Environmental Science and Pollution Research https://doi.org/10.1007/s11356-017-0814-4
ADVANCED OXIDATION PROCESSES FOR WATER/WASTEWATER TREATMENT
Transformation of sulfaquinoxaline by chlorine and UV light in water: kinetics and by-product identification Rania Nassar 1 & Samia Mokh 2 & Ahmad Rifai 2 & Fatmeh Chamas 1 & Maha Hoteit 1 & Mohamad Al Iskandarani 1,2 Received: 15 August 2017 / Accepted: 20 November 2017 # Springer-Verlag GmbH Germany, part of Springer Nature 2017
Abstract Sulfaquinoxaline (SQX) is an antimicrobial of the sulfonamide class, frequently detected at low levels in drinking and surface water as organic micropollutant. The main goal of the present study is the evaluation of SQX reactivity during chlorination and UV irradiations which are two processes mainly used in water treatment plants. The SQX transformation by chlorination and UV lights (254 nm) was investigated in purified water at common conditions used for water disinfection (pH = 7.2, temperature = 25 °C, [chlorine] = 3 mg L−1). The result shows a slow degradation of SQX during photolysis compared with chlorination process. Kinetic studies that fitted a fluence-based first-order kinetic model were used to determine the kinetic constants of SQX degradation; they were equal to 0.7 × 10−4 and 0.7 × 10−2 s−1corresponding to the half time lives of 162 and 1.64 min during photolysis and chlorination, respectively. In the second step, seven by-products were generated during a chlorination and phototransformation of SQX and identified using liquid chromatography with electrospray ionization and tandem mass spectrometry (MS-MS). SO2 extrusion and direct decomposition were the common degradation pathway during photolysis and chlorination. Hydroxylation and isomerization were observed during photodegradation only while electrophilic substitution was observed during chlorination process. Keywords Sulfaquinoxaline . Disinfection . Chlorination . UV photolysis . Kinetic study . By-products . LC-MS-MS
Introduction Antibiotics are organic micropollutants of great interest due to their occurrence in the aquatic environments. According to Baran et al. (2011), the worldwide consumption of antibiotics ranged from 100,000 to 200,000 t per year, including 50–75% that was used in veterinary medicine and animal husbandry. Sulfonamide (SN) antibiotics such as sulfaquinoxaline (SQX) are among the most important families due to their extensive use in veterinary medicine (Le fur et al. 2013). SQX has been widely used to prevent coccidiosis in poultry, swine, and sheep (Campbell 2008). It inhibits the synthesis of nucleic Responsible editor: Philippe Garrigues * Mohamad Al Iskandarani
[email protected] 1
Faculty of Public Health I, Lebanese University, Hadath, Lebanon
2
Laboratory for Analysis of Organic Compound LACO, National Council for Scientific Research CNRS, Lebanese Atomic Energy Commission LAEC, 11-8281, Riad El Solh, Beirut 1107 2260, Lebanon
acids and proteins in microorganisms (Hoff et al. 2014). SQX has been detected in surface water at concentrations ranging from 1.59 to 640 ng L−1, in groundwater at concentrations of 39.4 ng L−1 and in effluent at concentrations from 0.15 to 350 ng L−1 (Urbano et al. 2016). SQX consists of a sulfa and a quinoxaline group (Hoff et al. 2012). According to the literature, sulfas do not show high toxicities to larger organisms and human beings (De Liguoro et al. 2010); however, quinoxaline exhibits mutagenic and carcinogenic activities (Liao et al. 2016). Furthermore, the presence of SQX in environmental water can facilitate the proliferation of antimicrobial resistant microorganisms (Boxall et al. 2003; Doretto et al. 2014). Surface and groundwater are the main source of drinking water; therefore, it seems important to predict the behavior of SQX during chlorination and UV irradiation, the two most important processes used in water treatment plants because of their efficiency for disinfection (Klavarioti et al. 2009; Acero et al. 2010). Free chlorine including HOCl and ClO− species is applied for water disinfection due to its low cost and high activity for oxidation (Li et al. 2013). However, chlorination is rarely used for oxidation of micropollutants because the reaction can
Environ Sci Pollut Res
produce biologically active transformation products (El Najjar et al. 2013). Therefore, the behavior of SN during reaction with chlorine has been the aim of many studies, and several authors reported that free chlorine can react with SNs and reaction rates were first-order in both substrate and oxidant (Chamberlain and Adams 2006). In addition, other researchers identified oxidation by-products and proposed degradation pathways of reaction with chlorine (Gaffney et al. 2016; Dodd and Huang 2004). In another hand, ultraviolet (UV) treatment of water is being increasingly used for disinfection of wastewater and drinking water in North America, Europe, and numerous other countries around the world (Avisar et al. 2010). Numerous chemical contaminants as SQX absorb UV at wavelengths below 300 nm; hence, these can potentially undergo direct photolysis (Shemer et al. 2005). Cui et al. (2016) reported recently the removal of 12 SNs from drinking water by UV photolysis and calculated its first-order rate constants. Recently, Le fur et al. (2013) identified the generated byproducts of SQX after UV irradiation at pH 4.0 which is very low compared with drinking water one. Indeed, studies using UV irradiation to determine the kinetic rate constant of SQX photolysis and to identify the by-product structures under common condition of water disinfection are rare and to date, the oxidation of SQX by chlorine has not been the subject of intensive research. Therefore, our work focused on the behavior of SQX during chlorination and UV irradiations at pH 7.2. The aim of this study were to report the direct photolysis and chlorination rate constants, to calculate the quantum yield, and to identify the generated by-products by using highperformance liquid chromatography coupled to a tandem mass spectrometer (LC-MS-MS).
Materials and methods Chemical reagents SQX (purity > 97.5%) was purchased from Dr. Ehrenstorfer (Sigma-Aldrich). Sodium hydroxide was obtained from Riedel de Haen. N,N-diethyl-p-phenylenediamine (DPD), ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA), potassium iodide (KI), and organic solvents were purchased from Sigma-Aldrich. Ascorbic acid (C6H8O6) and orthophosphoric acid (85% of purity) was obtained from J.T. Baker. Chlorine stock solutions were prepared by dilution of commercial 5% sodium hypochlorite solution and standardized iodometrically. All the solutions are prepared using purified water (resistivity of 18.2 MΩ cm and dissolved organic carbon lower than 0.1 mg L−1) obtained with Barnstead-Easy pure II from Thermo Fisher Scientific (Hudson, USA).
Kinetic and by-product identification experiments UV irradiation (254 nm) experiments were performed in purified water at pH adjusted to 7.2 using phosphate buffer (Dodd and Huang 2004; Chamberlain and Adams 2006) with initial SQX concentration of 0.14 μM. The irradiation setup was a batch photoreactor (volume of irradiated solution 2 L, optical path length 3.6 cm). The lamp (Vilber-Lo urmat T6C–254 nm, low-pressure Hg lamp 6 W) was located at the center of the reactor, in a quartz sleeve. The photon fluence rate (I0) was evaluated by hydrogen peroxide (H2O2) actinometry as described Nicole et al. (1990). The photolysis of H2O2 was performed during 30 min with absorbance of actinometric solution less than 0.02. Known that the quantum yield of H2O2 photolysis is equal to 1, the value of I0 was calculated to be 1.36 × 10−6 E L−1 s−1. Hydrogen peroxide concentrations were measured by the Ti-complexometry method described by Eisenberg (1943). The reactor was thermostated at 298 K and wrapped with an aluminum foil. Kinetic chlorination studies were conducted in a 500-mL Pyrex glass sealed reactor surrounded by an aluminum foil to avoid light effect, and maintained under magnetic stirring. Experiments were performed in triplicate with initial chlorine concentrations of 35, 40, 45, and 50 μM at 25 °C and pH 7.2. At this pH, hypochlorous acid (HOCl) is the main oxidizing agent according to pKa value of HOCl/ClO−. pKa values of SQX were reported at 2.3 and 5.9 (Abdallah et al. 2014). Chlorination kinetics started by mixing the appropriate volumes of chlorine stock solutions to SQX (1.4 μM). At scheduled time, 1.0 mL of solution was transferred into vials containing 100 μL of ascorbic acid (1 mM) in order to quench the chlorination reaction. Then, for checking if the ascorbic acid concentration was in excess via the chlorine one, a sample containing SQX and ascorbic acid with corresponding concentrations was injected into high-performance liquid chromatography system coupled to a photo-diode array (HPLCDAD) without and with chlorine, respectively. No variation of SN concentrations was shown. In another hand, the presence of amine group in the molecular structure, reducing agent, could have an effect on the kinetic experiments by reacting with by-products for giving a reversal reaction to obtain the initial structure of the molecule (Yassine et al. 2017b). Therefore, for checking the feasibility of using ascorbic acid for quenching the chlorine action, unquenched samples were directly injected into the HPLC-DAD at different reaction times. No significant effect of ascorbic acid was observed accordingly (Fig. 1). In the experiments, the variation of chlorine concentration (measured by DPD procedure) was less than 5% and no pH variation was observed. Samples were analyzed using HPLC-DAD. The by-product identification experiments of photolysis and chlorination were performed with initial concentration of SQX of 5 μM at pH 7.2 and the last one was performed
Environ Sci Pollut Res 1
respectively. The limit of detection (LOD) and limit of quantification (LOQ) of DANO were determined by using a minimum signal to noise value of 3 for LOD and 10 for LOQ. LOD and LOQ values were determined to be 0.01 and 0.016 μM, respectively.
[SQX]/[SQX]0
0.8 0.6 0.4 0.2 0
Results and discussion 0
0.5
1
1.5
2
2.5
Time (min)
Fig. 1 Comparison between SQX chlorination kinetic by HPLC direct injection (multiplication sign) and by using ascorbic acid (white square) as quenching method with [SQX]0 = 1.4 μM and [chlorine] = 40 μM (pH 7.2 and 25 °C)
in equimolar concentration between chlorine and SQX without reaction quenching. One-milliliter samples were collected and analyzed by LC-MS-MS at 6 and 3 h of photolysis and chlorination, respectively, the time when more than 70% of SQX was degraded and all the by-products were presents in the solution.
Analytical method UV-vis spectra were recorded on a Hitachi high-technology spectrophotometer (U-2900 UV/VIS Spectrophotometer 200 V) equipped with a quartz cell of a 1-cm path length. The molar absorption coefficient at 254 nm was calculated by measuring the absorbance of solutions at known concentrations (pH = 7.2). Residual SQX concentrations were determined by a highperformance liquid chromatography system (LC-20— Shimadzu) coupled to a photo-diode array (PDA) (SPDM20A—Shimadzu). An Agilent Eclipse C18 (250 mm × 4.6; 5 μM) was used for SQX separation performed from a mobile phase of 60% water and 40% acetonitrile, flowing at 0.5 mL min−1and the sample injection volume was set to 50 μL. The structural identification of by-products was carried out with an Agilent 1200 LC system (Agilent Technologies, USA) coupled to an Agilent 6410 triple quadrupole mass spectrometer (LC-MS-MS). The eluents and columns used for the separation of the parent compound and its by-products were the same as those of HPLC-DAD analyses. The flow rate was set to 0.6 mL min −1 . Detection was performed with an electrospray ionization (ESI) source operating in positive mode. The following conditions were set: source temperature 450 °C and capillary voltage 3000 V. The collision energy (CE) was adjusted from 5 to 30 V to obtain the fragmentation patterns when performing product ion scans. Nitrogen was used as collision gas and nebulization gas at 30 and 40 psi,
UV-vis absorption spectra and kinetic data Figure 2 shows the UV-vis absorption spectra of SQX (23 μM) in purified water at pH 7.2. It displays maxima at 205, 248, and 263 nm. The molar absorption calculated at 254 nm was of 35,043 M−1 cm−1. The result of UV254 photolysis in purified water showed that 80% of SQX was removed after 4 h of irradiation. The photodegradation pattern of SQX was adjusted to the pseudo-first-order kinetic model, which assumes a decrease of the concentration through time proportional to the concentration remaining in purified water. The model follows: ln ½SQX=½SQX0 ¼ −kapp t ð1Þ where [SQX]0 and [SQX] are the SQX concentrations (M), respectively, before and during irradiation; kapp is the apparent first-order reaction rate constant (s−1); and t is the irradiation time (s). Aqueous solutions of SQX (0.14 μM) were irradiated at 254 nm. A disappearance of SQX is observed according to the reaction: SQX→degradation products ¼ ϕðSQXÞ I 0 1‐10‐A
with–d½SQX=dt ð2Þ
where ϕ(SQX) is the quantum yield of degradation at 254 nm, I0 is the photon fluence rate of the irradiation source (I0 = 1.36 × 10−6 E L−1 s−1), and A is the absorbance at 254 nm. Working concentration was chosen such as the absorbance at 254 nm is lower than 0.02 amu (hyper dilute medium). Thus, the rate of photodegradation of SQX can be simplified from (2) to (3) (Cui et al. 2016): ‐d½SQX=dt ¼ 2:303 AϕðSQXÞ I 0
ð3Þ
Equation (1) indicates that the photodegradation of SQX follows to an apparent first-order kinetic law. Thus, the expression of the monochromatic quantum yield is: ϕðSQXÞ ¼ kapp = 2:303 I 0 εSQX ℓ ð4Þ where ϕ(SQX) is the quantum yield of degradation at 254 nm, kapp is the apparent first-order reaction rate constant (s−1), I0 is the photon fluence rate of the irradiation source, ɛSQX is the molar absorption coefficient of the drug at 254 nm, and ℓ is the
Environ Sci Pollut Res Fig. 2 UV-vis absorption spectra of SQX (23 μM) in purified water at pH 7.2
90000
(mol-1 L-1 cm-1)
80000 70000 60000 50000 40000 30000 20000 10000 0 200
250
300
350
400
450
Wavelenght (nm)
internal radius of the reactor minus the radius of the monochromatic lamp (the UV source was placed at the center of the reactor). Apparent first-order rate constant (kapp) obtained for SQX photodegradation was determined from the slope of the linear time-course plot of ln([SQX]t/[SQX]0) (Fig. 3a) to be Fig. 3 Pseudo-first-order kinetic plot of SQX (0.14 μM) photolysis (a) and SQX (1.4 μM) chlorination (b) at pH 7.2
equal to 0.7 × 10−4 s−1 and the calculated quantum yield was 1.8 × 10−4. The photolysis rate constant of SQX obtained in our experiments was not close to those determined by Cui et al. (2016) after photolysis of 12 other sulfonamides. In the latest research, kapp values were at least 46 times fold higher Time (min)
ln [SQX]t/[SQX]0
0
0
100
-0.2
300
200
a)
y = -0.0043x + 0.0147 r² = 0.9962
-0.4 -0.6 -0.8 -1
b)
Time (min)
ln [SQX]t/[SQX]0
0 -0.4 -0.8 -1.2 -1.6 -2
0
1
2
3 y = -0.2439x r² = 0.9646
35 µM
40 µM
y = -0.4173x - 0.0077 r² = 0.9928 y = -0.5541x - 0.0492 r² = 0.9874
y = -0.6722x - 0.0306 r² = 0.9953
45 µM
50 µM
Environ Sci Pollut Res
than that of SQX photolysis due to the difference between irradiation systems and may be due to the special structure of SQX with quinoxaline moiety. In another hand, Nassar et al. (2017) reported the photodegradation of neutral species of sulfamethazine and sulfamethoxypyridazine with the same irradiation system employed in our study. The first-order rate constants obtained were equal to 0.9 × 10−3 and 1.1 × 10−3 min−1 which are approximately four fold lower than that of SQX anionic species. The latest result is in agreement with that obtained by Lian et al. (2015) who reported the UV254 photolysis of eight SNs. In fact, Lian and colleagues’ result showed that an increasing pH induced a hyperchromic effect and a blue shift of the UV-vis absorption spectra of selected SAs; thus, causing the anionic species to show a relatively higher specific ε value than the neutral species at 254 nm. The chlorination kinetic experiments were performed in the presence of a large excess of chlorine (35 < [chlorine] < 50 μM). The reaction is of apparent first-order with respect to SQX concentrations (Yassine et al. 2017a): d½SQX=dt ¼ k:½chlorine:½SQX
ð5Þ
d½SQX=dt ¼ kapp :½SQX
ð6Þ
where [SQX] and [chlorine] are the initial concentrations (M), respectively, of SQX and chlorine; k is the second-order rate constant of chlorination reaction (M−1 s−1); and kapp is the apparent first-order rate constant (s−1). The second-order rate constant was calculated by dividing the measured apparent first-order rate constant by the initial concentration of chlorine. Apparent first-order rate constants (kapp) obtained for chlorination were determined from the slopes of the linear time-course plot of ln([SQX] t /[SQX] 0) (Fig. 3b) to be enclosed between 4.0 × 10−3 and 11.2 × 10−3 s−1. The inset in Fig. 3b showed the reaction order relative to chlorine by representing kapp variation as function of chlorine concentrations. This figure illustrates that the apparent first-order kinetic constants were proportional to the chlorine concentrations with correlation coefficients r 2 = 0.99. The calculated second-order constants were enclosed between 114 and Table 1
134 M−1 s−1. These rate constants are considering low per comparison with the data concerning the chlorination of other SNs. The second-order rates obtained by Chamberlain and Adams (2006) after chlorination of six SNs were enclosed between 348 and 19,710 M−1 s−1 in distilled water at pH 7.6 and those reported by Adams et al. (2002) for three SNs at pH 7.5 were enclosed between 884 and 2651 M−1 s−1. These data do not correlate with our results due to the difference at initial experimental conditions d and may be due to the special structure of SQX.
By-product identification The antibiotic SQX yielded to the formation of four byproducts (SQX-1 to SQX-4) during 6 h of irradiation at 254 nm and three by-products (SQX-I to SQX-III) during 3 h of reaction with chlorine. LC-MS-MS analyses were performed in a positive mode. In addition, scanning mode performed in the range between m/z 50 and 500 and product ion scan mode were used to facilitate the proposition of byproduct structures and results that are gathered in Table 1. During SQX degradation, photoproducts showed m/z of 237.1 (SQX-1 and SQX-2), 146.0 (SQX-3), and 253.3 (SQX-4). All the photoproducts were eluted before SQX; therefore, they are more polar than SQX (Hamilton 1998). SQX-1 and SQX-2 are isomers formed after SO2 extrusion from SQX which is the main photochemical transformation process as previously reported for other sulfonamides (Cui et al. 2016; Nassar et al. 2017; Liao et al. 2016). SQX-1 and SQX-2 were proposed to be formed from the condensation of the aniline and the 2-aminoquinoxaline moieties. SQX-1 and SQX-2 structures were elucidated by MS-MS analysis at different CE (Fig. 4a, b). These two photoproducts were identified by Le fur et al. (2013) using LC/ESI-QTOFMS and the ion product spectra were similar. Indeed, unless the product ions at m/z 210 and 129, the fragmentation spectrum of SQX1 and SQX-2 showed the same product ions. SQX-1 and SQX-2 lost NH3(− 17), benzimidazole (− 118), quinoxaline
LC-MS-MS ESI+ analyses of SQX and its by-products
Photolysis
Chlorination
Name
Retention time (min)
m/z
Fragments
SQX SQX-1 SQX-2 SQX-3 SQX-4 SQX-I SQX-II SQX-III
15.7 10.5 15.1 12.9 14.0 13.0 14.9 17.6
301.0 237.1 237.1 146.0 253.3 146.0 237.1 334.9
208.0 (15), 156.0 (85), 146.1 (30), 108.0 (100), and 92.1 (85) 237.1 (100), 220.2 (30), 119.1 (35), 107.9 (30), and 92.2 (20) 237.1 (100), 220.2 (10), 118.9 (15), 107.9 (85), and 93 (15) 146 (30), 129.1 (100), and 102.1 (30) 253.3 (15) and 235.8 (100) 146.0 (100) and 128.9 (20) 237.1 (20), 118.9 (10), 107.9 (100), and 93.1 (22) 189.9 (95), 141.9 (100), 126 (100), and 89.7 (10)
Environ Sci Pollut Res x10 2 +ESI Product Ion:2 (15.133 min) Frag=100.0V
[email protected] (237.0 -> **) SQX pp4 h 20.d
a)
237.1
1
-129
NH2
107.9
0.9
H N
N
-118
0.8
-144
-17
N
0.7
NH2
NH2
0.6 0.5
NH2
SQX
H N
N
0.4 0.3
+
118.9
93.0
0.2
+
N
N
220.2
+
0.1 NH2
0 60
80
100
120
140
160
180
200 220 240 260 280 Counts vs. Mass-to-Charge (m/z)
x10 2 +ESI Product Ion:1 (10.580 min) Frag=100.0V
[email protected] (237.0 -> **) SQX pp4h 25.d
-118 -145
+
340
360
380
NH2
400
b)
-17
-109
NH2
0.8
-129 N
0.7
NH
N
NH2
0.6
NH2
-27
N
119.1
0.4
NH
N
NH2
0.5
N
220.2
+ N
0.3 0.2
320
237.1
1 0.9
300
+
92.2 65.0
+
+
NH2
N
N
210.0
128.8
0.1
N
0 60
80
100
120
140
160
180
200 220 240 260 280 Counts vs. Mass-to-Charge (m/z)
300
320
340
360
380
400
x10 2 +ESI Product Ion:2 (12.976 min) Frag=100.0V
[email protected] (146.0 -> **) SQX pp4 h 20.d 129.1
1
c)
N
+
0.9 0.8 0.7
N
+ -44
0.6
-17
N
N
0.5
NH2
0.4 146.0
102.1 0.3
N
0.2 0.1 0 60
80
100
120
140
160
180
200 220 240 260 280 Counts vs. Mass-to-Charge (m/z)
300
320
Fig. 4 MS-MS spectra obtained at different CE for SQX-1 (a), SQX-2 (b), SQX-3 (c), and SQX-4 (d and e)
340
360
380
400
Environ Sci Pollut Res
radical (−129), and quinoxalin-2-amine (−145) to give ions at m/z 220, 119, 108, and 93, respectively, while SQX-1 lost HCN (− 27) and benzene-1,4-diamine (− 108) to give the product ions at m/z 210 proposed to be (E)-6-((4aminophenyl)imino)-5-(methyleneamino)cyclohexa-2,4dien-1-ylium and 129 (quinoxaline ion). C8H8N3 was proposed as elemental composition of SQX-3. This photoproduct can be assigned as 2-aminoquinoxaline formed probably after the loss of aniline group and the extrusion of SO2 from SQX (Fig. 4c). [SQX-3+H]+ lost NH3 (− 17) to give quinoxaline moiety (m/z 129) followed by the loss of HCN (− 27) to give the ion at m/z 102 proposed to be 7-azabicyclo[4.2.0]octa1,3,5,7-tetraen-5-ylium. The proposed structure of SQX-4 occurred due to SO2 extrusion followed by the hydroxylation of aniline ring. MS-MS fragmentation spectrums presented in Fig. 4d, e showed that the product ion at m/z 235.8 might be formed after NH3 loss from SQX-4 and ions at m/z 148 and 123 represented probably the hydroxylated 3-amino6-(ethynylamino)cyclohexa-2,4-dien-1-ylium and hydroxylated aminoaniline, respectively. The low intensity of pics present in Fig. 4e was due to the high intensity of collision energy (35 V) compared with the other fragmentation spectrums.
The three by-products formed during chlorination of SQX show m/z of 146 (SQX-I), 237 (SQX-II), and 334.9 (SQX-III). Indeed, the MS-MS fragmentation spectrum of SQX-I SQX-II (Fig. 5f, g) were same to those obtained for the two photoproducts SQX-3 and SQX-2, respectively, which indicates that these by-products had the same structures. Therefore, SO2 extrusion and direct decomposition of SQX can be considered as a common degradation pathway during chlorination and photolysis. SQX-III was proposed as primary chloramine identified by the mass spectral isotope pattern on the molecular ion. The proposed structure of SQX-III was formed after electrophilic substitution occurred on the amine group of aminobenzene moiety as explained in the previous studies of other SNs (Garcia-Galan et al. 2008; Dodd and Huang 2004). The MS-MS spectrum of SQX-III (Fig. 5h) showed three product ions at high intensities (> 90%). The product ion at m/z 189.9 arises probably from the loss of aminoquinoxaline moiety from SQX-III. The loss of aminoquinoxaline was followed by the loss of SO2 (− 64) to give the ion product at m/z 126. The ion at m/z 142 might correspond to N1chlorobenzene-1,4-diamine radical ion.
x10 2 +ESI Product Ion:1 (14.042 min) Frag=100.0V
[email protected] (253.0 -> **) SQX pp4h 25.d 1 235.8
d)
0.9 0.8
H N
N
0.7
-17
0.6
+
N
0.5
N
H N
OH
0.4 NH2
N
0.3 91.6
253.3
0.2 65.9
137.3
109.5
176.2
207.7
276.0
303.3
372.7
330.7 347.6
398.9
0.1 0 60
80
100
120
140
160
180
200 220 240 260 280 Counts vs. Mass-to-Charge (m/z)
300
320
340
360
380
x10 1 +ESI Product Ion:1 (14.243 min) Frag=100.0V
[email protected] (253.0 -> **) SQX pp4h 35.d 148.0
5
e)
OH
H2N
400
4.5 OH
H2N
4 3.5
+
3
+
-130
NH2
-105
N H N
H N
OH
122.8 2.5 NH2
N
2 1.5
65.1
82.7
99.9
80
100
134.6
192.3 165.4
218.5
261.8 279.3
303.6
331.1
358.4
388.1
1 0.5 0 60
Fig. 4 (continued.)
120
140
160
180
200 220 240 260 280 Counts vs. Mass-to-Charge (m/z)
300
320
340
360
380
400
Environ Sci Pollut Res x10 2
+ESI Product Ion:2 (13.052 min) Frag=100.0V
[email protected] (146.0 -> **) SQX chlore 10 min pp1simscan10.d N
-17 0.9
f)
146.0
1
NH2
-44 N
0.8
+ N
0.7 N
0.6 0.5 0.4
+
0.3
N
0.2
128.9
0.1 0 60
x10 2
80
100
120
140
160
180 200 220 240 260 280 Counts vs. Mass-to-Charge (m/z)
300
320
340
360
380
+ESI Product Ion:3 (14.945 min) Frag=100.0V
[email protected] (237.0 -> **) SQX chlore 1.30h pp1simscan 30.d 108.1
1
g)
NH2
0.9
400
H N
N
0.8 NH2
-129
0.7
NH2
+.
N
NH2
-145 -118
0.6
-17 NH2
0.5
+ 0.4 0.3
93.0 N
0.2
119.2
+
H N
N
237.2
0.1
+ N
0 60
80
100
120
140
160
180 200 220 240 260 280 Counts vs. Mass-to-Charge (m/z)
300
320
340
360
380
x10 2 +ESI Product Ion:1 (17.629 min) Frag=100.0V
[email protected] (335.0 -> **) SQX chlore 10 min pp1simscan 20.d 141.9
1
+.
NH2
0.9
h)
189.9
-209
400
-193
N O
+
0.8
S
-127
0.7 Cl
0.6 0.5
S
O
-145
O
360
380
-102
Cl
O
S+
0.4
O
N
O
N
+ S
0.3
O
NH
N H
Cl
0.2
N
N H
HN
NH
N H
Cl
+
NH
O
89.7
208.0
0.1
NH
334.9
N H
232.7
Cl
0 60
80
100
120
140
160
180
200 220 240 260 280 Counts vs. Mass-to-Charge (m/z)
Fig. 5 MS-MS spectra obtained at different CE for SQX-I (f), SQX-II (g), SQX-III (h)
300
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Environ Sci Pollut Res
Conclusion The UV254 photolysis and the chlorination of SQX were investigated in purified water under common conditions used during water disinfection. The kinetic data obtained showed that SQX can be removed from drinking water during chlorination while no degradation was expected during UV disinfection because in real water treatment conditions the reaction time for UV is much lower than that observed in our study. However, the two processes yielded to the formation of several by-products with unknown toxicity. The MS-MS analysis allowed to propose the by-product structures and to indicate that photolysis and chlorination of SQX had common pathways explained by the generation of two common by-products after SO2 extrusion or molecule decomposition while electrophilic substitution and hydroxylation was observed during chlorination and photolysis, respectively. The proposed structures of SQX by-products could be confirmed by LC/ESIQTOFMS to help researchers study and predict their toxicity.
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