Detection of β-agonists in pork tissue with novel electrospun nanofibers-based solid-phase extraction followed ultra-high performance liquid chromatography/tandem mass spectrometry

A novel sample pretreatment of nanofiber-packed solid-phase extraction of aflatoxin B1, B2, G1 and G2 in foods and simultaneous determination with HPLC

A novel analytical method based on nanofiber-packed solid-phase extraction (PFSPE) combined with HPLC-FLD has been successfully developed and applied to determine aflatoxin B1, B2, G1, G2 in foods. In order to effectively adsorb analytes from complex food matrices, four types of nanofibers based on skeleton of polystyrene-polyvinyl pyrrolidone were prepared by electrospinning and applied as adsorbent to home-made solid-phase extraction device. The effects of type of nanofibers, pH of sample, type and concentration of salt ion, type of activation solvent, type and volume of eluent, amount of nanofibers, and extraction time on the adsorption/desorption were investigated and optimized. Under optimal conditions, the method showed satisfactory linear relationship, with limits of detection (LODs) of 0.07-0.17 ng g-1, intra-day and inter-day RSDs for spiked samples of 1.3-8.0 % and 1.9-5.8 %, and absolute recoveries in the range of 60.1-98.4 %. The results presented the great potential to be utilized to determine AFs in foodstuffs.

Determination of aflatoxin B1 by novel nanofiber-packed solid-phase extraction coupled with a high performance liquid chromatography-fluorescence detector

A novel analytical proposal based on nanofiber-packed solid-phase extraction coupled with high performance liquid chromatography-fluorescence detector (HPLC-FLD) has been successfully developed for determining aflatoxin B1 (AFB1) in foods. Four types of nanofibers, including polystyrene (PS) nanofibers, polypyrrole (PPY) nanofibers, polystyrene-acrylic resin (PS-AR) nanofibers, and polystyrene-polyvinyl pyrrolidone (PS-PVP) nanofibers, were fabricated by electrospinning and utilized to prepare a home-made extraction device. In this study, the factors of different fibers, namely, fiber dosage, pH of extraction solution, type of salt ion, concentration of salt ion, and volume of the eluent were optimized. Under optimized conditions, the method showed good linearity in the range of 0.1-40 ng mL^-1 with a correlation coefficient greater than 0.999 and good inter-day accuracy (90.8-112.7% recovery) and precision (1.8-3.6% intra-day RSDs, 2.6% inter-day RSD), and the limit of detection (LOD) was 0.05 ng mL^-1. Due to its cost-effective, time-saving, environmentally friendly, and simple performance, it has the potential to be utilized to determine aflatoxins in complicated matrices.

Electromembrane extraction of clenbuterol from swine urine for monitoring illegal use in livestock

The illegal use of clenbuterol seriously endangers food safety and human health. Accurate monitoring the illegal use of clenbuterol in livestock can efficiently prevent the clenbuterol residue pork products from entering the consumer market. Thus, in this study, a simple, rapid and sensitive method for the determination of clenbuterol in swine urine was developed using electromembrane extraction combined with liquid chromatography-tandem mass spectrometry. It should be noted that the electromembrane extraction method presented many advantages of simple operation, fast mass transfer rate, good sample clean-up capability and less organic solvent consumption. The effect of important factors on the extraction efficiency of clenbuterol was investigated. Under the optimal conditions, good linearity was achieved for clenbuterol over the range of 1-1000 ng/mL (R² = 0.9996). The recoveries of clenbuterol in swine urine at three spiked levels ranged from 83.7 to 110.0% with relative standard deviation values lower than 9.7% (n = 4). Limits of detection and quantification for clenbuterol were 0.07 and 0.25 ng/mL, respectively. These results suggested that the proposed method has great potential on the extraction and determination of trace analyte in complex sample matrix for monitoring the illegal use in livestock. This article is protected by copyright. All rights reserved.

[Determination of tetracycline and fluoroquinolone residues in fish by polydopamine nanofiber mat based solid phase extraction combined with ultra performance liquid chromatography-tandem mass spectrometry]

Tetracyclines and fluoroquinolones are common antibacterial drugs used in aquaculture, and their residues may pose a risk to human health. The low concentration of drug residues and complex matrixes such as fats and proteins in aquatic products necessitate the urgent development of efficient sample pretreatment methods. Solid phase extraction (SPE) is the most common sample pretreatment method, in which the core is an adsorbent. Compared with traditional SPE adsorbents, nanofiber mat (NFsM) has more interaction sites because of their large specific surface area. Furthermore, NFsMs modified with specific functional groups can significantly improve the extraction efficiency of tetracyclines and fluoroquinolones. Polydopamine (PDA) is spontaneously synthesized by the oxidative self-polymerization of dopamine-hydrochloride in alkaline solutions (pH>7.5). Because of its rich amino and catechol groups, PDA can form π-π stacking, electrostatic attraction, hydrophobic interaction, and hydrogen bonding interactions with target molecules. By exploiting the above advantages, polystyrene (PS) NFsM, as a template, was prepared by the electrostatic spinning method, and PDA-PS NFsM was obtained by functional modification of PDA through self-polymerization. Fourier transform infrared spectroscopy (FT-IR) and field-emission scanning electron microscopy (FESEM) were used to characterize the synthesized PS NFsM and PDA-PS NFsM. It was proved that PDA was successfully modified on the PS NFsM, with the SEM images revealing a rough outer core shell structure and an inner honeycomb structure. Subsequently, the handmade SPE column with PDA-PS NFsM was completed. A novel and efficient screening analytical method based on PDA-PS NFsM for the simultaneous determination of three tetracyclines (tetracycline (TET), chlortetracycline (CTC), and oxytetracycline (OTC)) and three fluoroquinolones (enrofloxacin (ENR), ciprofloxacin (CIP), and norfloxacin (NOR)) in fish by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was established. The SPE procedure was optimized to develop an efficient method for sample preparation. Evaluate parameters including the amount of NFsM usage, ionic strength, flow rate of the sample solution, composition of eluent, and breakthrough volume were investigated. Only (20±0.1) mg of PDA-PS NFsM was sufficient to completely adsorb the targets, and the analytes retained on NFsM could be eluted by 1 mL of formic acid-ethyl acetate (containing 20% methanol) (1∶99, v/v). The residues were redissolved in 0.1 mL 10% methanol aqueous solution containing 0.2% formic acid. In addition, no adjustment of the pH and ionic strength of the sample solutions was required, and the breakthrough volume was 50 mL. The limits of detection (LODs) and limits of quantification (LOQs) of the six target compounds were measured at 3 times and 10 times the signal-to-noise ratio (S/N), respectively. The LODs and LOQs were 0.3-1.5 μg/kg and 1.0-5.0 μg/kg, respectively. The linear ranges of the six target compounds were LOQ-1000 μg/kg, and the coefficient of determination (R²) was greater than 0.999. To evaluate the accuracy and precision, blank spiked samples at three levels (low, medium, and high) were prepared for the recovery experiments, and each level with six parallel samples (n=6). The recoveries ranged from 94.37% to 102.82%, with intra-day and inter-day relative standard deviations of 2.38% to 8.06% and 4.10% to 9.10%, respectively. To evaluate the purification capacity of PDA-PS NFsM, the matrix effects before and after SPE were calculated and compared. Matrix effects before SPE were -12.98% to -38.68%. After the completion of SPEbased on PDA-PS NFsM, the matrix effect of each target analyte was significantly reduced to -2.15% to -7.36%, which proved the significant matrix removal capacity of PDA-PS NFsM. Finally, the practicality of this method was evaluated by using it to analyze real samples. This SPE method based on PDA-PS NFsM is efficient, practical, and environmentally friendly, and it has great potential for use in the routine monitoring of drug residues in fish.

Meso-tetra(4-sulfonatophenyl)porphyrin silver/Ag nanoparticles/graphene-phase C3N4 with a sandwich-like structure and double-faced active centers via two-step room-temperature photocatalytic synthesis for ractopamine detection

Photochemical synthesis under visible light irradiation is a novel approach in the field of green chemistry, and composites with abundant active centers for electrochemical detection are highly attractive. Herein, a meso-tetra(4-sulfonatophenyl)porphyrin silver/Ag nanoparticles/graphene phase C₃N₄ nanosheets (Ag₂TPPS₄/AgNPs/ng-C₃N₄) material with a sandwich-like structure was synthesized using a two-step photocatalytic reaction at room temperature (25 °C). In the first visible light irradiation step and in the presence of a hole capture agent, Ag⁺ ions were photocatalytically reduced onto the surface of ng-C₃N₄ that was used as a photocatalyst. Then, the protons (H⁺) in the core of H₂TPPS₄ were substituted in situ by photo-oxidized Ag⁺ during the second visible light irradiation step and in the presence of an electron capture agent. The electrochemical response of Ag₂TPPS₄ and ng-C₃N₄ to ractopamine (RAC) results in the unique double-faced active centers of Ag₂TPPS₄/AgNPs/ng-C₃N₄, and the cores (AgNPs) are beneficial as bridges for the connection between Ag₂TPPS₄ and ng-C₃N₄ and for high-efficiency electron transfer. Hence, as-synthesized Ag₂TPPS₄/AgNPs/ng-C₃N₄ exhibits high sensitivity (a low detection limit of 5.1 × 10^-8 M, S/N = 3.0), a wide linear range (1 × 10^-7 to 1.2 × 10^-5 M), and long-term stability. Based on the experimental verification of the electrochemical dynamics and electrostatic attraction at the interface between the dual-active-center surface and RAC, the electrochemical mechanism has been clarified. Specifically, in the multi-cycle oxidation of RAC, the blue shift of specific UV-vis peaks also confirms the electrocatalytic oxidation of the two terminal hydroxyl groups of RAC. In brief, Ag₂TPPS₄/AgNPs/ng-C₃N₄ with a sandwich-like structure and double-faced active centers enhances the detection sensitivity and electrocatalytic efficiency towards RAC.

Mixed mode monolithic sorbent in pipette tip for extraction of ractopamine and clenbuterol prior to analysis by HPLC-UV and UHPLC-Q ExactiveTM Plus Orbitrap MS

This work developed a fast and simple method for the quantification of two important β-agonists, ractopamine (RAC) and clenbuterol (CLEN) in animal urines. The method was based on micro-extraction by a mixed mode monolithic material and analysis by HPLC-UV and UHPLC-Q ExactiveTM Plus Orbitrap mass spectrometer. A mixed functional monolith with nonpolar ester-based structure containing polar carboxylic groups was thermally synthesized in situ in the pipette tips. The material combines both hydrophobic and ionic interactions. Parameters including conditions and composition of reagents for the in-pipette tip monolith synthesis, as well as the extraction process, were investigated and optimized. The procedure for extraction is 800 μL washing solvent of 10:90 (v/v) ACN:water and 150 μL eluting solvent of 30:70 (v/v) ACN:200 mM acetate buffer pH 4.0. Extraction efficiencies of 92% and 100% for RAC and CLEN, respectively, were achieved within 5 min with total organic solvent consumption of 395 μL. The extracts of spiked cattle and swine urines were analyzed by HPLC-UV and UHPLC-Q ExactiveTM Plus Orbitrap mass spectrometer. Good recovery with acceptable precision was observed. The mass spectrometry data confirmed efficient matrix removal by the synthesized extraction sorbent allowing routine analysis by the HPLC-UV method.

An electrochemiluminescence energy resonance transfer system for highly sensitive detection of brombuterol

In this work, an electrochemiluminescence resonance energy transfer (ECL-RET) system was established based on the modified graphite phase carbon nitride to detect brombuterol residues in food. The ultrasonic-assisted acidification exfoliation modification improved the conductivity and specific surface area of the graphite phase carbon nitride (g-C₃N₄). In addition, the carboxylated g-C₃N₄ nanosheets as ECL donors and the Au-Ag alloy nanoparticles as ECL acceptors could respectively directly carry antigen and antibody. Therefore, the trouble of introducing additional bridge molecules was avoided. A competitive immunoassay strategy was used for the detection of brombuterol, where brombuterol in the sample would compete with the coating antigen for the limited binding sites on antibody. The proposed ECL immunosensor for brombuterol detection exhibited high sensitivity with a wide linear range from 0.001 ng mL^-1 to 1000 ng mL^-1 and a low detection limit at 0.31 pg mL^-1. This work adopts a very simple way to design the sensor without losing its sensitivity, bringing convenience to its possible future applications.

Selective extraction and detection of β-agonists in swine urine for monitoring illegal use in livestock breeding

The illegal use of β-agonists often endangers animal-derived food safety. In this study, a selective detection method for β-agonists in swine urine was established via the combination of polymeric ionic liquid-molecularly imprinted graphene oxide-miniaturized pipette tip solid-phase extraction and high-performance liquid chromatography. It is worth noting that this method relied mainly on the designed adsorbent, which presented a rich adsorption mechanism, fast mass transfer rate, and high selectivity, and was successfully utilized in the selective extraction of β-agonists from swine urine samples. The proposed method has low LOD (0.20-0.56 ng/mL), high recovery (94.9-107.9%), and high reusability (4 times, 91.9-108.8%), which indicates its high potential as a selective, sensitive, accurate, and nonfatal method for monitoring the illegal use of β-agonists in the livestock breeding stage.

Synthesis of 3D magnetic porous carbon derived from a metal–organic framework for the extraction of clenbuterol and ractopamine from mutton samples

Synthesis of MIL-100(Fe)-derived MPC and its application for the MSPE of CLB and RAC.

Gold nanoparticle-based signal enhancement of an aptasensor for ractopamine using liquid crystal based optical imaging

The authors report on a method for the determination of ractopamine (RAC) via liquid crystal (LC) optical imaging and gold nanoparticle-induced signal enhancement. The gold nanoparticles (AuNPs) were blended with the desired concentrations of RAC, and this is found to strongly improve the performance of the assay. The RAC aptamers were immobilized on the self-assembled film of a glass slide for specific recognition of RAC. This causes a homeotropic re-orientation of the LCs. Notably, the aptamers need not be immobilized on the nanoparticles like in other methods. The addition of RAC causes the formation of an AuNP-RAC-aptamer conjugate on the sensing interface. This disrupts the orientation of LCs and results in a change of the polarized images of the LCs. The method has a detection limit as low as 1 pM of RAC. Graphical abstract Schematic presentation of a method for the determination of ractopamine (RAC) using liquid crystal (LC) optical imaging and gold nanoparticle-induced signal enhancement. The aptamers need not be immobilized on the nanoparticles like in other methods.