Characterization of intermediate compounds formed upon photoinduced degradation of quinolones by high-performance liquid chromatography/high-resolution multiple-stage mass spectrometry

The paper deals with the photocatalytic transformation of two antibacterial agents, ofloxacin and ciprofloxacin, under simulated solar irradiation using titanium dioxide as photocatalyst. The investigation involved monitoring decomposition of the drugs, identifying intermediate compounds, assessing mineralization, and evaluating the toxicity of drug derivatives. High-resolution mass spectrometry was employed to assess evolution of the photocatalyzed process over time. Respectively 15 and 8 main species were identified after transformation of ofloxacin and ciprofloxacin. Through the full analysis of MS and MSn spectra and a comparison with parent drug fragmentation pathways, the different isomers were characterized. In the ofloxacin molecule, the initial transformation attacks are confined to the piperazine moiety and to the methyl groups, while the fluoroquinolone core is unmodified. Conversely, ciprofloxacin degradation involves two parts of the molecule: the piperazinic moiety and the quinolone moiety. All these intermediates are easily degraded and by 4 h mineralization is complete. Toxicity assays using Vibrio fischeri prove that neither ciprofloxacin nor its intermediates exhibit acute toxicity. In ofloxacin the secondary degradation products exhibit toxicity; a correlation exists between the evolution of the intermediate compounds and the toxicity connected to them.     

Photo-induced transformation of hexaconazole and dimethomorph over TiO2 suspension

The photo-induced transformation in aqueous solution of hexaconazole and dimethomorph over irradiated titanium dioxide was studied. The investigation involved monitoring pesticides decomposition, identifying intermediate compounds, assessing mineralization, and evaluating toxicity of pesticides derivatives. HPLC/UV and HPLC/MS were used to follow the disappearance of the initial pesticides and the formation of intermediate products, while the acute toxicity was evaluated by using the Vibrio fischeri luminescent bacteria assay.Hexaconazole photocatalytic transformation proceeds through the formation of highly persistent compounds. The formation of cyanuric acid, a non-toxic compound refractory to photocatalytic treatment, was recognized. Conversely, the toxicity assays prove that neither hexaconazole nor its intermediates exhibit acute toxicity.Dimethomorph under photocatalytic treatment is completely mineralized within 14 h of irradiation. However, its transformation proceeds through the formation of toxic intermediates. A correlation exists between the evolution of the intermediate compounds and the toxicity profile, as the highest toxicity is measured when the intermediates with lower EC50 (hydroquinone and 4-chlorophenol) are formed.     

Ion trap tandem mass spectrometric identification of thiabendazole phototransformation products on titanium dioxide

The purpose of this study is to artificially produce degradation intermediates of thiabendazole, which could be reasonably similar to those really present in the environment. The formation of by-products from thiabendazole transformation has been evaluated by adopting irradiated titanium dioxide as a photocatalyst. Several species more hydrophilic than the thiabendazole have been identified and characterized by HPLC-multiple MS. A pattern of reactions accounting for the observed intermediates is proposed. Two different parallel pathways are operating (and through these pathways the transformation of the molecule proceeds) leading to several intermediate compounds. The main steps involved are: (1) the hydroxylation of the molecule on the aromatic ring with the formation of a species having [M+H]+ 218; a further oxidation leads to the ring-opening and to the formation of aldehydic and alcoholic structures ([M+H]+ 270, 268 and 152); and (2) the cleavage of a C-C bond and the formation of a species having [M+H]+ 119.     

High-performance liquid chromatographic/tandem mass spectrometric identification of the phototransformation products of tebuconazole on titanium dioxide

Tebuconazole is a widely used fungicide. The formation of by-products on irradiated titanium dioxide as a photocatalyst was evaluated. Several species derived from tebuconazole degradation were identified and characterized by HPLC/MS(n). A pattern of reactions accounting for the observed intermediates is proposed. Different parallel pathways are operating (and through these pathways the transformation of the molecule proceeds), leading to a wide range of intermediate compounds. All these molecules are more hydrophylic than tebuconazole. The main steps involved are (1) the hydroxylation of the molecule with the formation of three species having [M + H](+) 324; the hydroxylation occurs on the C-1 carbon and on the aromatic ring in the two ortho-positions; (2) the cleavage of a C--C bond with the release of the tert-butyl moiety and the formation of a species having m/z 250; analogously to step 1, also on this species a further hydroxylation reaction occurs; (3) through the loss of the triazole moiety with the formation of a structure with m/z 257.     

On-line solid phase extraction-high performance liquid chromatography–isotope dilution–tandem mass spectrometry approach to quantify N,N-diethyl-m-toluamide and oxidative metabolites in urine

Human exposure to N,N-diethyl-m-toluamide (DEET) occurs because of the widespread use of DEET as an active ingredient in insect repellents. However, information on the extent of such exposure is rather limited. Therefore, we developed a fast on-line solid phase extraction–high performance liquid chromatography–isotope dilution tandem mass spectrometry (HPLC-MS/MS) method to measure in urine the concentrations of DEET and two of its oxidative metabolites: N,N-diethyl-3-(hydroxymethyl)benzamide and 3-(diethylcarbamoyl)benzoic acid (DCBA). To the best of our knowledge, this is the first HPLC-MS/MS method for the simultaneous quantification of DEET and its select metabolites in human urine. After enzymatic hydrolysis of the conjugated species in 0.1 mL of urine, the target analytes were retained and pre-concentrated on a monolithic column, separated from each other and from other urinary biomolecules on a reversed-phase analytical column, and detected by atmospheric pressure chemical ionization in positive ion mode. The limits of detection ranged from 0.1 ng mL⁻¹ to 1.0 ng mL⁻¹, depending on the analyte. Accuracy ranged between 90.4 and 104.9%, and precision ranged between 5.5 and 13.1% RSD, depending on the analyte and the concentration. We tested the usefulness of this method by analyzing 75 urine samples collected anonymously in the Southeastern United States in June 2012 from adults with no known exposure to DEET. Thirty eight samples (51%) tested positive for at least one of the analytes. We detected DCBA most frequently and at the highest concentrations. Our results suggest that this method can be used for the analysis of a large number of samples for epidemiological studies to assess human exposure to DEET.     

Characterization of atenolol transformation products on light-activated TiO2 surface by high-performance liquid chromatography/high-resolution mass spectrometry

We have studied the photocatalytic transformation of atenolol, 4-[2-hydroxy-3-[(1-methyl)amino]propoxyl]benzeneacetamide, a cardioselective beta-blocking agent used to treat cardiac arrhythmias and hypertension, under simulated solar irradiation using titanium dioxide as photocatalyst. The investigation involved monitoring drug decomposition, identifying intermediate compounds, assessing mineralization, and evaluating toxicity. High-performance liquid chromatography (HPLC) coupled to high-resolution mass spectrometry (HRMS) via an electrospray ionization (ESI) interface was a powerful tool for the identification and measurement of the degradation products; 23 main species were identified. Intermediates were characterized through their chromatographic behavior and evolution kinetics, coupled with accurate mass information. Through the full analysis of MS and MS(n) spectra and a comparison with parent drug fragmentation pathways, the diverse isomers were characterized. Neither atenolol nor the intermediates formed exhibit acute toxicity. All intermediates are easily degraded and no compound identified could withstand 2 h irradiation. Photomineralization of the substrate in terms of carbon mineralization and nitrogen release was rapid and, within 4 h of irradiation, organic nitrogen and carbon were completely mineralized.     

High resolution gas chromatography/mass spectrometric characterization of urinary metabolites of N,N-diethyl-m-toluamide (DEET) in man

Studies of the pharmacology and toxicology of the popular insect repellant, N,N-diethyl-m-toluamide (DEET), have largely been done in animal models using radioactive tracing without the structural elucidation of its metabolites. This paper describes a high resolution gas chromatography/mass spectrometry (GC/MS) technique and reports the results of the preliminary characterization of the metabolites of DEET in the urine of a 30-year-old man who had been exposed to DEET contained in a commercial product. The metabolites were extracted and separated with an OV-101 glass capillary column, 30 m × 0.3 mm, and mass spectrometric elucidations were carried out with both Electron Impact (EI) and Chemical Ionization-Methane (MCI) modes. Oxidation of the benzylic moiety and hydroxylation of the sidechain of DEET molecules appeared to be the predominate routes of metabolism in man. The artifacts were also proposed.     

Identification of the unknown transformation products derived from lincomycin using LC‐HRMS technique

In this paper, a comprehensive study of the fate of an antibiotic, lincomycin, in the aquatic environment is presented. High‐resolution mass spectrometry was employed to assess the evolution of the process over time. Formation of intermediate compounds was followed by high performance liquid chromatography‐high resolution mass spectrometry (LC‐HRMS); accurate mass‐to‐charge ratios of parent ions were reported with inaccuracy below 1 mmu, which guarantee the correct assignment of their molecular formula in all cases, while their MS² and MS³ spectra showed several structural‐diagnostic ions that allowed to characterize the different transformation products (TPs) and to discriminate the isobaric species. The simulation of phototransformation occurring in the aquatic environment and the identification of biotic and abiotic TPs of the pharmaceutical compound were carried out in different experimental conditions: dark experiments, homogeneous photolysis and heterogeneous photocatalysis using titanium dioxide, in order to recreate conditions similar to those found in the environment. Twenty‐one main species were identified afterwards lincomycin transformation. Several isomeric species were formed and characterized by analyzing MS and MSⁿ spectra and by comparison with parent molecule fragmentation pathways. The major transformation process for lincomycin is hydroxylation either at N‐alkyl side chain or at the pyrrolidine moiety. In addition, oxidation/reduction, demethylation or cleavage of pyranose ring occurs. Based on this information and additional assessment of profiles over time of formation/disappearance of each species, it was possible to recognize the transformation pathways followed by the drug. Copyright © 2012 John Wiley & Sons, Ltd.     

Combined Analytical Study on Chemical Transformations and Detoxification of Model Phenolic Pollutants during Various Advanced Oxidation Treatment Processes

Advanced oxidation processes (AOPs) have been introduced to deal with different types of water pollution. They cause effective chemical destruction of pollutants, yet leading to a mixture of transformation by-products, rather than complete mineralization. Therefore, the aim of our study was to understand complex degradation processes induced by different AOPs from chemical and ecotoxicological point of view. Phenol, 2,4-dichlorophenol, and pentachlorophenol were used as model pollutants since they are still common industrial chemicals and thus encountered in the aquatic environment. A comprehensive study of efficiency of several AOPs was undertaken by using instrumental analyses along with ecotoxicological assessment. Four approaches were compared: ozonation, photocatalytic oxidation with immobilized nitrogen-doped TiO₂ thin films, the sequence of both, as well as electrooxidation on boron-doped diamond (BDD) and mixed metal oxide (MMO) anodes. The monitored parameters were: removal of target phenols, dechlorination, transformation products, and ecotoxicological impact. Therefore, HPLC–DAD, GC–MS, UHPLC–MS/MS, ion chromatography, and 48 h inhibition tests on Daphnia magna were applied. In addition, pH and total organic carbon (TOC) were measured. Results show that ozonation provides by far the most suitable pattern of degradation accompanied by rapid detoxification. In contrast, photocatalysis was found to be slow and mild, marked by the accumulation of aromatic products. Preozonation reinforces the photocatalytic process. Regarding the electrooxidations, BDD is more effective than MMO, while the degradation pattern and transformation products formed depend on supporting electrolyte.     

Characterization of phenazone transformation products on light-activated TiO2 surface by high-resolution mass spectrometry

The paper examines the transformation of phenazone (2,3-dimethyl-1-phenyl-3-pyrazolin-5-one), a widely used analgesic and antipyretic drug, under simulated solar irradiation in pure water, using titanium dioxide, and in river water. High-resolution mass spectrometry was employed to monitor the evolution of photoinduced processes. Initially, laboratory experiments were performed to simulate drug-transformation pathways in aqueous solution, using TiO(2) as photocatalyst. Thirteen main phenazone transformation products were detected, and full analysis of their MS and MS(n) spectra identified the diverse isobaric species. All these transformation products were themselves easily degraded, and no compounds were recognized to remain until 1h of irradiation. From these findings, a tentative degradation pathway is proposed to account for the photoinduced transformation of phenazone in natural waters. These simulation experiments were verified in the field, seeking phenazone in River Po water samples.     

Titanosilicate molecular sieve for size-screening photocatalytic conversion

Titanosilicate molecular sieves, when activated by ultraviolet light irradiation in water in the presence of molecular oxygen, catalyze a conversion of molecules having a size close to the pore of the catalysts but are inactive for molecules having much larger or smaller size. This unprecedented size-screening photocatalytic activity is triggered by a combination of H2O-induced shortened lifetime of active species (charge-transfer excited state of tetrahedrally coordinated titanium oxide) and restricted diffusion of a molecule inside the pore. This catalytic property demonstrates a potential utility of the catalyst for selective transformation of molecules that is associated with a size reduction of molecules, so-labeled "molecular shave" transformation.     

Detection and occurrence of microconstituents in reclaimed water used for irrigation – a potentially overlooked source

An online SPE-HPLC-HESI-MS/MS method and an online SPE-HPLC-APPI-MS/MS method were developed to analyze 72 microconstituents in reclaimed water. In this study, 55 reclaimed water samples were collected from the sprinkler system for a year-long period at Florida International University Biscayne Bay Campus, where reclaimed water was reused for daily irrigation. Analysis results showed that several analytes were continuously detected in all reclaimed water samples and others will show rather transient signal increases. Coprostanol, bisphenol A, and DEET’s maximum concentration exceeded 10,000 ng/L. The four most frequently detected compounds were diphenhydramine (100 %), DEET (98 %), atenolol (98 %) and carbamazepine (96 %).     

Species transformation and structure variation of fulvic acid during ozonation

The species transformation and structure variation of fulvic acid (FA) during ozonation were investi- gated in this study. The molecular weight (MW) distribution, the species of intermediate products and the variation of polar functional groups were studied by ultrafiltration, gas chromatography/mass spectrometry (GC/MS) and titration analyses respectively. The average MW of FA decreased signifi- cantly during ozonation. The amount of polar functional groups (carboxylic and phenolic (ph-OH) groups) per unit DOC (mol/kg C) increased with increasing ozonation time. Furthermore, GC/MS ex- periments demonstrated the formation of polar species (e.g., hexadecanoic acid, benzoic acid and oc- tadecanoic alcohol) and less-polar species (e.g., aliphatic hydrocarbons and butanedioic acid, bis(2-methylpropyl) ester). Electron spin resonance (ESR) measurements proved the presence of ·OH radicals in the ozonation system. Based on our experimental results, it appears that the oxidations by ozone molecule and ·OH radicals were responsible for the transformation of organics (FA and its oxi- dation products) during ozonation. These two oxidants showed significant influence on organics transformation and exhibited different mechanisms contributing to these processes.     

Applications of electrospray laser desorption ionization mass spectrometry for document examination

We have employed electrospray laser desorption ionization mass spectrometry (ELDI‐MS) to rapidly characterize certain classes of compounds – the inks within the characters made by inks and inkjet printer on regular paper and the chemical compounds within thermal papers. This ELDI‐MS approach allowed the ink and paper samples to be distinguished in terms of their chemical compositions. Sample pretreatment was unnecessary and the documents were practically undamaged after examination. The ink chemicals on the documents were desorbed through laser irradiation (sampling spot area: <100 µm²); the desorbed molecules then entered an electrospray plume – prepared from an acidic methanol/water solution (50%) – where they became ionized through fusion or ion‐molecule reactions with the charged solvent species and droplets in the plume. Copyright © 2009 John Wiley & Sons, Ltd.     

Adsorption-driven photocatalytic activity of mesoporous titanium dioxide

Titanium dioxide with a mesoporous structure, when photoactivated in water, demonstrates an unprecedented photocatalytic activity, driven strongly by an adsorption degree of molecules onto the catalyst surface, which promotes a preferential conversion of a well-adsorbed molecule. This catalyzes a selective transformation of a well-adsorbed molecule into a less-adsorbed molecule, so-labeled "stick-and-leave" transformation, which promotes a direct hydroxylation of benzene to phenol, one of the most difficult synthetic reactions, with very high selectivity (>80%) and using water as a source of oxidant.     

Simulation of phase I metabolism reactions of clozapine by HLM and photocatalytic methods with the use of UHPLC‐ESI‐MS/MS

In this study the comparison of human liver microsomes in in vitro incubation as well as ZnO‐ and TiO₂‐assisted photocatalytic degradation of clozapine as a mimicking method of phase I metabolism transformation was performed. Based on reversed‐phase UHPLC separation and high‐resolution MS/MS data, eight transformation products were identified and seven of them were found to be hepatic metabolites of the parent compound. The multivariate chemometric comparison of the obtained results shows ZnO‐assisted photocatalysis to be a more suitable approach to phase I metabolism simulation. The photocatalytic experiments demonstrated that the disappearance of clozapine followed pseudo‐zero order kinetics.     

Determination of bifonazole and identification of its photocatalytic degradation products using UPLC‐MS/MS

The main goal of the presented work was to investigate the effect of ZnO or/and TiO₂ on the stability of bifonazole in solutions under UVA irradiation. To this end, a simple and reproducible UPLC method for the determination of bifonazole in the presence of its photocatalytic degradation products was developed. Linearity was studied in the range of 0.0046–0.15 mg mL⁻¹ with a determination coefficient of 0.9996. Bifonazole underwent a photocatalytic degradation process under the experimental conditions used. Comparative studies showed that combination of TiO₂/ZnO (1:1 w /w) was a more effective catalyst than TiO₂ or ZnO with a degradation rate of up to 67.57% after 24 h of irradiation. Further, kinetic analyses indicated that the photocatalytic degradation of bifonazole in the mixture of TiO₂/ZnO can be described by a pseudo‐first order reaction. Statistical comparison clearly indicated that the presence of TiO₂/ZnO also affected the stability of bifonazole from a cream preparation after 15 h of UVA exposure (p < 0.05). Ten photodegradation products of bifonazole were identified for the first time and their plausible fragmentation pathways, derived from MS/MS data, were proposed. The main pathway in the photocatalytic transformation of bifonazole in the presence of ZnO or/and TiO₂ involves hydroxylation of the methanetriyl group and/or adjacent phenyl rings and cleavage of the imidazole moiety.     

A novel structural analysis of glycerophosphocholines as TFA/K(+) adducts by electrospray ionization ion trap tandem mass spectrometry

When collisionally activated dissociation (CAD) of glycerophosphocholine (GPC) species is examined using quadrupole ion trap mass spectrometry (QITMS), the spectral patterns differ from those obtained using sector or quadrupole mass spectrometry. Methods employed in the structural analysis of GPCs using a sector or quadrupole mass spectrometers are not necessarily useful for an ion trap mass spectrometer. A novel method is presented for structurally analyzing GPCs that involves the CAD of trifluoroacetic acid (TFA) adducts of kaliated GPCs. Solutions of GPCs in 0.1% TFA/methanol were electrosprayed to produce precursor ions by attaching a trifluoroacetic acid (TFA) molecule to a kaliated GPC molecule. The CAD-MS/MS spectra obtained by QITMS revealed a dramatic increase in the abundance of fragment ions, corresponding to the losses of sn-1 and sn-2 fatty acyl substituents. A preferential loss of the sn-1 fatty acyl group over the loss of the sn-2 fatty acyl group was observed among the GPC standards examined. A GPC extract from egg yolk was directly analyzed by this method without prior separation. The identities and positions of fatty acyl substituents of over 20 GPC species were identified. Some isomers present in very low relative abundance, which could not be analyzed by QITMS/MS using other ions as precursors, were identified by the TFA attachment method.     

Liquid chromatography time‐of‐flight mass spectrometry evaluation of fungicides reactivity in free chlorine containing water samples

Liquid chromatography (LC) combined with tandem mass spectrometry (MS/MS), based on the use of a hybrid quadrupole‐time‐of‐flight mass analyzer, was used to investigate the reactivity of nine fungicides in free chlorine‐containing water samples. Three of the selected compounds (fenhexamid, FEN; pyrimethanil, PYR; and cyprodinil, CYP) displayed a poor stability in presence of moderate chlorine levels; thus, the effects of different parameters on their half‐lives (t_1/2) were evaluated. Sample pH, bromide traces, and the water matrix affected their relative stabilities. Despite such variations, the three fungicides are degraded at significant rates not only in ultrapure, but also in surface water spiked with chlorine levels up to 2 µg ml^?1, and when mixed with chlorinated tap water, generating several transformation products (TPs). The time‐course of precursor species and their TPs was followed in the LC‐MS mode, using the information contained in accurate, full scan mass spectra (MS) to propose the empirical formulae of TPs. Thereafter, their ion product scan (MS/MS) spectra were considered to set their chemical structures; allowing, in some cases, to distinguish between isomeric TPs. The reaction pathway of FEN, the less stable fungicide, involved just an electrophilic substitution of hydrogen per chlorine, or bromine, and cleavage of the molecule to render an amide. PYR and CYP shared common reaction routes consisting of halogenation, hydroxylation, and condensation processes leading to complex mixtures of TPs, which were relatively stable to further transformations. Copyright © 2013 John Wiley & Sons, Ltd.     

Ionic‐Liquid‐Assisted Synthesis of Uniform Fluorinated B/C‐Codoped TiO2 Nanocrystals and Their Enhanced Visible‐Light Photocatalytic Activity

Exploiting advanced photocatalysts under visible light is of primary significance for the development of environmentally relevant photocatalytic decontamination processes. In this study, the ionic liquid (IL), 1‐butyl‐3‐methylimidazolium tetrafluoroborate, was employed for the first time as both a structure‐directing agent and a dopant for the synthesis of novel fluorinated B/C‐codoped anatase TiO₂ nanocrystals (T_IL) through hydrothermal hydrolysis of tetrabutyl titanate. These T_IL nanocrystals feature uniform crystallite and pore sizes and are stable with respect to phase transitions, crystal ripening, and pore collapse upon calcination treatment. More significantly, these nanocrystals possess abundant localized states and strong visible‐light absorption in a wide range of wavelengths. Because of synergic interactions between titania and codopants, the calcined T_IL samples exhibited high visible‐light photocatalytic activity in the presence of oxidizing Rhodamine B (RhB). In particular, 300 °C‐calcined T_IL was most photocatalytically active; its activity was much higher than that of TiO_1.98N_0.02 and reference samples (T_W) obtained under identical conditions in the absence of ionic liquid. Furthermore, the possible photocatalytic oxidation mechanism and the active species involved in the RhB degradation photocatalyzed by the T_IL samples were primarily investigated experimentally by using different scavengers. It was found that both holes and electrons, as well as their derived active species, such as ^.OH, contributed to the RhB degradation occurring on the fluorinated B/C‐codoped TiO₂ photocatalyst, in terms of both the photocatalytic reaction dynamics and the reaction pathway. The synthesis of the aforementioned novel photocatalyst and the identification of specific active species involved in the photodegradation of dyes could shed new light on the design and synthesis of semiconductor materials with enhanced photocatalytic activity towards organic pollutants.