Application of liquid chromatography/electrospray ionization tandem mass spectrometry for the elucidation of hydroxyl radical oxidation of metsulfuron methyl and related sulfonylurea pesticide products: evidence for the triazine skeleton scission

Article abstract of DOI:10.1002/rcm.7234

Rationale Sulfonylureas are among the most important class of antidiabetic and herbicides. Solar light excitation and Advanced Oxidation Processes may result in the formation of a wide array of products owing to the relative complex structure. These products, that should be identified, may present a more toxic effect than the parent compound. Methods Liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry (LC/ESI-QTOFMS) with accurate mass determination emerges as a valuable technique for the precise elucidation of all possible byproducts. The hydroxyl radical was generated by excitation of the iron(III) aquacomplex [Fe(H₂O)OH]²⁺ and hydrogen peroxide at pH3.5. Three different sulfonylureas were studied: metsulfuron methyl, cinosulfuron and thifensulfuron methyl. Results Several products owing to the reactivity of hydroxyl radicals with sulfonylurea were obtained. They arise from scission of the sulfonylurea bridge, hydroxylation of the aromatic ring, demethylation of the methoxy group and more importantly and unequivocally from the rupture of the triazine skeleton. To reach such scission, a primary demethylation of the methoxy group on the triazine moiety seems to act as a precursor process. Such a process was observed with the three studied sulfonylurea compounds. Conclusions The reported results demonstrated the usefulness of accurate mass measurements undertaken by LC/ESI-QTOFMS for structural elucidation of the unknown byproducts that were generated during hydroxyl radical reactions with some sulfonylureas. It has been possible herein to identify the structures of products arising from the opening of the recalcitrant triazine structure via hydrolysis processes in acidic solutions.

Full text of DOI:10.1002/rcm.7234

Research Article
Received: 7 January 2015
Revised: 20 May 2015
Accepted: 20 May 2015
Published online in Wiley Online Library
Rapid Commun. Mass Spectrom. 2015, 29, 1370–1380
wileyonlinelibrary.com) DOI: 10.1002/rcm.7234
(
Application of liquid chromatography/electrospray ionization
tandem mass spectrometry for the elucidation of hydroxyl radical
oxidation of metsulfuron methyl and related sulfonylurea pesticide
products: evidence for the triazine skeleton scission
1
,2,3
3
1,2
Rajae Chahboune
, Hafida Mountacer and Mohamed Sarakha *
1
Clermont Université, Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand (ICCF), Equipe Photochimie, BP 10448,
F-63000 Clermont-Ferrand, France
2
CNRS, ICCF UMR 6296, Photochemistry Team, BP 80026, F-63171 Aubière, France
Laboratoire des Sciences de l’Environnement et du Développement, Equipe de Chimie Ecologique, FST Université Hassan 1 ,
3
er
Km 3 route de Casablanca, BP 577, Settat, Morocco
RATIONALE: Sulfonylureas are among the most important class of antidiabetic and herbicides. Solar light excitation and
Advanced Oxidation Processes may result in the formation of a wide array of products owing to the relative complex
structure. These products, that should be identified, may present a more toxic effect than the parent compound.
METHODS: Liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry (LC/ESI-QTOFMS)
with accurate mass determination emerges as a valuable technique for the precise elucidation of all possible byproducts.
2+
The hydroxyl radical was generated by excitation of the iron(III) aquacomplex [Fe(H O)OH] and hydrogen peroxide at
2
pH 3.5. Three different sulfonylureas were studied: metsulfuron methyl, cinosulfuron and thifensulfuron methyl.
RESULTS: Several products owing to the reactivity of hydroxyl radicals with sulfonylurea were obtained. They arise
from scission of the sulfonylurea bridge, hydroxylation of the aromatic ring, demethylation of the methoxy group and
more importantly and unequivocally from the rupture of the triazine skeleton. To reach such scission, a primary
demethylation of the methoxy group on the triazine moiety seems to act as a precursor process. Such a process was
observed with the three studied sulfonylurea compounds.
CONCLUSIONS: The reported results demonstrated the usefulness of accurate mass measurements undertaken by
LC/ESI-QTOFMS for structural elucidation of the unknown byproducts that were generated during hydroxyl radical
reactions with some sulfonylureas. It has been possible herein to identify the structures of products arising from the
opening of the recalcitrant triazine structure via hydrolysis processes in acidic solutions. Copyright © 2015 John Wiley
&
Sons, Ltd.
Pesticides, pharmaceuticals and personal care products have
been the subject of intense research activity due to their
widespread occurrence in the various environment
portion of the solar spectrum causing their degradation
through direct light excitation. However, this process may
lead to the formation of various stable products that
accumulate well in the solution since the total mineralization
of polluted aqueous solutions is not possible with such
[1–5]
compartments such as water resources.
Among the
various environmental challenges, those concerning the
preservation of clean and safe water are of great importance
in spite of a continuous change in the employed chemicals.
A large body of literature is available on these compounds
regarding their stability, fate and behavior in different
[7,15–18]
photochemical reaction.
In order to reach a high degree
of mineralization of contaminated media, several Advanced
Oxidation Processes (AOPs) using solar light excitation have
[19–21]
been developed and studied in depth.
They have
[6–11]
matrices such as water, soil and food.
Their degradation
emerged as interesting ways for an efficient decontamination
of polluted media because of their large-scale use. These
processes mainly require the generation of highly reactive
species among them the hydroxyl radical that efficiently react
with the majority of organic compounds with a rate constant
processes are mainly controlled by different parameters such
[12–14]
as solar light, microbial activity, temperature, pH, etc.
Some of these organic contaminants may absorb in the actinic
[22]
close to that of a diffusion-controlled process.
However, in
several cases the mineralization occurs at a much slower rate
than that obtained for the parent compounds leading to the
accumulation of some of the products in the solution.
Because of the possible higher toxicity when compared to
the parent compounds, their precise elucidation is pertinent.
*
Correspondence to: M. Sarakha, Clermont Université,
Université Blaise Pascal, Institut de Chimie de Clermont-
Ferrand (ICCF), Equipe Photochimie, BP 10448, F-63000
Clermont-Ferrand, France.
[23,24]
E-mail: mohamed.sarakha@univ-bpclermont.fr
Rapid Commun. Mass Spectrom. 2015, 29, 1370–1380
Copyright © 2015 John Wiley & Sons, Ltd.

Triazine skeleton scission in sulfonylurea herbicides
Among these contaminants, sulfonylurea herbicides that
belong to an important class of herbicides are of great interest.
More than 27 different active ingredients are currently
was not controlled. The change in pH of the solutions was
obtained by addition of perchloric acid or sodium
hydroxide.
[25]
registered around the world.
They are used as selective
systemic weed control products and are highly water soluble
Irradiations setups
[26]
and may also be found in natural and drinking waters.
[
27]
Fenoll et al.
performed the photocatalytic degradation of
Irradiation experiments (365 nm) were carried out in an
elliptical stainless steel cylinder. A high-pressure mercury
lamp (Philips HPW, 125 W) was located at a focal axis of the
elliptical cylinder. An inner filter selected the emission at
365 nm permitting the selective excitation of the photo-
catalyst. The reactor (water-jacketed Pyrex tube – diameter
2.8 cm) was centred at the other focal axis. The solution
(roughly 50 mL) was continuously stirred with a magnetic
bar during irradiation. For experiments on UV/H O , the
irradiation was performed by excitation at 254 nm. Under
our experimental conditions, the UV light was mainly
absorbed by hydrogen peroxide. A cylinder reactor made in
stainless steel equipped with two germicidal lamps (Mazda
T815 15 W) emitting selectively at 254 nm and symmetrically
installed around the cylinder were used. The reactor, a quartz
tube (d = 2.5 cm) containing a maximum of 50 mL solution,
was located in the centre of the container.
five sulfonylurea herbicides (chlorsulfuron, flazasulfuron,
nicosulfuron, sulfosulfuron and triasulfuron) using various
semiconductors such as zinc oxide (ZnO), tungsten(VI) oxide
(
WO ), tin(IV) oxide (SnO ) under natural sunlight. Under
3
2
ZnO photocatalysis, with Na S O as an oxidant, the process
2
2
8
strongly enhances the degradation rate of the herbicides.
The removal of metsulfuron methyl, a sulfonyl from
contaminated water, was investigated using the Fenton
2
2
[
28]
method.
This appeared to be effective at pH 3.0 with a
conversion percentage of 70%. From the analytical point of
view, it had already been shown that triazine-based
sulfonylureas are susceptible to photodegradation under
environmental conditions and are efficiently eliminated by several
[29]
photocatalytic processes without complete mineralization.
This was mainly related to the presence of the triazine skeleton
that leads to the formation of cyanuric acid, a recalcitrant
[
30,31]
compound.
The latter compound was found to be stable
photocatalytic
In the present work, we focused our attention
Solutions were de-aerated or oxygen saturated, by bubbling
nitrogen and oxygen respectively during 30 min at room
temperature prior to irradiation, and the bubbling was
maintained for the entire irradiation time.
even after long illumination using TiO
2
[
32]
treatments.
on the elucidation of the transformation products of three
sulfonylurea compounds, metsulfuron methyl, cinosulfuron
and thifensulfuron methyl, formed through their oxidation
via the hydroxyl radical. This was selectively generated by
Analytical and spectroscopic equipment
[
33–36]
excitation at 365 nm of iron(III) aquacomplex
photo Fenton process and under illumination of hydrogen
peroxide with UVC (254 nm).
or the
The disappearance of the pesticide and the formation of
the products were followed by high-performance liquid
chromatography using a Waters 2695 HPLC (Alliance)
[37]
The exact and unequivocal
characterization of the products was performed by the careful
analysis of the LC/MS/MS spectra in positive as well as in
negative ion mode.
chromatograph system equipped with a Waters 2998
photodiode-array detector. The experiments were performed
by UV detection at either 250 nm or 280 nm and by using a
reversed-phase Nucleodur column (Macherey-Nagel, 100–5
C18 ec; 150–4.6 mm). The flow rate was 1.0 mL/min and the
injected volume was 50 μL. The elution was accomplished
with water, formic acid (0.1%) and acetonitrile (60/40 v/v).
A Waters/Micromass LC/QTOF tandem mass spectrometer
EXPERIMENTAL
Materials
(Micromass, Manchester, UK), with an orthogonal geometry
Metsulfuron-methyl (MTSM, 99.2%), 2-[[[[(4-methoxy-6-
methyl-1,3,5-triazin-2-yl) amino]-carbonyl]amino]sulfonyl] benzoate,
and thifensulfuron-methyl (TFS, 97.6%) (methyl 3-[(4-methoxy-
Z-spray ionization source, was used for LC/ESI-MS and
LC/ESI-MS/MS experiments. LC separation was performed
using the gradient program reported in the literature.
[11,38]
6
-methyl-1,3,5-triazin-2-yl) carbamoylsulfamoy] thiophene-2-
The eluate was subjected to electrospray ionization (ESI) in the
positive ion as well as negative mode and resulted in the
formation of protonated molecules and deprotonation of the
sample components. Scanning was performed in the range
between m/z 60 and 600. The elemental composition of the
recorded ions was further determined using MassLynx Elemental
Composition software (version 4.1, Micromass). C, H, N, O, and S
were selected as possible elements present. In LC/MS analyses, in
order to assign the elemental formulas, the minimum and
maximum atoms of each element were set as follows: C from 1
to 20; H from 1 to 20; N from 0 to 5; O from 0 to 10, and S from
0 to 2. No nitrogen rule, ring and double-bond equivalents were
applied. The maximum deviation was set to 10 ppm. Five scans
were combined before the integration of the individual peaks.
The desolvation and ion source temperatures were set at
250 °C and 100 °C, respectively. Nitrogen was used as the
nebulizer (35 L/h) as well as a desolvation gas (350 L/h).
carboxylate were obtained from Riedel-de Haën and used as
received. Cinosulfuron (CNS, 98.9%), ethyl 2-(4-chloro-6-
methoxypyrimidin-2-ylcarbamoylsulfamoyl) benzoate, was
purchased from Fluka. 2-Amino-4-methoxy-6-methyl-1,3,5-
triazine and 2-(carbomethoxy) benzenesulfonamide were
obtained from Aldrich at the purest grade available. Iron(III)
solutions were prepared from ferric perchlorate nonahydrate
(Fluka). Iron(II) perchlorate was purchased from Aldrich.
Hydrogen peroxide (30%) was obtained from Fluka and was
diluted to the desired concentrations. Except when stated, all
the other reagents were of the purest grade commercially
available and were used without further purification. All
the solutions were diluted with deionized ultrapure water
that was purified with a Milli-Q device (Millipore) and its
purity was controlled by its resistivity. pH measurements
were carried out with a JENWAY 3310. The ionic strength
Rapid Commun. Mass Spectrom. 2015, 29, 1370–1380
Copyright © 2015 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/rcm

R. Chahboune, H. Mountacer and M. Sarakha
The optimized voltages for the probe and ion source components
to produce maximum intensity) were 3 kV for the stainless-steel
(
capillary, 35 V for the sample cone and 1 V for the extractor
cone. A sampling rate of approximately 20 scans/s and a
resolution of 5000 were used for the TOFMS analyses.
Tandem mass spectrometric (MS/MS) experiments in
collision-induced dissociation (CID) mode were performed
using argon in the collision cell at
a pressure of
À3
4
.0 × 10 mbar. A collision energy gradient (15–35 V) was
used for preliminary fingerprints and specific energies were
then used to unambiguously assign the product ions. The
+
À
[
M + H] or [M–H] precursor ions were used as a lock mass
for the MS/MS experiments and allowed for accurate mass
measurements to be undertaken. The ion formulas were
determined by restricting the possible elements present to
those in the precursor ion formulas, and setting the maximum
allowed deviation in the mass measurements to 20 ppm.
UV-visible spectra were recorded with a Cary 3 double
beam spectrophotometer.
Figure 1. Total ion chromatogram (TIC) in positive ion
mode (ESI+) of an irradiated solution of metsulfuron
À4
À1
À1
methyl (1.0 × 10 mol L
) in the presence of iron(III)
À4
(
3.0 × 10 mol L ) obtained for 25% conversion: (A) initial
solution and (B) irradiated solution. The inset shows the
HPLC/DAD chromatogram at λdetection = 254 nm.
RESULTS AND DISCUSSION
the process is mainly due to the excitation of the iron(III)
species. As clearly observed by HPLC/MS and DAD analyses,
the degradation of MTSM leads to the formation of various
products that present retention times lower than that of the
parent compound (Fig. 1). All these products were also
generated by excitation of hydrogen peroxide at 254 nm and
also by Fenton reaction in the presence of MTSM. As largely
The irradiation at 365 nm of an aerated mixture of [Fe(H
2
O)
2+
OH] and metsulfuron methyl (MTSM, pH 3.5), at the
À4
À4
concentrations of 3.0 × 10 mol/L and 1.0 × 10 mol/L,
respectively, permitted an efficient degradation of the pesticide.
Under our experimental conditions, such disappearance is
mainly due to the selective excitation of iron(III) species
within the ligand to metal charge transfer band leading to
reported in the literature, these conditions permit an efficient
[33–36]
[37]
the production of the hydroxyl radical.
species reacts with MTSM with
This reactive
rate constant of
This is confirmed by the inhibition of
the reaction in the presence of 2-propanol (0.1%) used as
production of hydroxyl radicals.
It should be pointed out
a
that within the early stages of the reaction, the degradation rate
of MTSM and the amount of all the generated products
increased when the dissolved oxygen concentration increased.
The generated products were labeled P1 to P6 in the order
of their retention times and their elucidation was performed
9
À1
À1 [24]
3
.5 × 10 mol L s .
[22,24]
hydroxyl radical trap.
degradation of MTSM was observed when [Fe(H
was omitted from the solution leading us to the conclusion that
It should be pointed out that no
2+
2
O)OH]
2
using HPLC/MS and HPLC/ESI-MS in positive as well as
Table 1. Accurate and exact masses and elemental compositions for the products P1 to P6 as obtained by LC/MS in ESI+ and
+
+
ESI– modes. The ratio [M + H + 2] /[M + H] (determined using MassLynx V4.1 software) was used to ensure the presence of
3
4
the sulfur atom (the relative abundance for S is 4.44%)
Ratio*
+
Accurate
mass
Calculated
Elemental
composition
Error
(ppm)
[M + H + 2] /
+
Products
m/z
mass
[M + H] %
+
ESI+
MTSM
P1
382
141
386
259
216
368
387
380
384
257
366
385
382.0828
141.0765
386.0766
259.0393
216.0336
368.0655
387.0598
380.0612
384.0673
257.0248
366.0492
385.0420
382.0821
141.0776
386.0770
259.0389
216.0331
368.0665
387.0611
380.0665
384.0614
257.0232
366.0508
385.0454
C
C
14
H
9
16
N
N
4
5
O
O
6
S
+1.8
À7.8
À1.0
+1.5
+2.3
À2.7
À3.3
À5.3
+5.9
+1.6
À4.4
À8.8
8.1
0.6
7.3
8.8
8.5
8.8
7.8
8.4
8.9
6.3
7.9
8.0
+
5
H
+
P2
C H N O S
1
3
16
5
7
+
P3
C
9
H
11
N
2
O
5
S
+
P4
C H NO S
8
10
4
+
P5
C
C
13
H
H
13
14
N
N
5
O
O
6
S
S
+
P6
15
4
8
À
À
ESI–
MTSM
P2
C H N O S
1
4
14
5
6
C
13
H
14
N
5
O
7
S
À
P3
C H N O S
9 9 2 5
À
À
P5
C H N O S
1
3
12
5
6
P6
C
13
H
13
N
4
O
8
S
À
À
*
In ESI–, the given ratio is for [MÀH + 2] /[M–H] .
wileyonlinelibrary.com/journal/rcm
Copyright © 2015 John Wiley & Sons, Ltd.
Rapid Commun. Mass Spectrom. 2015, 29, 1370–1380

Triazine skeleton scission in sulfonylurea herbicides
CID spectral analyses of MTSM
In a first step, the fragmentation processes of MTSM were
studied in depth in positive and in negative ESU detection
mode (Fig. 2). This will be of great help for the elucidation
of products P1–P6. The accurate masses, elemental compo-
sitions and calculated masses of the various fragment ions
are gathered in Table 2. The CID spectrum obtained with a
collision energy of 20 eV shows an efficient fragmentation
+
À
of both precursors [MTSM + H] and [MTSM–H] . In
ESI+, three main peaks are clearly observed, m/z 199
(1d), 167 (1f), 141 (1 g), together with several minor
fragments ions m/z 242 (1a), 216 (1b), 210 (1c), 184 (1e),
and 135 (1 h). The fragmentation processes will be proposed
by taking into account the obtained elemental composition
given in Table
2 and by using the more favorable
protonation site of MTSM, namely the oxygen atom of
the carbonyl group.
The protonation of MTSM at the carbonyl group
Scheme 1) followed by the elimination of 2-amino-4-
methoxy-6-methyl-1,3,5-triazine through hydrogen transfer,
+
À
Figure 2. CID spectra of [MTSM + H] (A) and [MTSM-H]
(
(
B) obtained at a collision energy of 20 eV.
leads to the formation of the fragment ion 1a (m/z 242.0108)
+
with elemental composition C H NO S (error: À6.2 ppm).
9
8
5
negative ion mode. The elemental composition of each
product was obtained by extracting the accurate mass and
by using the elemental composition tool in the MassLynx
V4.1 software. We took care to keep the error within
Its main fragmentation gives rise to the ion 1d (m/z
199.0068; C H O S , error: +1.5 ppm) by the loss of NHCO
+
8
7
4
which then undergoes a desulfonation process yielding
+
ion 1 h with the elemental composition of C H O . Moreover,
8
7
2
±
10 ppm. Once the ion accurate mass had been obtained, this
the concurrent cyclization of 1a by the elimination of
methanol permits the formation of 1c (m/z 209.9875) corres-
was used as lock mass for the accurate mass measurements of
2
+
the generated fragment ions in MS experiments. For these
ponding to C H NO S with an error of +6.7 ppm.
8
4
4
fragment analyses, the accepted error was maintained within
A similar process involving the NH adjacent to the sulfonyl
group (Scheme 1) is the first step for the formation of the
most abundant fragment ion 1f under the used collision
energy. This also proceeds through hydrogen transfer and
the elimination of 2-(carbomethoxy) benzenesulfonamide.
The obtained accurate mass for 1f is m/z 167.0578 which
±
20 ppm.
The results from LC/MS in ESI+ as well as in ESI– mode
are gathered in Table 1. At first sight, the relative high isotope
+
abundance at [M + H + 2] (roughly 8%), owing mainly to the
34
presence of S, gives evidence, except in the case of P1, for
+
the presence of a sulfur atom in the chemical structure of all
is consistent with the elemental composition C H N O
2
6
7
4
[39]
the other generated products.
Prior to their identification,
(error: +5.4 ppm).
the performance of the QTOF mass spectrometry system was
first tested by the analysis of the starting compound, MTSM.
As clearly shown in Table 1, its elemental composition was
obtained with accepted errors of +1.8 ppm and À5.3 ppm in
the LC/MS ESI+ and ESI– mode, respectively.
The formation of the fragments ions 1b and 1 g, with
accurate masses of m/z 216.0351 and 141.0768, respectively,
may be through the protonation of the carbonyl group
and two hydrogens transfer processes, as shown in
+
Scheme 2. 1b with the elemental composition C H NO S
8
10
4
2
Table 2. Accurate and exact masses and elemental compositions of the fragment ions obtained from MTSM by LC/MS in
ESI+ and ESI– modes
Error
(ppm)
Fragment ion
m/z
Accurate mass
Elemental composition
Calculated mass
+
ESI+
1a
242
216
210
199
184
167
141
135
214
182
139
82
242.0108
216.0351
209.9875
199.0068
184.0051
167.0578
141.0768
135.0456
214.0159
181.9890
139.0605
82.0392
C H NO S
242.0123
216.0331
209.9861
199.0065
184.0068
167.0569
141.0776
135.0446
214.0174
181.9912
139.0620
82.0405
À6.2
+9.3
9
8
5
+
1
1
1
b
C H NO S
8
10
4
+
c
C
8
H
4
NO
4
S
+6.7
+
d
C H O S
+1.5
8
7
6
7
6
7
4
+
1
e
C
C
H
H
NO
3
S
À9.2
+
1
1
1
f
N O
4 2
+5.4
+
g
h
C H N O
À5.7
+7.4
5
9
4
+
2
C
8
H
7
O
À
À
ESI–
1i
C H NO S
À7.0
À12.1
À10.8
À15.8
8
7
5
8
4
7
4
1
1
1
j
C
C
H
H
NO
3
S
À
k
N
4
O
À
m
C H N
3 4 3
Rapid Commun. Mass Spectrom. 2015, 29, 1370–1380
Copyright © 2015 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/rcm

R. Chahboune, H. Mountacer and M. Sarakha
+
Scheme 1. Fragmentation pathways for [MTSM + H] permitting the
formation of fragment ions: 1a, 1c, 1d, 1f and 1 h.
The structures of P2, P3, P5 and P6 were elucidated by a
2
meticulous study of their LC/MS and LC/MS spectra.
+
Table 1 shows that they were all well detected in ESI and
À
ESI modes and incontestably contain one sulfur atom in
their chemical structures, as evidenced by the relative high
+
+
ratio [M + H + 2] /[M + H] , roughly 8.5%. Table 3 displays
all the data concerning the fragment ions as obtained using
a collision energy of 20 eV for the four compounds. Assuming
that all fragments are even-electron numbers (as observed in
the case of MTSM), the total number of nitrogen atoms in
the fragment ions can be known easily according to the parity
of the accurate mass.
+
Scheme 2. Formation of 1b, 1e and 1 g from [MTSM + H] .
(
error: +9.3 ppm) may lose ammonia giving rise to a
supplementary pathway for the formation of 1d and may
also eliminate methanol via a cyclization process, similar
Product P5
to that proposed for 1a, that permits the generation of 1e
+
(
m/z 184.0051) with the elemental composition C
7
H
6
NO
3
S .
P5 is formed from the early stages of the irradiation and
accumulates well in the solution for conversion lower than
40%. Its retention time is 9.8 min. Both ESI modes give accurate
masses that correspond to the neutral elemental composition
In contrast to the ESI+ results, the CID spectrum in
negative mode shows a limited number of fragment ions: 1i
214), 1j (182), 1 k (139) and 1 m (82) with 1 k as the most
abundant ion (Table 2 and Fig. 2). 1i and 1 k formed through
the deprotonation at the two NH groups (Scheme 3) and
concurrent scissions of the CO–N bonds. They have accurate
(
C
H
N
O
S with errors of À2.7 and À4.4 ppm by ESI+ and
13
13
5
6
ESI–, respectively (Table 1). Several interesting and abundant
fragment ions are observed in the ESI+ spectrum (Table 3).
Some of them are similar to those obtained for MTSM, e.g.
m/z 242 (1a), 210 (1c), 199 (1d) and 135 (1 h), implying the
conservation of the benzenesulfonamide structure. However,
the presence of the two fragments ions at m/z 153 and 127
(instead of 167 and 141 in the MTSM spectrum) indicates
chemical changes in the triazine part. Their accurate masses
masses of m/z 214.0159 and 139.0605, respectively, and
À
compatible with the elemental compositions C
8
H
8
NO
4
S
À
(
error: À7.0 ppm) and C
5
H
7
N
4
O
(error: À10.8 ppm). As
proposed above for 1a and 1b, the ion 1i permits formation
À
of 1j (m/z 181.9890; C H NO S ) by a cyclization process with
7
4
3
the loss of methanol while 1 k gives rise to 1 m (m/z 82.0392;
À
C H N ) through a triazine skeleton scission.
of m/z 153.0407 and 127.0614 confirm th+eir elemental
3
4
3
+
2
5 5 4
compositions to be C H N O
4 7 4
and C H N O
(errors: À3.9
and À4.7 ppm), respectively. Taking into account these results,
P5 evidently lacks the methoxy substituent and contains a
hydroxyl group instead. The analysis of the ESI– spectrum
confirms such a statement, since the intense ion at m/z 125
observed for P5 replaces that at m/z 139 (1 k) that was observed
in the MTSM spectrum while the other fragment ions remain
similar, e.g. 1j and 1 m. Scheme 4 displays the proposed
fragmentation scheme for P5 that arises from the
demethylation process of MTSM.
Product identifications
Products P1 and P4 were easily identified as 2-amino-
4
-methoxy-6-methyl-1,3,5-triazine and 2-(carbomethoxy)
benzenesulfonamide, respectively. Their elucidation was
based on comparison with authentic samples through their
retention times, LC/MS and UV spectra. Under our
2
experimental conditions, P1 and P4 were found to represent
11% and 16% of MTSM conversion, respectively.
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Copyright © 2015 John Wiley & Sons, Ltd.
Rapid Commun. Mass Spectrom. 2015, 29, 1370–1380

Triazine skeleton scission in sulfonylurea herbicides
Scheme 3. Formation of 1i, 1j, 1k and 1m obtained from the fragmentation
À
of [MTSM–H] . It is worth noting that, under our experimental
conditions, no SO2 elimination process occurs in the fragmentation of
[40]
sulfonylurea compounds in contrast to what is observed for sulfonamides.
Table 3. CID data in ESI+ and ESI– modes for products P2, P3, P5 and P6
Error
Product
m/z
Major ions
327
Accurate mass
Calculated mass
Elemental composition
(ppm)
+
ESI+
P2
386
327.0375
216.0310
199.0052
184.0084
171.0500
216.0312
199.0060
184.0085
242.0101
209.9863
199.0049
153.0407
135.0459
127.0614
242.0133
216.0321
209.9865
199.0055
184.0076
172.0368
146.0581
135.0457
130.0253
129.0300
87.0205
299.0431
257.0260
214.0175
181.9940
143.0556
126.0295
101.0339
84.0212
181.9932
181.9900
125.0479
82.0416
327.0399
216.0331
199.0065
184.0068
171.0518
216.0331
199.0065
184.0068
242.0123
209.9861
199.0065
153.0413
135.0446
127.0620
242.0123
216.0331
209.9861
199.0065
184.0068
172.0358
146.0566
135.0446
130.0253
129.0300
87.0195
299.0450
257.0232
214.0174
181.9912
143.0569
126.0304
101.0351
84.0198
181.9912
181.9912
125.0463
82.0405
C
11
H
10
11
N
4
O
6
S
À7.3
À9.7
À6.5
+8.7
À10.5
À8.8
À2.5
+9.2
À9.1
+1.0
À8.0
À3.9
+9.6
À4.7
+4.1
À4.6
+1.9
À5.0
+4.3
+5.8
+10.3
+8.1
0.0
+
2
1
1
1
16
99
84
71
C H NO S
8
8
7
4
+
C
C
H
H
7
O S
4
+
6
NO
3
S
3
+
C H N O
5
7
4
+
P3
P5
259
368
216
C
8
H10NO
4
S
+
1
1
99
84
C H O S
8
7
9
7
6
8
4
+
+
+
C
C
H
H
NO
NO
3
S
S
242
5
2
1
1
1
1
10
99
53
35
27
C H NO S
8
4
4
+
C
8
H
7
O
4
S
+
C H N O
5
8
4
5
7
7
4
2
+
C
C
H
H
O
2
+
4
N O
+
P6
387
242
C H NO S
9
8
5
+
2
2
1
1
1
1
1
1
1
16
10
99
84
72
46
35
30
29
C
8
H10NO
4
S
+
C H NO S
8
4
4
+
C H O S
8
7
4
+
C
7
H
6
NO
3
3
S
4
+
C H N O
5
4
8
6
8
7
+
C
C
H
H
N
2
3
O
3
+
O
+
+
+
C H N O
3
4
3
3
3
2
C
4
H
5
N
2
O
0.0
11.5
8
7
C H N O
2
3
2
À
ESI–
P2
384
299
C
10
H
H
9
11
N
N
2
4
O
5
S
À6.4
+10.9
+0.5
+9.3
À9.1
À7.1
À11.9
+16.9
+11.0
À6.6
+12.8
+13.4
À5.0
À7.8
+4.7
+9.9
À6.9
À11.8
+7.0
À11.9
À14.1
À
2
2
1
1
1
1
57
14
82
43
26
01
C
9
O
5
S
À
À
À
À
À
C H NO S
8
8
4
C
7
H
4
NO
3
S
C H N O
4
4
3
7
4
5
4
3
2
2
2
2
C
C
H
H
N
N
O
O
À
8
4
C H N O
2
2
3
À
P3
P5
257
366
182
182
C
7
H
4
NO
3
S
À
3
C H NO S
7
4
À
1
25
C H N O
4
5
4
À
8
2
C
3
H
4
N
10
3
À
6
P6
385
300
300.0275
257.0212
214.0184
181.9930
144.0399
127.0129
128.0105
101.0339
85.0026
300.0290
257.0232
214.0174
181.9912
144.0409
127.0144
128.0096
101.0351
85.0038
C H N O S
1
0
3
À
2
2
1
1
1
1
1
57
14
82
44
27
28
01
C
C
9
H
H
9
N
2
O
5
S
À
À
À
À
À
À
8
8
NO
4
S
C H NO S
7
4
3
C
4
H
6
N
3
O
3
3
3
2
C H N O
4
3
3
3
2
5
2
3
2
C
C
H
H
N
N
O
O
À
8
5
C HN O
2 2 2
Rapid Commun. Mass Spectrom. 2015, 29, 1370–1380
Copyright © 2015 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/rcm

R. Chahboune, H. Mountacer and M. Sarakha
Scheme 4. Fragmentation pathways for product P5 in ESI+ and ESI– at a collision energy of 20 eV.
The fragmentations that lead to m/z 242 (1a), 210 (1c), 199 (1d), 135 (1 h), 214 (1j) and 82 (1 m) are
similar to those proposed for MTSM.
Product P2
P2 presents a retention time of 8.4 min. Its neutral elemental
In ESI+ mode, two new additional ions were obtained,
namely m/z 327 and 171. Their accurate masses of m/z
327.0375 and 171.0500 are in agreement with the elemental
+
+
3
composition was found to be C H N O S (errors: À1.0
compositions C H N O S and C H N O (errors: À7.3
1
3
15
5
7
11 11
4
6
5
7
4
and +5.9 ppm in ESI+ and ESI–, respectively). It shows a
difference of 18 u (addition of a water molecule) when
compared to P5 implying its formation via a hydrolysis
process. The presence of fragments ions at m/z 216 (1b),
and À10.5 ppm), respectively. The CID data in ESI– mode
appears more informative and helpful since it shows the
emergence of several additional fragment ions, e.g. m/z 299,
257, 143, 126, 101 and 84. By taking into account these results,
an opening of the triazine cycle through the hydrolysis of
P5 may then be proposed for the formation of P2 (Scheme 5).
The generation of the fragment ions m/z 171, 327 (in ESI+)
and 299, 257, 143 and 101 (in ESI–) may be considered
to be the result of the successive NH group protonation
(or deprotonation in ESI– mode) and concurrent scission
1
99 (1d), 184 (1e) in ESI+ and 214 (1i), 182 (1j) in ESI–, that
are also obtained in the MTSM and P5 spectra, clearly
indicates that the hydrolysis reaction did not involve the
benzenesulfonamide moiety but the triazine part instead.
This is also confirmed by the absence of fragment ions at
m/z 167 and 141 in ESI+ and also at m/z 139 in ESI–.
Scheme 5. Formation of P2 and its fragmentation pathways upon ESI+ and ESI– at 20 eV collision energy. See
fragmentation mechanism in MTSM results for the formation of fragment ions 1b, 1d, 1e, 1i and 1j.
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Triazine skeleton scission in sulfonylurea herbicides
of NH–CO bonds, as displayed in Scheme 5. The ions at
m/z 126 and 84 more likely arise from a rearrangement process
of the fragment ion m/z 143 involving intramolecular
hydrogen atom transfer and leading to the loss of ammonia
and acetamide, respectively. They are more likely stable due
to the mesomeric effect of the adjacent structures.
(1Da difference). Figure 3 presents, for comparison purposes,
the CID spectra of [P6–H] and [P2–H] obtained at a collision
energy of 20eV.
À
À
As is clearly seen, the common fragment ions at m/z 214
À
(1i) and 182 (1j), also obtained in the [MTSM–H]
spectrum, are representative for the benzenesulfonamide
structure. P6 is then also the result of some modification
in the triazine moiety. Moreover, the presence of the
product ions m/z 257 and 101 (elucidated in Scheme 5) in
both spectra suggests the hydrolysis of the imine structure
C = NH to yield a carbonyl structure in slightly acidic
Product P6
P6 shows a retention time of 11.0 min. An accurate mass of
m/z 387.0598 (385.0420 in ESI–) matches the neutral elemental
composition C H N O S with an error of À3.3 ppm
[41,42]
medium (Scheme 6).
Since both products reveal similar
13
12
4
8
(
À8.8 ppm in ESI–). Its comparison with the structure of
chemical structures, one may suggest similar fragmentation
pathways leading to several product ions with 1 Da
difference, as clearly visible in Fig. 3 (Scheme 6). All the
chemical structures were confirmed by the elemental
composition as obtained through the determination of
accurate masses with tolerated errors (Table 3). The
formation of the ion m/z 128 in ESI–, corresponding to a
deprotonated form of cyanuric acid, arises from the intense
fragment ion m/z 144 through a cyclization process by the
loss of methane. CID in positive mode perfectly confirms
the proposed structures for product P6. The complete
fragmentation pathways are given in Supplementary Fig. S1
and Scheme S1 (see Supporting Information).
P2 guides us, at a first guess, that a direct substitution of
the NH group by an oxygen atom would seem possible
Product P3
P3 was observed at a retention time of 8.9 min. The accurate
masses in ESI+ (m/z 259.0393) and ESI– (m/z = 257.0248)
correspond to the neutral elemental composition of C
Its CID spectrum showed a limited number of fragment ions
Table 3). Those specific to the benzenesulfonamide part of the
9 10 2 5
H N O S.
(
molecule are present in both positive as well as in negative mode,
namely 1b, 1d, 1e and 1j. No additional product ions were
observed pointing to the loss of the entire triazine moiety in the
P3 structure. Taking into account these results, the scission of
À
Figure 3. Collision-induced dissociation spectra of [P6–H]
À
(
A) and [P2–H] (B) obtained at a collision energy of 20 eV.
Scheme 6. Formation of P6 and its fragmentation pathways upon ESI– at a collision energy of 20 eV. See
fragmentation mechanism in MTSM results for the formation of fragment ions 1b, 1d, 1e, 1i and 1j.
Rapid Commun. Mass Spectrom. 2015, 29, 1370–1380
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R. Chahboune, H. Mountacer and M. Sarakha
Scheme 7. Fragmentation pathways for P3 in ESI+ and ESI–.
the NH–triazine linkage may be involved more likely assisted by
(Scheme 9). These two compounds present roughly the same
triazine skeleton as metsulfuron methyl. They both clearly
show similar scissions of the triazine part with the formation
of two products that are similar to P2 and P6. Under our
experimental conditions, no differences in the fragmentation
pathways were observed. The LC/MS/MS spectra in
[24,30]
hydroxyl radicals.
The structure may be proposed as given
in Scheme 7, where the formation of the fragment ions is similar
+
À
to that proposed in the case of [MTSM +H] and [MTSM–H] .
Hydroxylated compounds
The hydroxylated compounds at the aromatic ring of MTSM
(m/z 398 in ESI+ and 396 in ESI-) were not directly observed in
the LC/MS spectrum. However, since hydroxyl radicals are
involved in the photochemical process, their formation is
more likely to happen under our experimental conditions as
[24,30]
largely proposed in the literature.
With the help of the
MassLynx V4.1 software, the selective extraction at their m/z
values clearly shows the presence of three hydroxylated
compounds with retention times of 11.0, 11.3 and 11.6 min
(Fig. 4). The ions of these three compounds were used as
precursor compounds, and the ion filtering function of the
used quadrupole system permitted only ions of m/z 398
Scheme 8. Fragmentation pathways for hydroxylated
compounds. The detail in the fragmentation is similar to that
(in ESI+) to pass to the collision cell. Thus the MS/MS
+
reported for [MTSM + H] .
spectra can be obtained even in the presence of other
products under the LC/MS conditions.
In ESI+ experiments, commons fragment ions with
+
+
[
MTSM + H ] are present, e.g. m/z 167 and 141, implying the
conservation of the triazine part of the molecule. However,
the presence of ions at m/z 215 and 151 clearly indicates
that the hydroxylation process occurs at the aromatic ring in
agreement with the results reported in the literature
[
24,30]
Scheme 9. Chemical formulas of cinosulfuron and
thifensulfuron methyl.
(Scheme 8).
The CID data are presented in Supplementary
Table S1 (see Supporting Information).
The complete study was extended to two other sulfonylurea
compounds, namely cinosulfuron and thifensulfuron methyl
Figure 5. Kinetic evolution of products P2, P5 and P6.
À4
À1
Irradiation at 365 nm of metsulfuron methyl (1.0 × 10 mol L
)
À4
À1
Figure 4. Selective detection at m/z 398 (ESI+) and 396 (ESI–)
for the formation of hydroxylated compounds.
in the presence of iron(III) (3.0×10 mol L ) (pH3.5 and
detection wavelength 230 nm).
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Copyright © 2015 John Wiley & Sons, Ltd.
Rapid Commun. Mass Spectrom. 2015, 29, 1370–1380

Triazine skeleton scission in sulfonylurea herbicides
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[
[
In the present study an unequivocal elucidation of the
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the CID spectra in both ESI+ and ESI– modes. The reaction
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Rapid Commun. Mass Spectrom. 2015, 29, 1370–1380