The Experts below are selected from a list of 468 Experts worldwide ranked by ideXlab platform
Gregorio Castañeda - One of the best experts on this subject based on the ideXlab platform.
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Voltammetric behavior of pyrimethamine in veterinary formulations using square‐wave and adsorptive square‐wave techniques
Electroanalysis, 1995Co-Authors: J.j. Berzas, José M. Lemus, Juana Rodríguez, Gregorio CastañedaAbstract:The voltammetric behavior of pyrimethamine (PMT) was studied by square-wave (SW) and square-wave stripping (SWS) techniques, leading to two methods for its determination [in presence of Sulfaquinoxaline (SQX)] in aqueous samples and veterinary formulations. Due to overlapping response of SQX and PMT the first derivative was used for the simultaneous determination of these two components. The relative standard deviations obtained for concentration levels of PMT as low as 3 × 10−6 M (SW) and 5 × 10−7 M (SWS) were 2.2% and 2.7% (n = 10), respectively.
Susanne Rath - One of the best experts on this subject based on the ideXlab platform.
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sorption and desorption of sulfadimethoxine Sulfaquinoxaline and sulfamethazine antimicrobials in brazilian soils
Science of The Total Environment, 2014Co-Authors: Keity Margareth Doretto, Livia Maniero Peruchi, Susanne RathAbstract:Abstract Adsorption and desorption are important processes that influence the transport, transformation and bioavailability of antimicrobials in soils. The adsorption–desorption characteristics of sulfadimethoxine, Sulfaquinoxaline and sulfamethazine in Brazilian soils (sandy, sandy-clay and clay) were evaluated using the batch equilibrium method. The sulfonamides were quantified in the soil solutions by a previously in house validated HPLC-PAD method. The adsorption/desorption data for the sulfonamides in soils fit the Freundlich isotherms well in the logarithmic form. The Freundlich adsorption coefficients ranged from 1.4 to 19.0 μg1 − 1 / n(cm3)1 / n g− 1, suggesting that all of the sulfonamides weakly adsorbed on the evaluated soils. The Freundlich desorption coefficients ranged from 0.85 to 24.8 μg1 − 1 / n(cm3)1 / n g− 1, indicating that the sulfonamides tend to be leached from soils with high sand and low organic carbon contents, suggesting that there is high potential for surface and groundwater contamination.
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Use of experimental design and effective mobility calculations to develop a method for the determination of antimicrobials by capillary electrophoresis.
Talanta, 2008Co-Authors: Mónica Cecilia Vargas Mamani, Felix Guillermo Reyes Reyes, Jaime Amaya-farfan, José Alberto Fracassi Da Silva, Susanne RathAbstract:A capillary zone electrophoresis (CZE) method for the determination of chloramphenicol (CLP), danofloxacin (DANO), ciprofloxacin (CIPRO), enrofloxacin (ENRO), sulfamethazine (SMZ), Sulfaquinoxaline (SQX) and sulfamethoxazole (SMX) is described. For the development, the effective mobilities were estimated and a central composite design was performed. The method was in-house validated for CLP, CIPRO, ENRO and SMX determination in pharmaceuticals. In comparison with the HPLC method recommended by the United States Pharmacopoeia, this CZE method exhibited the same performance, with the advantage that seven different antimicrobials in pharmaceutical formulations could be simultaneously determined.
Cyril Le Fur - One of the best experts on this subject based on the ideXlab platform.
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Evaluation et compréhension du devenir photochimique de composés organiques émergents en solution aqueuse et à la surface du sol
2015Co-Authors: Cyril Le FurAbstract:Cette étude a eu pour objectif de contribuer à une meilleure compréhension du comportement photochimique de certains micropolluants de type antibiotiques vétérinaires (Sulfaquinoxaline, pyriméthamine) ou antibactérien (triclosan) en solution aqueuse et à la surface de la kaolinite, utilisée comme un modèle de sol.L’étude du comportement photochimique de la Sulfaquinoxaline a été réalisée sous excitation à 254 nm et 365 nm. Dans tous les cas, une dégradation efficace est observée avec un rendement quantique qui dépend de la longueur d’onde d’excitation, du pH et la concentration d’oxygène dissous. De plus, la présence de l’oxygène moléculaire dans le milieu conduit à une inhibition partielle la photodégradation mettant en évidence l’implication partielle de l’état excité triplet. Ce dernier a pu être mis en évidence par photolyse laser nanoseconde à travers un transfert Triplet-Triplet (T-T) en employant le β-carotène comme accepteur. Sur le plan analytique, la phototransformation de la Sulfaquinoxaline conduit à la formation d’un grand nombre de produits qui ont été identifiés par HPLC/ESI/MS/MS en identifiant les processus de fragmentation intervenant pour chaque molécule étudiée. L’étude a permis de montrer que les états excités singulet et triplet sont tout les deux impliqués dans la photodegradation et que les processus principaux intervenant sont la photohydrolyse, la désulfonation avec un réarrangement intramoléculaire, l'hydroxylation des motifs aromatiques et l'isomérisation selon un processus de type photo Fries.L’étude de la photoréactivité de la pyriméthamine a montré que la dégradation est plus efficace avec la forme neutre. Le rendement quantique a été évalué à environ 4,0x10-2 en milieu aéré et sous excitation à 254 nm. L’étude par photolyse laser a montré la formation intermédiaire de l’état excité triplet mais également de l’électron solvaté (absorption à 700 nm). Les processus de formation des photoproduits primaires sont la substitution de l’atome de chlore par un groupement hydroxyle ou par un atome d’hydrogène et l’hydroxylation du noyau aromatique.La dégradation des micropolluants à la surface du sol a pu être abordée en utilisant l’argile kaolinite comme support modèle. Ce système simplifié nous a permis d’étudier la photodégradation sous excitation en Suntest sur le plan cinétique et analytique. L’étude cinétique a été entreprise en fonction de différents paramètres tels que l’épaisseur de la kaolinite et la concentration initiale du substrat. Le premier effet nous a permis de montrer que pour des épaisseurs inférieures à 70 µm, la vitesse de diffusion du composé des zones sombres vers les zones irradiées est très rapide devant la photolyse et de ce fait, elle peut être négligée. Cet aspect a conduit à la détermination du rendement quantique de disparition à la surface de la kaolinite. Sur le plan analytique, les réactions observées sur l’argile sont différentes de celles observées en solution aqueuse. En effet, dans le cas de la Sulfaquinoxaline, seul le produit de désulfonation est observé. Au contraire de la Sulfaquinoxaline, l’étude complète de la molécule de triclosan a montré la formation de plusieurs produits et notamment des dimères ou des oligomères ce qui suggère la présence du substrat sous forme d’agrégats à la surface de l’argile. Afin de confirmer cette observation expérimentale, nous avons abordé une étude de modélisation par dynamique moléculaire. Celle-ci a donnée des informations très importantes sur l’organisation des molécules à la surface de la kaolinite. Ainsi, l’adsorption du triclosan fait intervenir d'importantes liaisons hydrogène avec la surface de la kaolinite. En présence de plusieurs molécules, la formation d’agrégats est gouvernée par une importante interaction entre les noyaux aromatiques de type π-stacking.
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Liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry for the analysis of Sulfaquinoxaline by products formed in water upon solar light irradiation
Rapid Communications in Mass Spectrometry, 2013Co-Authors: Cyril Le Fur, Bertrand Légeret, Pascal De Sainte Claire, Pascal Wong-wah-chung, Mohamed SarakhaAbstract:RATIONALE Sulfonamides such as Sulfaquinoxaline (SQX) are among the most important antibiotic families due to their extensive use in veterinary medicine. The prediction of their fate under solar irradiation through the identification of the generated metabolites is required. However, unambiguous structural characterizations often remain a challenge particularly when several isomers could match with the same MS2 data. METHODS Liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry (LC/ESI-Q-TOFMS) in the positive ion mode, leading to the formation of the protonated forms of the studied compounds, [M+H+] ions, was employed. Collision-induced dissociation tandem mass spectrometry (CID-MS/MS) of the protonated molecules was carried out, and the effect of the collision energy as well as the elemental compositions of the product ions were used to propose chemical structures. Validation of the hypothesized structures was performed by the calculation of key fragmentation pathway energies using density functional theory (DFT) calculations (B3LYP/6-31G (d,p)). RESULTS The photoproducts were identified as 2-aminoquinoxaline, SQX isomers, 2-(N-parabenzoquinoneimine)quinoxaline and isomers resulting from SO2 extrusion. The direct fragmentations of [SQX+H]+ and its protonated isomers mostly occurred through the loss of 2-aminoquinoxaline and/or the 4-sulfoaniline radical ion, while their rearrangements involved the migration of H and/or O atoms. For the desulfonated byproducts in their protonated forms, the main neutral losses were of the quinoxaline radical, aminoquinoxaline and NH3. The fragmentation of the protonated 2-aminoquinoxaline mainly involved the elimination of NH3 and HCN. CONCLUSIONS LC/ESI-Q-TOFMS and DFT calculations have been shown to be useful and complementary methods for the identification of unknown isomeric compounds and the elucidation of fragmentation patterns, in the case of the Sulfaquinoxaline veterinary antibiotic
J.j. Berzas - One of the best experts on this subject based on the ideXlab platform.
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Voltammetric behavior of pyrimethamine in veterinary formulations using square‐wave and adsorptive square‐wave techniques
Electroanalysis, 1995Co-Authors: J.j. Berzas, José M. Lemus, Juana Rodríguez, Gregorio CastañedaAbstract:The voltammetric behavior of pyrimethamine (PMT) was studied by square-wave (SW) and square-wave stripping (SWS) techniques, leading to two methods for its determination [in presence of Sulfaquinoxaline (SQX)] in aqueous samples and veterinary formulations. Due to overlapping response of SQX and PMT the first derivative was used for the simultaneous determination of these two components. The relative standard deviations obtained for concentration levels of PMT as low as 3 × 10−6 M (SW) and 5 × 10−7 M (SWS) were 2.2% and 2.7% (n = 10), respectively.
Mohamed Sarakha - One of the best experts on this subject based on the ideXlab platform.
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liquid chromatography electrospray ionization quadrupole time of flight mass spectrometry for the analysis of Sulfaquinoxaline byproducts formed in water upon solar light irradiation
Rapid Communications in Mass Spectrometry, 2013Co-Authors: Bertrand Légeret, Pascal De Sainte Claire, Mohamed Sarakha, Le C Fur, Pascal WongwahchungAbstract:RATIONALE Sulfonamides such as Sulfaquinoxaline (SQX) are among the most important antibiotic families due to their extensive use in veterinary medicine. The prediction of their fate under solar irradiation through the identification of the generated metabolites is required. However, unambiguous structural characterizations often remain a challenge particularly when several isomers could match with the same MS2 data. METHODS Liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry (LC/ESI-Q-TOFMS) in the positive ion mode, leading to the formation of the protonated forms of the studied compounds, [M + H+] ions, was employed. Collision-induced dissociation tandem mass spectrometry (CID-MS/MS) of the protonated molecules was carried out, and the effect of the collision energy as well as the elemental compositions of the product ions were used to propose chemical structures. Validation of the hypothesized structures was performed by the calculation of key fragmentation pathway energies using density functional theory (DFT) calculations (B3LYP/6-31 G (d,p)). RESULTS The photoproducts were identified as 2-aminoquinoxaline, SQX isomers, 2-(N-parabenzoquinoneimine)quinoxaline and isomers resulting from SO2 extrusion. The direct fragmentations of [SQX + H]+ and its protonated isomers mostly occurred through the loss of 2-aminoquinoxaline and/or the 4-sulfoaniline radical ion, while their rearrangements involved the migration of H and/or O atoms. For the desulfonated byproducts in their protonated forms, the main neutral losses were of the quinoxaline radical, aminoquinoxaline and NH3. The fragmentation of the protonated 2-aminoquinoxaline mainly involved the elimination of NH3 and HCN. CONCLUSIONS LC/ESI-Q-TOFMS and DFT calculations have been shown to be useful and complementary methods for the identification of unknown isomeric compounds and the elucidation of fragmentation patterns, in the case of the Sulfaquinoxaline veterinary antibiotic. Copyright © 2013 John Wiley & Sons, Ltd.
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Liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry for the analysis of Sulfaquinoxaline by products formed in water upon solar light irradiation
Rapid Communications in Mass Spectrometry, 2013Co-Authors: Cyril Le Fur, Bertrand Légeret, Pascal De Sainte Claire, Pascal Wong-wah-chung, Mohamed SarakhaAbstract:RATIONALE Sulfonamides such as Sulfaquinoxaline (SQX) are among the most important antibiotic families due to their extensive use in veterinary medicine. The prediction of their fate under solar irradiation through the identification of the generated metabolites is required. However, unambiguous structural characterizations often remain a challenge particularly when several isomers could match with the same MS2 data. METHODS Liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry (LC/ESI-Q-TOFMS) in the positive ion mode, leading to the formation of the protonated forms of the studied compounds, [M+H+] ions, was employed. Collision-induced dissociation tandem mass spectrometry (CID-MS/MS) of the protonated molecules was carried out, and the effect of the collision energy as well as the elemental compositions of the product ions were used to propose chemical structures. Validation of the hypothesized structures was performed by the calculation of key fragmentation pathway energies using density functional theory (DFT) calculations (B3LYP/6-31G (d,p)). RESULTS The photoproducts were identified as 2-aminoquinoxaline, SQX isomers, 2-(N-parabenzoquinoneimine)quinoxaline and isomers resulting from SO2 extrusion. The direct fragmentations of [SQX+H]+ and its protonated isomers mostly occurred through the loss of 2-aminoquinoxaline and/or the 4-sulfoaniline radical ion, while their rearrangements involved the migration of H and/or O atoms. For the desulfonated byproducts in their protonated forms, the main neutral losses were of the quinoxaline radical, aminoquinoxaline and NH3. The fragmentation of the protonated 2-aminoquinoxaline mainly involved the elimination of NH3 and HCN. CONCLUSIONS LC/ESI-Q-TOFMS and DFT calculations have been shown to be useful and complementary methods for the identification of unknown isomeric compounds and the elucidation of fragmentation patterns, in the case of the Sulfaquinoxaline veterinary antibiotic
