enolic

functionalities of LH2. In this process, the anionic part of the IL

([emim][DCA]) would enhance the nucleophilicity of the

probe and the cationic part will help to improve the electrophilic

ability of SM. The remarkable eﬀects of both the cation and

anion on the reactivity of reactants will facilitate this reaction

between LH2 and SM. This hypothesis was supported by the

report where dicyanamide-based ILs act as active basic catalysts

(

0.056 mM) and [emim][DCA] (1.24 M) in a bicarbonate-

hydroxide buﬀer (pH 8.5). This wipe was allowed to react with

the probe solution for 30 s. The solution ﬂuoresces, which was

photographed. The same procedure was followed when there

was no mustard on the surface (Figure 7c).

Preparation of the Portable Paper Test Strip. A solution

containing LH2 (0.056 mM) and [emim][DCA] (1.24 M) in a

bicarbonate-hydroxide buﬀer (pH 8.5) was spread over

Whatman ﬁlter paper 41 (1″ × 1.2″), and then, it was dried

with the blow of nitrogen. A drop of SM solution (2.0 μL of SM

50−54

in the O-acetylation reactions of alcohols.

As a part of our ongoing research, then, we devised an

approach for SM detection (Figure 2) where the reacting site

Scheme 1. LH2 and Its Chemical Reactions in the Diﬀerent Basic Media

Anal. Chem. XXXX, XXX, XXX−XXX

Analytical Chemistry

Article

and signaling element are present in a single molecule. This

protocol was purposefully designed to use commercially

available components (LH2 and [emim][DCA]) and to analyze

the feasibility of chemosensing at room temperature. The idea

was inspired by the formation of the luminescent product due to

of error with respect to the known values. Furthermore, for the

determination of LOD, the probe was further allowed to interact

with 10 solutions of SM with concentrations from 20 to 200 μM

and the ﬂuorescence response was measured (Figure 6). The

regression coeﬃcient (R = 0.98) of the sensing system also

S-alkylation of the acridine probe with SM and by following

the reaction strategy of O-alkylation of LH2 with mono-

produced a very linear calibration curve even at the lower

concentrations. The LOD of 6 ppm, as determined using Figure

6 , also displayed the visual response under a UV lamp

(Supporting Information , Figure S2). To measure the minimum

detection limits with reliability, the ﬂuorescence of ﬁve SM

samples with the concentration of 6 ppm on the same day was

recorded and the standard deviation was calculated; 0.23% of

relative standard deviation indicates that the developed sensing

system is completely reliable while dealing with a low

concentration of the analyte (Supporting Information, Figure

S3).

saccharide derivatives. LH2 is weekly ﬂuorescent (λ = 420

8−41

nm) in water and organic solvents.

At pH 8.5, its

ﬂuorescence property is quenched owing to the formation of

its monosodium salt. The alkylation of the salt by SM takes place

to yield the O-alkylated product (1) of LH2, making it highly

ﬂuorescent because of the enhanced conjugation with an

emission shift of 42 nm.

Fluorogenic Detection of SM. LH2 in the presence of

emim][DCA] and water reacts instantaneously with SM at

[

room temperature to generate a turn-on ﬂuorescence. With an

optimized pH (8.5) and concentration of the IL ([emim]-

Optimization of Sensing Modules and Chromogenic

Response. It is mandatory to ascertain that for the detection of

SM, the combination of LH2 and [emim][DCA] is indis-

pensable. It was observed that LH2 or [emim][DCA] alone

shows negligible ﬂuorescence at pH 8.5. Even SM along with the

probe or IL did not produce any ﬂuorescence enhancement

(Supporting Information, Figure S4). Therefore, a permutation

of the probe and IL has successfully shown the presence of SM

with bright sky-blue ﬂuorescence. It is also interesting to note

that with a higher concentration of the probe, a ﬂuorescent green

color also developed, which can be even visualized with the

naked eye. Hence, we further optimized the concentration of all

three components and observed that LH2 (0.56 mM),

[emim][DCA] (1.24 M), and SM (0.25 mM, 0.04 mg/mL)

can demonstrate the detection with the naked eye within

minutes (Figure 7a) without the use of any instrument, thus

expanding the application of the developed sensing technique

for chromo-ﬂuorogenic detection of SM. In chromogenic

detection, a green color is developed, which shows the UV

absorbance at 392 nm. In both the cases (chromogenic and

ﬂuorogenic), the response persisted for more than 48 h,

indicating the stability of the chemosensing ensemble.

[

DCA]) (1.24 M), we allowed LH2 (0.056 mM) to react with

SM (0.8 mM) at 25 °C. The reaction took place in less than a

minute, as indicated by the formation of strong sky blue

ﬂuorescence as seen under a handheld UV lamp (365 nm)

(

Figure 4a). The ﬂuorescence titrations of solution LH2 (14.1

μM) in the presence of [emim][DCA] (0.31 M) were carried

out at pH 8.5 (bicarbonate-hydroxide buﬀer, 0.05 M) at room

temperature, and the emission spectra were recorded (λ : 392

nm). The new peak appeared at a λ_e_mof 462 nm with the gradual

addition of SM, and a saturation maximum was achieved with a

total concentration of 1.0 mM, as indicated by the binding

isotherm (Figure 3). Because the observed response was fast,

titration did not require any waiting time.

Selectivity Studies. The selectivity studies revealed that the

present method is highly selective for SM over more or less

reactive interferences such as sarin, tabun, VX, DECP, acetyl

chloride, BCEE, diethyl sulﬁde, and benzyl bromide. Under

similar reaction conditions, these analytes were allowed to react

with an excess of 2.4 mM (3 times more than SM). In all the

cases, no response was observed either by the naked eye under a

UV lamp or by the ﬂuorescence study using LH2 (14.1 μM),

On-Site Detection Procedure. During the war scenario,

[

emim][DCA] (0.31 M), and interfering agents (3.0 mM), as

SM may be present in the environment in various matrixes (soil,

56,57

shown in Figure 4b. Most of the reactive interferences such as

sarin, soman, tabun, VX, DECP, and acetyl chloride could not

endure the sustained basic conditions created by the IL

surface, and vapor).

Therefore, it is imperative to showcase

the detection in these matrixes. SM is highly persistent in soil

(for hours to several weeks), causing serious lethality to human

beings. In this attempt, the SM-contaminated soil matrix was

ﬁrst chosen to display the detection. SM-spiked and unspiked

soil samples were extracted with DCM and ﬁltered, and the

ﬁltrate was evaporated to dryness. This sample was further

allowed to react with LH2 (0.056 mM) and [emim][DCA]

(1.24 M). The ﬂuorescent color appeared immediately with the

SM-spiked sample, while no change with the unspiked sample

was observed (Figure 7b). Using gas generation assembly, the

generated SM vapors were directly exposed to the solution

containing LH2 (0.056 mM) and [emim][DCA] (1.24 M), and

the solution ﬂuoresces within 2 min (Figure 7b).

(

[emim][DCA]) in the buﬀer solution (pH: 8.5) and hence

did not react with LH2. On the other hand, less reactive

interferences such as BCEE, ethyl iodide, diethyl sulﬁde, and

benzyl bromide are not suﬃciently reactive electrophilic to

compete with SM under sensing conditions; therefore, no

response was perceived. As can be seen from Figure 4a, a

nonsigniﬁcant response was observed with 3.0 equiv of benzyl

bromide but no result with 1.0 equiv of it.

Calibration Curve and LOD. In order to quantify the

concentration of SM, a calibration plot was created by measuring

ﬂuorescence responses of LH2 at various concentrations of SM

(

0.1−1.4 mM). Following similar reaction conditions, with each

For “detect to warn” under warﬁeld conditions, wipe sampling

and analysis of CWAs from surfaces require sample pretreat-

ment and use of the sophisticated instrument at the site of the

addition of 0.1 mM of SM to LH2, the intensity increases with a

regular pattern and becomes a plateau at 1.0 mM, as shown in

Figure 5. These results have produced a linear calibration curve

attack. To circumvent this, our sensing solutions can detect

SM after physically decontaminating the surface using wipes

(Supporting Information , S5). The contaminated wipe was

placed in a vial containing LH2 (0.056 mM) and [emim][DCA]

(1.24 M) in the buﬀer solution, and the ﬂuorescence developed

(R = 0.97) from the ﬂuorescence measurement at 462 nm.

Using this calibration curve, we also analyzed the concentration

of two unknown samples of SM as prepared in our lab

(

Supporting Information, Figure S1). Interestingly, good

14−16

agreements were found for both the samples with less than 5%

within 30 s (Figure 7c). The detector papers/strips

are also

Anal. Chem. XXXX, XXX, XXX−XXX

Analytical Chemistry

Establishment, Gwalior 474002, India; orcid.org/0000-

Article

a promising platform and do not warrant any technical support

and can be applied as a possible ﬁeld-deployable sensor.

Detector strips itself have many advantages over devices because

of a low cost, disposability, and easy transportation. Because of

this, we prepared a paper test strip and coated with a solution

containing LH2 (0.056 mM) and [emim][DCA] (1.24 M) that

develops ﬂuorescence with a drop of SM solution (2.0 μL in 1.0

mL of MeOH) (Figure 7d).

In an attempt to support our hypothesis for the proposed O-

alkylation of LH2 in the presence of [emim][DCA], we sought

after the role of dicyanamide in the product formation. Sodium

dicyanamide was prepared and used in place of the IL in the

reaction (Supporting Information, S4). At room temperature,

no reaction took place even after 1 h, but after heating the

solution at 80 °C for 1 min, the solution emits sky-blue

ﬂuorescence in UV light (365 nm), which was similar to the case

when the IL was used. Fluorescence data reveal that the emission

maxima occur at the same wavelength (462 nm) (Supporting

Information , Figure S5). This study conﬁrms that [emim]-

Fluorescence data of unknown concentrations of SM

samples, naked eye response with 6 ppm of SM, analytical

studies, optimization of sensing constituents, titration

study between LH2 and SM in the presence of sodium

dicyanamide, preparation of wipe samples, and mass

spectra (PDF)

AUTHOR INFORMATION

Corresponding Author

■

Vinod Kumar − Defence Research and Development

0001-9909-2686 ; Email: vkpal77@yahoo.co.in

Authors

Virendra V. Singh − Defence Research and Development

Establishment, Gwalior 474002, India

Utpal Biswas − Defence Research and Development

Establishment, Gwalior 474002, India

Mannan Boopathi − Defence Research and Development

Establishment, Gwalior 474002, India

Kumaran Ganesan − Defence Research and Development

Establishment, Gwalior 474002, India

[

DCA] provides both basic and ionizing media which help

reaction occur at room temperature. To explore the possibility of

further alkylation at the C-1 position, we increased the pH to

0.5 after the formation of monoalkylated product 1. The

Arvind K. Gupta − Defence Research and Development

Establishment, Gwalior 474002, India

ﬂuorescence of the solution gets quenched because of

deprotonation of 1, and upon the further addition of SM

(Scheme 1), the ﬂuorescence is not turned on again. This may be

Complete contact information is available at:

attributed to the fact that at higher pH, SM might not be able to

survive to react with anionic species of the monoalkylated

product and hence resulted in no further reaction. The

formation of the product was conﬁrmed with the help of mass

spectrometry by analyzing the reaction mixtures, which was

obtained from the reaction of LH2 with the SM simulant (2-

chloroethyl ethyl sulﬁde). The mass data indicate formation of a

https://pubs.acs.org/10.1021/acs.analchem.0c04464

Notes

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

We thank the Director, DRDE, Gwalior, for his keen interest and

encouragement. The DRDE Accession number of this manu-

script is DRDE/PTDD/18/2020.

sodiated peak (M + Na : 288.14) (Supporting Information,

Figure S6).

CONCLUSIONS

■

REFERENCES

■

In summary, we have engineered a new chemosensing system

that displays a turn-on ﬂuorescence detection of SM using LH2

and an IL ([emim][DCA]). The IL plays a crucial role by

enhancing the nucleophilicity of LH2 and electrophilicity of SM,

which brings down the reaction temperature from 80 to 25 °C.

The critical attributes and desirable properties of the new

method are as follows: very high selectivity (over nerve agents

and alkylating agents), a low LOD (6 ppm), very fast response

(

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(

(3) Falkenrath, R. A.; Newman, R. D.; Thayer, B. A. America’s Achilles’

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