Photolysis and photocatalysis of ibuprofen in aqueous medium: Characterization of by-products via liquid chromatography coupled to high-resolution mass spectrometry and assessment of their toxicities against Artemia Salina

Article abstract of DOI:10.1002/jms.3320

The degradation of the pharmaceutical compound ibuprofen (IBP) in aqueous solution induced by direct photolysis (UV-A and UV-C radiation) and photocatalysis (TiO₂/UV-A and TiO₂/UV-C systems) was evaluated. Initially, we observed that whereas photocatalysis (both systems) and direct photolysis with UV-C radiation were able to cause an almost complete removal of IBP, the mineralization rates achieved for all the photodegradation processes were much smaller (the highest value being obtained for the TiO ₂/UV-C system: 37.7%), even after an exposure time as long as 120 min. Chemical structures for the by-products formed under these oxidative conditions (11 of them were detected) were proposed based on the data from liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) analyses. Taking into account these results, an unprecedented route for the photodegradation of IBP could thus be proposed. Moreover, a fortunate result was achieved herein: tests against Artemia salina showed that the degradation products had no higher ecotoxicities than IBP, which possibly indicates that the photocatalytic (TiO₂/UV-A and TiO₂/UV-C systems) and photolytic (UV-C radiation) processes can be conveniently employed to deplete IBP in aqueous media. Copyright

Full text of DOI:10.1002/jms.3320

Research article
Received: 16 September 2013
Revised: 20 November 2013
Accepted: 28 November 2013
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/jms.3320
Photolysis and photocatalysis of ibuprofen in
aqueous medium: characterization of by-
products via liquid chromatography coupled to
high-resolution mass spectrometry and
assessment of their toxicities against
Artemia Salina
Júlio César Cardoso da Silva,a Janaina Aparecida Reis Teodoro,a
Robson José de Cássia Franco Afonso,b Sérgio Francisco Aquinob
and Rodinei Augustia*
The degradation of the pharmaceutical compound ibuprofen (IBP) in aqueous solution induced by direct photolysis (UV-A and
UV-C radiation) and photocatalysis (TiO2/UV-A and TiO2/UV-C systems) was evaluated. Initially, we observed that whereas
photocatalysis (both systems) and direct photolysis with UV-C radiation were able to cause an almost complete removal of
IBP, the mineralization rates achieved for all the photodegradation processes were much smaller (the highest value being
obtained for the TiO2/UV-C system: 37.7%), even after an exposure time as long as 120 min. Chemical structures for the by-
products formed under these oxidative conditions (11 of them were detected) were proposed based on the data from liquid
chromatography coupled to high-resolution mass spectrometry (LC-HRMS) analyses. Taking into account these results, an unprec-
edented route for the photodegradation of IBP could thus be proposed. Moreover, a fortunate result was achieved herein: tests
against Artemia salina showed that the degradation products had no higher ecotoxicities than IBP, which possibly indicates that
the photocatalytic (TiO2/UV-A and TiO2/UV-C systems) and photolytic (UV-C radiation) processes can be conveniently employed
to deplete IBP in aqueous media. Copyright © 2014 John Wiley & Sons, Ltd.
Keywords: photodegradation; ibuprofen; high-resolution mass spectrometry; liquid chromatography; characterization of by-products
has been properly assessed by studies with brine shrimp (Artemia
Introduction
salina), an organism that is particularly sensitive to the degree of
toxicity of organic compounds in solution.[20–24]
The presence of various pharmaceutical pollutants in the envi-
ronment has received much attention because of their unknown
impact on flora and fauna present in aquatic systems.[1,2] These
compounds have been detected in natural aquatic environments
at trace concentrations (from ng LÀ1 to μg LÀ1).[3–7] The major
sources of these pollutants arise from emissions of production
sites, direct disposal of over plus drugs in households and hospi-
tals, excretion of urine or feces after drug administration to
humans/animals and water treatment in fish farms.[8]
To improve the efficiency of removal of pharmaceutical com-
pounds in aqueous media, novel and powerful technologies have
been developed, especially the so-called advanced oxidation pro-
cesses (AOPs). Moreover, there has been a growing interest in the
detection and identification of degradation products resulting
from the application of AOPs.[9,10] Among the AOPs, the following
processes are noteworthy: photolysis,[11–16] photocatalysis,[17]
electrochemistry and photoelectrochemistry.[18,19] However,
many challenging issues still remain, which are mainly related to
the fact that products arising from the degradation of pollutants
may present higher toxicity than their predecessors. This possibility
The compound 2-[3-(2-methylpropyl)phenyl] propanoic acid,
commercially available as ibuprofen (IBP), is one of the most con-
sumed pharmaceuticals worldwide.[25] It is a nonsteroidal agent,
analgesic, antipyretic and anti-inflammatory, used for the treat-
ment of fever and to relieve pain in general.[25] Once adminis-
tered, only 15% is eliminated as the original form, while 26% is
excreted as hydroxy-IBP and 43% as carboxy-IBP (Fig. 1).[26]
There are reports on the presence of IBP and its metabolites in
effluents from sewage treatment plants and surface waters. A
*
Correspondence to: Rodinei Augusti, Departamento de Química, Universidade
Federal de Minas Gerais, Belo Horizonte, MG 31270–901, Brazil. E-mail:
augusti.rodinei@gmail.com
a Departamento de Química, Universidade Federal de Minas Gerais, Belo
Horizonte, MG, 31270-901, Brazil
b Instituto de Ciências Exatas e Biológicas, Universidade Federal de Ouro Preto,
Ouro Preto, MG, 35400-000, Brazil
J. Mass Spectrom. 2014, 49, 145–153
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J. C. C. da Silva et al.
types of assays were performed: photocatalysis (using TiO2 and UV
radiation simultaneously), photolysis (with UV radiation solely) and
hydrolysis (with no TiO2 and UV radiation). In the photocatalysis
and photolysis experiments, two different types of UV radiation,
UV-C and UV-A, were tested. UV-C and UV-A radiations were
provided by the following lamps, respectively: germicidal (power:
9 W, emission wavelength range: 200–280 nm, model: PL-S,
manufacturer: Philips) and dark light (power: 9 W, emission
wavelength range: 315–400 nm, model: LY9-H, manufacturer:
Ecolume). Each photocatalytic or photolytic experiment was
performed using three UV lamps (UV-A or UV-C) simultaneously
with a total nominal power of 27 W. The three UV lamps were
placed together into a cylindrical quartz tube, which was immersed
in the aqueous solution of IBP. A volume of 2.0 L of this solution,
prepared at an abnormally high concentration of 5 mg LÀ1, was
transferred to the rectangular container of the jar-test vessel
(2.5 L volumetric capacity). The concentration of the IBP solution
(5 mg LÀ1), although much higher than those typically found in
environmental samples, was chosen to make the subsequent
chromatographic analysis easy, with no need of extraction and
pre-concentration steps. The solution, kept protected from external
light, was stirred for about 30 min before the beginning of the
degradation tests. Control experiments (results not shown) indi-
cated that the amount of IBP adsorbed by the TiO2 material in
the dark for 120min was negligible. All tests were conducted within
a narrow range of temperature (24–25°C), which certainly has neg-
ligible effects on the course of the photodegradation processes.[48]
In the photocatalysis experiments, 240 mg of TiO2 (comprising a
dosage of about 120 mgLÀ1) was used. The reaction flasks (jar-test
containers) were externally coated with a refractory material
applied to ensure that ambient radiation would not dissipate into
the medium. During the degradation experiments, the jar-test
instrument was operated with a rotational speed of 250 rpm,
corresponding to a gradient velocity of 400 sÀ1. The tests were
conducted in batch mode for a period of 2 h, during which aliquots
were collected at intervals of 0, 5, 10, 15, 30, 60 and 120 min.
The aliquots collected during the photocatalysis experiments
were centrifuged at 4000 rpm for 10 min (centrifugal model 80–20,
Centribio, São Paulo, Brazil) to remove any suspended material
(TiO2). The supernatant was then recovered and stored protected
from light at a temperature lower than 4 °C. The aliquots collected
from the photolysis and hydrolysis tests were also maintained under
identical conditions until the moment of the total organic carbon
(TOC) and chromatographic analyses. Because of their high polarity,
the degradation products are certainly more soluble in water than
IBP (the structures proposed for all by-products will be displayed
later in this paper). Hence, the occurrence of precipitation of any
by-product during the centrifugation step is quite unlikely.
Figure 1. Chemical structures of ibuprofen (IBP), hydroxy-ibuprofen and
carboxy-ibuprofen.
survey conducted between 2006 and 2010 confirmed the presence
of IBP in concentrations ranging from 65 to 7100 ngLÀ1 in sewage
treatment plants and raw sewage effluents and up to 360 ngLÀ1 in
freshwater.[27] The lower concentration of IBP reported in surface
waters is probably due to a combination of factors such as photol-
ysis, biotransformation, sorption, volatilization and dispersion in the
environment.[28]
Studies have demonstrated that IBP is partially removed in
treatment stations; in some cases, a removal rate of 70% can be
obtained, especially when using biological oxidation.[29] However,
the main metabolites (carboxy-IBP and/or hydroxy-IBP) persist after
the biological treatment as toxic by-products that may affect
the aquatic environment.[26–30] Even reaching moderate levels of
removal (70%), IBP is not easily depleted by conventional biological
processes; as a consequence, an inconveniently long withholding
time (usually days) is required to attain higher degradation rates.
Therefore, a series of new technologies have been applied in order
to more effectively reduce the presence of IBP in the environment,
such as photodegradation, solar photodegradation,[30–34] biological
treatment[35–43] and other AOPs.[44–47]
Although some studies involving the removal of IBP from aqueous
solution have been reported, detailed information regarding the
overall degradation process remains scarce. The present study aims,
therefore, to investigate the degradation of IBP in a watery medium
induced by two distinct methods: direct photolysis (by employing
UV-A and UV-C irradiation) and photocatalysis (by using the TiO2/
UV-A and TiO2/UV-C systems). The detection and identification of
recalcitrant by-products, possibly formed under these oxidative
conditions, via liquid chromatography coupled to high-resolution
mass spectrometry (LC-HRMS) are the main focus of the present
paper. Additionally, the level of ecotoxicity of such compounds is
appraised in tests against A. salina.
Experimental section
Chemicals
Ibuprofen (C13H18O2, nominal mass 206.1307), whose chemical
structure is shown in Fig. 1, was purchased from Sigma-Aldrich
(St. Louis, MO, USA). Solvents for analytical determinations were
methanol (chromatographic grade, JT Baker) and ultrapure water.
Ultrapure water, from a Millipore Milli-Q system (Milford, MA, USA),
was employed to prepare all solutions. Commercial TiO2 (99% ana-
tase), acquired from Sigma-Aldrich company (St. Louis, MO, USA),
was used as a catalyst in the photocatalytic experiments.
Total organic carbon analyses
Total organic carbon (TOC) analyses were carried out on a TOC
analyzer (Shimadzu, model TOC-VCPH, Kyoto, Japan). The TOC
content of each collected aliquot was obtained by the indirect
method that corresponds to the difference between the total
carbon and inorganic carbon values.
Ecotoxicity tests against Artemia Salina
Degradation experiments
The ecotoxicity tests with brine shrimp (A. salina) were carried out
following a previous protocol.[49] By following this procedure, an
aqueous solution of sea salt (at 38 g LÀ1) was prepared, filtered
The experiments were conducted in a jar-test apparatus (model
218/LDB06, Nova Ética, Jundiaí, São Paulo, Brazil). Three distinct
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J. Mass Spectrom. 2014, 49, 145–153

Photodegradation of ibuprofen monitored by LC-HRMS
and added to a small (15 cm diameter) round plastic container.
Subsequently, many A. salina eggs were added in only one-half
of this container, which was kept protected from light for 24 h,
whereas the opposite half was continuously irradiated by a
100 W lamp. After the eggs hatched, the A. salina organisms
migrated to the lit side. A small portion of this solution with the
adult individuals was then collected and transferred to a cylindrical
glass vial (3 cm diameter) and the volume completed to 1.0 mL by
adding the aforementioned salt solution. Afterwards, 4.0 mL of a
given aliquot, collected from the degradation experiments, was
put into the vial (at the end the total volume in each vial was
5.0 mL). The vial was then left to stand under light for a period
of up to 24 h. After this time, the percentage of the immobilized
organisms was determined. The assays with each aliquot were
conducted in triplicate to estimate the accurate toxicity of each
by-product.
Figure 2. Relative concentration of ibuprofen achieved for different systems:
photolysis (UV-A and UV-C), photocatalysis (TiO2/UV-A and TiO2/UV-C) and
hydrolysis. The concentrations of IBP were determined via extracted-ion
chromatograms for deprotonated ibuprofen (m/z 205.1235). An initial IBP
concentration of 100 was arbitrarily assigned in each assay.
Liquid chromatography coupled to mass spectrometry
The analyses were performed on a liquid chromatographer (LC)
coupled to a hybrid mass spectrometer (MS) system. The liquid
chromatographer (Prominence LC-20 AD; Shimadzu Corporation,
Kyoto, Japan) was equipped with a binary pump and an
autosampler (SIL 20 AC; Shimadzu Corporation, Kyoto, Japan).
The mass spectrometer (IT-TOF; Shimadzu Corporation, Kyoto,
Japan) provides high sensitivity and accuracy with a resolving power
over 10.000 at mass-to-charge (m/z) 1000. The mass spectrometer
was equipped with an electrospray ionization (ESI) source operating
in both the negative (À3.5 kV) and positive modes (+4.5 kV) modes.
Direct infusion analyses were conducted by simultaneously operat-
ing the electrospray source in the positive and negative modes
The heterogeneous photocatalytic and direct photolytic systems
operating under UV-C irradiation promoted the removal of IBP with
high efficiencies, at rates reaching 100% and 98.9%, respectively,
after 120 min of exposure. The reason for the high degradation rates
achieved upon application of the photolytic system is probably
due to the overlapping of the emission spectrum of the UV-C
lamp (100–280 nm with a maximum emission at 254 nm) with
the absorption spectrum of IBP (absorption up to 240 nm with a
λ
max at 222 nm).[50] This effect can also be attributed to the in situ
generation of OH● radicals directly from the homolysis of water
molecules by the 185 nm irradiation.[51] Although the use of TiO2
seems not to make a remarkable difference regarding the removal
of IBP, its beneficial effects will be discussed following this paper.
The TiO2/UV-A and TiO2/UV-C photocatalytic systems showed
similar capacities in promoting the depletion of IBP (the first one
was able to degrade 92.6% of the original IBP after a treatment
time of 120 min). Conversely, the direct photolysis with UV-A
radiation exhibited a much lower efficiency (roughly 12.5%) than
the analogous assay with UV-C (98.9%). This result indicates
that the catalyst (TiO2) is of prime importance to achieve higher
degradation yields when UV-A radiation (that mimics solar radia-
tion and is generated by means of a dark lamp; see Experimental
Section for more details) is employed. The low removal efficiency
achieved by the application of direct UV-A photolysis can be easily
explained considering that neither IBP can absorb in the emission
region of the UV-A lamp (315–400 nm with λmax = 360 nm) nor
OH● radicals can be generated upon the homolysis of H2O
molecules by the UV-A irradiation. This set of findings therefore
indicates that the depletion of IBP induced by the TiO2/UV-A
system is mostly caused by hydroxyl radicals (OH●), quite reactive
species that are generated in situ by the interaction of H2O molecules
with the positive holes (h+) at the valence band of excited TiO2
catalyst.
and adjusting the nebulizer gas (N2) to a flow rate of 1.5 L minÀ1
.
The interface and curved line dessolvation were operated at a
constant temperature of 200 °C. An m/z range of 50–500 was
recorded. The samples were directly introduced into the ESI source
by injecting 5 μL of sample via the LC autosampler. For the LC-HRMS
analyses, the mass spectrometer was set to operate under the
conditions specified earlier. The chromatographic conditions were
as follows: an ACE C18 column (2.1× 100 mm × 3 mm particle
diameter) was used, whereas water (A) and methanol (B) (at
assorted proportions) were employed as the mobile phases at a
flow rate of 0.2mLminÀ1. The gradient program started with 30%
B, rising to 50% B in 4 min, then to 100% B in 3 min, which was then
held for 3 min. At the end of the chromatographic run, the column
was re-equilibrated to the initial conditions and stabilized for
4 min, which led to a total run time of 14 min. The injection
volume was 5 μL.
Results and discussion
Kinetics of ibuprofen degradation
All aliquots were analyzed by direct infusion ESI-HRMS in both
the positive and negative modes (see Experimental Section for
more details). However, because by-products were detected
exclusively in the negative mode of acquisition, only this set of
data will be presented and discussed herein. Hence, Fig. 2 shows
the continuous decrease in the concentration of IBP as a function
of reaction time observed for the photocatalysis, photolysis and
hydrolysis tests. The results from the hydrolysis experiments
(conducted in the absence of TiO2 and UV radiation) indicated
that IBP is quite stable in aqueous solution.
Table 1 shows the rate constants (k) and half-life times (t1/2)
calculated for the degradation of IBP induced by the photocatalytic
(TiO2/UV-A and TiO2/UV-C) and photolytic (UV-A and UV-C)
systems. The experimental data, i.e. the relative concentration of
IBP as a function of time, achieved for each one of the four
systems, were properly adjusted by a first-order kinetic model.
Hence, in all the first-order kinetic plots, i.e. ln (Ct/Co) (Co and Ct
refer to the concentrations of IBP at the beginning and at a given
reaction time, respectively) versus time, correlation coefficients
(R2) ranging from 0.943 to 0.994 (for the UV-A and TiO2/UV-A
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J. C. C. da Silva et al.
Table 1. Kinetic parameters obtained for the degradation of ibuprofen
in aqueous solution induced by four distinct systems: TiO2/UV-C, UV-C,
TiO2/UV-A and UV-A
in the negative ion mode. Some examples of the mass spectra
recorded are depicted in Fig. 3. Note the continuous decrease
in the relative abundance of the ion ascribed to be the
deprotonated form of IBP (m/z 205.1235). This finding thus
indicates the continuous consumption of IBP by the photolytic
and photocatalytic systems. A meticulous search in these mass
spectra revealed the presence of 11 ions clearly distinguishable
from the ‘background’. Based on the HRMS data, molecular
formulae for these ions, which were ascribed to be the
deprotonated forms of degradation products possibly formed
under these conditions, are displayed in Table 2. A maximum
error of 8 ppm between the experimental and theoretical
accurate masses of IBP and its by-products was observed.
All these intermediates were detected at least in one of the
aliquots of the photocatalytic (TiO2/UV-C and TiO2/UV-A) or
photolytic (UV-C and UV-A) processes. Extracted-ion chromato-
grams (Fig. 4) were obtained for each one of these 11 ions
to confirm the formation of by-products in solution. Under
the chromatographic conditions employed, some by-products
co-eluted (1 and 6 as well as 7 and 8), whereas other ones
(8, 9 and 11) eluted at very close retention times (Fig. 4). In
spite of these chromatography limitations, the HRMS data allowed
the proposition of chemical structures for each one of these by-
products.
Degradation system
R2
k (minÀ1
)
t1/2(min)
TiO2/UV-C
UV-C
0.991
0.987
0.994
0.943
0.054
0.037
0.021
0.001
12.83
18.73
33.00
693.00
TiO2/UV-A
UV-A
A first-order model was used to adjust the experimental data.
systems, respectively) were achieved. An accurate analysis of
Table 1 reveals that although the TiO2/UV-C and UV-C processes
yielded similar degradation rates after an identical treatment time
(120 min, see previous discussion), the photocatalytic systems are
more efficient to deplete IBP than the analogous photolytic
processes, given that t1/2 (TiO2/UV-A) < t1/2 (UV-A) and that t1/2
(TiO2/UV-C) < t1/2 (UV-C). As previously stated, the superior perfor-
mance of the photocatalytic systems can be related to the ability
of the TiO2 material (upon exposure to UV radiation) to generate a
substantial amount of hydroxyl radicals, which promote a prompt
and nonspecific attack towards target molecules present in the
reaction medium.
Based on these results as well as on the well-known reactivity
of hydroxyl radical towards organic molecules in aqueous
medium, a route for the photodegradation of IBP could thus be
proposed, as outlined in Fig. 5. Hence, hydroxylated derivatives
were identified by the increase of one or more oxygen atoms
in the molecular formulae of IBP or some of its intermediates,
with no alterations in the double bond equivalence. Among the
by-products detected (1–11) several isomeric structures can be
postulated. The correct structure (or structures), however, could
not be firmly established herein based on the information
provided by HRMS. Moreover, the fragmentation profile (not
shown) of each ionic species (deprotonated forms of 1–11) was
useless to accomplish this task as in the MS/MS product ions
arising from loss of water were dominant. For a matter of
simplicity, however, only one among the several isomers possibly
formed under these conditions are represented in Fig. 5. Some
intermediates were proposed to be formed by successive
hydroxylation starting from IBP (C13H18O2). That is the case of 1
(C13H18O3), (represented as two isomeric forms: α-hydroxy-
carboxy-IBP and α-hydroxy-isopropyl-IBP), 2 (C13H18O4) and 3
(C13H18O5). Another by-product (5, C12H18O6) was proposed
herein to arise from hydroxylation of 4 (C12H18O5). In addition,
other by-products were suggested to be generated via
alternative pathways. For instance, intermediates 4 (C12H18O5) and
6 (C12H18O) were possibly formed by decarboxylation of 3
(C13H18O5) and 1 (C13H18O3), respectively. In sequence, by-product
6 (C12H18O) could undergo hydroxylation and loss of 2-propanol to
yield intermediate 9 (C9H10O). By-product 7 (C9H10O3) could be
formed by two consecutive hydroxylations of 9 (C9H10O). It is also
suggested that the subsequent oxidation of the alcohol function
of 9 (C9H10O) could furnish intermediate 8 (C9H8O3). Lastly, the
acyclic intermediates 10 (C6H10O3) and 11 (C5H10O3) could be
generated by successive hydroxylation of intermediates 8 and 5
that could ultimately lead to the opening of their aromatic rings.
These intermediates (10 and 11) could be easily mineralized
under these oxidative conditions. It is important to mention that
some of these intermediates (1, 2, 6, 8 and 9) have been previ-
ously reported by several research groups.[25,32,36,38,45,51,53,54]
Furthermore, it is important to state that in all experiments
(photolytic and photocatalytic), the maximum variation between
the pHs of the initial and final solutions was about 0.25 units. The
solution pH is a complex factor that can affect photocatalytic
reactions in many ways. For instance, factors such as the ionization
state of TiO2 surface, the influence of electron holes on OH●
generation and the reduction of surface area by the agglomeration
of TiO2 particles are affected by the solution pH.[52] This small
difference between the pHs of the initial and final solutions could
not cause therefore remarkable changes in the reaction kinetics.
Mineralization
Although impressive IBP degradation rates (over 90%) were
achieved by the employment of the TiO2/UV-C, TiO2/UV-A and
UV-C systems (Fig. 2), the TOC data revealed that IBP was not
mineralized to a similar extent, even after a treatment time as
long as 120 min. For instance, the highest mineralization rate
was only 37.7% achieved upon the application of the TiO2/UV-C
system. Moreover, the mineralization rates derived from direct
photolysis (UV-C and mainly UV-A) were negligible. These
findings indicate that whereas most of the original IBP was not
mineralized, recalcitrant by-products were generated under
these conditions. The fact that the direct photolysis processes
are unable to reduce the TOC content in solution strongly indi-
cates that such refractory by-products absorb neither UV-A nor
UV-C radiation. It is also evident that the highest rates of mineral-
ization obtained by the photocatalytic systems (TiO2/UV-C and
TiO2/UV-A) can be attributed again to their superior ability to pro-
mote the in situ generation of hydroxyl radicals upon exposure of
the TiO2 catalyst to UV radiation.
Identification of by-products: proposal of a degradation
route
The aliquots collected during the photocatalysis and photolysis
experiments were firstly analyzed via direct infusion HRMS
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Photodegradation of ibuprofen monitored by LC-HRMS
Figure 3. High resolution mass spectrometry (HRMS) recorded for aliquots collected from the TiO2/UV-C system after the following reaction times: 0,
30, 60 and 120 min. The molecular formulae for some of the intermediates observed in these mass spectra are shown in Table 2. Note that relative abun-
dance of the ion of m/z 235.1235 (deprotonated IBP) decreases as a function of reaction time.
Table 2. High-resolution mass spectrometry data and the molecular formulae calculated for the by-products generated during the photodegradation
of ibuprofen in water
Molecular
formula
Molecular
mass (M)a
[M À H]À
[M À H]À
Double bond
equivalence
Compound
(theoretical)
(experimental)
Error (ppm)
IBP
1
C13H18O2
206.1307
222.1256
238.1205
254.1154
242.1154
258.1103
178.1358
166.0630
164.0473
134.0732
130.0630
118.0630
205.1234
221.1183
237.1132
253.1076
241.1081
257.1031
177.1285
165.0557
163.0401
133.0653
129.0557
117.0557
205.1235
221.1165
237.1138
253.1082
241.1088
257.1033
177.1295
165.0570
163.0388
133.0651
129.0563
117.0556
0.47
À5.88
2.38
3.16
2.70
0.92
5.64
7.72
7.73
À1.50
4.64
1.00
5
5
5
5
4
4
4
5
6
5
2
1
C
C
C
C
C
C
13H18O3
13H18O4
13H18O5
12H18O5
12H18O6
2
3
4
5
6
12H18O
7
C9H10O3
C9H8O3
8
9
C9H10O
10
11
C6H10O3
C5H10O3
aAccurate mass calculated by the LCMS solutions software.
The evolution of each intermediate (1–11) formed during
the photodegradation processes could then be monitored by
LC-HRMS. The results from the extracted-ion chromatograms
(Fig. 4) were handled to build plots of the relative concentra-
tion of each by-product (a value of 100 was attributed to the
highest concentration) versus reaction time for all the four
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J. C. C. da Silva et al.
Figure 4. Extracted-ion chromatograms for the following ions [deprotonated forms of ibuprofen (IBP) and degradation products]: (a) m/z 205.1235
(IBP), (b) m/z 221.1165 (1), (c) m/z 177.1295 (6), (d) m/z 163.0388 (8), (e) m/z 129.0563 (10) and (f) m/z 117.0556 (11). The analyses refer to an aliquot
collected after submitting an aqueous solution of IBP to the TiO2/UV-C system for 60 min.
degradation processes evaluated (Fig. 6). Hence, for the TiO2/UV-C
photocatalytic system practically only intermediates 10 and 11
remained in solution after 120 min of exposure (Fig. 6(a)). The
remarkable ability of the TiO2/UV-C system to generate hydroxyl rad-
icals possibly caused the prompt depletion of the other intermediates
(1–9), thus preventing their accumulation and detection. For the UV-C
direct photolysis (Fig. 6(b)), however, several intermediates (1, 6, 7, 8,
10 and 11) were persistent in solution after identical treatment time.
These findings seem to confirm the results from TOC analyses,
which revealed that higher mineralization rates were achieved
by the TiO2/UV-C photocatalytic system. For the tests involving
the TiO2/UV-A system (Fig. 6(c)), only intermediates 7, 8 and 3
were not persistent. Conversely, after 120 min of treatment by
UV-A photolysis, intermediate 1 was by far predominant (Fig. 6(d)).
This result suggests that UV-A radiation is not energetic enough
to excite 1 and thus to cause its conversion into the subsequent
intermediates (2–11), as observed for the other systems (TiO2/
UV-C, TiO2/UV-A and UV-C) evaluated herein.
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J. Mass Spectrom. 2014, 49, 145–153

Photodegradation of ibuprofen monitored by LC-HRMS
Figure 5. Proposed route for the photodegradation of ibuprofen in water as induced by the photolytic (UV-A and UV-C) and photocatalytic (TiO2/UV-A
and TiO2/UV-C) systems. Isomeric structures can also be proposed for the degradation products. However, to facilitate visualization, only the struc-
tures 1–11 are displayed herein.
Toxicity assessment
rates determined in each case. A control test with saline solution was
also conducted (see Experimental Section for further details).
At the end of these tests, a fortunate result emerged: just as
observed for the IBP solution, the aliquots collected after an
exposure time of 120 min (taken from the reaction vessels of the
four degradation systems: TiO2/UV-C, TiO2/UV-A, UV-C, UV-A)
exhibited a very low toxicity against A. salina (mortality rates of
about 5%). This finding ensures that both the photocatalytic
and photolytic systems can therefore be conveniently used to
degrade IBP as toxic by-products are probably not formed under
these conditions.
Although several reports have described the degradation of IBP,
little is known about the possible by-products generated and their
degree of toxicity. As can be observed in Fig. 6, after the complete
disappearance of IBP, many compounds still remain in solution,
which may have a potential impact on the environment and possi-
bly on human health. To evaluate the toxicity of IBP and its transfor-
mation products, toxicity tests against A. salina were conducted.
These tests were performed with all aliquots taken during the deg-
radation reactions (0, 5, 10, 15, 30, 60 and 120 min), and the mortality
J. Mass Spectrom. 2014, 49, 145–153
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J. C. C. da Silva et al.
Figure 6. Plots of the relative concentrations of by-products (1, 6, 8, 10, 11) as a function of reaction time for the following systems: (a) TiO2/UV-C, (b)
UV-C, (c) TiO2/UV-A and (d) UV-A. A value of 100 was attributed to the maximum concentration of each by-product. To facilitate visualization, only 5
among the 11 by-products detected are plotted.
Conclusions
References
The degradation of IBP, one of the most consumed pharmaceuticals
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and TiO2/UV-A) and photolytic (UV-A and UV-C) systems was inves-
tigated herein. It was verified that all the systems (excepting UV-A)
were able to cause an almost complete degradation of IBP after a
reaction time of 120 min. However, it was also demonstrated that
among the systems evaluated, the TiO2/UV-C photocatalytic process
was the most efficient in promoting both the degradation and min-
eralization of the substrate. Results from high-resolution MS analyses
allowed the detection and characterization of 11 by-products, many
of them persistent even after an exposure of as long as 120 min.
These intermediates were proposed to be formed via a prompt attack
of hydroxyl radicals, reactive species produced in situ under the con-
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original substrate as well as on the subsequent by-products. Based
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revealed that the 120-min aliquots collected from the four systems
contained compounds with no higher toxicities than IBP. This
fortunate result therefore ensures that any of these systems
(excluding UV-A) can be used to deplete IBP in water bodies.
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