Rapid Determination of Trace Sulfonamides in Milk by Graphene Oxide-Based Magnetic Solid Phase Extraction Coupled with HPLC–MS/MS

Novel CoOOH-based fluorescent aptasensor for rapid and sensitive detection of sulfamethazine in environmental samples

Sulfamethazine (SMZ) has been widely used in animal husbandry and exposed to water and soil environments, posing potential threat to human health and ecological environment. Hence, we designed a CoOOH-based aptasensor, the fluorescence resonance energy transfer between FAM-labeled aptamer and CoOOH was used to sensitively and selectively detect SMZ in water and soil environments. Molecular docking and molecular dynamics simulations were used to predict binding mechanisms of SMZ and aptamer. Under optimized conditions, the aptasensor exhibited high sensitivity and selectivity with a linear range of 5-40 ng/mL and a limit of detection of 2.43 ng/mL. The recoveries of the aptasensor were 84.6-115.8% in water and soil samples with relative standard deviations below 9%, and the detection results were highly consistent with high-performance liquid chromatography. Therefore, this developed aptasensor was a reliable tool and could be applied to monitoring of SMZ in environmental samples.

2D MOF-enhanced SPR sensing platform: Facile and ultrasensitive detection of Sulfamethazine via supramolecular probe

Sulfamethazine (SMZ) is widely present in the environment and can cause severe allergic reactions and cancer in humans. Accurate and facile monitoring of SMZ is crucial for maintaining environmental safety, ecological balance, and human health. In this work, a real-time and label-free surface plasmon resonance (SPR) sensor was devised using a two-dimensional metal-organic framework with superior photoelectric performance as an SPR sensitizer. The supramolecular probe was incorporated at the sensing interface, allowing for the specific capture of SMZ from other analogous antibiotics through host-guest recognition. The intrinsic mechanism of the specific interaction of the supramolecular probe-SMZ was elucidated through the SPR selectivity test in combination with analysis by density functional theory, including p-π conjugation, size effect, electrostatic interaction, π-π stacking, and hydrophobic interaction. This method facilitates a facile and ultrasensitive detection of SMZ with a limit of detection of 75.54 pM. The accurate detection of SMZ in six environmental samples demonstrates the potential practical application of the sensor. Leveraging the specific recognition of supramolecular probes, this direct and simple approach offers a novel pathway for the development of novel SPR biosensors with outstanding sensitivity.

Magnetic solid-phase extraction based on GO/Fe3O4 coupled with UPLC-MS/MS for determining nitroimidazoles and their metabolites in honey

A magnetic graphene oxide (GO/Fe₃O₄) nanocomposite was synthesized in one step by a chemical coprecipitation method, which was further used for magnetic solid-phase extraction (MSPE). This study aimed to combine GO/Fe₃O₄ with ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) to detect the nitroimidazoles (NDZs) and their three major metabolites in honey samples. GO/Fe₃O₄ was characterized by transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR) spectroscopy, and magnetic property measurement system (MPMS), and the influencing parameters such as adsorbent amount, pH of the dissolved sample solution, sample volume, type and volume of the eluent, shaking speed, and adsorption and desorption time were optimized. Under the optimized conditions, the limits of detection (LOD) and quantitation (LOQ) of the method were 0.003-0.08 μg kg^-1 and 0.009-0.3 μg kg^-1, respectively, with good linearity reported in the range of 0.5-20 μg kg^-1 (R² ≥ 0.9991). The average recoveries of 10 analytes were in the range of 66.0%-90.8% with relative standard deviations (RSD) lower than 6.9% (n = 6). The preparation of GO/Fe₃O₄ and the extraction process were convenient and rapid, and consumed small amounts of organic solvents. The optimized method was successfully applied for extracting NDZs and their three major metabolites from honey samples with good accuracy.

Magnetic Solid-Phase Extraction Based on Silica and Graphene Materials for Sensitive Analysis of Emerging Contaminants in Wastewater with the Aid of UHPLC-Orbitrap-MS

With the advancement of technology and nanotechnology, new extraction sorbents have been created and effectively used for the magnetic solid-phase extraction of target analytes. Some of the investigated sorbents have better chemical and physical properties, exhibiting high extraction efficiency and strong repeatability, combined with low detection and quantification limits. In this study graphene oxide (GO) magnetic composites were prepared and used as magnetic solid-phase extraction (MSPE) adsorbents along with synthesized silica based magnetic nanoparticles (MNPs) functionalized with the C18 group for the preconcentration of emerging contaminants (ECs) in wastewater samples generated from hospital and urban facilities. The sample preparation with magnetic materials was followed by UHPLC-Orbitrap MS analysis for the accurate identification and determination of trace amounts of pharmaceutical active compounds and artificial sweeteners in effluent wastewater. Optimal conditions were used for the extraction of ECs from the aqueous samples, prior to UHPLC-Orbitrap MS determination. The proposed methods achieved low quantitation limits between 1.1-33.6 ng L^-1 and 1.8-98.7 ng L^-1 and satisfactory recoveries in the range of 58.4%-102.6%. An intra-day precision of less than 23.1% was achieved, while inter-day RSD% values in the range of 5.6-24.8% were observed. These figures of merit suggest that our proposed methodology is suitable for the determination of target ECs in aquatic systems.

Sulfide-Doped Magnetic Carbon Nanotubes Developed as Adsorbent for Uptake of Tetracycline and Cefixime from Wastewater

In this study, a magnetic solid-phase extraction method was developed based on multi-wall carbon nanotubes decorated by magnetic nanoparticles (Fe₃O₄) and cadmium sulfide nanoparticles (Fe₃O₄@MWCNT-CdS) for trace extraction of cefixime and tetracycline antibiotics from urine and drug company wastewater. The adsorbent features were characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), and energy dispersive X-ray analysis (EDX). Various effective parameters on the sorption and desorption cycle, such as sorption time, the mass of adsorbent, pH, salt addition, and material ratio, were investigated and optimized. The data were evaluated using isotherm models, and experimental data were well-fitted to both Langmuir (R² = 0.975) and Freundlich (R² = 0.985) models. Moreover, kinetic of reaction was agreement with pseudo-second-order (R² = 0.999) as compared pseudo-first-order (R² = 0.760). The maximum adsorption capacity for tetracycline and cefixime was achieved at 116.27 and 105.26 mg·g^-1, respectively. Hence, the prepared adsorbent can be used as an alternative material for enhanced determination of pharmaceutical substances in biological fluids.

Strategies for studying in vivo biochemical formation pathways and multilevel distributions of sulfanilamide metabolites in food (2012-2022)

Sulfonamide metabolites are a major source of food pollution worldwide. However, the formation of internal sulfanilamide metabolites has only been investigated for selected compounds. In this paper, the fragmentation mechanism and characteristic ions of sulfonamide metabolites are reviewed using density functional theory and Q-Orbitrap high-resolution mass spectrometry. The result of the protonation site, rearrangement and bond breaking induced fragmentations at C₆H₆NO₂S⁺m/z 156.01138, C₆H₆NO⁺m/z 108.04439, and C₆H₆N⁺m/z 92.04948. Mass shifts are calculated for derivative metabolites, including hydrogenation, acetylation, oxidation, glucosylation, glucosidation, sulfation, deamination, formylation, desulfonation and O-aminomethylation. Given their homologous series, it is demonstrated that similar metabolic reactions occur for all sulfonamides. The suspicious sulfonamide metabolites are confirmed by d-labelling experiments and reference standards. This is the first review of the latest advances in the field of sulfonamide metabolite prediction (2012-2022), and scheme design for metabolite multirresidue screening, as well as the challenges in the mass spectrometry evolution.

MIL-88B(Fe)/cellulose microspheres as sorbent for the fully automated dispersive pipette extraction towards trace sulfonamides in milk samples prior to UPLC-MS/MS analysis

MIL-88B(Fe)/cellulose microspheres (MIL-88B(Fe)/CMs) were characterized by the means of SEM, XRD, TGA and N₂ adsorption-desorption test. The composite was used as the sorbent for fully automated dispersive pipette extraction (DPX), after introducing CMs as the support, the loss of MIL-88B(Fe) in DPX was avoided. Coupled to UPLC-MS/MS, the proposed method was employed for the analysis of trace sulfonamides (SAs) in milk samples. The parameters affecting the extraction efficiency, including pH of sample solution, the rate of aspiration and dispense, amount of the adsorbent, type and volume of elution solvent were optimized. Under the optimal conditions, good linearity (r ≥ 0.9978 for five analytes), high sensitivity (limit of detection: 0.00660-0.0136 μg kg^-1) and satisfactory recovery (69.8%-100.9%) were achieved. Furthermore, the sorbent showed desirable reusability over eight extraction cycles. Compared with other methods for the pretreatment of SAs, the proposed method showed advantages of high sensitivity, less sorbent consumption, environmental friendliness and automation, providing a promising protocol for sample preparation.

S. M. Montenegro MC, Rodríguez-Díaz JM. Contaminants in the cow's milk we consume? Pasteurization and other technologies in the elimination of contaminants

Cow's milk is currently the most consumed product worldwide. However, due to various direct and indirect contamination sources, different chemical and microbiological contaminants have been found in cow's milk. This review details the main contaminants found in cow's milk, referring to the sources of contamination and their impact on human health. A comparative approach highlights the poor efficacy and effects of the pasteurization process with other methods used in the treatment of cow's milk. Despite pasteurization and related techniques being the most widely applied to date, they have not demonstrated efficacy in eliminating contaminants. New technologies have appeared as alternative treatments to pasteurization. However, in addition to causing physicochemical changes in the raw material, their efficacy is not total in eliminating chemical contaminants, suggesting the need for new research to find a solution that contributes to improving food safety.

[Research progress in the application of magnetic solid phase extraction based on carbon based magnetic materials in food analysis]

Trace toxic substances in food pose a serious threat to human health, and need to be detected and analyzed to ensure food safety. However, there are many kinds of toxic substances in food, with small amounts and complex matrices, making it necessary to select an appropriate sample pretreatment technology for extraction and purification. There are some disadvantages to sample pretreatment methods such as solid phase extraction and liquid-liquid extraction, in terms of poor selectivity, significant influence of matrix interference, large sample requirement, long extraction time, use of a large amount of harmful organic solvents, and cumbersome and time-consuming operation. Magnetic solid phase extraction (MSPE) combines the advantages of magnetic separation and traditional SPE technology, avoids time-consuming column loading, and can extract the target analyte efficiently. Because of its advantages, in that it has simple operation, is time-saving and fast, requires no centrifugal filtration, and is environmentally friendly, it is considered an efficient sample pretreatment technology and applied in food analysis. The adsorption capacity and selectivity of the magnetic adsorbent used in MSPE are the key factors affecting the extraction efficiency and selectivity of MSPE, and play a key role in the accuracy of the established method. Carbon-based magnetic materials are a type of new functional magnetic materials prepared by the co-precipitation of carbon-based materials (carbon nanotubes, graphene, metal-organic framework-derived carbon, or activated carbon) and magnetic materials. In order to endow carbon-based magnetic materials with the advantages of both, carbon materials and magnetic materials, while also reflecting the advantages of high specific surface area, good stability, low cost, environmental friendliness, excellent physical and chemical properties, high porosity, and high adsorption capacity, proper functional modification is needed. Carbon-based magnetic materials modified by functionalization can efficiently enrich organic and inorganic analytes with different properties, and have seen significant progress in environmental analysis, biological detection, pollution control, and other fields. In recent years, MSPE technology based on carbon-based magnetic materials has been gradually applied in food analysis and pretreatment, but its use is still in infancy and holds immense application potential. Reference to more than 50 papers published in SCI and Chinese core journals over the past four years reveals that carbon-based materials include carbon nanotubes modified by functional groups, reagents, or materials; graphene, graphene oxide, and reduced graphene oxide; carbon derived from a gold organic framework; activated carbon biochar; and nanodiamond. The harmful substances in food samples include esters, mycotoxins, polycyclic aromatic hydrocarbons, antibiotics, alkaloids, phenols, vitamins, and antibiotics. Based on the classification of carbon-based materials, this review reveals that carbon-based magnetic materials have good preconcentration ability for harmful substances in food samples. MSPE can be combined with GC-MS, liquid chromatography-high resolution mass spectrometry (LC-HRMS), ultra-fast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS), ultra high performance liquid chromatography-Q-Exactive high resolution mass spectrometry (UHPLC-Q-Exactive HRMS), high performance liquid chromatography-diode array detection (HPLC-DAD), gas chromatography micro-electron capture detection (GC-μECD), high performance liquid chromatography fluorescence with post-column photochemical derivatization (HPLC-PCD-FLD), and HPLC-UV to analyze food samples. These combined technologies have high accuracy and recovery. However, the synthesis methods of carbon-based magnetic materials such as carbon nanotubes and graphene, incur high energy consumption and high cost, and involve complex processes, which limit their application. Therefore, a carbon-based magnetic adsorbent with low cost, high selectivity, and high extraction efficiency was developed by further exploring functional modification with biochar as a carbon base. This is a very promising direction to develop MSPE technology utilizing biochar-based magnetic materials for food sample pretreatment. This review provides a theoretical basis and technical support for the wide application of carbon-based magnetic materials in MSPE technology for food analysis.

Current Applications of Magnetic Nanomaterials for Extraction of Mycotoxins, Pesticides, and Pharmaceuticals in Food Commodities

Environmental pollutants, such as mycotoxins, pesticides, and pharmaceuticals, are a group of contaminates that occur naturally, while others are produced from anthropogenic sources. With increased research on the adverse ecological and human health effects of these pollutants, there is an increasing need to regularly monitor their levels in food and the environment in order to ensure food safety and public health. The application of magnetic nanomaterials in the analyses of these pollutants could be promising and offers numerous advantages relative to conventional techniques. Due to their ability for the selective adsorption, and ease of separation as a result of magnetic susceptibility, surface modification, stability, cost-effectiveness, availability, and biodegradability, these unique magnetic nanomaterials exhibit great achievement in the improvement of the extraction of different analytes in food. On the other hand, conventional methods involve longer extraction procedures and utilize large quantities of environmentally unfriendly organic solvents. This review centers its attention on current applications of magnetic nanomaterials and their modifications in the extraction of pollutants in food commodities.

Solvent-free mechanochemical preparation of graphene oxide-Fe3 O4 and its application in magnetic dispersive solid-phase extraction of illegal dyes in food samples

A simple, green, and efficient mechanochemical approach was developed herein to prepare tunable magnetic graphene oxide nanoparticles. The obtained nanoparticles were successfully used as adsorbents in a magnetic dispersive solid-phase extraction method to extract three cationic dyes (i.e., thioflavine T, auramine-O, and basic orange 2) found in food samples. Our proposed approach also utilized high-performance liquid chromatography with ultraviolet detection. Several key variables affecting the extraction recovery were investigated. These included the sample pH, amount of extractant, extraction time, sample volume, elution solvent type and volume, and the stability and reusability of the magnetic graphene oxide nanoparticles. Under optimized conditions, the calibration curve was linear at a concentration range of 0.005-1.0 μg/mL with a correlation coefficient of 0.9992-0.9996. Moreover, the limits of detection were determined at 0.97-1.35 μg/mL. The extraction mechanism was investigated via ultraviolet-visible spectrophotometry and zeta-potential analyses. The developed method was used to analyze the above-mentioned cationic dyes in bean products and yellow fish samples. Notably, satisfactory spiked recoveries ranging from 90.7 to 104.9% were achieved.

An Ultrasensitive Label-Free Fluorescent Aptasensor Platform for Detection of Sulfamethazine

Purpose

Sulfamethazine (SMZ) exposed in the environment can enter the human body through the food chain and pose a serious threat to human health. Therefore, it is important to develop a rapid and sensitive method for detecting SMZ in environmental samples. In order to fastly and quantitatively detect SMZ in environmental samples, we developed a label-free fluorescent aptasensor based on specific aptamer (SMZ1S) and fluorescence resonance energy transfer (FRET) between gold nanoparticles (AuNPs) and rhodamine B (RhoB).

Methods

In the absence of SMZ, SMZ1S was adsorbed on the surface of AuNPs, which led to dispersion of the AuNPs in high concentration saline solution, thus effectively quenching the fluorescence of RhoB. With the increase of the SMZ concentration, the specific binding of SMZ1S and SMZ led to the aggregation of AuNPs in the presence of NaCl, which reduced the quenching of RhoB fluorescence and increased the fluorescence intensity. The sensitivity and linearity curve of the label-free fluorescent aptasensor were determined with different concentrations of sulfamethazine standard solutions. The specificity of this fluorescent aptasensor was determined by replacing sulfamethazine with different antibiotics. In addition, the actual water and soil samples were spiked and recovered.

Results

Under optimized conditions, the proposed fluorescent aptasensor demonstrated a good linear detection of SMZ in binding buffer from 1.25 ng mL^-1 to 40 ng mL^-1 and the limit of detection was 0.82 ng mL^-1. The spiked recoveries for SMZ were 94.4% to 108.8% with a relative standard deviation of 1.8-10.3% in water and soil samples, respectively.

Conclusion

The label-free fluorescent aptasensor investigated in the current study is a promising tool to detect and quantify SMZ in water and soil samples.

Review: Microextraction Technique Based New Trends in Food Analysis

Food chemistry is the study and classification of the quality and origin of foods. The identification of definite biomarkers and the determination of residue contaminants such as toxins, pesticides, metals, human and veterinary drugs, which are a very common source of food-borne diseases. The food analysis is continuously demanding the improvement of more robust, sensitive, highly efficient, and economically beneficial analytical approaches to promise the traceability, safety, and quality of foods in the acquiescence with the consumers and legislation demands. The traditional methods have been used at the starting of the 20th century based on wet chemical methods. Now it existing the powerful analytical techniques used in food analysis and safety. This development has led to substantial enhancements in the analytical accuracy, precision, sensitivity, selectivity, thereby mounting the applied range of food applications. In the present decade, microextraction (micro-scale extraction) pays more attention due to its futures such as low consumption of solvent and sample, throughput analysis easy to operate, greener, robotics, and miniaturization, different adsorbents have been used in the microextraction process with unique nature recognized with wide range applications.

Magnetic Solid-Phase Extraction of Organic Compounds Based on Graphene Oxide Nanocomposites

Graphene oxide (GO) is a chemical compound with a form similar to graphene that consists of one-atom-thick two-dimensional layers of sp²-bonded carbon. Graphene oxide exhibits high hydrophilicity and dispersibility. Thus, it is difficult to be separated from aqueous solutions. Therefore, functionalization with magnetic nanoparticles is performed in order to prepare a magnetic GO nanocomposite that combines the sufficient adsorption capacity of graphene oxide and the convenience of magnetic separation. Moreover, the magnetic material can be further functionalized with different groups to prevent aggregation and extends its potential application. Until today, a plethora of magnetic GO hybrid materials have been synthesized and successfully employed for the magnetic solid-phase extraction of organic compounds from environmental, agricultural, biological, and food samples. The developed GO nanocomposites exhibit satisfactory stability in aqueous solutions, as well as sufficient surface area. Thus, they are considered as an alternative to conventional sorbents by enriching the analytical toolbox for the analysis of trace organic compounds.

Magnetic Graphene Oxide Composite for the Microextraction and Determination of Benzophenones in Water Samples

Magnetite nanoparticles (Fe₃O₄) functionalized with graphene oxide (GO) have been synthesized through a silanization process of the magnetic nanoparticles with tetraethyl orthosilicate and (3-aminopropyl)triethoxysilane and further coupling of GO. The synthesized nanomaterials have been characterized by several techniques, such as transmission electron microscopy (TEM), and infrared and Raman spectroscopy, which enabled the evaluation of the different steps of the functionalization process. The hybrid nanomaterial has been employed for the extraction of five benzophenones (benzophenone-1, benzophenone-3, 4-hydroxybenzophenone, benzophenone-6 and benzophenone-8) in aqueous samples by dispersive micro-solid phase extraction, combining the magnetic properties of magnetite nanoparticles with the excellent sorption capacity of graphene oxide via hydrophobic interactions with the analytes. The subsequent separation and quantification of the analytes was performed by liquid chromatography with tandem mass spectrometric detection, achieving limits of detection (LODs) in the range 2.5 to 8.2 μg·L^-1, with relative standard deviations ranging from 1.3-9.8% and relative recovering in the range 86 to 105%. Positive swimming pool water samples analysed following the developed method revealed the presence of benzophenones in from 14.3 to 39 μg·L^-1.

Determination of Chloramphenicol in Honey and Milk by HPLC Coupled with Aptamer-Functionalized Fe3 O4 /Graphene Oxide Magnetic Solid-Phase Extraction

An aptamer-functionalized Fe₃ O₄ /graphene oxide was synthesized by chemical co-precipitation method and then employed in the magnetic solid-phase extraction for selective enrichment of chloramphenicol before HPLC. The aptamer was covalently bonded to the Fe₃ O₄ /graphene oxide complex by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide. Parameters affecting extraction efficiency including solution pH, extraction time and temperature, types and volume of elution solvent, and elution time were investigated in detail. Under the optimal conditions, good linearity was obtained between the peak area and analyte concentration in the range of 7.0 to 1.0 × 10³  µg/L with the correlation coefficient of 0.9994. The limit of detection and quantitation were 0.24 µg/L and 0.79 µg/L, respectively. The developed method was employed to the analysis of chloramphenicol in honey and milk samples. The recoveries ranged from 80.5% to 105.0% with relative standard deviations less than 8.9%. PRACTICAL APPLICATION: An aptamer-functionalized Fe₃ O₄ /graphene oxide was synthesized and employed in magnetic solid phase extraction for the enrichment of chloramphenicol before HPLC. The presented assay was employed for the determination of chloramphenicol in honey and milk with satisfactory results.

C8-modified magnetic graphene oxide based solid-phase extraction coupled with dispersive liquid-liquid microextraction for detection of trace phthalate acid esters in water samples

Phthalate acid esters (PAEs) are extensively applied in plastic and plastic products, and have caused potential hazards on human and animal health. In this study, a highly sensitive method was proposed for trace detection of selected PAEs in water by gas chromatography-mass spectrometry, after solid-phase extraction (SPE) using octyl (C8)-modified magnetic graphene oxide (MGO-C8) as the adsorbent followed by dispersive liquid-liquid microextraction (DLLME). The prepared MGO-C8 was characterized by Fourier transform infrared spectroscopy (FT-IR), thermo gravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The recoveries of the PAEs using MGO-C8 as the adsorbent were found to be significantly higher those obtained by MGO. The influences of solution pH, adsorption and desorption time, eluent and extractant, and salt addition on the extraction efficiency of PAEs were investigated. Under the optimized conditions, limits of detection (LODs) of 0.5-1.0 ng L^-1 for PAEs, and related standard deviations (RSDs) of 4.8-7.5% were obtained. The proposed method was utilized in the detection of trace PAEs in real environmental water samples, with spiked recoveries of 89.5-112.3%, 91.5-105.0% and 98.0-110.0% for DBP, DEHP and DNOP, respectively.

Simultaneous analysis of coccidiostats and sulphonamides in non-target feed by HPLC-MS/MS and validation following the Commission Decision 2002/657/EC

Taking into consideration the maximum level (ML) for coccidiostats included in the European Regulation 574/2011 and the fact that the presence of residues of sulphonamides in non-target feed is forbidden, the aim of this article is to present an analytical method based on HPLC-MS/MS for the identification and quantification of sulphonamides and coccidiostats in non-target feeds. The method was validated following Commission Decision 2002/657/EC, and recovery, repeatability and reproducibility were within the limits established in the Decision. For coccidiostats, the decision limit and detection capability were calculated for the different species taking into account the ML allowed in Regulation 574/2011. The applicability of the method was investigated in 50 feed samples collected from dairy farms, 50 obtained from feed mills and 10 interlaboratory feed samples.

Internal Extractive Electrospray Ionization Mass Spectrometry for Quantitative Determination of Fluoroquinolones Captured by Magnetic Molecularly Imprinted Polymers from Raw Milk

Antibiotics contamination in food products is of increasing concern due to their potential threat on human health. Herein solid-phase extraction based on magnetic molecularly imprinted polymers coupled with internal extractive electrospray ionization mass spectrometry (MMIPs-SPE-iEESI-MS) was designed for the quantitative analysis of trace fluoroquinolones (FQs) in raw milk samples. FQs in the raw milk sample (2 mL) were selectively captured by the easily-lab-made magnetic molecularly imprinted polymers (MMIPs), and then directly eluted by 100 µL electrospraying solvent biased with +3.0 kV to produce protonated FQs ions for mass spectrometric characterization. Satisfactory analytical performance was obtained in the quantitative analysis of three kinds of FQs (i.e., norfloxacin, enoxacin, and fleroxacin). For all the samples tested, the established method showed a low limit of detection (LOD ≤ 0.03 µg L⁻¹) and a high analysis speed (≤4 min per sample). The analytical performance for real sample analysis was validated by a nationally standardized protocol using LC-MS, resulting in acceptable relative error values from −5.8% to +6.9% for 6 tested samples. Our results demonstrate that MMIPs-SPE-iEESI-MS is a new strategy for the quantitative analysis of FQs in complex biological mixtures such as raw milk, showing promising applications in food safety control and biofluid sample analysis.

Purification and characterization of a novel phloretin-2'-O-glycosyltransferase favoring phloridzin biosynthesis

Phloretin-2'-O-glycosyltransferase (P2'GT) catalyzes the last glycosylation step in the biosynthesis of phloridzin that contributes to the flavor, color and health benefits of apples and processed apple products. In this work, a novel P2'GT of Malus x domestica (MdP2'GT) with a specific activity of 46.82 μkat/Kg protein toward phloretin and uridine diphosphate glucose (UDPG) at an optimal temperature of 30 °C and pH 8.0 was purified from the engineered Pichia pastoris broth to homogeneity by anion exchange chromatography, His-Trap affinity chromatography and gel filtration. The purified MdP2'GT was low N-glycosylated and secreted as a stable dimer with a molecular mass of 70.7 kDa in its native form. Importantly, MdP2'GT also exhibited activity towards quercetin and adenosine diphosphate glucose (ADPG), kaempferol and UDPG, quercetin and UDP-galactose, isoliquiritigenin and UDPG, and luteolin and UDPG, producing only one isoquercitrin, astragalin, hyperoside, isoliquiritin, or cynaroside, respectively. This broad spectrum of activities make MdP2'GT a promising biocatalyst for the industrial preparation of the corresponding polyphenol glycosides, preferably for their subsequent isolation and purification. Besides, MdP2'GT displayed the lowest K_m and the highest k_cat/K_m for phloretin and UDPG compared to all previously reported P2'GTs, making MdP2'GT favor phloridzin synthesis the most.