Extraction of melamine from milk using a magnetic molecularly imprinted polymer

Efficient enrichment and sensitive determination of endocrine disruptors in PPCPs by novel magnetic covalent organic framework extraction coupled with HPLC-MS/MS

Endocrine-disrupting chemicals (EDCs) are a growing class of pollutants commonly found in environmental matrices due to their extensive use in pharmaceuticals and personal care products (PPCPs). In this study, a novel magnetic covalent organic framework (COF), Fe3O4-COOH@TFP-BHBD, was successfully synthesized and utilized as an adsorbent for magnetic solid-phase extraction (MSPE) of EDCs from PPCPs. The core-shell structured adsorbent demonstrated a high specific surface area, strong magnetic responsiveness and excellent stability. A COF-MSPE-high-performance liquid chromatography-tandem mass spectrometry (COF-MSPE-HPLC-MS/MS) method was developed for the quantitative analysis of EDCs in PPCPs. Under the optimized condition, the detection and quantification limits of this method reached as low as 0.001-0.007 ng/mL and 0.004-0.025 ng/mL, respectively. This method was validated and proven capable to analyze real PPCP samples, while the spiked recovery rates in ranged from 85.62 to 107.83 % with RSD of 2.28-8.58 %. Moreover, the adsorption mechanism was investigated using density functional theory (DFT) calculations. The DFT results revealed that the efficient enrichment capacity of Fe3O4-COOH@TFP-BHBD for EDCs can be attributed to π-π interactions and hydrogen bondings. This proposed method provides excellent adsorption ability and sensitivity for the extraction and precise detection of EDCs in PPCPs.

Construction of three-face recognition molecularly imprinted polymers for extraction and detection of melamine via specific hydrogen bonding

Based on the principle that poly(thymine) ssDNA could recognize melamine (Mel) in aqueous media and the third face of Mel could be accessed by other hydrogen bonding molecules, UiO-66-NH2 was functionalized with poly(thymine) ssDNA and as the matrix to construct three-face recognition molecularly imprinted polymers (UDMIPs). The adsorption processes of UDMIPs towards Mel were accorded to Sips model and exhibited high adsorption capacity (QS=10.60 mg/g) and good imprinting factor (IF=2.67). UDMIPs could reach the adsorption equilibrium within 20 min. Competitive adsorption and regeneration experiments demonstrated that UDMIPs exhibited good selectivity and reusability. The adsorption machanism was investigated by CD spectroscopy. Combined with HPLC, UDMIPs were successfully employed to detect Mel in milk samples with recovery rates ranging from 88.4 % to 94.8 %.

Melamine and Cyanuric Acid in Milk and Their Quantities, Analytical Methods and Exposure Risk: A Systematic Review and Meta-analysis

Melamine, as a toxic compound, needs to be controlled in food, especially in dairy products. In this systematic study, quantities of melamine and cyanuric acid in various types of milk were investigated. A comprehensive database search was performed using the keywords pasteurized milk, milk, sterilized milk, melamine, and cyanuric acid without time limitation. A total of 24 articles related to melamine and cyanuric acid were thoroughly reviewed. The overall mean concentration of melamine in milk was estimated by meta-analysis to be 11.3 μg/L. Publication bias was not addressed in the associated assays; however, it was addressed as highly heterogeneous between studies. Subgroup analysis was carried out, and the milk type was a cause of heterogeneity. This systematic review investigated a range of melamine in milk products and discussed different analytical methods.

Fabricating Ultrathin Imprinting Layer for Fast Capture of Valsartan via a Metal Affinity-Oriented Surface Imprinting Method

Rapid separation and enrichment of targets in biological matrixes are of significant interest in multiple life sciences disciplines. Molecularly imprinted polymers (MIPs) have vital applications in extraction and sample cleanup owing to their excellent specificity and selectivity. However, the low mass transfer rate, caused by the heterogeneity of imprinted cavities in polymer networks and strong driving forces, significantly limits its application in high-throughput analysis. Herein, one novel metal affinity-oriented surface imprinting method was proposed to fabricate an MIP with an ultrathin imprinting layer. MIPs were prepared by immobilized template molecules on magnetic nanoparticles (NPs) with metal ions as bridges via coordination, and then polymerization was done. Under the optimized conditions, the thickness of the imprinting layer was merely 1 nm, and the adsorption toward VAL well matched the Langmuir model. Moreover, it took just 5 min to achieve adsorption equilibrium significantly faster than other reported MIPs toward VAL. Adsorption capacity still can reach 25.3 mg/g ascribed to the high imprinting efficiency of the method (the imprinting factor was as high as 5). All evidence proved that recognition sites were all external cavities and were evenly distributed on the surface of the NPs. The obtained MIP NPs exhibited excellent selectivity and specificity toward VAL, with good dispersibility and stability. Coupled with high-performance liquid chromatography, it was successfully used as a dispersed solid phase extraction material to determine VAL in serum. Average recoveries are over 90.0% with relative standard deviations less than 2.14% at three spiked levels (n = 3). All evidence testified that the MIPs fabricated with the proposed method showed a fast trans mass rate and a large rebinding capacity. The method can potentially use high-throughput separation and enrichment of target molecules in batch samples to meet practical applications.

Dispersive micro solid phase extraction of glibenclamide from plasma, urine, and wastewater using a magnetic molecularly imprinted polymer followed by its determination by a high-performance liquid chromatography-photodiode array detector

The present study describes the development of a simple and selective analytical method for dispersive micro solid phase extraction and determination of glibenclamide (GLB) using magnetic molecularly imprinted polymer (MMIP) as a sorbent. MMIP was fabricated by the non-covalent method on the surface of silicated Fe3O4 and had a high affinity for glibenclamide; dual monomers, itaconic acid and allylamine, were used for this. Polymerization was achieved by the precipitation method in the presence of glibenclamide as the template and ethylene glycol dimethacrylate as the cross-linker. The morphology and structural properties of the MMIP were characterized by different analytical methods. To achieve maximum extraction efficiency, influencing parameters were optimized. The linearity range was 1-2000 and 12-2000 μg L-1 by high-performance liquid chromatography-photodiode array detector (HPLC-PDA) and UV-vis spectroscopy, respectively. The detection and quantification limits with UV-vis and HPLC-PDA analyses were 4 and 12 μg L-1 and 0.3 and 1 μg L-1, respectively. Under optimized conditions, recovery of glibenclamide spiked in plasma, human urine, and wastewater was between 89.4 and 102.9% at the concentration levels of 25, 250, and 500 μg L-1; relative standard deviations were below 3.7% by HPLC-PDA. The developed method has a favorable pre-concentration factor of 140.0. Equilibrium data and sorption isotherms fitted well with the Langmuir model. A maximum sorption capacity of 24.260 mg g-1 was acquired based on the Langmuir model. The synthesized sorbent with high selectivity was used to separate GLB from complex biological systems and wastewater before measurement with UV-vis or HPLC-PDA.

Application of molecularly imprinted polymers as the sorbent for extraction of chemical contaminants from milk

Milk is one of the most consumed and balanced foods with a high nutritional value which could be contaminated with different chemicals such as antibiotics, melamine, and hormones. Because of the low concentration of these compounds and the complexity of milk samples, there is a need to use sample pre-treatment methods for purification and preconcentration of these compounds before instrumental techniques. Molecular imprinting polymers (MIPs) are synthetic materials with specific recognition sites complementary to the target molecule. MIPs have selectivity for a specific analyte or group of analytes, which could be used to extract and determine contaminants and remove the interfering compounds from complex samples. Compared to other techniques, sample preparation, high selectivity, excellent stability, and low cost are other advantages of using MIPs. The present article gives an overview of the synthesis of MIPs and their application for extracting antibiotics, hormones, and melamine in milk samples.

Synthesis of molecularly imprinted polymer by precipitation polymerization for the removal of ametryn

Ametryn (AME) is a triazine herbicide which is mainly used to kill unwanted herbs in crops. Despite its importance in agriculture, the usage of AME also poses a risk to humans and the ecosystem due to its toxicity. Hence, it is important to develop a method for the effective removal of AME from various water sources which is in the form of molecular imprinting polymer (MIP). In this study, MIP of AME was synthesized via precipitation polymerization using AME as the template molecule with three different functional monomers including methacrylic acid (MAA), acrylamide (AAm) and 2-vinylpyridine (2VP). The three different synthesized polymers namely MIP (MAA), MIP (AAm) and MIP (2VP) were characterized using Fourier Infra-red spectroscopy (FTIR) and Field Emission Electron Microscopy (FESEM). Then, the batch binding study was carried out using all three MIPs in which MIP (MAA) attained the highest rebinding efficiency (93.73%) among the synthesized polymers. The Energy-Dispersive X-ray spectroscopy (EDX) analysis, Brunauer-Emmett-Teller (BET) analysis and thermogravimetric analysis (TGA) were also conducted on the selected MIP (MAA). Adsorption studies including initial concentration, pH and polymer dosage were also conducted on MIP (MAA). In this study, the highest adsorption efficiency was attained at the optimum condition of 6 ppm of AME solution at pH 7 with 0.1 g of MIP (MAA). MIP (MAA) was successfully applied to remove AME from spiked distilled water, tap water and river water samples with removal efficiencies of 95.01%, 90.24% and 88.37%, respectively.

Magnetic Molecularly Imprinted Polymers for the Separation and Enrichment of Cannabidiol from Hemp Leaf Samples

Cannabidiol (CBD) has attracted immense attention due to its excellent clinical effects in the treatment of various diseases. However, rapid and accurate extraction of CBD from hemp plant concentrates remains a challenge. Thus, novel magnetic molecularly imprinted polymers (CBD-MMIPs) with specific recognizing capability for CBD were synthesized using ethylene glycol dimethacrylate as the cross-linker, CBD as the template, methacrylic acid as the functional monomer, azobisisobutyronitrile as the initiator, and Fe₃O₄ nanoparticles modified with SiO₂ as the magnetic carrier. The morphological, magnetic, and adsorption properties of obtained CBD-MMIPs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry, surface area and porosity analyses, and various adsorption experiments. The results showed that the CBD-MMIPs had selective specificity and high adsorption capacity for CBD. The adsorption of CBD by CBD-MMIPs could reach equilibrium in a short time (30 min), and the maximum adsorption capacity was as high as 26.51 mg/g. The specific recognition and selectivity properties of CBD-MMIPs to CBD were significantly higher than that of other structural analogues, and the regeneration tests established that the CBD-MMIPs had good recyclability. Furthermore, the CBD-MMIPs could be successfully used as an adsorbent to the extraction of CBD from hemp leaf sample concentrates with high recovery efficiencies (93.46-97.40%).

Metal-Organic Framework Fluorescence Sensors for Rapid and Accurate Detection of Melamine in Milk Powder

In this research, a simple, label-free, and ultra-sensitive fluorescent platform based on a metal-organic framework (MOF) has been developed to detect melamine in milk powder. This fluorescence sensor was fabricated from sensitized terbium (Tb)@NH₂-MIL-253 (Al) MOF using a hydrothermal method that involved combining the green emission of Tb (λ_em = 545 nm) with the blue emission of NH₂-MIL-253(Al) MOF (λ_em = 430 nm) under a single excitation wavelength (λ_ex = 335 nm). The fluorescence sensor was then used under optimized conditions (pH = 9.0; sensor concentration = 30 mg/L; response time = 30 s) to quantify melamine in milk powder. The accuracy, sensitivity, and reproducibility of this sensor were established compared to the high-performance liquid chromatography (HPLC) method. The linear range and lower limit of detection (LLOD, computed with 3σ/S) of the sensor were between 40-396.45 nM (equal to 25 µg/kg-0.25 mg/kg) and 40 nM (equal to 25 µg/kg), respectively, which is much less than the maximum residual level (MRL) for the detection of melamine in infant formula (1 mg/kg) and other foods/feeds (2.5 mg/kg). Additionally, the results had good agreement with the HPLC outcomes, suggesting that the NH₂-MIL-253(Al) MOF sensing probe has great precision and repeatability. To conclude, the new fluorescence sensor developed in this study can accurately and sensitively detect melamine in food samples, which may be useful for screening for adulteration of milk powders and other foods.

A Molecularly Imprinted Polymer-Based Thermal Sensor for the Selective Detection of Melamine in Milk Samples

In recent years, melamine-sensing technologies have increasingly gained attention, mainly due to the misuse of the molecule as an adulterant in milk and other foods. Molecularly imprinted polymers (MIPs) are ideal candidates for the recognition of melamine in real-life samples. The prepared MIP particles were incorporated into a thermally conductive layer via micro-contact deposition and its response towards melamine was analyzed using the heat-transfer method (HTM). The sensor displayed an excellent selectivity when analyzing the thermal response to other chemicals commonly found in foods, and its applicability in food safety was demonstrated after evaluation in untreated milk samples, demonstrating a limit of detection of 6.02 μM. As the EU/US melamine legal limit in milk of 2.5 mg/kg falls within the linear range of the sensor, it can offer an innovative solution for routine screening of milk samples in order to detect adulteration with melamine. The results shown in this work thus demonstrate the great potential of a low-cost thermal platform for the detection of food adulteration in complex matrices.

Ultrasound-assisted dispersive magnetic solid-phase extraction of cadmium, lead and copper ions from water and fruit juice samples using DABCO-based poly (ionic liquid) functionalized magnetic nanoparticles

A poly (ionic liquid) (PIL) functionalized magnetic nanoparticles methodology was developed and utilized as an efficient adsorbent for the simultaneous extraction of cadmium, lead, and copper ions from water and fruit juice samples. The novel adsorbent was fabricated by grafting DABCO-based PIL onto silica-coated Fe₃O₄ nanoparticles via copper (0)-mediated reversible-deactivation radical polymerization. Different techniques properly characterized the developed nanoparticles. The central composite design was used to analyze the simultaneous effects of various parameters on the extraction efficiency. The detection limits for water samples ranged between 3.2 and 9.2 ng.L^-1, and fruit juice samples varied from 0.0103 to 0.1082 μg.kg^-1. The recovery ranged from 94.1 to 101.3% and 93.6 to 105.1% for water and fruit juice samples, respectively. The relive measurement uncertainty ranged from 7.7 to 13.6%. The proposed method is rapid, sensitive, environmentally friendly, and useful for monitoring the residues of heavy metal ions in water and fruit juice samples.

Purification of Andrographolide Methanolic Extract Using Molecularly Imprinted Polymer Prepared by Precipitation Polymerization

Molecularly Imprinted Polymer (MIP) has a specific cavity in which the conformity of shape, size, and functionalities corresponds with its template molecule and has been widely used in separation processes. Therefore, this study aims to examine the application of MIP for the purification of andrographolide. The MIP was synthesized by precipitation polymerization using methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) as the functional monomer and cross-linker, andrographolide as a template, and acetonitrile:toluene (3:1) as porogen solvent. The results showed that the binding capacity of Synthesized MIP was 1.2486 mg/g, while the particle size was 295.5 nm with a polydispersity index of 0.064. Furthermore, the imprinting and selectivity factors were 1.148 and 12.37, respectively. The purification process by MIP increased the purity from 55.37 ± 0.69 to 94.94% ± 0.34, while the isolate characterization showed that purified andrographolide had a similar character compared to the standard.

Fabrication and characterization of magnetic molecularly imprinted polymer based on deep eutectic solvent for specific recognition and quantification of vanillin in infant complementary food

A magnetic molecularly imprinted polymer based on deep eutectic solvent was synthesized for specific identification and quantification of vanillin. Fe₃O₄@SiO₂-CC and deep eutectic solvent were applied as the carrier of magnetic material and functional monomer, respectively. According to composition and morphology characterizations and adsorption kinetics, the imprinted polymer had excellent advantages on adsorption capacity and identification specificity for vanillin compared with non-imprinted polymer, while its reusability still remained stable. According to the high-performance liquid chromatography, the detection method based on imprinted polymer produced satisfactory analytical results. The limit of quantification was 0.2 μg·mL^-1. The mean spiked recoveries for vanillin ranged from 91.2% to 100.2% with intra- and inter-day precision were both less than 7.2%. Compared to traditional extraction methods, this method presented best adsorption and extraction performances. In summary, the method could be further applied to the specific separation and quantification of vanillin in infant complementary food.

Magnetic molecularly imprinted polymer for the simultaneous selective extraction of phenoxy acid herbicides from environmental water samples

A selective magnetic molecularly imprinted polymer (MMIP) was synthetized with 4-chloro-2-methylphenoxyacetic acid as template and 4-vinylpiridine as monomer in presence of vinylized magnetite nanoparticles. Scanning electron microscopy, nitrogen adsorption-desorption isotherms, Fourier transform infrared spectrometry and vibrating sample magnetometry were applied to characterize the resulting material. The synthesized MMIP was applied as sorbent in magnetic molecularly imprinted solid-phase extraction (MMISPE) for selective extraction of a mixture of the five herbicides 4-chloro-2-methylphenoxyacetic acid (MCPA), 4-(4-chloro-2-methylphenoxy)butyric acid (MCPB), mecoprop (MCPP), fenoxaprop (FEN) and haloxyfop (HAL). Several parameters affecting the extraction conditions were optimized to achieve the best extraction performance. The best MMISPE combined with HPLC-DAD gave detection and quantification limits between 0.33 and 0.71 μg L^-1 and 1.1-2.4 μg L^-1, respectively, were obtained. The precision of the whole method provided RSD values below 7.3%, and the accuracy was demonstrated by the analysis of several water samples of different origins, with recoveries ranged from 77 to 98%. Moreover, a remarkable re-usability of the MMIP sorbent, more than 65 uses without losses in extraction capacity, was obtained.

Eco-friendly ionic liquid imprinted polymer based on a green synthesis strategy for highly selective adsorption tylosin in animal muscle samples

A novel eco-friendly molecularly imprinted polymer (MIP) was proposed as solid-phase extraction (SPE) adsorbent to selective adsorption tylosin (TYL) in animal muscle samples. The MIP was synthesized in aqueous by using 1,4-butanediyl-3,3-bis-1-vinyl imidazolium chloride and 2-acrylamide-2-methylpropanesulfonic acid as bifunctional monomer. The obtained MIP had excellent selectivity towards TYL in water, and the maximum binding capacity can reach 123.45 mg g^-1. Combined with high-performance liquid chromatography, the presented MIP can be used as SPE sorbent to recognize and detect TYL in the range of 0.008 to 0.6 mg L^-1 (R² = 0.9995). The limit of detection and limit of quantification were 0.003 mg L^-1 and 0.008 mg L^-1, and the intraday and interday precision were 1.05% and 3.36%, respectively. Under the optimal condition, the established MIP-SPE-HPLC method was successfully applied to separate and determine trace TYL in chicken, pork, and beef samples with satisfactory recoveries ranged from 94.0 to 106.3%, and the MIP-SPE cartridge can be cycled at least 20 times. This study implies a promising green MIP-SPE-HPLC method for highly selective adsorption and analysis trace TYL in complex matrices.

Sample treatment based on molecularly imprinted polymers for the analysis of veterinary drugs in food samples: a review

The use of veterinary drugs in medical treatments and in the livestock industry is a recurrent practice. When applied in subtherapeutic doses over prolonged times, they can also act as growth promoters. However, residues of these substances in foods present a risk to human health. Their analysis is thus important and can help guarantee consumer safety. The critical point in each analytical technique is the sample treatment and the analytical matrix complexity. The present manuscript summarizes the development, type of synthesis, characterization, and application of molecularly imprinted polymers in the separation, identification, and quantification techniques for the determination of veterinary drug residues in food samples in extraction, clean-up, isolation, and pre-concentration systems. Synthesized sorbents with specific recognition properties improve the interactions between the analytes and the polymeric sorbents, providing better analysis conditions and advantages in comparison with commercial sorbents in terms of high selectivity, analytical sensitivity, easy performance, and low cost analysis.

Magnetic molecularly imprinted conducting polymer for determination of praziquantel enantiomers in milk

A new selective adsorbent based on magnetic molecularly imprinted conducting polymer was firstly synthetized and applied to the magnetic solid phase extraction (MSPE) for the determination of PZQ enantiomers in milk samples.

Acrylamide-Modified 3-Aminopropyltriethoxysilanes Hybrid Monomer for Highly Selective Imprinting Recognition of Theophylline

The hybrid monomer synthesized with 3-aminopropyltriethoxysilanes and acrylamide was applied for synthesis of molecularly imprinting polymers, and the obtained polymers were used as sorbent in solid-phase extraction for purification of theophylline (THP) in green tea. The static adsorption curves showed better molecular recognition ability and binding capability of the polymers for the target. On the optimized condition, a method was developed for increasing extraction of THP with satisfactory recovery of 93.7%. Good calibration linearity obtained in a range of 5-500 μg·mL-1. The recoveries at three spiked levels ranged from 86.7% to 100.7% with relative standard deviations ≤6.6% (n = 3). The result showed that the obtained polymers exhibited highly selective imprinting recognition to the analyte, and the number of templates was an important factor affecting the selective recognition ability of polymers. The proposed method with hybrid monomer imprinting polymers was successfully applied for purification of THP in green tea.

Theoretical design, preparation, and evaluation of Ginkgolide B molecularly imprinted polymers

Ginkgolide B is in great demand worldwide on account of its extensive and excellent pharmacological effects, however, it is difficult to separate and purify ginkgolide B. In this study, ginkgolide B molecularly imprinted polymers were prepared by combining software simulation and molecular imprinting technique, and its characterization and adsorption performed evaluation were performed to understand the adsorption behavior of the polymers. The adsorption equilibrium concentration of molecularly imprinted polymers was 0.70 mg/mL, and the adsorption equilibrium time was 4 h. Meanwhile, the adsorption isotherm of the polymers for ginkgolide B fitted well with the Langmuir model, and the adsorption kinetics was in line with the pseudo-second-order kinetics. In contrast, the adsorption capacity of molecularly imprinted polymers on ginkgolide B was higher than that of non-molecular imprinted polymers, with better selectivity and better adsorption after repeated use for six times. The application experiments showed that molecular imprinted polymers have a good adsorption effect in low purity samples. Therefore, the polymers reported herein can be expected to apply in the adsorption and separation of ginkgolide B samples.

Molecularly Imprinted Phase-Change Microcapsule System for Bifunctional Applications in Waste Heat Recovery and Targeted Pollutant Removal

An innovative design of a molecularly imprinted phase-change microcapsule (MIM) system for bifunctional applications in waste heat recovery and targeted pollutant removal was reported in this work. This molecularly imprinted system was successfully constructed by encapsulating n-eicosane with a SiO₂ base shell through emulsion-templated interfacial polycondensation and then coating a molecularly imprinted polymeric layer with bisphenol A (BPA) as a template molecule through surface free-radical polymerization. The morphology, microstructure, and chemical structure of the resultant molecularly imprinted phase-change microcapsules (MIMs) were characterized, and their phase-change behavior, thermal energy-storage performance, and selective adsorption capability were investigated intensively. The MIMs developed in this study achieved an outstanding latent heat-storage capability with a high capacity more than 165 J/g and also showed an excellent phase-change reliability with a very small fluctuation in phase-change temperatures and enthalpies after 500 thermal cycles. Moreover, the MIMs also presented a high thermal stability over 200 °C and good shape stability up to 120 °C. Most of all, an effective specific recognition capability and high recognition efficiency were achieved for the MIMs due to the formation of BPA-molecular imprinting sites on their surface. As a result, the MIMs exhibited good adsorption selectivity toward the BPA molecules and satisfactory reusability for targeted removal of BPA with a removal efficiency of 61.7% after 10 cycles of the rebinding-elution procedure. In view of a smart combination of thermal energy-storage and selective adsorption functions, the MIMs developed in this study demonstrate a great potential in applications for waste heat recovery and targeted pollutant removal of industrial and domestic wastewaters.

Preparation and application of magnetic molecular imprinted polymers for extraction of cephalexin from pork and milk samples

A highly selective and effective method was successfully developed using magnetic molecular imprinted polymers (MMIPs) as solid-phase extraction (SPE) coupled with high performance liquid chromatography-ultraviolet detector (HPLC-UV) to rapidly determine cephalexin (CFX) in complex animal-derived food. MMIPs were creatively synthesized via suspension polymerization using Fe₃O₄ magnetic nanoparticles as supporter, CFX as template, acrylamide (AM) as functional monomer, and ethylene glycol dimethacrylate (EGDMA) as cross-linker. The MMIPs were characterized using X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). The binding process fitted well with pseudo-second-order model with good selectivity. Scatchard plot analysis suggested that MMIPs have two types of binding sites with the Q_max of 24.18 mg g^-1 and 40.25 mg g^-1, respectively. And Langmuir model proved that the recognition sites were uniformly distributed in a monolayer on the surface of MMIPs. The methodological assessment showed good applicability of MMIPs with excellent recovery (85.5%-94.0%), precision (1.2%-2.4%), and stability (intra-day 1.3%-3.6%; inter-day 2.6%-4.3%) in determining CFX content. In addition, the linearity of the calibration curve was good in the range of 0.02-5.00 mg L^-1, with a sensitive detection limit of 5.00 μg kg^-1. The results above suggest that the obtained MMIPs exert good performance for separation of CFX in animal-derived food, and the proposed method is suitable for the reliable determination of CFX in complex samples.

Review on Nanomaterial-Based Melamine Detection

Illegal adulteration of milk products by melamine and its analogs has become a threat to the world. In 2008, the misuse of melamine with infant formula caused serious effects on babies of China. Thereafter, the government of China and the US Food and Drug Administration (FDA) limited the use of melamine of 1 mg/kg for infant formula and 2.5 mg/kg for other dairy products. Similarly, the World Health Organization (WHO) has also limited the daily intake of melamine of 0.2 mg/kg body weight per day. Many sensory schemes have been proposed by the scientists for carrying out screening on melamine poisoning. Among them, nanomaterial-based sensing techniques are very promising in terms of real-time applicability. These materials uncover and quantify the melamine by means of diverse mechanisms, such as fluorescence resonance energy transfer (FRET), aggregation, inner filter effect, surface-enhanced Raman scattering (SERS), and self-assembly, etc. Nanomaterials used for the melamine determination include carbon dots, quantum dots, nanocomposites, nanocrystals, nanoclusters, nanoparticles, nanorods, nanowires, and nanotubes. In this review, we summarize and comment on the melamine sensing abilities of these nanomaterials for their suitability and future research directions.

Efficient and selective separation of metronidazole from human serum by using molecularly imprinted magnetic nanoparticles

Magnetic molecularly imprinted nanoparticles were prepared through surface-initiated reversible addition fragmentation chain transfer polymerization by using metronidazole as a template. The molecularly imprinted magnetic nanoparticles were characterized by attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, and vibrating sample magnetometry. The adsorption characteristics were also investigated and the kinetics of the adsorption of metronidazole on the imprinted nanoparticles were described by the second-order kinetic model with the short equilibrium adsorption time (30 min). The adsorption isotherm was well matched with the Langmuir isotherm in which the maximum adsorption capacity was calculated to be 40.1 mg/g. Furthermore, the imprinted magnetic nanoparticles showed good selectivity as well as reusability even after six adsorption-desorption cycles. The imprinted magnetic nanoparticles were used as a sorbent for the selective separation of metronidazole from human serum. The recoveries of metronidazole from human serum changed between 97.5 and 99.8% and showed similar sensitivity as an enzyme-linked immunoassay method. Therefore, the molecularly imprinted magnetic nanoparticles might have potential application for the selective and reliable separation of metronidazole from biological fluids in clinical applications.

Adsorption studies of cadmium onto magnetic Fe3O4@FePO4 and its preconcentration with detection by electrothermal atomic absorption spectrometry

Superparamagnetic Fe₃O₄@FePO₄ nanoparticles with core shell structure were prepared by coating iron phosphate on the surface of Fe₃O₄ nanoparticles by liquid phase deposition method. The prepared materials were characterized by vibrating sample magnetometer, scanning electron microscopy, X-ray diffractometer, Fourier transform infrared spectrometer, nano Zetasizer, X-ray photoelectron spectroscopy and Raman spectrometer. These characterization methods were also used to describe the adsorption mechanism. The obtained composite material was used for the adsorption of a heavy metal element, cadmium. Its unique magnetic properties are favorable for rapid separation and preconcentration of trace cadmium from aqueous solutions. About 100% sorption was achieved at pH 7 for 1mL, 10μgL^-1 of cadmium. Batch adsorption experiments show that the adsorption fits Langmuir model, and a maximum adsorption capacity 13.51mgg^-1 is derived for Cd(II). The retained Cd(II) could be readily recovered by 200μL of HNO₃ (0.01molL^-1). The cadmium in the eluate is quantified with detection by electrothermal atomic absorption spectrometry (ETAAS). A sample volume of 2000μL creates an enrichment factor of 10.3, along with a detection limit of 0.021µgL^-1 (3σ, n=7) and a RSD of 1.3% (0.1µgL^-1, n=7) within a linear calibration range of 0.05-0.5µgL^-1. The practical applicability of this procedure was validated by analyzing cadmium contents in a certified reference material (GBW08608) and two environmental water samples.