Photolysis of enrofloxacin, pefloxacin and sulfaquinoxaline in aqueous solution by UV/H2O2, UV/Fe(II), and UV/H2O2/Fe(II) and the toxicity of the final reaction solutions on zebrafish embryos.

In this work, the photolysis of enrofloxacin (ENR), pefloxacin (PEF), and sulfaquinoxaline (SQX) in aqueous solution by UV combined with H2O2 or ferrous ions (Fe(II)), as well as Fenton (Fe(II)/H2O2) processes, was investigated. In addition, the toxicity of the final reaction solution after UV/H2O2/Fe(II) treatment toward zebrafish embryos was determined. The degradation of the test compounds followed pseudo-first-order reaction kinetics. The optimum concentrations of H2O2 for ENR, PEF and SQX removal under UV/H2O2 treatment were 20, 20 and 5 mM, respectively. The optimum concentrations of Fe(II) for ENR, PEF and SQX removal in the UV/Fe(II) system were 0.25, 10, and 1 mM, respectively. For the UV/H2O2/Fe(II) system, pH = 3 is the best initial pH for the degradation of ENR, PEF and SQX with the degradation efficiencies at 100%, 79.1% and 100% after 180 min, respectively. Considering the degradation rate and electrical energy per order of the test compounds, the UV/H2O2/Fe(II) process was better than the UV/H2O2 and UV/Fe(II) processes because of the greater OH generation. Based on major transformation products of ENR, PEF, and SQX detected during UV/H2O2/Fe(II) treatment, the probable degradation pathway of each compound is proposed. The fluorine atom of ENR and PEF was transformed into fluorine ion, and the sulfur atom was transformed into SO2/SO42-. The nitrogen atom was mainly transformed into NH3/NH4+. Formic acid, acetic acid, oxalic acid, and fumaric acid were identified in the irradiated solutions and all the test compounds and their intermediates can be finally mineralized. In addition, after the UV/H2O2/Fe(II) process, the acute toxicity of the final reaction solutions on zebrafish embryos was lower than that of the initial solution without any treatment. In summary, UV/H2O2/Fe(II) is a safe and efficient technology for antibiotic degradation.

Catalytic degradation of sulfaquinoxalinum by polyester/poly-4-vinylpyridine nanofibers-supported iron phthalocyanine.

Iron (II) phthalocyanine (FePc) supported on electrospun polyester/poly-4-vinylpyridine nanofibers (PET/P4VP NFs) was prepared by stirring in tetrahydrofuran. The resulting product was confirmed and characterized by ultraviolet-visible diffuse reflectance spectroscopy, attenuated total reflection Fourier transform infrared spectra, X-ray photoelectron spectroscopy, gas chromatography/mass spectrometry, and ultra-performance liquid chromatography. More than 95% of sulfaquinoxalinum (SQX) could be removed by the activation of hydrogen peroxide in the presence of FePc-P4VP/PET with a PET and P4VP mass ratio of 1:1. This system exhibited a high catalytic activity across a wide pH and temperature range. The degradation rates of SQX achieved 100, 95, and 78% at a pH of 3, 7, and 9, respectively, and the degradation rates of SQX are more than 80% at the temperature ranging from 35 to 65 °C. DMSO2 could be detected by gas chromatography/mass spectrometry after the addition of DMSO, suggesting the formation of the high-valent iron intermediates in this catalytic system. In addition, the electron paramagnetic resonance experiments proved that free radicals did not dominate the reaction in our system. Therefore, the high-valent iron intermediates were proposed to the main active species in the FePc-P4VP/PET/hydrogen peroxide system. In summary, the heterogeneous catalytic processes with non-radical catalytic mechanism might have better catalytic performance for the removal of organic pollutants, which can potentially be used in wastewater treatment.

Transformation of sulfaquinoxaline by chlorine and UV light in water: kinetics and by-product identification.

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 photo-transformation 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.

Ferrous-activated peroxymonosulfate oxidation of antimicrobial agent sulfaquinoxaline and structurally related compounds in aqueous solution: kinetics, products, and transformation pathways.

Sulfaquinoxaline (SQX) is a coccidiostatic drug widely used in poultry and swine production and has been frequently detected in various environmental compartments such as surface water, groundwater, soils, and sediments. In the present study, degradation of SQX by ferrous ion-activated peroxymonosulfate oxidation process (Fe(II)/PMS), a promising in situ chemical oxidation (ISCO) technique, was systematically investigated. Experimental results showed that Fe(II)/PMS process appeared to be more efficient for SQX removal relative to Fe(II)/persulfate process (Fe(II)/PS). An optimal Fe(II):PMS molar ratio of 1:1 was found to be necessary for efficient removal of SQX. Increasing the solution pH hampered the degradation of SQX, and no enhancement in SQX degradation was observed when chelating agents S,S'-ethylenediamine-N,N'-disuccinic acid (EDDS) and citrate were present. The presence of Suwannee River fulvic acid (SRFA), as a representative of aquatic natural organic matter (NOM), could inhibit the degradation of SQX. SQX was more susceptible to Fe(II)/PMS oxidation in comparison to its substructural analog 2-amino-quinoxaline (2-AQ) and other sulfonamides, i.e., sulfapyridine (SPD) and sulfadiazine (SDZ). Transformation products of SQX were enriched by solid-phase extraction (SPE) and identified by liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI-MS/MS). On the basis of the TPs identified, detailed reaction pathways for SQX degradation including sulfonamide bond cleavage, SO2 extrusion, and aniline moiety oxidation were proposed. Our contribution may provide some useful information for better understanding the kinetics and mechanisms of SQX degradation by sulfate radical-based advanced oxidation processes (SR-AOPs).

Development of a novel carbon paste sensor for determination of micromolar amounts of sulfaquinoxaline in pharmaceutical and biological samples.

A potentiometric carbon paste sensor was fabricated for determination of sulfaquinoxaline (SQX) based on the use of ion-association complex of sulfaquinoxaline sodium with 2,3,5-triphenyltetrazolium chloride. The proposed sensor exhibited Nernstian slope of 58.4 ± 0.3 mV per decade for sulfaquinoxaline over a wide concentration range of 5.0 × 10(-6) to 1.0 × 10(-2)M, with a low detection limit of 3.0 × 10(-6)M. The sensor manifested advantages of fast response time, satisfactory reproducibility, long life time, high thermal stability and, most importantly, excellent selectivities for sulfaquinoxaline relative to a wide variety of common foreign inorganic cations, anions, sugars and amino acids. The sensor was successfully used for determination of sulfaquinoxaline in pharmaceutical solution, blood serum, urine and milk samples. The isothermal coefficient of the electrode was calculated by the investigation of temperature effects on the electrode potential response.

Structural elucidation of sulfaquinoxaline metabolism products and their occurrence in biological samples using high-resolution Orbitrap mass spectrometry.

Four previously unreported metabolism products of sulfaquinoxaline (SQX), a widely used veterinary medicine, were isolated and analyzed using liquid chromatography coupled to high-resolution Orbitrap mass spectrometry. Metabolites were structurally elucidated, and a fragmentation pathway was proposed. The combination of high-resolution MS(2) spectra, linear ion trap MS(2), in-source collision-induced dissociation (CID) fragmentation, and photolysis were used to analyze SQX and its metabolites. All metabolism products identified showed a similar fragmentation pattern to that of the original drug. Differential product ions were produced at m/z 162 and 253 which contain the radical moiety with more 16 Da units than sulfaquinoxaline. This occurs by a hydroxyl attachment to the quinoxaline moiety. With the exception of two low-intensity compounds, all the mass errors were below 5.0 ppm. The distribution of these metabolites in some animal species are also presented and discussed.

Porous molecularly imprinted monolithic capillary column for on-line extraction coupled to high-performance liquid chromatography for trace analysis of antimicrobials in food samples.

A novel porous molecularly imprinted monolithic capillary column (MIMCC) based on ternary porogen was synthesized by in situ technique with sulfaquinoxaline as the template molecule. The characteristics of the MIMCC were investigated by scanning electron microscopy, infrared spectrum, thermogravimetric analysis and solvent resistance test. The saturated adsorption amount of sulfaquinoxaline on MIMCC was 2.7 times over that on the non-imprinted monolithic capillary column (NIMCC). The MIMCC also exhibited good enrichment ability to its analogs and the enrichment factors were 46-211 for five antimicrobials. High permeability and imprinting factors as well as good stability, reproducibility and long lifetime were obtained. An on-line method based on MIMCC solid-phase microextraction coupled with high-performance liquid chromatography was developed for the determination of trace antimicrobials in complex samples. The good linearity for sulfametoxydiazine, sulamethoxazole and sulfaquinoxaline was 0.05-10 µg/L, the limits of detection (LODs) were 10.0-14.0 ng/L. The linear range for mequindox and quinocetone were 0.10-10.0 µg/L, the LODs were 20.0-27.0 ng/L respectively. The recoveries were 71.0-108.2% with relative standard deviation of 1.6-8.5%, correspondingly. The results showed that MIMCC could effectively enrich antimicrobials from complex matrices. The on-line method based on MIMCC and HPLC was selective, sensitive and convenient for trace determination of antimicrobials in complex samples.

Sorption and desorption of sulfadimethoxine, sulfaquinoxaline and sulfamethazine antimicrobials in Brazilian soils.

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 µg(1-1/n)(cm(3))(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 µg(1-1/n)(cm(3))(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.

Liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry for the analysis of sulfaquinoxaline byproducts formed in water upon solar light irradiation.

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 MS(2) 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 SO(2) 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 NH(3). The fragmentation of the protonated 2-aminoquinoxaline mainly involved the elimination of NH(3) 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.

[Qualification and quantification of 10 sulfonamides in animal feedstuff by high performance liquid chromatography-electrospray tandem mass spectrometry].

The presence of sulfonamide (SA) residues in foods is largely due to the raising of animals with sulfonamide antibiotics added or polluted feedstuff. Because of interference from the matrices, the commonly used immunoassay or chromatographic method is not suitable for the analysis of multi-SAs in feedstuff. A high performance liquid chromatographic-electrospray tandem mass spectrometric (HPLC/ESI-MS-MS) method has been established for the simultaneous determination of multi-SAs including sulfadiazine (SD), sulfapyridine (SPD), sulfamerazine (SM1), sulfameter (SM), sulfamethazine (SM2), sulfamethoxypyridazine (SMP), sulfamethoxazole (SMZ), sulfamonomethoxine (SMM), sulfadimethoxine (SDM) and sulfaquinoxaline (SQX). After solvent extraction, solid phase extraction, dilution and reversed-phase HPLC separation, SAs were detected by ESI-MS-MS under multi-reaction monitoring mode. The qualification analysis was done by using retention time and distribution of diagnostic ion pairs, and the quantification was based on the peak intensity of common fragment ion m/z 156. The limits of quantification for 10 SAs were 0.5 - 2.0 microg/kg (S/N = 10). The correlation coefficient of linear calibration curve was over 0.9995 within the SAs concentration range 2.0 - 200 microg/L except for SDM and SQX. At the spiked level of 1.0 mg/kg, the average recoveries for the 10 SAs were between 70% and 92%, the relative standard deviations were under 10% for intra-day and under 15% for inter-day. Routine tests showed the method was fast, sensitive, specific, and practical for the SAs determination in feedstuff.

[Determination of residual sulfonamides in meat by high performance liquid chromatography with solid-phase extraction].

A method was developed for determining residual sulfonamides (SAs) such as sulfamethazine (SM2), sulfamonomethoxine (SMM), sulfamethiazole (SMZ), sulfadimethoxine (SDM) and sulfaquinoxaline (SQ) in pork and chicken using solid-phase extraction (SPE) and high performance liquid chromatography (HPLC) with a photodiode array detector. The samples were extracted with ethyl acetate. An NH2 column was used for clean up. For the HPLC determination, an Intersil ODS-2 column was used with a mixture of methanol-acetonitrile-water-acetic acid (2: 2: 9: 0.2, v/v) as the mobile phase. The detection limits (S/N = 3) were 3 microg/kg for SM2, SMM and SMZ, and 7 microg/kg for SDM and SQ. The quantitation limits (S/N = 10) were 10 microg/kg for SM2, SMM and SMZ, and 25 microg/kg for SDM and SQ. The linear ranges were 30 - 5 000 microg/L for SM2, SMM and SMZ, and 60 - 5 000 microg/L for SDM and SQ. The recoveries were between 73.2% and 97.3% with the relative standard deviations between 2.5% and 11.6% originated from the spiked level of 50 microg/kg.

Stability of sulfonamide antibiotics in spiked pig liver tissue during frozen storage.

A bulk portion of homogenized pig liver tissue was spiked at room temperature with 0.2 mg/kg (twice the Australian maximum residue limit) of each of sulfathiazole, sulfachlorpyridazine, sulfadimidine (sulfamethazine), sulfaquinoxaline, and sulfadimethoxine. After subsampling and packaging, selected individual packaged units were tested to confirm homogeneity of the prepared material. The material was stored frozen at -20 degrees C and analyzed in replicate by liquid chromatography on 11 sampling dates over a period of about 6 months. Analytical data were plotted on a log-linear scale and subjected to linear regression on the basis of first-order kinetics for the decay. Storage stabilities (decay half-lives at -20 degrees C) calculated from the mean slope of regression lines were sulfadimethoxine, 567 days; sulfadimidine, 457 days; sulfachlorpyridazine, 312 days; sulfathiazole, 291 days; and sulfaquinoxaline, 271 days. Significant depletion (65% loss) of residue was observed for sulfaquinoxaline during preparation of spiked bulk liver tissue. An extension of the study to measure the storage stability of sulfaquinoxaline under accelerated decay conditions (refrigerator temperature, 4 degrees C) showed it to be relatively unstable, with a decay half-life of 11 days. Results demonstrate the need for both regulatory agencies and testing laboratories to be aware of potential errors associated with improper transport, storage, and handling of tissue samples submitted for antibiotic testing.

Comparison of supercritical CHF3 and CO2 and methanol-modified CHF3 and CO2 for extraction of sulfonamides from chicken liver.

Supercritical CHF3 and methanol-modified CHF3 were compared with supercritical CO2 and methanol-modified CO2 for extraction of sulfonamides from fortified chicken liver admixed with Hydromatrix. Results showed that solvating power and selectivity were higher for supercritical and methanol-modified CHF3 than for supercritical and methanol-modified CO2. Visual observation showed that chicken liver extract obtained with methanol-modified CHF3 was cleaner than that obtained with methanol-modified CO2. Fat precipitated in the solvent trap when CO2 was used as the extraction medium. Also, simple off-line collection of fortified chicken liver extract obtained with CO2 in a solid-phase extraction cartridge (packed with either C18 or alumina) followed by phosphate buffer-methanol (50 + 50) rinse yielded an extract that required no further cleanup for analysis.