Development of analytical methods for multiresidue determination of quinolones in pig muscle samples by liquid chromatography with ultraviolet detection, liquid chromatography–mass spectrometry and liquid chromagraphy–tandem mass spectrometry

Graphene oxide mediated CdSe quantum dots fluorescent aptasensor for high sensitivity detection of fluoroquinolones

In view of the urgent need for fluoroquinolones contamination detection in the fields of food safety, a novel aptasensor based on the fluorescence quenching property of graphene oxide (GO) and the fluorescence characteristic of cadmium selenide quantum dots (CdSe QDs) was developed for fluoroquinolones highly sensitive detection in this work. The CdSe QDs with carboxyl-rich surface were synthesized successfully and fluoresced at 525 nm under the optimal excitation light of 366 nm. Based on the hydrophobic and π-π stacking between GO and aptamer, aptamer labeled by CdSe QDs fluorescence (CdSe QDs-apt) were adsorbed by GO and the fluorescence of CdSe QDs was quenched. After the aptamer combined specifically with fluoroquinolones, greater specific force lead to the desorption of CdSe QDs-apt from GO and fluorescence recovery. Represented by Ciprofloxacin (CIP), a member of fluoroquinolones, the fluorescence emission increased with the increasing of CIP concentrations from 8 nM to 500 nM, and the detection limit was 0.42 nM. The spiked recoveries in real samples of honey and milk were 91.5-96.9 % and 90.3-95.2 %, respectively, indicating that the aptasensor was reliable. Moreover, the fluorescence responses of multiple members of fluoroquinolones were found to be consistent, denoting that the fluorescence aptasensor can be used to detect the total amount of multiple members of fluoroquinolones. These results showed that the aptasensor can be used as a promising platform for fluoroquinolones detection.

Molecularly imprinted polymers by reflux precipitation polymerization for selective solid-phase extraction of quinolone antibiotics from urine

Molecularly imprinted polymers (MIPs) possess high specific cavities towards the template molecules, thus solid-phase extraction (SPE) based on MIPs using the target as the template has been widely used for selective extraction. However, the performance of SPE depends strongly on the shape and the distribution of the MIP sorbents, and rapid synthesis of MIPs with uniform particles remains a challenge. Our previous studies have shown that reflux precipitation polymerization (RPP) was a simple and rapid method for the synthesis of uniform MIPs. However, synthesis of MIPs by RPP for a group of targets using only one of the targets as the template has rarely been reported. In this work, MIPs with specific recognition capability for a group of quinolone antibiotics were synthesized for the first time via RPP with only ofloxacin as the template. The synthesized MIPs displayed good adsorption performance and selectivity (IF > 3.5) towards five quinolones, and subsequently were used as SPE adsorbents. Based on this MIPs-SPE, after systematic optimization of the SPE operation parameters during loading, washing and elution, an efficient and sensitive enough SPE method for separation and enrichment of the five quinolones in urine was developed and evaluated in combination with LC-MS/MS. The results showed that MIPs-SPE-LC-MS/MS has a good correlation (R2 ≥ 0.9961) in the linear range of 1-500 μg L-1. The limit of detection (LOD) and limit of quantification (LOQ) for the five quinolones were 0.10-0.14 μg L-1 and 0.32-0.48 μg L-1, respectively. In addition, the proposed method demonstrated good reproducibility (≤ 13 %) and high accuracy (92 %-113 %). We are confident that this method holds significant promise for the analysis of quinolones within the contexts of forensic medicine, epidemiology, and environmental chemistry.

Establishment of an immunological detection method of fleroxacin by fluorescence-linked immunosorbent assay

The direct and indirect competitive fluorescence-linked immunosorbent assay (FLISA and icFLISA) incorporating quantum dots (QDs) for the detection of fleroxacin (FLE) was established for the first time in this study. The monoclonal antibody specific for FLE was successfully conjugated with QDs after purification by the caprylic acid-ammonium sulphate method. The limits of detection of FLISA and icFLISA were 0.012 ng/mL and 0.006 ng/mL, respectively; IC₅₀ were 0.32 ng/mL and 0.19 ng/mL; and the detection ranges were 0.012-24.490 ng/mL and 0.006-16.210 ng/mL. The recovery was 93.8%-112.4% and the coefficient of variation was below 11.75%. The fabricated FLISA and icFLISA are cost-effective, high sensitive and can be an alternative method in the detection of FLE residues.

Immunoassays on thiol-ene synthetic paper generate a superior fluorescence signal

The fluorescence-based detection of biological complexes on solid substrates is widely used in microarrays and lateral flow tests. Here, we investigate thiol-ene micropillar scaffold sheets ("synthetic paper") as the solid substrate in such assays. Compared to state-of-the-art glass and nitrocellulose substrates, assays on synthetic paper provide a stronger fluorescence signal, similar or better reproducibility, lower limit of detection (LOD), and the possibility of working with lower immunoreagent concentrations. Using synthetic paper, we detected the antibiotic enrofloxacin in whole milk with a LOD of 1.64 nM, which is on par or better than the values obtained with other common tests, and much lower than the maximum level allowed by European Union regulations. The significance of these results lays in that they indicate that synthetically-derived microstructured substrate materials have the potential to improve the performance of diagnostic assays.

Immobilized imidazolium-based ionic liquids in C18 for solid-phase extraction

In this work, two solid-phases based on imidazolium-based ionic liquids were obtained and characterized for solid-phase extraction of fluoroquinolones. The process of immobilization was performed replacing a toxic reagent by UV-irradiation to get a harmless process. The obtained solid-phases were characterized by nuclear magnetic resonance spectroscopy and elemental analysis. Each solid-phase was packed in a cartridge and was used in solid-phase extraction processes for norfloxacin and ciprofloxacin, after the optimization of some parameters such as the elution solvent, the eluent volume and, the sample volume to be used during the loading step. The developed solid-phases with immobilized ionic liquids were successfully implemented for the studied compounds and indicate high probabilities to be useful in solid-phase extractions of other fluoroquinolones.

A rapid and reliable assay to determine flumequine, marbofloxacin, difloxacin, and sarafloxacin in commonly consumed meat by micellar liquid chromatography

BACKGROUND

Micellar liquid chromatography - fluorescence detection was used to determine the antibiotics flumequine, marbofloxacin, difloxacin, and sarafloxacin in porcine, bovine, poultry, ovine, caprine, rabbit, and equine meat, to verify compliance with EU Regulation 37/2010 with regard to the occurrence of veterinary drugs in food.

RESULTS

The analytes were isolated from the matrix by ultrasonication-assisted leaching in a micellar solution, and the supernatant was filtered and directly injected. The fluoroquinolones were resolved in < 19 min using a C18 column, with an isocratic mobile phase of 0.05 mol L^-1 sodium dodecyl sulfate - 8% 1-butanol - 0.5% triethylamine buffered at pH 3. The limits of quantification (0.01-0.05 mg kg^-1 ) were below the maximum residue limits (0.15-0.4 mg kg^-1 ). The method was validated by EU Commission Decision 2002/657/EC guidelines.

CONCLUSION

The method shows practical advantages such as simplicity, low cost, eco-friendliness, safety, and applicability for routine analysis, and is useful for surveillance programs. © 2018 Society of Chemical Industry.

Inter-Laboratory Validation of Method to Determine Residual Enrofloxacin in Chicken Meat

An inter-laboratory study was performed to evaluate the performance of a method developed for the quantification of enrofloxacin in chicken meat. Liquid-liquid extraction combined with a clean-up procedure based on solid-phase extraction followed by a liquid chromatography-tandem mass spectrometric method was used by three individual laboratories. All the investigated results of calibration curves and limits of quantification were within the acceptable range for regulatory testing of enrofloxacin. The three laboratories received blind a certified reference material to analyze in triplicate and assess using statistical analysis. From the results, no statistical differences were found between the laboratories in the precision of the method. Additionally, all the results of the z-score, which is an indication of fixed interval bias criteria for accuracy from the laboratories, fell within the allowable limits (±2σ). Based on this proficiency testing by inter-laboratory comparisons, the analytical method including the sample preparation step was proven to be applicable.

Efficient Reduction of Antibacterial Activity and Cytotoxicity of Fluoroquinolones by Fungal-Mediated N-Oxidation

Extensive usage of fluoroquinolone antibiotics in livestock results in their occurrence in manure and subsequently in the environment. Fluoroquinolone residues may promote bacterial resistance and are toxic to plants and aquatic organisms. Moreover, fluoroquinolones may enter the food chain through plant uptake, if manure is applied as fertilizer. Thus, the presence of fluoroquinolones in the environment may pose a threat to human and ecological health. In this study, the biotransformation of enrofloxacin, marbofloxacin, and difloxacin by the fungus X. longipes (Xylaria) was investigated. The main metabolites were unequivocally identified as the respective N-oxides by mass spectrometry and nuclear magnetic resonance spectroscopy. Fungal-mediated N-oxidation of fluoroquinolones led to a 77-90% reduction of the initial antibacterial activity. In contrast to their respective parent compounds, N-oxides showed low cytotoxic potential and had a reduced impact on cell proliferation. Thus, biotransformation by X. longipes may represent an effective method for inactivating fluoroquinolones.

Bioanalysis of drug in tissue: current status and challenges

Distribution of drugs into tissues is an important determinant of the overall PK and PD profile. Thus, bioanalysis of drugs and their metabolites in tissues can play an important role in understanding the pharmacological and toxicological properties of new drug candidates. Unlike liquid matrices, bioanalysis in tissues offers unique challenges such as proper tissue sampling, appropriate tissue sample preparation, efficient extraction of the analytes from the tissue homogenates, and demonstration of stability and recovery of analytes in intact tissues. This article provides a systematic review of tissue sample analysis for small molecules using LC–MS/MS. The authors provide rationale for tissue sample analysis, and discuss strategies for method development, method qualification or validation, and sample analysis. Unique aspects of method development and qualification/validation are highlighted based on authors’ direct experiences and literature summary. Analysis using intact tissue samples such as MALDI imaging is also briefly discussed.

Micelle enhanced and terbium sensitized spectrofluorimetric determination of danofloxacin in milk using molecularly imprinted solid phase extraction

An efficient molecularly imprinted solid phase extraction (MISPE)-spectrofluorimetric method was developed to sensitively determine danofloxacin (DAN) in milk samples. Solid phase extraction procedure using MISPE cartridges was first performed on milk samples and then spectrofluorimetric determination was done at 546 nm using an excitation wavelength of 285 nm in presence of terbium and sodium dodecyl benzene sulfonate (SDBS). It was found that SDBS significantly enhanced the fluorescence intensity of the DAN-Tb(3+) complex. Various factors affecting the fluorescence intensity of DAN-Tb(3+)-SDBS system were studied and conditions were optimized. The enhanced fluorescence intensity of the system (ΔF) showed a good linear relationship with the concentration of DAN over the range of 8.4×10(-9)-3.4×10(-7) mol L(-1) with a correlation coefficient of 0.9996. The detection limit was determined as 2.0×10(-9) mol L(-1) and the limit of quantification was determined as 6.5×10(-9) mol L(-1). The MISPE-spectrofluorimetric procedure was successfully applied to the determination of DAN in milk samples. The method is simple, rapid, sensitive and allows interference free determination of DAN in complex fluorescent matrices like milk. The method can be used to determine whether the DAN residues in milk exceed MRLs or not.

Highly sensitive synchronous fluorescence measurement of danofloxacin in pharmaceutical and milk samples using aluminium (III) enhanced fluorescence

A simple, rapid and sensitive constant wavelength synchronous fluorescence method is developed for the determination of danofloxacin (DAN) in pharmaceutical formulations and its residue in milk based on Al(III) enhanced fluorescence. The synchronous fluorescence intensity of the system is measured at 435 nm using ∆ λ = 80 nm and an excitation wavelength of 280 nm. A good linear relationship between enhanced fluorescence intensity and DAN concentration is obtained in the range of 3-100 ng mL(-1)(r (2) = 0.9991). The limit of detection (LOD, S/N = 3) of the present method is 0.9 ng mL(-1). The proposed method can be successfully applied to the determination of DAN in pharmaceutical formulations and in milk without serious interferences from common excipients, metal ions and other co-existing substances. The method can be used as a rapid screening to judge whether the DAN residues in milk exceed Maximum Residue Limits (MRLs) or not.

Effect of protein on the detection of fluoroquinolone residues in fish meat

Using fish serum albumin (FSA) as the model protein, molecular fluorescence spectrometry and high-performance liquid chromatography (HPLC) were applied to study the effect of protein on the extraction of fluoroquinolone (FQ) residues in fish meat. There was a strong interaction between FQs and protein through hydrogen bonds, which could be broken as protein degenerated with 60-100% (v/v) acetonitrile acid solution, and FQs bound with protein were released in various degrees. On the basis of the results, a novel sample preparation procedure loosely based on QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) methodology was developed for the determination of FQ residues in fish muscle samples, using 90% (v/v) acetonitrile acid solution as the extractant, combined with a dispersive solid-phase extraction (DSPE) cleanup step. Mean recoveries of four FQs from spiked samples at a concentration range of 50-200 ng g(-1) were 73.3-95.9% with relative standard deviations (RSD) lower than 10.7%.

Determination of antibiotics in Brazilian surface waters using liquid chromatography-electrospray tandem mass spectrometry

A liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS) method for the determination of antibiotics in water was developed and applied to Brazilian surface waters. Amoxicillin, ampicillin, cefalexin (CEF), ciprofloxacin (CIP), norfloxacin (NOR), sulfamethoxazole, tetracycline (TET), and trimethoprim were selected as target compounds due to their high consumption pattern in Brazil. LC and MS conditions were optimized to produce the maximum analytic response for each compound. Anion exchange and polymeric solid-phase extraction cartridges, in series, were employed during the extraction procedures. Recovery, linear range, limit of detection (LOD), and limit of quantification were calculated. LOD varied from 0.13 ng L(-1) for CIP and NOR to 0.76 ng L(-1) for TET. Surface water samples from the Atibaia watershed (São Paulo State, Brazil) were analyzed. Results showed that seasonal and anthropogenic aspects dictated the levels of antibiotics in the samples. An overall frequency of detection of 55% was observed during the rainy period, whereas a higher percentage (88%) was noticed for samples collected during the dry season. In the Atibaia River, sample concentrations ranged from 29 ng L(-1) for CEF to 0.5 ng L(-1) for NOR. In a sewage-affected stream, however, concentrations up to 2422 ng L(-1) CEF were found.

Determination of penicillins in milk using LC-UV, LC-MS and LC-MS/MS

The aim of this work is to establish a method for the simultaneous determination of eight penicillins in milk samples by LC-UV, LC-MS and LC-MS/MS. The procedure involves a step for clean-up and to preconcentrate the analytes by SPE and a subsequent chromatographic analysis. LC-UV, LC-MS and LC-MS/MS have been used for the simultaneous quantification of penicillins in milk. The proposed methods have been validated according to the EU guideline and present LOQ below the maximum limits of residues (MRLs) established by the European Union for penicillins in milk. The developed methods were applied to different milk samples obtained from cows medicated with penicillins.

Simultaneous determination of fluoroquinolones, sulfonamides and tetracyclines in sewage sludge by pressurized liquid extraction and liquid chromatography electrospray ionization-mass spectrometry

A new scheme for the quantitative determination of traces of fluoroquinolones (FQs), tetracyclines (TCs) and sulfonamides (SAs) in sewage sludge was developed. The compounds were simultaneously extracted from sewage sludge by pressurized liquid extraction (PLE). A novel and effective method for PLE was developed. Solid-phase extraction was used for cleaning up the extracts. Identification and quantification of the compounds was done using high-performance liquid chromatography with electrospray ionization mass spectrometry in selected reaction monitoring mode. The best recovery of FQs and TCs was obtained by using hydrophilic-lipophilic balance cartridges, recoveries ranged 59% for norfloxacin to 82% for ofloxacin and 95% for doxycycline; for SAs strong cation-exchange cartridges were more efficient, recoveries were 96% for sulfamethoxazole and 43% for sulfadimethoxine. Limit of quantification ranged from 0.1 ng/g for SAs to 160 ng/g for tetracycline. Method precision for TCs was 5.06% and 1.12%, and for SAs 0.43% and 2.01%. FQs precision ranged from 0.77% to 1.89%.

Are liquid chromatography/electrospray tandem quadrupole fragmentation ratios unequivocal confirmation criteria?

Multiple reaction monitoring (MRM) ratios as provided by tandem mass spectrometers are used to confirm positive residue findings (e.g. veterinary drugs or pesticides). The Commission Decision 2002/657/EEC defines tolerance levels for MRM ratios, which are intended to prevent the reporting of false positives. This paper reports findings where blank sample extracts have been spiked by a drug (difloxacin) and the corresponding measured MRM ratios significantly deviated from MRM ratios observed in matrix-free solution. The observation was explained by the formation of two different [M+H](+) analyte ions within the electrospray ionization (ESI) interface. These two ions vary only by the site of analyte protonation. Since they are isobaric, they are equally transmitted through the first quadrupole, but are differently fragmented in the collision chamber. The existence of two isobaric ions was deduced by statistical data and the observation of a doubly charged analyte ion. It was hypothesized that the combined presence of [M+H](+) and [M+2H](2+) implies the existence of two different singly charged ion species differing only by the site of protonation. Low- and high-energy interface-induced fragmentation was performed on the samples. The surviving precursor ion population was mass selected and again fragmented in the collision chamber. Equal product ion spectra would be expected. However, very different product ion spectra were observed for the two interface regimes. This is consistent with the assumption that the two postulated isobaric precursor ions show different stability in the interface. Hence the abundance ratio among the two types of surviving precursor ions will shift and change the resulting product ion spectra. The existence of the postulated singly charged ions with multiple chargeable sites was finally confirmed by successful ion mobility separation.