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Monitoring of b-Blockers Ozone Degradation via Electrospray Ionization Mass Spectrometry
J. Braz. Chem. Soc.
common oxidizing reagents such as H2O2 or chlorine, is more
efficient in pollutant degradation and less harmful to most
living organisms.10 In water, ozone can oxidize contaminants
via direct selective reactions11 such as ozone addition to
doublebondsortheinitiationofchainradicalreactionsbythe
productionoffreehydroxyradicals(equations1-4). Hydroxy
radicals are generated from ozone decomposition, which is
catalyzed by the presence of hydroxyl anions or by traces of
other substances, such as transition metal cations.
data on substrate degradation rates and mineralization and
to investigate the presence of residual organic compounds
in the aqueous solutions.24
Experimental
Chemicals
Nadolol (NAD), atenolol (ATE) and acebutolol (ACE)
were purchased from Sigma. All the solvents were of
HPLC grade and purchased from Merck and used without
purification. Doubly distilled water was used to prepare
all the solutions in the experiments. Ozone was generated
using a laboratory ozone generation (OZOCAV) ozonizer
fed with air/oxygen.
O3 + H2O→ 2 HO· + O2
O3 + OH- → O2·– + HO2·
O3 + HO· → O2 + HO2·
O3 + HO2· → 2 O2 + HO·
(1)
(2)
(3)
(4)
Degradation procedures
The decomposition of ozone in aqueous solutions
is known to proceed via the chain reactions shown in
equations 1-4.12 Ozone therefore indirectly attacks organic
compounds since such reactions are faster than direct
O3 attack. In previous studies,13,14 we described the O3
interaction with pharmaceutical compound nadolol (anti-
hypertensive). In this study, we report the characterization
via electrospray ionization mass spectrometry (ESI-MS)15,16
of the oxidation intermediates and products of degradation
of nadolol generated during O3 oxidation. Furthermore, the
O3 degradation of two other b-blockers compounds atenolol
and acebutolol was also studied.
The ozonation reactions were performed in a batch glass
reactor thermostated at 25 °C. The reactor was charged with
100 mL of the drug aqueous solutions (1.6 × 10-4 mol L-1)
and fed with 1.2 × 10-4 mol L-1 of ozone at a constant
flow of 46 1 mL min-1. The ozone concentration was
monitored measuring the absorbance at 254 nm, using the
molar extinction coefficient of ozone of 2900 L mol-1 cm-1.
Aliquots (1.0 mL) were taken at several reaction times
and promptly analyzed by ESI-MS(/MS) and HPLC. All
samples were protected from light and refrigerated at 4 °C
prior to analyses.
ESI-MS (and its tandem version ESI-MS/MS) has
been used extensively to monitor the composition and
degradation of organic compounds in the environment.17,18
ESI-MS(/MS) with its unique characteristics has become a
major technique to elucidate reaction mechanism especially
in aqueous solutions via the detection and identification of
reactants, products, and intermediates,19,20 even the short-
lived ones that occur at very low concentrations.21,22
Gas chromatography-mass spectrometry (GC-MS) has
often been the technique of choice for reaction screening
and product elucidation.23 However, GC-MS is an
offline technique that demands extraction and sometimes
derivatization pre-steps, transient, most polar, or relatively
unstablecompoundsmaybemissed.Wehavethenperformed
ESI-MS(/MS) monitoring of the O3 advanced oxidation of
nadolol, atenolol and acebutolol in water to search for all
intermediatesandproductsofthisenvironmentallyimportant
process. These products are the ones most likely to be found
in treated wastewaters.We also used high performance liquid
chromatography(HPLC), ultravioletspectroscopy(UV), and
total organic carbon (TOC) analyses to collect additional
Analytic methods
Drugs concentrations were monitored using a Perkin
Elmer Series 200 chromatograph HPLC system equipped
with a UV-Vis detector.A Merck-Chromolith Performance
RP-18 column (4.6 mm × 100 mm) was used with
H2O:MeOH (70:30, v/v) mobile phase at a flow rate of
0.6 mL min-1. Water was previously acidified to pH 3 using
aqueous solution of HCl. Organic acids were quantified
with a transgenomic ORH-801 column (6.5 mm × 300 mm)
using 5.0 × 10-3 mol L-1 sulphuric acid as mobile phase at
a flow rate of 0.8 mL min-1.
Ultraviolet (UV) absorbance measurements were
performed using a HP 8453 (Agilent) spectrophotometer
equipped with a quartz cell with a 1.0 cm path length.
Absorbances were measured with baseline correction,
scan rate of 200-600 nm, and integrate time of 0.5 s and
intervals of 1 nm.
Total organic carbon (TOC) experiments were carried
out in a TOC 5000A (Shimadzu) instrument at 680 °C using
a platinum catalyst.