Preparation of a Magnetic Nanoporous Polymer for the Fast and Efficient Extraction of 5-Nitroimidazoles in Milk

Green synthesis of azo-linked porous organic polymer for enrichment of nitroimidazoles from water, shrimp and Basa fish

Reliable monitoring of nitroimidazoles (NDZs) is of great significance to public health. Herein, an azo-linked porous organic polymer (Res-POPs) was prepared by green synthesis method using natural resveratrol as monomer for the first time. Using Res-POPs as sorbent, a facile method coupling solid-phase extraction with high performance liquid chromatography-diode array detection was developed for effective detecting NDZs. The method achieved good linearities (0.06 ∼ 100 ng mL-1 for water, 1.8 ∼ 200 ng g-1 for shrimp, and 1.5 ∼ 200 ng g-1 for Basa fish) with determination coefficients above 0.995, low detection limits (0.02 ∼ 0.05 ng mL-1, 0.60 ∼ 1.00 ng g-1 and 0.50 ∼ 0.90 ng g-1 for water, shrimp and Basa fish), high method recovery (85 %∼114 %) and relative standard deviations below 8.2 %. The results demonstrated the superiority and the promising potential of the established method for detection of NDZs compared with the reported method.

Multicolor emissive carbon dot-based fluorometric analysis platform for rapid quantification and discrimination of nitroimidazole antibiotic residues

The development of efficient, rapid, portable, and accurate analysis of veterinary drug residues in food matrices is in great demand for food safety assessment. Here, we have developed a smartphone-integrated platform for fluorometric quantification of metronidazole (MNZ) residues and constructed a sensor array for discrimination of different nitroimidazole antibiotics (NIIMs). Multicolor CDs (B-CDs, C-CDs, Y-CDs, and R-CD) were prepared and showed different fluorescence response to MNZ. The fluorescence of C-CDs was quenched Because of the inner filter effect (IFE) between the C-CDs and MNZ, while that of R-CDs was enhanced due to the passivation of surface defects by MNZ. Based on the response pattern, the fluorometric quantification of MNZ based on the fluorescence images of C-CD + R-CD system (R/G values) was achieved with a low detection limit of 0.45 μM. By designing a smartphone-integrated platform, the analysis can be completed within 20 min. In addition, a fluorescence sensor array based C-CDs and R-CDs was also developed. The unique fingerprint of each NIIMs was obtained by linear discriminant analysis (LDA) of the response patterns, indicating an effective discrimination of five NIIMs. Moreover, the platform was used for quantification of MNZ in food samples and the recoveries were within 84.0-106.3 % with relative standard deviations 1.2-10.2 %. Therefore, the proposed method shows great potential as a universal platform for rapid detection of veterinary drug residues.

Hydroxyl and carboxyl group functionalized conjugated microporous nanomaterial as adsorbent for the solid-phase extraction of phenolic endocrine disrupting chemicals from freshwater fish samples

Endocrine disruption chemicals (EDCs) in food can seriously harm human health. In this study, a hydroxyl and carboxyl group functionalized conjugated microporous nanomaterial (CMP) was prepared by Friedel-Crafts reaction and used as solid-phase extraction (SPE) adsorbent. A functionalized CMP based SPE combined with high performance liquid chromatography-diode array detection was built for the determination of phenolic EDCs from nine fish samples. The extraction conditions were optimized by both single factor and response surface methodology (Box-Behnken Design). The established method performed well in terms of the response linearity (in the range of 0.50-100 ng g-1 with coefficient of determination larger than 0.9942), limits of detection (0.15-0.30 ng g-1, S/N of 3), limits of quantification (0.50-1.00 ng g-1, S/N = 10), method recoveries (78.4-121 %) and repeatability (relative standard deviation < 11 %). It can be used as an efficient method to detect trace phenolic EDCs in real fish samples.

Green construction of magnetic azo porous organic polymer for highly efficient enrichment and detection of phenolic endocrine disruptors

Porous organic polymers (POPs) are prominent sorbents for effective extraction of endocrine disrupting chemicals (EDCs). However, green and sustainable construction of functional POPs is still challenging. Herein, we developed a magnetic azo POP (Mazo-POP) for the first time using hydroxy-rich natural kaempferol and low-toxic basic fuchsin as monomers through a diazo coupling reaction. The Mazo-POP exhibited excellent extraction capabilities for EDCs with a phenolic structure. Consequently, it was used as a magnetic sorbent for extracting phenolic EDCs from water and fish samples, followed by ultrahigh-performance liquid chromatography-tandem mass spectrometric detection. The Mazo-POP based analytical method afforded a good linearity of 0.06-100 ng mL-1 and 0.3-500 ng g-1 for water and fish samples respectively, with detection limits (S/N = 3) of 0.02-0.5 ng mL-1 and 0.1-1.5 ng g-1, respectively. The method recovery was from 85.2% to 109% and relative standard deviation was less 5.3%. Moreover, the effective adsorption was mainly contributed by hydrogen bond, π-π interaction, pore filling and hydrophobic interaction. This work not only provides an efficient method for sensitive determination of phenolic EDCs, but also highlights the significance of green preparation of environmentally friendly sorbents for enriching/adsorbing pollutants.

Preparation of a magnetic phosphazene-based hyper crosslinked polymer for the fast and efficient extraction of chlorophenols from water and peach juice

Two magnetic phosphazene-based hyper crosslinked polymers (M-HCP-OP-TMC and M-HCP-OP-TCL) were newly synthesized by the reaction of Friedel-Crafts acylation, and the M-HCP-OP-TMC showed an excellent extraction capability and rapid adsorption kinetics for chlorophenols as an adsorbent. Then, an efficient analytical method was built for the preconcentration and quantification of chlorophenols from water and peach juice samples by combining M-HCP-OP-TMC based magnetic solid-phase extraction (MSPE) with HPLC-UV detection. The linear response range for the chlorophenols by the method was 0.21-100.0 ng mL-1 for water sample, and 0.36-100.0 ng mL-1 for peach juice sample. The detection limits (S/N = 3) of the proposed method for the analytes were 0.07- 0.25 ng mL-1 and 0.12-0.45 ng mL-1 for water and peach juice samples, respectively. The method recoveries for the spiked samples were in the range of 93.1%-117.1%, and the relative standard deviations were less than 10%. The adsorption of the chlorophenols with the M-HCP-OP-TMC was mainly contributed by π-π stacking and hydrophobic interactions. The results indicate that the method was sensitive and accurate enough for the determination of the chlorophenols from real samples.

Carboxyl functionalized sorbent based solid-phase extraction for sensitive determination of endocrine disrupting chemicals in bottled water, juice and milk

Endocrine disrupting chemicals (EDCs) pose a serious threat to human health even at extremely low concentration. Three carboxyl functionalized porous polymers (PDA-DPBP, PTCDA-DPBP and ODPA-DPBP) were synthesized for the first time and employed as solid-phase extraction sorbent to enrich phenolic EDCs at trace level. Compared with PTCDA-DPBP, ODPA-DPBP and corresponding carboxyl-free counterpart (PC-DPBP), PDA-DPBP delivered superior enrichment efficiency for the phenolic EDCs, which can be ascribed to the strong hydrogen bonding, pore filling, hydrophobic interaction and π-π interaction between PDA-DPBP and phenolic EDCs. Coupled with high performance liquid chromatography, phenolic EDC residues in bottled water, juice and milk samples were enriched and determined. At the optimum conditions, the PDA-DPBP based method provided a good linear response in the range of 0.04-100ng mL-1 for bottled water, 0.07-100ng mL-1 for juice and 0.15-500ng mL-1 for milk samples. The detection limits (S/N=3) were 0.01-0.04, 0.02-0.06 and 0.05-0.10ng mL-1 for bottled water, juice and milk, respectively. The method recoveries were in the range from 81.6% to 116%, with RSDs ≤ 7.7%. This work provides an attractive and reliable alternative method for sensitive determination of phenolic EDCs.

Porphyrin-based hypercrosslinked polymers as sorbents for efficient extraction of nitroimidazoles from water, honey and chicken breast

In this work, a series of 5,10,15,20-tetraphenylporphyrin (TPP)-based hyper crosslinked polymers were prepared by Friedel-Crafts reaction. Among them, the HCP-TPP-BCMBP, which was prepared by using TPP as the monomer and with 4,4'-Bis(chloromethyl)-1,1'-biphenyl (BCMBP) as the cross-linking agent, had the best adsorption capability for the enrichment of the nitroimidazoles of dimetridazole, ronidazole, secnidazole, metronidazole, and ornidazole. Then, a solid-phase extraction (SPE) method with the HCP-TPP-BCMBP as adsorbent coupled with HPLC-UV detection for the determination of nitroimidazole residues in honey, environmental water, and chicken breast samples was established. The influence of the main factors that affect the SPE, i.e., sample solution volume, sample loading rate, sample pH, and eluent and its volume, were studied. Under the optimal conditions, the limits of detection (S/N = 3) for the nitroimidazoles were measured to be in the range of 0.02-0.04 ng mL^-1, 0.4-1.0 ng g^-1 and 0.5-0.7 ng g^-1 for environmental water, honey, and chicken breast samples, with the determination coefficients being in the range of 0.9933-0.9998. The analytes recoveries by the method in fortified samples fell in the range from 91.1% to 102.7% for environmental water, from 83.2% to 105.0% for honey, and from 85.9% to 103.0% for chicken breast samples, and the relative standard deviations for the determination were less than 10%. It shows that the HCP-TPP-BCMBP has a strong adsorption capability for some polar compounds.

Design of hydroxyl-functionalized nanoporous organic polymer with tunable hydrophilic-hydrophobic surface for solid phase extraction of neonicotinoid insecticides

As being widely used insecticides, neonicotinoid residues are toxic and harmful to human health and aquatic ecosystems. Thus, the sensitive monitoring of neonicotinoids in water and food samples is highly desirable to reduce their risks to humans. Herein, four novel hydroxyl-functionalized nanoporous organic frameworks (OH-NOP1, OH-NOP2, OH-NOP3 and OH-NOP4) with tunable hydrophilic-hydrophobic surface have been designed and fabricated for the first time by employing luteolin as monomer and 4,4'-bis(chloromethyl)-1,1'-biphenyl as crosslinker at the molar ratio of 3:1, 1:1, 1:3 and 1:6, respectively. When the molar ratio of luteolin to crosslinker was 1:3, OH-NOP3 was obtained and it presented the highest affinity with excellent adsorption performance towards the studied neonicotinoids. The adsorption mechanism was proposed to be the strong hydrogen bond, polar interaction, Lewis acid-base interaction and pore adsorption between OH-NOP3 and neonicotinoids. Then, utilizing OH-NOP3 as sorbent for solid phase extraction cartridges, an effective method for extraction and preconcentration of neonicotinoids followed by high performance liquid chromatography analysis has been developed for quantitative detection of neonicotinoids from water and edible fungi. The method provided good linearity over the range of 0.06-100.0 ng mL^-1 for lake water, 1.5-100.0 ng g^-1 for pleurotus eryngii and sea-shroom. Low detection limit (at the signal to noise ratio of 3) was achieved in the range of 0.02-0.08 ng mL^-1 for water, 0.50-0.60 ng g^-1 for pleurotus eryngii and 0.50-0.80 ng g^-1 for sea-shroom, while the limit of quantification was 0.06-0.25 ng mL^-1, 1.50-1.80 ng g^-1 and 1.50-2.50 ng g^-1, respectively. Satisfactory method recoveries (85.1-112%) were obtained, with relative standard deviations below 8.2%. This study offered a new strategy for designing efficient sorbents to adsorb or remove organic pollutants based on the structure and properties of substrates.

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.

Monolithic and compressible MIL-101(Cr)/cellulose aerogel/melamine sponge based microextraction in packed syringe towards trace nitroimidazoles in water samples prior to UPLC-MS/MS analysis

In this study, MIL-101(Cr)/cellulose aerogel/melamine sponge composite was fabricated through a simple soaking method. The composite was packed in the syringe barrel and used as the sorbent for microextraction in packed syringe. Coupled to UPLC-MS/MS, the proposed method was employed for the analysis of trace nitroimidazoles in water samples. The parameters affecting the extraction efficiency, including sorbent type, pH value of sample solution, sample solution volume and elution solvent were optimized. Under the optimal conditions, good linearity (r > 0.99 for five analytes), high sensitivity (limit of detection: 8.250-16.33 ng L^-1), ideal precision (intra-day precision: 1.1%-5.3%, inter-day precision: 1.8%-6.7%) and satisfactory accuracy (recovery: 70.4%-96.7%) were achieved. The proposed method was proved to be efficient, easily operative and environmentally friendly.

Facile fabrication of hydroxyl-functionalized hypercrosslinked polymer for sensitive determination of chlorophenols

Three hydroxyl-functionalized hypercrosslinked polymers (HCP-POL, HCP-HQ and HCP-PG) were synthesized by Friedel-Crafts reaction. The HCP-HQ displayed the largest surface area and highest adsorption capacity for chlorophenols (CPs). Thus, the HCP-HQ was further modified with magnetism to obtain M-HCP-HQ. An efficient magnetic solid-phase extraction method with M-HCP-HQ as adsorbent was developed for the first time to simultaneously extract four CPs from water and honey samples before analysis by high performance liquid chromatography-diode array detection. Under optimized conditions, the low detection limits (S/N = 3) were obtained to be 0.06-0.10 ng mL^-1 for water and 0.80-1.75 ng g^-1 for honey. The method recovery was 80.7%-119%, with relative standard deviations below 9.5%. The enrichment factors of the CPs were in the range of 57-220. The extraction mechanism could be attributed to the strong polar interaction, hydrogen bonding and π-π interactions between the M-HCP-HQ and CPs. The M-HCP-HQ based method can be served as a reliable and sensitive tool for detection CPs in water and honey samples.

Amino-functionalized hypercrosslinked polymer as sorbent for effective extraction of nitroimidazoles from water, drink and honey samples

The three hypercrosslinked polymers (HCP) materials, designated as OPD-HCP, MPD-HCP and PPD-HCP, were synthesized by using o-phenylenediamine (OPD), m-phenylenediamine (MPD) and p-phenylenediamine (PPD) as monomers. They were characterized by infrared spectroscopy, powder X-ray diffraction, nitrogen sorption isotherms, and scanning electron microscopy. Then, the HCPs were explored as solid-phase extraction (SPE) adsorbent for the extraction of five nitroimidazoles (NDZs) (metronidazole, ronidazole, secnidazole, dimetridazole and ornidazole). Among the three HCPs, the MPD-HCP has the best adsorption performance for the NDZs. With the help of high-performance liquid chromatography with ultraviolet detection (HPLC-UV), good linear response range (0.07-40.0 ng mL^-1), high method recovery (86.8%-113.3%), low limits of detection (0.02-0.15 ng mL^-1) and good precision with the relative standard deviations of less than 8.1% were achieved for the determination of the NDZs in water samples. The effective determination of the NDZs in peach juice, honey tea, and honey samples were also realized by the developed method with satisfactory results. Based on both the experimental results and density functional theory calculation, the adsorption mechanism can be attributed to multiple interactions between the MPD-HCP and the NDZs, including hydrogen bonding, hydrophilic, and electrostatic interactions. The method provides a new alternative of choice for the determination of some NDZs in real samples.

Construction of hydrophilic hypercrosslinked polymer based on natural kaempferol for highly effective extraction of 5-nitroimidazoles in environmental water, honey and fish samples

A series of novel hydroxyl-functional hypercrosslinked polymers (named as HCPs-Kae) were fabricated using natural and environmentally benign kaempferol as monomer via one-step Friedel-Crafts reaction. The prepared HCP-Kae1-24 h exhibited large surface area, good hydrophilicity and excellent adsorption performance to 5-nitroimidazoles (5-NDZs). Thus, by applying HCP-Kae1-24 h as a solid-phase extraction adsorbent, a sensitive method was developed for enrichment of 5-NDZs including metronidazole, ronidazole, secnidazole, dimetridazole and ornidazole prior to high performance liquid chromatography analysis. Under the optimum conditions, good linearities were achieved in the range of 0.10-100.0 ng mL^-1 for water, 1.3-500.0 ng g^-1 for honey, and 1.7-100.0 ng g^-1 for fish meat. The detection limits of the method were 0.03-0.05 ng mL^-1, 0.4-1.0 ng g^-1, 0.5-1.0 ng g^-1 for water, honey and fish meat, respectively. High method recovery was obtained in the range of 84-118% with relative standard deviations lower than 8.9%. The established method was successfully applied to the detection of 5-NDZs in environmental water, honey and fish samples. This work provides a new strategy for constructing hydroxyl-functional HCPs by using natural resource as robust adsorbent for adsorption/extraction applications.

Evaluation of a porous imine-based covalent organic framework for solid-phase extraction of nitroimidazoles

Covalent organic framework materials (COFs), a kind of porous organic material, have excellent potential application in the field of sample pretreatment due to their high surface areas and thermal stability. In this work, a porous imine-based COF, named BP-COF, was fabricated by a solvothermal method using 2,2'-bipyridine-5,5'-dicarboxaldehyde and 1,3,5-tris(4-aminophenyl) benzene as monomers. After a series of structural characterization studies, the BP-COF was used as a solid-phase extraction (SPE) adsorbent for the extraction and enrichment of nitroimidazoles and their metabolites. Several parameters were investigated during the extraction process, including the sorbent dosage, loading pH value, the washing and elution solvent, and the breakthrough volume. By coupling with UPLC-QTOF-MS/MS, a sensitive and facile method was established for the quantitation analysis of NDZs. Under the optimum conditions, a low detection limit (0.015-0.12 ng mL^-1) and wide linearity (0.2-500 ng mL^-1) with higher R² were obtained. In addition, the developed method was applied for the determination of NDZs in four water samples with recoveries in the range of 71.7-115.9% and RSDs less than 8.3%. The results indicated that the BP-COF shows great potential for the enrichment of NDZs in water samples.

Fabrication of carbonyl-functional hypercrosslinked polymers as solid-phase extraction sorbent for enrichment of chlorophenols from water, honey and beverage samples

Three carbonyl-functional novel hypercrosslinked polymers (HCP-TPS, HCP-TPA, and HCP-TPP) were successfully fabricated through an one-step Friedel-Crafts acylation reaction by copolymerizing paraphthaloyl chloride with triphenylsilane, triphenylamine, and triphenylphosphine, respectively. The resultant HCPs contained plenty of carbonyl-functional groups. Among the series of such HCPs, HCP-TPS displayed the best adsorption capability to chlorophenols (CPs), and thus it was employed as solid-phase extraction (SPE) adsorbent for enrichment of chlorophenols from water, honey, and white peach beverage prior to determination by high-performance liquid chromatography. Under the optimal conditions, the detection limits of the method (S/N = 3) were 0.15-0.3 ng mL^-1 for tap water and leak water, 2.5-6.0 ng g^-1 for honey sample and 0.4-0.6 ng mL^-1 for white peach beverage sample. The recoveries of CPs in the spiked water, honey samples, and white peach beverage were in the range of 89.0-108.4%, 81.4-118.2%, and 85.0-113.5%, respectively. This work provides a new strategy for constructing functionalized HCPs as efficient SPE adsorbents. In this work, three novel hypercrosslinked polymers (HCPs) were synthesized by the Friedel-Crafts alkylation reaction (paraphthaloyl chloride as the alkylating agent, triphenylsilane, triphenylamine, and triphenylphosphine as the aromatic units). Then, HCP-TPS was applied to soild-phase extraction sorbent for enrichment CPs from water, honey, and white peach beverage samples.

Construction of imine-linked covalent organic framework as advanced adsorbent for the sensitive determination of chlorophenols

Food safety is a great concern of the general public. Chlorophenols (CPs) as organic pollutant can be found in drinking water and foods, causing serious harm to human health. Herein, imine-linked covalent organic frameworks (COFs), named as TAPT-AN-COF, was synthesized by aniline modulation strategy through condensation of 1,3,5-triformylphoroglucinol and 4,4',4''-(1,3,5-Triazine-2,4,6-triyl)trianiline with aniline as modulator. The prepared TAPT-AN-COF possesses good crystallinity and regular morphology, displaying excellent adsorption capability towards CPs pollutants. Thus, the TAPT-AN-COF was used as novel adsorbent for off-line solid-phase extraction of four CPs (2-CP, 3-CP, 2,3-CPs, 2,4-CPs) from bottled water, tea drink and honey samples before high performance liquid chromatography-ultraviolet detection. Under optimal conditions, wide linear range, low detection limits and satisfactory extraction recovery were gained. The π-stacking and hydrophobic interactions between the TAPT-AN-COF and the analytes played an important role in the adsorption. The established method has a great potential in determining other hydrophobic aromatic compounds.

Combination of pipette tip solid phase extraction and high performance liquid chromatography for determination of plant growth regulators in food samples based on the electrospun covalent organic framework/polyacrylonitrile nanofiber as highly efficient sorbent

Facile and sensitive determination of plant growth regulators (PGRs) in food samples is important but still remains great challenge. Herein, a pipette tip solid phase extraction (PT-SPE) method was developed for fast and sensitively detecting PGRs. The PT-SPE adsorbent was prepared by integrating a novel covalent organic framework (COF) of schiff base network 3 (SNW-3) and polyacrylonitrile (PAN) through electrospinning. The SNW-3 can easily adsorb PGRs with high special affinity through electrovalent bands between the ammonium ions of SNW-3 and the carboxy groups of PGRs. The polymer of PAN acts as scaffold material for SNW-3, which can lower seepage pressure hence accelerates adsorption/desorption kinetics. By combination with HPLC-DAD, a satisfactory method was successfully developed for simultaneous determination of ten PGRs in watermelon. Good analytical performances were achieved with this proposed method, including good linearity (5-500 ng/mL) with high correlation coefficients (R ≥ 0.9981), low limits of detection (S/N = 3, 0.24-3.19 ng/mL) and limits of quantification (S/N = 10, 1.65-5.72 ng/mL), satisfactory precision (intra-day RSDs ≤ 2.7%, inter-day RSDs ≤ 3.7%), and high accuracy (recovery: 82.8-113.0%). The method developed in this study shows high potential for design of high target-affinity adsorbents for food sample preparing.

A single method to analyse residues from five different classes of prohibited pharmacologically active substances in milk

In the European Union, the use of veterinary drugs belonging to the A6 group is prohibited in food-producing animals according to Commission Regulation (EU) No. 2010/37. The aim of this study was to improve the analytical control strategy by developing a single method to analyse residues of prohibited pharmacologically active substances in milk. For this, a single method was developed to analyse 16 prohibited pharmacologically active substances belonging to five different substance classes at required or recommended levels: nitroimidazoles at 3 μg kg^-1, nitrofurans at 0.5 μg kg^-1, chloramphenicol at 0.1 μg kg^-1, dapsone at 5 μg kg^-1 and chlorpromazine at 1 μg kg^-1. Milk sample preparation started with an acid hydrolysis combined with a derivatisation. These steps were followed by a clean-up consisting of a dispersive solid-phase extraction and a liquid-liquid extraction. Finally, the sample extracts were analysed by liquid chromatography combined with tandem mass spectrometry, operating alternately in the positive and negative mode. The method was fully validated according to Commission Decision 2002/657/EC for bovine milk and additionally validated for caprine milk. The validation proved that the method is highly effective to detect and confirm all 16 substances in bovine and caprine milk and, additionally to quantify 15 of these substances in bovine milk and 13 of these substances in caprine milk. This study resulted in a new multi-class method to detect, quantify and confirm the identity of 16 prohibited pharmacologically active substances belonging to five different substance classes in two types of milk.

Room-temperature synthesis of amino-functionalized magnetic covalent organic frameworks for efficient extraction of perfluoroalkyl acids in environmental water samples

The novel amino-functionalized magnetic covalent organic framework nanocomposites (Fe₃O₄@[NH₂]-COFs) were fabricated at room temperature, which were explored as a magnetic adsorbent for magnetic solid-phase extraction (MSPE). On the basis of the hydrophobic surfaces of magnetic nanocomposites and introduction of primary amines into the COFs shell, Fe₃O₄@[NH₂]-COFs displayed excellent enrichment capacity in "catching" ultratrace perfluoroalkyl acids (PFAAs) from water samples because of the synergistic combination of hydrophobic and electrostatic interactions between PFAAs and Fe₃O₄@[NH₂]-COFs. Under the optimized pretreatment and instrumental parameters, the proposed pretreatment approach, which hybridized MSPE using Fe₃O₄@[NH₂]-COFs and HPLC-MS/MS, displayed favorable linearity (10-10,000 ng L^-1) with R² (0.9990-0.9999), low limits of detection (0.05-0.38 ng L^-1), and excellent repeatability (3.7-9.2%). Moreover, the established approach was successfully utilized to determine PFAAs in real water samples with spiked recoveries ranging from 72.1% to 115.4%. Results indicated that Fe₃O₄@[NH₂]-COFs would be a potential alternative for MSPE of PFAAs at ultra-low levels.

Magnetic mesoporous carbon nanosheets derived from two-dimensional bimetallic metal-organic frameworks for magnetic solid-phase extraction of nitroimidazole antibiotics

We prepared two-dimensional (2D) bimetallic metal-organic frameworks (Ni-ZIF-8) nanosheets by a simple solvent-free method at room temperature. The morphology and composition of Ni-ZIF-8 can be controlled through adding different amounts of Ni. And then, the 2D magnetic mesoporous nanosheets (Ni/ZnO@C) were synthesized by directly pyrolyzing Ni-ZIF-8 under argon atmosphere and explored as magnetic solid phase extraction (MSPE) adsorbents for the determination of nitroimidazole antibiotics (NIABs). Magnetic Ni nanoparticles embedded in carbon nanosheets uniformly resulted in high magnetization saturation of Ni/ZnO@C for easy separation. The Ni/ZnO@C can form hydrogen bond and π-π interaction with three NIABs resulting from their rich N-H containing imidazole, π-electron. Due to the high specific surface area and high mass transfer rate of 2D Ni/ZnO@C, the materials showed satisfactory adsorption capacity and rapid adsorption kinetics for NIABs. A rapid and effective method of Ni/ZnO@C-MSPE combined with high-performance liquid chromatography was proposed for the determination of NIABs. Several main parameters affecting MSPE were investigated. Under the optimal conditions, wide linear was achieved ranging from 0.1 to 500 µg⋅L^-1 with a low detection limit of 0.025-0.05 µg⋅L^-1. The established method has been successfully applied to analyze NIABs from environmental water samples with satisfactory recovery from 74.33 to 105.71%.

Improved Solid-Phase Extraction for Simple, Sensitive, and Efficient Determination of Trace Plant Growth Regulators in Cherry Tomatoes by High-Performance Liquid Chromatography

The overuse of plant growth regulators (PGRs) in agricultural products has gradually increased in recent years, resulting in hazardous effects on food safety and human health. For the first time, a sensitive, accurate, and low-cost analytical method involving improved solid-phase extraction coupled with high-performance liquid chromatography was developed to determine trace PGRs in cherry tomatoes. Thereafter, the extraction mechanism and conditions were elucidated. Under optimized conditions, good linearity (0.04-400 ng g^-1; r ≥ 0.9996) and lower limits of detection (0.005-0.006 ng g^-1) were observed. The recoveries were 81.4-90.1%, with relative standard deviations of ≤6.7% (three levels). Finally, the developed method was successfully used to detect trace PGRs in cherry tomatoes. The results illustrated that this sensitive method shows great potential for application to monitor trace PGRs in agricultural products and, thus, provide technical support for food safety and public health.

Fabrication of magnetic porous organic framework for effective enrichment and assay of nitroimidazoles in chicken meat

A magnetic porous organic framework (M-POF) was rationally designed and served as a sorbent for magnetic solid-phase extraction of six nitroimidazoles from chicken meat prior to their assay by high-performance liquid chromatography with diode array detection. The M-POF exhibited good magnetic responsiveness and outstanding affinity to nitroimidazoles with large adsorption capacity up to 36 mg g^-1. Under optimal conditions, the developed method offered good linearity (r greater than 0.992) in the range of 1.5-100.0 ng g^-1, low limits of detection (S/N = 3) of 0.5-0.8 ng g^-1, low limits of quantification of 1.5-2.5 ng g^-1 and high enrichment factors of 80-175 for the nitroimidazoles. The method was successfully applied to analyze nitroimidazoles in chicken meat. The recoveries were 80.2-118% with relative standard deviations lower than 12%. The adsorption mechanism was further explored and the results showed that the M-POF exhibited adsorption potential for compounds with strong polar interactions.

Zeolitic imidazolate framework-8 coated Fe3O4@SiO2 composites for magnetic solid-phase extraction of bisphenols

A new magnetic composite material ZIF-8 coated Fe₃O₄@SiO₂ was employed for preconcentration and detection of trace BPs in water and plastic products.