Exploring the economic viability of electrochemical assessment for water contaminants with NiFe-PBA/ZIF-67 core shell modified GCE.

Zeolitic Imidazolate (metal organic) Frameworks (ZIFs) and Prussian Blue Analogues (PBAs) are promising materials in electrochemical sensing due to their unique properties. In this study, a composite material comprising NiFe-PBA and ZIF-67 was synthesized and made to form a uniform layer onto a glassy carbon electrode (GCE) to enhance electrochemical performance for furazolidone (FZD) detection. The synthesized NiFe-PBA/ZIF-67 composite exhibited excellent sensitivity, selectivity, and stability towards FZD detection, with a low limit of detection (LOD). The electrochemical behaviour of FZD on the NiFe-PBA/ZIF-67/GCE electrode was investigated, revealing a diffusion-controlled process. Differential pulse voltammetry (DPV) analysis demonstrated the synergetic effect of the PBA/MOF core-shell structure in enhancing FZD electro-reduction. The sensor exhibited exceptional LOD of 0.007 µM. Selectivity studies confirmed the sensor's ability to distinguish FZD from potential interferents. Extensive evaluations demonstrated the sensor's reproducibility, repeatability, and long-term stability, affirming its practical utility. Real sample analysis further validated the sensor's excellent analytical capabilities in diverse matrices.

Colorimetric immunoassay of furazolidone metabolites based on iron-copper bimetallic organic framework nanoenzyme.

Based on the peroxidase activity of Cu-hemin metal-organic framework (Cu-hemin MOF) nanozyme, a colorimetric enzyme-linked immunosensor was developed for the detection of furazolidone (FZD). Cu-hemin MOF is a bimetallic nanozyme that exhibited a stronger catalytic effect compared with single-metal organic framework nanoenzymes. Cu-hemin-MOF catalyzes hydrogen peroxide (H2O2) to produce hydroxyl radicals (•OH), which oxidizes the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB). The absorbance change is at 650 nm. The content of AOZ in animal food can be quickly and accurately determined by changes in absorbance. The linear range of the colorimetric biosensor for detecting FZD was 0.01 ~ 62.52 ng/mL, and the limit of detection was as low as 0.01 ng/mL. The recovery of spikes samples was in the range 94.2-108.0 % and reproducibility was less than 4.8%. In addition, the cross-reaction rate was less than 0.1% when detecting other metabolites except AOZ, indicating that the sensor has good applicability and specificity. This study not only provides a better understanding of the relationship between the dispersion of nanoenzymes and enzyme-like activity but also offers a general method for detecting antibiotics using the nanoenzyme colorimetric method.

MoS2_CNTs_aerogel-based PEDOT nanocomposite electrochemical sensor for simultaneous detection of chloramphenicol and furazolidone in food samples.

Toxic intermediates in food caused by chloramphenicol (CP) and furazolidone (FZ) have gained interest in research toward their detection. Hence, fast, reliable, and accurate detection of CP and FZ in food products is of utmost importance. Here, a novel molybdenum disulfide-connected carbon nanotube aerogel/poly (3,4-ethylenedioxythiophene) [MoS2/CNTs aerogel/PEDOT] nanocomposite materials are constructed and deposited on the pretreated carbon paste electrode (PCPE) by a facile eletropolymerization method. The characterization of MoS2/CNTs aerogel/PEDOT nanocomposite was analyzed by scanning electron microscopy (SEM), cyclic voltammetry, and differential pulse voltammetry. The modified MoS2/CNTs aerogel/PEDOT nanocomposite has improved sensing characteristics for detecting CP and FZ in PBS solution. For this work, we have studied various parameters like electrocatalytic activity, the effect of scan rates, pH variation studies, and concentration variation studies. Under optimum conditions, the modified electrode exhibited superior sensing ability compared to the bare and pretreated CPE. This improvement in electrocatalytic activity can be the higher conductivity, larger surface area, increased heterogeneous rate constant, and presence of more active sites in the MoS2/CNTs aerogel/PEDOT nanocomposite. The modified electrode demonstrated distinct electrochemical sensing toward the individual and simultaneous analysis of CP and FZ with a high sensitivity of 0.701 µA. µM-1 .cm-2 for CP and 0.787 µA. µM-1 .cm-2 for FZ and a low detection limit of 3.74 nM for CP and 3.83 nM for FZ with good reproducibility, repeatability, and interferences. Additionally, the prepared sensor effectively detects CP and FZ in food samples (honey and milk) with an acceptable recovery range and a relative standard deviation below 4%.

A Water-Stable Lanthanide Coordination Polymer as Multicenter Platform for Ratiometric Luminescent Sensing Antibiotics.

As a hot topic of global concern, the distinguishing and detecting of antibiotic pollution is crucial owing to its adverse effect on ecosystems and human health stemming from excessive use and poor management. Herein, a water-stable lanthanide coordination polymer sensor (Dy-TCPB) with multiple emitting centers is prepared. The versatile Dy-TCPB can conveniently differentiate various antibiotics, and displays a self-calibration luminescent response to nitrofurazone (NFZ) and furazolidone (FZD). Each antibiotic exhibits notable correlation to a unique combination of the two ligand-to-Dy ion emission intensity ratios, enabling two-dimensional fingerprint recognition. Furthermore, the novel self-calibration sensor demonstrates effective recognition of NFZ and FZD with excellent sensitivity and selectivity, and detection limits as low as 0.0476 and 0.0482 µm for NFZ and FZD, respectively. The synthetic approach for the fabrication of a singular coordination polymer exhibiting multiple emissions provides a promising strategy for the development of facile and effective ratiometric sensors.

Highly sensitive detection of a small molecule by a paired labels recognition system based lateral flow assay.

Small molecules are difficult to detect by conventional gold lateral flow assay (GLFA) sensitively because the test system must satisfy the conflict requirements between enough signal intensity and limited antibody (Ab) amount. In this work, a paired labels recognition (PLR)-based biosensor was designed by utilizing the specific binding of Ab and secondary antibody (anti-Ab) to enhance signal intensity and reduce antibody amount applied in small molecule detection. The PLR amplification system is fabricated by self-assembling the common detection probe, Au-labeled Ab (Au-Ab), and the signal booster, Au-labeled anti-Ab (Au-anti-Ab). Benefiting from this, a powerful network structure can be generated to accumulate numerous gold nanoparticles (GNPs) and thus significantly strengthen the signal intensity of detection. Therefore, a lower Ab amount will be applied to offer adequate signal strength, and further, the limit of detection will be obviously downregulated due to the more effective competition reaction. Using furazolidone (FZD) as a model analyte, we achieve a detection limit of as low as 1 ng mL-1, which was at least fivefold improved over that of the traditional GLFA. Furthermore, the practicality of this strategy was certificated in five different food samples. Graphical abstract A paired labels recognition (PLR) amplification system is fabricated by self-assembling the common detection probe, Au-labeled Ab (Au-Ab), and the signal booster, Au-labeled anti-Ab (Au-anti-Ab). In this novel strategy, owing to the recognition of both Ab and anti-Ab labeled on gold nanoparticles (GNPs), a powerful network structure can be generated to accumulate numerous GNPs and thus significantly strengthen the signal intensity of detection.

Rapid determination of furazolidone residues in animal foods by time-resolved fluorescence immunochromatography.

Although furazolidone (FZD) was completely banned from livestock production in many countries many years ago due to its mutagenicity and carcinogenicity, the abuse of FZD is still common today. Accurate and rapid detection of FZD residues in animal-derived food products is highly important for human health. Here, a time-resolved fluorescence immunochromatography (TRFI) test strip for rapid and quantitative detection of 3-amino-2-oxazolidinone (AOZ) residues in animal foods was developed and validated. Its limit of detection and limit of quantification were 0.05 and 0.14 µg/kg, respectively. The typical recovery rates were 95-105 % in chicken breast samples spiked with the AOZ standard substance at concentrations of 0.05-2 µg/kg, with a coefficient of variation value ≤8.5 %. The cross-reaction rates of the TRFI-AOZ test strips with 3-amino-5-morpholinomethyl-2-oxazolidone, semicarbazide, and 1-amino-imidazolidin-2,4-dione were less than 1 %. The newly developed TRFI test strip has high sensitivity, high specificity, cost effectiveness and user-friendly control, and is suitable for the rapid and large-scale screening of AOZ residues in animal foods.

In-situ growth of MOF-derived Co3S4@MoS2 heterostructured electrocatalyst for the detection of furazolidone.

The over-exploitation of antibiotics in food and farming industries ruined the environmental and human health. Consequently, electrochemical sensors offer significant advantages in monitoring these compounds with high accuracy. Herein, MOF-derived hollow Co3S4@MoS2 (CS@MS) heterostructure has been prepared hydrothermally and applied to fabricate an electrochemical sensor to monitor nitrofuran class antibiotic drug. Various spectroscopic methodologies have been employed to elucidate the structural and morphological information. Our prepared electrocatalyst has better electrocatalytic performance than bare and other modified glassy carbon electrodes (GCE). Our CS@MS/GCE sensor exhibited a highly sensitive detection by offering a low limit of detection, good sensitivity, repeatability, reproducibility, and stability results. In addition, our sensor has shown a good selectivity towards the target analyte among other potential interferons. The practical reliability of the sensor was measured by analyzing various real-time environmental and biological samples and obtaining good recovery values. From the results, our fabricated CS@MS could be an active electrocatalyst material for an efficient electrochemical sensing application.

Furazolidone in chicken: case study of an incident of widespread contamination.

1. Furazolidone, a nitrofuran antibiotic, was prohibited from the use in food-producing animals in the European Union (EU) in 1997. In 2002, the EU restricted the import of poultry meat and aquaculture species from countries where furazolidone residues had been detected. 2. By 2004, however, residues of the side-chain metabolite, 3-amino-2-oxazolidinone (AOZ) of furazolidone, were detected in chicken meat produced in Northern Ireland. 3. With the random spread of positive results across farms of a single integrated organisation, including organically reared flocks, it seemed unlikely that the source of residues was due to illegal use of the drug, but more likely caused by a source of contamination. 4. Potential sources investigated were as follows: furazolidone contamination of feedstuffs, a "hot spot" of furazolidone in poultry houses, contamination occurring within breeding stocks and transferred with the birds to broiler growing houses, and furazolidone contamination of the water supply. 5. Furazolidone contamination was associated with birds reared in houses more than 10 years old. 6. Contamination was traced to the water supply of poultry houses, where un-dissolved furazolidone, legally administered prior to 1997, had settled to the bottom of water storage tanks. It remained un-disturbed until 2004 when the integrator changed the procedure for cleaning water tanks between crops of birds. 7. The use of Proxitane, a hydrogen peroxide disinfectant, caused effervescence within the tank such that small quantities of furazolidone were dissolved, delivered to birds via drinkers and subsequently caused residues in the broiler meat. 8. The environmental impact of the contamination was investigated by testing soil and grass from land adjacent to an organic poultry house to which birds had access. 9. Mechanisms of contamination and how residues may be spread throughout a large integrated poultry system are not restricted to furazolidone. Incidents of contamination are even more likely when using licensed drugs where the drugs may be present on-farm in large quantities.

Novel UV-spectrophotometric method for quantitative estimation of furazolidone using mixed hydrotropic agent.

A novel, eco friendly, accurate, sensitive, economic and safe spectrophotometric method was developed by application of mixed hydrotropy using 2 M sodium acetate, 8 M urea, 2 M niacinamide and 2 M sodium benzoate solution (25:25:25:25% V/V) as hydrotropic agent, for the solubalizing of poorly water-soluble Furazolidone (FZ) (solubility:- 3.64e-01 mg/mL in water). There were more than 32 times enhancements in the solubility of FZ were found in mixed hydrotropic solution as compared to solubilities in distilled water. FZ shows maximum absorbance at 360 nm where sodium acetate, urea, niacinamide, sodium benzoate and other tablets excipients did not show any absorbance above 300 nm, and thus no interference in the estimation was seen. FZ was obeyed Beers law in the concentration range of 10 to 50 µg/ml (r(2)=0.9992) in mixed hydrotropic solvent with mean recovery ranging from 97.32% to 98.9%. Proposed method is new, simple, economic, safe, rapid, accurate and reproducible and was validated according to ICH guidelines and values of accuracy, precision and other statistical analysis were found to be in good accordance with the prescribed values.

Furazolidone and Nitrofurazone Metabolic Studies in Crucian Carp by Ultra-Performance Liquid Chromatography Tandem Mass Spectrometry.

In this work, the detection of the furazolidone (FZD) and nitrofurazone (NFZ) metabolites residuals in crucian carp are focused. Crucian carps of identical size were exposed to the mixed nitrofuran antibiotics under optimized bath conditions at a concentration of 50 mg/L, 26 ± 0.5°C for 24 h. Then, liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI-MSMS) was performed after the drug exposure experiments when the nitrofuran metabolites were enriched in organisms. During the period of 0-144 h, residue levels of the 3-amino-2-oxazolidinone (AOZ) gradually decreased with a prolonged sampling time. The changing trend in semicarbazide (SEM) with the sample collection duration is divided into two stages, and its concentration showed a trend of rising first and then falling. The metabolite concentration-time curve demonstrates that 24 h was used as a sampling time, and fish muscle was selected as tissue samples in the further quantitative study. A novel crucian carp-enrichment procedure coupled to LC-ESI-MSMS quantitative method was further explored based on much metabolite data. According to the exponential curve of the SEM-to-AOZ concentration ratio at a precisely designed FZD-to-NFZ mass ratio, the final FZD content of the veterinary NFZ antibiotics was 0.069 ± 0.005% (in terms of mass).

Lateral flow immunoassay for furazolidone point-of-care testing: Cater to the call of saving time, labor, and cost by coomassie brilliant blue labeling.

Furazolidone (FZD) and its metabolite called 3-amino-2-oxazolidinone (AOZ) would induce carcinogenic and mutagenic effects to human. In this work, to develop a novel, stable, and simple point of care testing (POCT) with a potential to social applied for FZD detection, we utilized the aspect of protein staining of coomassie brilliant blue (CBB) to exploit a new CBB-LFIA strategy free of NPs. Only one mixing step is needed during the probe manufacturing process, which requires just 2 h and is a great time saving strategy compared with other methods (requiring 4-33 h for probe preparation). Besides, the cost of CBB-LFIA is 300 times lesser than other LFIA with respect to obtaining the label. The developed CBB-LFIA was successfully applied to detect AOZ with a detection limit of 2 ng mL-1, without any influence from other potential interfering compounds. The proposed CBB-LFIA exhibited prominent practical application, and possesses considerable utilization potential in the related field.

Competitive Lateral Flow Immunoassay Relying on Au-SiO2 Janus Nanoparticles with an Asymmetric Structure and Function for Furazolidone Residue Monitoring.

Gold nanoparticles (AuNPs) are the most commonly used signal materials in lateral flow immunoassay (LFIA). However, the assay sensitivity of traditional AuNP-based LFIA is usually limited by the incomplete competition between free target analytes and immobilized antigens for the binding of AuNP-labeled antibodies. To unfreeze this limitation, here, asymmetric Au-SiO2 Janus NPs (about 66 nm) were designed and synthesized. Au-SiO2 Janus NPs can assemble into snowman-like anisotropic structures and combine two different physicochemical properties at their opposite sides, where the AuNP side mainly possesses the antibody conjugating and signal providing functions and the SiO2 side primarily offers the stable function. In virtue of the unique asymmetric nanostructure, only the AuNP side can interact with target analytes by specific antigen-antibody interactions, which could significantly improve the efficiency of competition. Selecting furazolidone as a model analyte, the immunoassay biosensor showed a limit of detection as low as 0.08 ng/mL, 10-fold decreased than that of the AuNPs-LFIA. Moreover, the Au-SiO2 Janus NP lateral flow immunoassay was well applied in chicken, pork, honey, and beef food samples with visual detection limits of 0.8 ng/g, 0.16 ng/g, 0.4 ng/mL, and 0.16 ng/g, respectively. The Au-SiO2 Janus NPs possess the advantages of both materials, which will broaden their applications as a potential alternative in the rapid and sensitive detection of antibiotic residues.

Polydopamine nanospheres as high-affinity signal tag towards lateral flow immunoassay for sensitive furazolidone detection.

Currently, the low sensitivity and poor binding stability of detection probe prepared via electrostatic adsorption have become the dilemmas of colloidal gold-based lateral flow immunoassays (Au-LFIAs). In this connection, polydopamine nanospheres (PDA NPs) with an eminent covalent connectivity property were introduced as a promising substitute to improve the stability of probe and sensitivity of LFIA. Whereafter, the PDA NPs-based LFIA was applied for the monitoring of furazolidone (FZD) in food samples because of the potential carcinogenic/mutagenic effects to human of its metabolite (3-amino-2-oxazolidinone, AOZ). Compared with electrostatic adsorption, the binding stability of PDA NPs-based probes was superior. And, as expected, the PDA NPs-based LFIA biosensor exhibited higher sensitivity than that of the Au-LFIA with a detection limit of 3.5 ng mL-1 for AOZ by naked-eye readout. Based on the significant enhanced binding stability and sensitivity, the PDA NPs-based LFIA is of certain spreading value for detecting other analytes.

Small size nanoparticles-Co3O4 based lateral flow immunoassay biosensor for highly sensitive and rapid detection of furazolidone.

Lateral flow immunoassay (LFIA) biosensor is a paper-based tool and widely utilized in various fields. Here, we developed a novel LFIA biosensor by introducing Co3O4 nanoparticles (NPs) as signal labels for highly sensitive detection of 3-amino-2-oxazolidinone (AOZ), a metabolite of furazolidone. The characteristic brown color of Co3O4 NPs enabled AOZ to be visually detected by the LFIA. Significantly, the size of Co3O4 NPs is relatively small compared with most of other signal labels, which could remarkably reduce steric hindrance, increase immunoreaction probability and shorten the analysis time. Under optimal conditions, the novel Co3O4 NPs-LFIA could possess high sensitivity for the detection of AOZ with a detection limit of 0.4 ng mL-1 by naked eyes, which was at least 3-fold improved than that of the conventional gold nanoparticles (GNPs) based LFIA. Moreover, the detection could be achieved within 6 min and without cross-reactions with other analogue small molecules. Taking merits of convenience, rapid and sensitivity, the proposed Co3O4 NPs-LFIA may be readily adapted for the detection of other small molecules.

Development of a multi-class method to determine nitroimidazoles, nitrofurans, pharmacologically active dyes and chloramphenicol in aquaculture products by liquid chromatography-tandem mass spectrometry.

LC-MS/MS method was developed for the efficient identification and quantification of 21 banned substances including various nitroimidazoles, nitrofurans, pharmacologically-active dyes and chloramphenicol, respectively in aquaculture products. The sample preparation was started by acid-treatment with 2-nitrobenzaldehyde (NBA) to liberate matrix-bound residues of nitrofurans. A modified QuEChERS method was optimized for the extraction and clean-up of the target analytes. The metabolites of the four conventional nitrofurans (nitrofurantoin, furazolidone, nitrofurazone and furaltadone) and of three other nitrofurans (nifursol, nifuroxazide, and nitrovin), and an underivatizable nitrofuran (nifurpirinol) were simultaneously detected. Furthermore, 21 banned substances were quantified by LC-MS/MS with ESI using one single injection. To evaluate and validate the performance of the method, the criteria of the Decision (EC) no 2002/657 were applied. Decision limit (CCα) of target analytes ranged 0.067-1.655 µg/kg in aquaculture products. The recovery ranged 77.2%-125.6%, and the relative standard deviations of inter-day analyses (RSD) were less than 25%.

Ultrasonic preparation of near-infrared emission cluster-based YbIII and NdIII coordination materials: Ratiometric temperature sensing, selective antibiotics detection and "turn-on" discrimination of l-arginine.

Currently near-infrared (NIR) luminescence of lanthanide ions has received great attention because of their unique emissions in the near-infrared region (800-1700 nm). These NIR luminescent materials behave excellent applications in many fields such as sensors and probes in optical amplification, laser systems, biological systems and organic light-emitting diodes. In this work, two new near-infrared (NIR) emission three-dimensional (3D) YbIII and NdIII cluster-based coordination materials, namely {[Yb2(L)2(DMF)(H2O)4]·(DMF)2 (H2O)}n (NIR-MOF 1) and [Nd(L)(DMF)2]n (NIR-MOF 2) (H3L = terphenyl-3,4″,5-tricarboxylic acid) have been synthesized through the facile sono-chemical preparation methods. Both the near-infrared materials 1 and 2 have been characterized by single crystal X-ray diffraction, powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Further the mixed-lanthanide near-infrared emission material Nd0.35Yb0.65L (NIR-MOF 3) can also be prepared under the sono-chemical conditions. NIR-MOF 3 can be successfully applied as the ratiometric NIR-MOF-based thermometer, which should origin from the emission intensity ratio between Yb3+ (976 nm) and Nd3+ (1056 nm) in the temperature range of 308-348 K. Besides these, the micro-morphologies of NIR-MOF 1 can be deliberately tuned through different sono-chemical reaction factors (reaction time, reaction temperature and sono-chemical powers). These tuned nano-sized materials NIR-MOF 1 (100 W, 80 min) can be utilized as the fluorescent sensing material to distinguish furazolidone and sulfasalazine from other antibiotics. At the same time, NIR-MOF 2 can be applied as the first example of MOFs-based sensors for discriminating l-arginine from other amino acids through the "turn-on" mode in the near-infrared emission region.

Development of an indirect competitive ELISA for the detection of furazolidone marker residue in animal edible tissues.

Due to its carcinogenicity and mutagenicity, furazolidone has been prohibited completely from being used in food animal production in the world since 1995. To monitor the illegal abuse of furazolidone, a polyclonal antibody-based indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was developed for the determination of tissue-bound furazolidone metabolite 3-amino-2-oxazolidone (AOZ). The highly specific antibody was targeted for PAOZ, the benzaldehyde derivative of AOZ. The 50% inhibition values (IC 50) of 0.91 microg/L for AOZ was achieved with the most sensitive antibody Ab-B1 by altering ELISA conditions. In the ELISA, sample extraction and cleanup were performed by an is MAX cartridge following combined hydrolysis of the tissue-bound AOZ and derivatization of the homogenized tissues with benzaldehyde. The limits of detection (LOD) calculated from the analysis of 20 known negative tissue samples (swine liver, swine muscle, chicken liver, chicken muscle,and fish muscle) were 0.3-0.4 microg/kg (mean+3 SD). Recoveries of AOZ fortified at the levels of 0.4, 1, and 5 microg/kg ranged from 55.8 to 96.6% in the tissues. The coefficients of variation were less than 20% over the range of AOZ concentrations studied. The linear detection range was between 0.1 and 25.6 microg/L. Validation of the ELISA method with swine muscle and liver from furazolidone-treated pigs was carried out using HPLC, resulting in a similar correlation in swine muscle (r=0.99) and in swine liver (r=0.98). The results suggest that this ELISA is a specific, accurate, and sensitive method of detecting AOZ residues in animal edible tissues.

Highly sensitive furazolidone monitoring in milk by a signal amplified lateral flow assay based on magnetite nanoparticles labeled dual-probe.

We presented a signal amplified lateral flow assay (LFA) based on magnetite nanoparticles (MNPs) labeled dual-probe and applied it in the high sensitive and rapid on-site detection of furazolidone metabolite of 3-amino-2-oxazolidinone (AOZ). The amplified signal benefited from high affinity between two probes of MNPs labeled murine monoclonal antibody (MNPs-MAb) and goat anti-mouse antibody (MNPs-GAMA) and was achieved by the generation of dual-probe network complex. This developed method could realize high sensitive detection of AOZ with a threshold value of 0.88 ng mL-1 and a detection limit of 0.044 ng mL-1, the sensitivity was at least 10-fold improved than that of the traditional gold nanoparticle based LFA. This facile developed assay was successfully applied for rapid detection of AOZ in milk samples. The proposed method paves a new way for on-site screening of other hazardous substances in food and can be referred in all lateral flow assays.

Determinations of residual furazolidone and its metabolite, 3-amino-2-oxazolidinone (AOZ), in fish feeds by HPLC-UV and LC-MS/MS, respectively.

The antibacterial drug furazolidone belonging to the group of nitrofuran antibacterial agents has been widely used as an antibacterial and antiprotozoal feed additive for poultry, cattle, and farmed fish in China. During application a large proportion of the administered drug may reach the environment directly or via feces. Although the use of furazolidone is prohibited in numerous countries, there are indications of its illegal use. It is known that furazolidone can be rapidly metabolized to 3-amino-2-oxazolidinone (AOZ) in the body of the target organism. In this study, a total of 21 fish feed samples, including 17 commercial fish feeds from local markets in China (representing 15 different formulations) and 4 fish feeds obtained from Germany and Turkey, respectively, are analyzed to determine whether the drug is still illegally used or commercially available feeds are contaminated by this drug. High-performance liquid chromatography (HPLC) and liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) methods have been implemented to determine furazolidone and its metabolite AOZ in fish feeds containing animal protein, respectively. An efficient and convenient cleanup method for the determination of furazolidone in fish feeds is developed, and a simple cleanup method for the determination of AOZ is used. Method recoveries for samples used were determined as 87.7-98.3% for furazolidone at two spike levels of 2.0 and 5.0 ng g-1 and as 95.6-102.8% for AOZ at spike levels of 0.4 and 0.8 ng g-1. Limits of detections were 0.4 ng g-1 for furazolidone and 0.05 ng g-1 for AOZ. The established methods are therefore suitable for the determination of furazolidone and its metabolite AOZ in fish feeds at trace contamination levels. Using the established methods, all fish feed samples have been proved to be furazolidone negative; however, AOZ is tested in 16 of 17 fish feeds obtained from local markets in the Hubei province of China, with a positive rate as high as 94.1%.

Multi-class method for the determination of nitroimidazoles, nitrofurans, and chloramphenicol in chicken muscle and egg by dispersive-solid phase extraction and ultra-high performance liquid chromatography-tandem mass spectrometry.

This study describes the development of a multiresidue method for the efficient identification and quantification of nitroimidazoles, nitrofurans, and chloramphenicol in chicken and egg. After derivatization of nitrofuran metabolites, dispersive-solid phase extraction was used for the extraction of target analytes. An optimization strategy involved the selection of sorbents and extraction solutions for dispersive-solid phase extraction in order to achieve acceptably high recoveries and reduce co-extractives in the final extracts. Analytes were determined by ultra-high performance liquid chromatography-tandem mass spectrometry, in one single injection with a chromatographic run time of 7.5min. Mean recoveries ranged from 86.4% to 116.7% and interday precision was lower than 18%. The limits of quantification were between 0.1 and 0.5µg/kg, which were satisfactory to support surveillance monitoring. Finally, the method was applied to real samples, and metabolite of furazolidone, metronidazole and its metabolite, dimetridazole and its metabolite were detected in both chicken and egg samples.