MIL-101(Cr)/MWCNTs-functionalized melamine sponges for solid-phase extraction of triazines from corn samples, and their subsequent determination by HPLC-MS/MS

Melamine sponges incorporated azo-linked porous organic polymer as adsorbent for extraction and determination of six B vitamins using pipette tip micro solid-phase extraction

A novel azo-linked porous organic polymer (AL-POP) was synthesized from caffeic acid and benzidine via an azo-coupling reaction and characterized by FTIR, SEM-EDS, BET, TGA, XRD and zeta potential analysis. AL-POPs were incorporated into melamine sponges and used for pipette tip micro solid-phase extraction (PT-MSPE) of six types of B vitamins (including thiamine, riboflavin, nicotinamide, pyridoxine, folic acid, and cyanocobalamin). After extraction, the samples were analyzed using high performance liquid chromatography-diode array detection (HPLC-DAD) system. The effect of AL-POP composition on the extraction efficiency (EE) of vitamins was investigated and benzidine to caffeic acid mol ratio of 1.5, 3.35 mmol of NaNO2, and reaction time of 8 h were selected as optimum conditions. The efficiency of the extraction process was improved by optimizing various parameters such as the amount of sorbent, pH and ionic strength of the sample, sample volume, number of sorption and desorption cycles, type of wash solvent, and type and volume of eluent solvent. Linearity (R2≥0.9987), Limit of detection (LOD) (11.88-18.97 ng/mL), limit of quantification (LOQ) (39.62-63.23 ng/mL), and enrichment factor (EF) (1.27-4.31) were obtained using calibration curves plotted under optimum conditions. Recovery values of these six B vitamins in the spiked multivitamin syrup samples varied from 80.01% to 108.35%, with a relative standard deviation (RSD) below 5.44%. Eventually, the optimized method was successfully used to extract and quantify the B vitamins in multivitamin syrup and non-alcoholic beer.

Three robust Cd(II) coordination polymers as bifunctional luminescent probes for efficient detection of pefloxacin and Cr2O72- in water

The accurate and rapid detection of antibiotics and heavy-metal-based toxic oxo-anions in water media employing coordination polymers (CPs) as luminescent probes has attracted a lot of attention. Three new Cd(II)-based ternary CPs derived from first-presented L ligands, including [Cd(DCTP)(L)(OH)]n (1), [Cd(TBTA)(L)(OH)]n (2), and [Cd(NPHT)(L)(H2O)]n (3) (L = 2-((1H-imidazol-1-yl)methyl)-5,6-dimethyl-1H-benzo[d]imidazole, H2DCTP = 2,5-dichloroterephthalic acid, H2TBTA = tetrabromoterephthalic acid and H2NPHT = 3-nitrophthalic acid), were successfully assembled and characterized. 1 and 2 show 2D hcb layers, which can be further extended into a 3D supramolecular framework via classic hydrogen bonding interactions. 3 features a 1D double chain that ultimately spreads into a 2D network through weak hydrogen bonding interactions. With the advantages of high stability and excellent luminescent properties, the three CPs display high sensitivity, selectivity, and good anti-interference for the sensing of pefloxacin (PEF) and Cr2O72- ions (LOD values toward PEF: 3.82 × 10-7 mol L-1 for 1, 4.06 × 10-7 mol L-1 for 2, and 1.36 × 10-8 mol L-1 for 3, and toward Cr2O72- ions: 5.97 × 10-7 mol L-1 for 1, 5.87 × 10-7 mol L-1 for 2, and 8.21 × 10-8 mol L-1 for 3). These CPs are the first examples of bifunctional luminescent sensors to detect PEF and Cr2O72- in aqueous solutions. The luminescence quenching mechanisms are explored in detail.

Porous poly(bismaleimide-co-divinylbenzene) microspheres as dispersive solid-phase extraction adsorbent coupled to high-performance liquid chromatography for the determination of triazine herbicide residues in vegetable samples

In this work, monodisperse and nano-porous poly(bismaleimide-co-divinylbenzene) microspheres with large specific surface area (427.6 m2 /g) and rich pore structure were prepared by one-pot self-stable precipitation polymerization of 2,2'-bis[4-(4-maleimidophenoxy) phenyl] propane and divinylbenzene. The prepared poly(bismaleimide-co-divinylbenzene) microspheres were employed as dispersive solid-phase extraction (DSPE) adsorbent for the extraction of triazine herbicides. Under optimized conditions, good linearities were obtained between the peak area and the concentration of triazine herbicides in the range of 1-400 µg/L (R2 ≥ 0.9987) with the limits of detection of 0.12-0.31 µg/L. Triazine herbicides were detected using the described approach in vegetable samples (i.e., cucumber, tomato, and maize) with recoveries of 93.6%-117.3% and relative standard deviations of 0.4%-3.5%. In addition, the recoveries of triazine herbicides remained above 80.7% after being used for nine DSPE cycles, showing excellent reusability of poly(bismaleimide-co-divinylbenzene) microspheres. The adsorption of poly(bismaleimide-co-divinylbenzene) microspheres toward triazine herbicides was a monolayer and chemical adsorption. The adsorption mechanism between triazine herbicides and adsorbents might be a combination of hydrogen bonding, electrostatic interaction, and π-π conjugation. The results confirmed the potential use of the poly(bismaleimide-co-divinylbenzene) microspheres-based DSPE coupled to the high-performance liquid chromatography method for the detection of triazine herbicide residues in vegetable samples.

A novel scalable polycationic melamine sponge-based filtration matrix for continuous ultrafast adsorption of anionic pollutants

Effective capturing of anionic pollutants from wastewater under industrial operating conditions, which requires high processing flux and fast adsorption rate remains a challenge. Here, a commercially available melamine sponge (MS) with reticulated 3D macroporous structures was covalently modified with positively charged moieties using a single step functionalization under mild conditions. The developed novel polycationic melamine sponge (MS+) was formed by a nucleophilic addition reaction between glycidyltrimethylammonium chloride (GMTA) and MS, followed by a self-propagation of GMTA. The produced MS+ possessed strong electrostatic interactions with different anions such as Rose Bengal (RB) and phosphates (P) under a wide pH range (3-11). The MS+ exhibited promoted static adsorption efficiencies of 400 mg g-1 (P) and 600 mg g-1 (RB), within 5 min and 60 s, respectively. Furthermore, the MS+ showed high stability and recyclability for up to 15 cycles of uses, and the recycling process was environmentally friendly by using 1 M NaCl as a releasing solution. Benefiting from fast flow through the macroporous MS+ and highly positive charged skeleton, the MS+ was applied for rapid dynamic enrichment process of P from real manure wastewater with an enrichment factor of 4.4. Utilization of the MS+ as the substrate brings additional advantages such as low cost, availability, and flexibility to fit into existing filtration devices. The developed MS+ could be expanded for enrichments of other anionic species from various polluted water sources.

Magnetic solid-phase extraction of polycyclic aromatic hydrocarbons from water samples using magnetic carbon nanofiber/MIL-101(Cr) nanocomposites

In this study, magnetic carbon nanofibers (Fe3O4@CNF) were modified with MIL-101(Cr) (Fe3O4@CNF@MIL-101) and used as sorbents for magnetic solid-phase extraction (MSPE) to extract polycyclic aromatic hydrocarbons (PAHs) from real water samples. Gas chromatography coupled with a flame ionization detector (GC-FID) was used for the determination of the PAHs. The effect of experimental variables on the extraction efficiency of PAHs was investigated and optimized. These variables include the quantity of sorbent, the kind and volume of the elution solvent, the duration of extraction and desorption, and the salt concentration. The linear range was found to be 0.01 to 200 ng mL-1 with correlation coefficients ranging from 0.9906 to 0.9931 after the effective extraction parameters were optimized. Its detection limits (LOD) were also calculated to be between 0.003 and 0.005 ng mL-1 (S/N = 3). The method's repeatability was tested at three different concentration levels (0.1, 1, and 10 ng mL-1), and relative standard deviations (RSDs%) were obtained in the range of 2.3 to 5.0%. Finally, using the MSPE-GC-FID method, PAHs were extracted from tap water, wastewater, seawater, and spring water samples. The relative recoveries were in the range of 95.7 to 99.8%.

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.

A Novel Method for Carbendazim High-Sensitivity Detection Based on the Combination of Metamaterial Sensor and Machine Learning

Benzimidazole fungicide residue in food products poses a risk to consumer health. Due to its localized electric-field enhancement and high-quality factor value, the metamaterial sensor is appropriate for applications regarding food safety detection. However, the previous detection method based on the metamaterial sensor only considered the resonance dip shift. It neglected other information contained in the spectrum. In this study, we proposed a method for highly sensitive detection of benzimidazole fungicide using a combination of a metamaterial sensor and mean shift machine learning method. The unit cell of the metamaterial sensor contained a cut wire and two split-ring resonances. Mean shift, an unsupervised machine learning method, was employed to analyze the THz spectrum. The experiment results show that our proposed method could detect carbendazim concentrations as low as 0.5 mg/L. The detection sensitivity was enhanced 200 times compared to that achieved using the metamaterial sensor only. Our present work demonstrates a potential application of combining a metamaterial sensor and mean shift in benzimidazole fungicide residue detection.

Recent progress in organic-inorganic hybrid materials as absorbents in sample pretreatment for pesticide detection

Sample pretreatment is essential for trace analysis of pesticides in complex food and environment matrices. Recently, organic-inorganic hybrid materials have gained increasing attention in pesticide extraction and preconcentration. This review highlighted the common organic-inorganic hybrid materials used as absorbents in sample pretreatment for pesticide detection. Furthermore, the preparation and characterization of organic-inorganic hybrid materials were summarized. To obtain a deep understanding of adsorption toward target analytes, the adsorption mechanism and absorption evaluation were discussed. Finally, the applications of organic-inorganic hybrid materials in sample pretreatment techniques and perspectives in the future are also discussed.

Ultrasensitive electrochemiluminescence sensor based on perovskite quantum dots coated with molecularly imprinted polymer for prometryn determination

A highly effective molecularly imprinted electrochemiluminescence sensor was constructed for prometryn determination in environmental and biological samples by using perovskite quantum dots coated with a molecularly imprinted silica layer (MIP/CsPbBr₃-QDs) as the recognition and response element. MIP/CsPbBr₃-QDs were immobilized on a glassy carbon electrode (GCE) through electropolymerization, and the electrochemiluminescence (ECL) response of MIP/CsPbBr₃-QDs could be motivated under the condition of H₂O₂ as co-reactant. ECL signal was selectively quenched with prometryn by hindering electron transfer and directly proportional to the logarithm of prometryn concentration (0.10-500.0 μg/L) with a correlation coefficient of 0.9960. Limits of detection in fish and seawater samples were 0.010 μg/kg and 0.050 μg/L, respectively. Excellent recoveries of 88.0%-106.0% were acquired for fish and seawater samples with a relative standard deviation below 4.2%. The constructed MIECL sensor based on MIP/CsPbBr₃-QDs showed good stability, accuracy, and precision for sensitive detection of prometryn in aquaculture products and environmental samples.

Metal organic framework/chitosan/polyethylene oxide composite columnar foam as a sorbent for the enrichment and determination of estrogens in environmental aqueous solutions

A MIL-53(Al)/CS/PEO columnar foam was fabricated for the determination of estrogens in larger-volume environmental water samples by VA-SPE and HPLC-FLD.

Preparation of porous carbon-based molecularly imprinted polymers for separation of triazine herbicides in corn

A synthesis route of using cellulose as the precursor to prepare porous carbon (PC) had been established in this study. The as-prepared PC was introduced as carriers in the synthesis process of porous carbon-molecularly imprinted polymers (PC-MIPs), which greatly improved the absorption capacity of MIPs. Triazine pesticides in corn were extracted with matrix solid-phase dispersion (MSPD) using the PC-MIPs as dispersants and determined by ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Under the optimal MSPD condition for extracting six kinds of triazines (simazine, terbutryn, simetryne, prometryne, ametryn, and atrazine), the detection limits were 0.005-0.02 ng g^-1, while the precisions were 1.2-5.9%, and the recoveries were 92.6-104.7%. The method has been extensively applied to analyze various corn samples. Atrazine residue (1.2 μg kg^-1) was detected in one corn sample, which was lower than the maximum residual limit indicated by the Chinese stated standards (50 μg kg^-1).

Extraction of parabens by melamine sponge with determination by high-performance liquid chromatography

In the present study, we propose a novel method for the extraction of parabens in personal care products. A new, simple adsorptive material was obtained by combining metal-organic frameworks and melamine sponges using the adhesive property of polyvinylidene fluoride. This new material, metal-organic frameworks/melamine sponges, was found to be particularly suitable for solid-phase extraction. The structural characteristics of metal-organic frameworks/melamine sponges were first analyzed by scanning electron microscopy. Subsequently, solid-phase extraction was performed on sample solutions, and the extracted substances were then analyzed by high-performance liquid chromatography. Following optimization of important experimental conditions, excellent recovery rates were obtained. Our novel method was then applied to the extraction of four parabens (methylparahydroxybenzoates, ethylparahydroxybenzoates, propylparahydroxybenzoates, and butylparahydroxybenzoates) from real samples. The results yielded LODs of 0.26-0.41 ng/mL. The inter- and intra-day recoveries were 104.0-109.7% and 91.2-98.1%, respectively (relative standard deviation, <13.8%).

Development of a SPE/GC-MS method for the determination of organophosphorus pesticides in food samples using syringe filters packed by GNP/MIL-101(Cr) nanocomposite

In this study, we report the synthesis and application of a nanocomposite comprising metal-organic framework MIL-101(Cr) and graphene nanopowder (GNP) as a promising sorbent for the extraction of organophosphorus pesticides (OPPs) in juices, water, vegetables and honey samples. A syringe filter, for the first time, was used to host the synthesized nanocomposite and extract the OPPs followed by GC-MS analysis. Different characterization methods including XRD, FTIR, TGA, BET and SEM were employed to confirm the formation of studied nanocomposite. The results indicated that the GNP/MIL-101(Cr) could provide higher capacity for adsorption of OPPs and lower detection limit compared to pristine MIL-101(Cr). The detection limits were 0.005 to 15.0 µg/Kg and the linear range found between 0.05 and 400 µg/Kg. The proposed method showed very good repeatability with the RSD values ranging from 2.9% to 7.1%. The recoveries were between 84% -110% with the spiked levels of 2.0-100.0 µg/Kg.

Development of a modified quick, easy, cheap, effective, rugged, and safe method based on melamine sponge for multi-residue analysis of veterinary drugs in milks by ultra-performance liquid chromatography tandem mass spectrometry

The purpose of this study was to develop a modified QuEChERS method based on melamine sponge for rapid determination of multi-class veterinary drugs in milks by UPLC-MS/MS. Through simple infiltration and extrusion, fast and convenient matrix purification could be achieved within several seconds, and there was no need of extra phase separation operations. Good linearity with correlation coefficient (R²) ≥0.999 was obtained for all drugs in the range of 2~500 µg·kg^-1. The obtained matrix effects were within ±20% for all monitored drugs. The recoveries of all monitored drugs ranged from 60.7% to 116.0% at three spiked levels (50, 100, and 200 µg·kg^-1), with relative standard deviations less than 7.4%. Comparatively low LODs and LOQs were obtained in the ranges of 0.1~3.8 µg·kg^-1 and 0.2~6.3 µg·kg^-1, respectively. Compared with conventional purification adsorbents, melamine sponge yielded an equal or higher purification performance with matrix removal rate as high as 52.5% and acceptable recoveries in range of 60%-120% for all monitored drugs. The satisfactory results have demonstrated the good potential of melamine sponge in matrix purification for rapid determination of multiclass residues in food safety.

Metal-organic frameworks for food applications: A review

Metal-organic frameworks (MOFs) are high surface-to-volume ratio crystalline hybrid porous coordination materials composed of metal ions as nodes and organic linkers. The goal of this paper was to provide an updated and comprehensive state-of-the-art review of MOFs for different food applications such as active food contact materials, antimicrobial nanocarriers, controlled release nanosystems for active compounds, nanofillers for food packaging materials, food nanoreactors, food substance nanosensors, stabilizers and immobilizers for active compounds and enzymes, and extractors of food contaminants. Extraction and sensing of several food contaminants have been the main food applications of MOFs. The other applications listed above require further investigation, as they are at an early stage. However, interesting results are being reported for these other fields. Finally, an important limitation of MOFs has been the use of non-renewable feedstocks for their synthesis, but this has recently been solved through the manufacture and use of γ-cyclodextrin-based MOFs.

Moisture-sensitive metal-organic framework constructed from cobalt and 4-(4-pyridyl) benzoic acid for dispersive solid-phase extraction of polycyclic aromatic hydrocarbons in apple

A moisture-sensitive metal-organic framework Co^II (pybz)₂ ·2DMF was synthesized and applied as the adsorbent of dispersive solid-phase extraction. The structure changed after water treatment due to the fact that two chelate carboxylate groups on the skeleton were transformed to monodentate because of the coordination of water molecules. The material showed good adsorption for fluorene, phenanthrene, fluoranthene, and pyrene in water because of the π-π conjugation and π-complexation effects. Coupled with high-performance liquid chromatography, a dispersive solid-phase extraction method of determining the content of fluorene, phenanthrene, fluoranthene, and pyrene in apple samples was established after optimizing the extraction conditions. Methanol containing 4% acetic acid was used as the effective eluent. The linearities were 0.5-1000 μg/kg for fluorene, phenanthrene and 5-1000 μg/kg for fluoranthene, pyrene. The limits of detection were 0.06-0.6 μg/kg, and the recoveries were 94.4-116.4%. The method has a high sensitivity for the determination of four polycyclic aromatic hydrocarbons in apple samples.

Sponges and Sponge-Like Materials in Sample Preparation: A Journey from Past to Present and into the Future

Even though instrumental advancements are constantly being made in analytical chemistry, sample preparation is still considered the bottleneck of analytical methods. To this end, researchers are developing new sorbent materials to improve and replace existing ones, with the ultimate goal to improve current methods and make them more efficient and effective. A few years ago, an alternative trend was started toward sample preparation: the use of sponge or sponge-like materials. These materials possess favorable characteristics, such as negligible weight, open-hole structure, high surface area, and variable surface chemistry. Although their use seemed promising, this trend soon reversed, due to either the increasing use of nanomaterials in sample preparation or the limited scope of the first materials. Currently, with the development of new materials, such as melamine sponges, along with the advancement in nanotechnology, this topic was revived, and various functionalizations were carried out on such materials. The new materials are used as sorbents in sample preparation in analytical chemistry. This review explores the development of such materials, from the past to the present and into the future, as well as their use in analytical chemistry.