Extraction Of Melamine Research Articles

An air-assisted dispersive liquid phase microextraction method based on a hydrophobic magnetic deep eutectic solvent for the extraction and preconcentration of melamine from milk and milk-based products.

In the current research, a fast and sustainable air-assisted hydrophobic magnetic deep eutectic solvent-based dispersive liquid phase microextraction followed by UV-Vis spectrophotometry measurements was optimized for the extraction and determination of melamine in milk and milk-based products. The central composite design was applied for the optimization of factors affecting the recovery of melamine. Quantitative extraction of melamine was achieved using hydrophobic magnetic deep eutectic solvents prepared from a mixture of octanoic acid, aliquat-336, and cobalt(II) chloride. The optimum conditions for extraction were found as follows: 6 extraction cycles, pH 8.2, extraction solvent volume 260µL, and acetone volume 125µL.Interestingly, a centrifugation step was not required to achieve phase separation. Under the optimum conditions, melamine was determined in the linear range of 3-600ngmL-1, the limit of detection (3Sblank/m) of 0.9ngmL-1, and the enrichment factor of 144. The validation of the method was investigated by the analysis of reference materials. Consequently, the method was successfully applied for the analysis of melamine residues in milk and milk-based products.

Synthesis of a magnetic micro-eutectogel based on a deep eutectic solvent gel immobilized in calcium alginate: Application for green analysis of melamine in milk and dairy products

A new three-component magnetic eutectogel composed of a crosslinked copolymeric deep eutectic solvent (DES) and polyvinylpyrrolidone-coated Fe3O4 nano-powder impregnated in calcium alginate gel was synthesized and applied as a sorbent material in a green alternative micro solid-phase extraction of melamine in milk and dairy products. The analyses were performed using the HPLC-UV technique. The copolymeric DES was prepared through thermally-induced free-radical polymerization of [2-hydroxyethyl methacrylate]:[thymol] DES (1:1 mol ratio) as functional monomer, azobisisobutyronitrile (as initiator), and ethylene glycol dimethacrylate (as crosslinker). The sorbent was characterized using ATR-FTIR, 1H &13C FT-NMR, SEM, VSM, and BET techniques. The stability of the eutectogel in water and its effect on the pH of the aqueous solution was studied. A one-at-a-time approach was applied to optimize the impact of significant factors influencing sample preparation efficiency (sorbent mass, desorption conditions, adsorption time, pH, and ionic strength). The method validation was performed by evaluating matrix-matched calibration linearity (2–300 μg kg−1, r2 = 0.9902), precision, system suitability, specificity, enrichment factor, and matrix effect. The obtained limit of quantification (0.38 μg kg−1) was lower than the established maximum level for melamine by Food and Drug Administration (FDA) (0.25 mg kg−1), Food and Agriculture Organization (FAO) (0.5 & 2.5 mg kg−1), and The European Union (EU) (2.5 mg kg−1) in milk and dairy products. The optimized procedure was applied for the analysis of melamine in bovine milk, yogurt, cream, cheese, and ice cream. The obtained normalized recoveries of 77.4–105.3% (RSD% <7.0%) were acceptable regarding the practical default range set by the European Commission (70–120%, RSD≤20%). The sustainability and green aspects of the procedure were evaluated by the Analytical Greenness Metric Approach (0.6/1.0) and the Analytical Eco-Scale tool (73/100). This paper presents the first-time synthesis and application of this micro-eutectogel for the analysis of melamine in milk and milk-based dairy products.

Developed and rapid extraction of melamine in infant formulae by combined electromembrane with nanographene oxide reinforced hollow fiber

Melamine is a high nitrogen compound used as an adulteration to high protein foods such as infant formulae. There are many different methods for extraction and analysis of melamine which are time-consuming, complex, and need large volumes of organic solvents.A validated method for extraction and cleanup of melamine (MEL) in infant formulae, water, and powdered coffee creamer was developed using a Nanographene oxide (NGO) assisted with electromembrane extraction (NGO/EME) followed by HPLC-UV detection. Supported liquid membrane (SLM) with NGO was used as the adsorbent interface in this study. Synthesized NGO was characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM). Effective parameters such as voltage magnitude, SLM solvent, pH of acceptor and donor phases, extraction time, and stirring rate were optimized. The method provided the LOD and LOQ 0.03, and 0.1µg/kg in infant formula, respectively. The accuracy was in the satisfaction recovery rate between 106-109% with RSD 4.83-5.31 for infant formulae as well as the other tested matrices. The developed method based on NGO/EME extraction presents a reliable and rapid analysis for melamine in infant formula.

A simple and quick ionic liquid-based ultrasonic-assisted microextraction for determination of melamine residues in dairy products: Theoretical and experimental approaches

In this study, a simple and quick ionic liquid- based ultrasonic-assisted microextraction (IL-UA-ME) procedure has been improved for extraction of melamine in dairy productsfollowed by UV–VIS spectrometry. For the analysis of stability and reactivity of melamine and its some metal complexes, quantum chemical parameters like frontier orbital energy-HOMO-LUMO energy gap, hardness and softness were calculated using computational chemistry tools. The results regarding to stability analysis made considering density functional theory showed that theoretical data obtained are compatible with experimentally obtained results, and Fe-melamine complex is more stable compared to others. Under optimum conditions, the linearity was in the range of 0.05–400 ng mL−1 with detection limit of 0.015 ng mL−1. Following the validation studies, recovery and relative standard deviation were obtained in range of 92.5–104.3% and 1.4–2.1%, respectively. The first research article in which experimental and theoretical studies are used together for the determination of melamine in dairy products.

Accordion-like Ti3C2Tx MXene nanosheets as a high-performance solid phase microextraction adsorbent for determination of polycyclic aromatic hydrocarbons using GC-MS.

Two dimensional accordion-like Ti3C2Tx MXene, where Tx represents surface termination groups such as -OH, -O-, and -F, is synthesized by selective etching of aluminum layers from Ti3AlC2. This manuscript reports on the adsorption of organic molecules from head-space and aqueous environments containing Ti3C2Tx, a representative of the MXene family. Ti3C2Tx coated by gluing method on a stainless steel wire was successfully utilized as a highly sensitive and stable head-space solid-phase microextraction (SPME) fiber. A SPME method with the MXene as the adsorbent combined with gas chromatography with MS detector was used to determine the polycyclic aromatic hydrocarbons (PAHs) in water samples. Low detection limits in the range of 0.2-5ngL-1, wide linearity and good reproducibility (RSD = 4.6 to 7.4% for n= 6) under the optimized extraction conditions was achieved. Finally, the MXene coated fiber was successfully used for the determination of PAHs in real water samples. The relative recoveries for six PAHs are from 91.3-105.0%, which proved the applicability of the method. Also, melamine was selected as a polar analyte and it has been shown that Ti3C2Tx MXene has good capability in extraction of melamine (the extraction recovery for melamine = 80.1%) from aqueous media by dispersive micro solid-phase extraction. Graphical abstractTwo dimensional accordion-like Ti3C2 MXene was synthesized by selective etching of aluminum layers from Ti3AlC2. Ti3C2 MXene was employed as solid phase microextraction fiber coating for the extraction of polycyclic aromatic hydrocarbons from water samples.

Synthesis, characterization, and application of molecular imprinting polymer for extraction of melamine from spiked milk, water, and blood serum

Molecularly imprinted polymers (MIPs) of melamine (MEL) were synthesized by non-covalent approach with precipitation polymerization. In this research, MEL was used as the template molecule, acrylamide (AAm) as the functional monomer, divinylbenzene (DVB) as the cross-linker, 2,2′-azobisisobutyronitrile (AIBN) as an initiator, and the mixture of dimethyl sulfoxide (DMSO) and acetonitrile (ACN) was used as a reaction medium. The imprinted and non-imprinted polymer particles were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and thermogravimetric analysis (TGA). The rebinding efficiency was evaluated for all the synthesized polymers by batch binding analysis. The adsorption studies such as adsorbent dosage of polymer, initial concentrations, and pH of MEL solution were successfully conducted on the selected polymer. For selectivity test, 2,4,6-trichlorophenol (2,4,6-TCP) was selected as competitive molecule against the MEL. A good removal efficiency of MEL from different samples such as milk (81.97%), river water (91.52%), and human blood serum (90.66%) was achieved.

Ionic liquid based ion-pairing microextraction combined with spectrophotometry for preconcentration and quantitation of melamine in milk and milk-based products

A simple, rapid and economical ultrasound-assisted microextraction (UA-ME) procedure was developed for extraction and determination of trace amounts of melamine in milk products, followed at 310 nm by UV-Visible spectrophotometry. In the study, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C6mim][Tf2N] as ionic liquid (IL) was used in presence of sodium dodecyl sulfate (SDS) as an oppositely charged auxiliary ligand at pH 4.0 for extraction of melamine, and methanol was selected as a disperser solvent. Under the optimal conditions, the analytical features of method were established by calibration curves prepared from both solvent based calibration and matrix-matched calibration solutions. The method exhibits a linear relationship (from 5 to 250 μg L−1), low detection limit (1.6 μg L−1), good recovery (93.5–97.8%), and high sensitivity enhancement factor (125) by solvent based calibration curve while it allows a detection limit of 2.1 μg L−1 in range of 5–210 μg L−1 by the matrix-matched calibration curve. The method accuracy (trueness and precision) was checked by applying matrix-matched calibration strategy to all the spiked samples including quality control samples as well as comparison with an independent micellar LC method, and then it was successfully applied to the determination of melamine in milk based products.

Integrated photografted molecularly imprinted polymers with a cellulose acetate membrane for the extraction of melamine from dry milk before HPLC analysis.

In this study, a new separation technique based on membrane extraction is described for the determination of melamine in dry milk. The water-compatible cellulose acetate membrane, which is photografted by melamine imprinted nanospheres, was prepared by placing the membrane into the polymerization solution containing methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as cross-linker, acetonitrile as porogen, and melamine as the template molecule. The characterization of the polymeric membrane was performed by Fourier transmission infrared spectroscopy and scanning electron microscopy. This integrated composite membrane was used as a solid-phase extraction medium for the extraction of melamine from dry milk samples. Various parameters affecting the extraction efficiency of the membrane were evaluated. The results showed higher binding capacity for melamine imprinted membranes in comparison with the nonimprinted membranes. High-performance liquid chromatography analysis showed that the extraction of melamine from dry milk by the photografted cellulose acetate membrane had a linear calibration curve in the range of 0.02-11.80μg/mL with an excellent precision of 2.73%. The limit of detection and quantification of melamine was 0.007 and 0.020μg/mL, respectively. The recoveries of melamine were in the range of 88.7-94.8%.

Incorporation of a Basil-Seed-Based Surface Enhanced Raman Scattering Sensor with a Pipet for Detection of Melamine

A basil-seed-based surface enhanced Raman scattering (SERS) sensor has been incorporated with a transfer pipet via a plastic chamber to create an integrated portable device, in which the transfer pipet is used for flow injection. A small amount of liquid sample is loaded to the dry basil-seed-based SERS sensor using the transfer pipet. The dry basil-seed can store the liquid sample like a sponge so that the plasmonic silver nanoparticles deposited on the basil-seed keep an intimate contact with the liquid sample containing the analyte, which enhances the sensitivity of the device. The excessive liquid sample is then ejected out of the plastic box by the transfer pipet, leaving the basil-seed-based SERS substrate exposed to air. This reduces the interference of the opaque liquid sample on the SERS signal, and avoids the tedious procedure for extraction of melamine from the milk. As a result, the pipet-basil-seed-based SERS device can be used to detect melamine in milk rapidly. This work has demonstrated a ...

Synthesis of novel monolithic cartridges with specific recognition sites for extraction of melamine

Synthesis of melamine (ME) imprinted polymeric sorbent for use as solid phase extraction adsorbent was targeted and the benefits of the synthesis in the monolith format were combined with imprinting technology advantages. Melamine as template and 2-vinylimidazole-Cu2+ as complexing agent were used as the first time for pre-complex formation, followed by the preparation of monolith by bulk polymerization method in the presence of ethyleneglycol dimethacrylate as crosslinker, azobisisobutyronitrile as initiator, and ethyl alcohol as solvent for a duration of 4h at 80°C. 1.0M NaOH solution was used as a desorption agent to remove template. Non-imprinted monolith (NIP) were synthesized as a control without template in same receipt. The monolith samples were characterized by Fourier Transformed Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), elementary analysis, and Branauer- Emmett- Teller (BET) studies. Melamine adsorption from aqueous solution was studied in continuous mode, and some parameters such as pH, temperature, concentration and flow-rate were optimized for melamine adsorption. The maximum adsorption capacities were determined as 147.9mg/g for imprinted polymer (MIP), 82.0mg/g for non-imprinted polymer (NIP) and 4.0mg/g for polymer without pre-complex (E) at 25°C, and pH5.0 with 500ppm melamine initial concentration for 1.0mL/min flow-rate. In addition to interaction characterized by metal coordination bond formation, non- covalent interactions were responsible for melamine adsorption. No significant change in adsorption performance was recorded after 10 consecutive adsorption-desorption cycles.Kinetic analysis indicated compliance with pseudo-second order kinetics. The Freundlich isotherm was found suitable for description of the process. Cyanuric acid (CY), aniline (AN), and phenol (PH) were used as competing agents in selectivity studies, and relative selectivity coefficients were calculated (k'CY=4.45; k'AN=7.08; k'PH=3.98).The performance of melamine imprinted polymeric monolith (MIP) as solid-phase extraction adsorbent for extraction of melamine from milk samples was investigated and the recovery of melamine in spiked milk samples was 97.6% with the relative standard deviation (RSD) (8.1%).

Using activated attapulgite as sorbent for solid-phase extraction of melamine in milk formula samples

In this study, a simple solid-phase extraction (SPE) approach by using activated attapulgite as sorbent was successfully developed for the determination of melamine in milk formula samples. Crucial factors impacting the extraction efficiency, including sample solvent, elution solvent, and sample loading volume, were investigated. Under the optimal extraction conditions, the sample loading volume was up to 200mL and the adsorption capacity of the melamine gave rise to 1154μgg(-1). Excellent linear calibration curves (r (2) > 0.999) were achieved, and then the limit of detection (S/N = 3) and the limit of quantification (S/N = 10) were found to be 0.15 and 0.5ngmL(-1), respectively. The recoveries of the melamine spiked in four milk formula samples at three concentration levels ranged from 83.5 to 111.0% with relative standard deviations (RSDs) less than 10.2%. Furthermore, RSDs of batch to batch (n = 4) of the acidified attapulgite used in this developed method were in the range of 2.3∼7.3%. In comparison to the commercial Oasis MCX, the acidified attapulgite sorbent even outperformed (at least in terms of reproducibility) for melamine analysis in real food samples. Because of its simplicity, the newly developed SPE method based on acidified attapulgite nanoparticles should provide a promising tool for daily monitoring of doped melamine in milk formula or other complex matrices.

Cyromazine imprinted polymers for selective stir bar sorptive extraction of melamine in animal feed and milk samples.

In this work, a molecularly imprinted polymer (MIP) coated stir bar was prepared using a self-designed polytetrafluoroethylene (PTFE) mold and in situ polymerization, with cyromazine as the dummy template for the target melamine. The prepared MIP coated stir bar presented a uniform and porous surface as well as good chemical stability and selectivity for melamine. Based on it, a method of MIP coated stir bar sorptive extraction (SBSE) combined with high performance liquid chromatography-ultraviolet detection (HPLC-UV) was developed for the quantification of melamine in food samples. Significant factors affecting the extraction efficiency of melamine by MIP-SBSE, such as the extraction solvent and time, stirring rate, desorption solvent and time, were investigated thoroughly. Under the optimal conditions, the analytical performance of this method was evaluated. The detection limit of the developed method was 0.54 μg L(-1) for melamine with an enrichment factor of 42-fold and the relative standard deviation (RSD) of 6.1% (c = 5 μg L(-1), n = 7), and the linear range was 2-200 μg L(-1). The established method was applied for the determination of melamine in a variety of real samples including cat food, dog food, chicken feed A, chicken feed B and milk powder, and the recoveries for melamine in the spiked samples were in the range of 76.2-98.2%, 80.0-85.5%, 89.5-113%, 85.0-95.5% and 65.0-111%, respectively. The proposed method presented a good specific recognition ability and matrix interference resistance, and was demonstrated to be effective and sensitive for the analysis of melamine in animal food and milk samples.

Determination of melamine in soil samples using surfactant-enhanced hollow fiber liquid phase microextraction followed by HPLC–UV using experimental design

Surfactant-enhanced hollow fiber liquid phase (SE-HF-LPME) microextraction was applied for the extraction of melamine in conjunction with high performance liquid chromatography with UV detection (HPLC–UV). Sodium dodecyl sulfate (SDS) was added firstly to the sample solution at pH 1.9 to form hydrophobic ion-pair with protonated melamine. Then the protonated melamine–dodecyl sulfate ion-pair (Mel–DS) was extracted from aqueous phase into organic phase immobilized in the pores and lumen of the hollow fiber. After extraction, the analyte-enriched 1-octanol was withdrawn into the syringe and injected into the HPLC. Preliminary, one variable at a time method was applied to select the type of extraction solvent. Then, in screening step, the other variables that may affect the extraction efficiency of the analyte were studied using a fractional factorial design. In the next step, a central composite design was applied for optimization of the significant factors having positive effects on extraction efficiency. The optimum operational conditions included: sample volume, 5mL; surfactant concentration, 1.5mM; pH 1.9; stirring rate, 1500rpm and extraction time, 60min. Using the optimum conditions, the method was analytically evaluated. The detection limit, relative standard deviation and linear range were 0.005μgmL−1, 4.0% (3μgmL−1, n=5) and 0.01–8μgmL−1, respectively. The performance of the procedure in extraction of melamine from the soil samples was good according to its relative recoveries in different spiking levels (95–109%).

Rapid extraction of melamine in powdered milk for direct electrospray ionization tandem mass spectrometry analysis

A combination of a simple pretreatment for melamine extraction and direct analysis in electrospray ionization tandem mass spectrometry (ESI–MS/MS) is proposed. Three pretreatments were evaluated. The first was based on suppressing interference using acetonitrile. The second used sulphuric acid and trichloroacetic acid to suppress interference and for melamine extraction, respectively. The third used sulphuric acid to suppress milk interference, trichloroacetic acid for melamine precipitation, and ethyl acetate for melamine extraction. However, only the last pretreatment suppressed milk interference in melamine detection and a good linearity (R2=0.99) was obtained. The presence of MS/MS 85 on melamine fragmentation spectrum showed the selectivity of this method. The limit of detection and limit of quantification were 0.269µgL−1 and 0.897µgL−1, respectively. The recoveries and relative standard deviation (RDS) of method were lower than 114% and 7.86%, respectively. Further, the research was extended to elucidate the nature of the melamine in the extract through infrared spectroscopy and microscopy analyses. The precipitate was characterized as melaminium bis(trichloroacetate) dihydrate, which is generated through hydrogen bound formation in an interaction between melamine and trichloroacetic acid. Therefore, a simple, fast, and easy method for melamine extraction and direct ESI–MS/MS analysis was developed.

Microwave-Assisted Solvent Extraction of Melamine from Seafood and Determination by Gas Chromatography–Mass Spectrometry: Optimization by Factorial Design

Melamine attracts considerable attention because of its toxicity. The determination of melamine in seafood was performed by gas-chromatography–mass spectrometry, using an optimized version of a method adopted by the U.S. Food and Drug Administration. The melamine was extracted by closed-vessel microwave-assisted solvent extraction (MAE), as a valid alternative in sample preparation, to reduce analysis time and provide less ambiguous data. The procedure was optimized by means of experimental factorial design considering the three main variables that affect this process: microwave oven power, the maximum temperature inside the extraction tube, and the hold time. The recovery of melamine in spiked samples was used as the elemental response value of the design. Temperature and hold time had a more positive effect on the response than the microwave power. A significant positive interaction was observed between oven power and hold time. A temperature of 70°C and a hold time of 1 min gave a recovery of 92 ± 5% for a microwave power of 600 W. Under these conditions, the total microwave extraction time was approximately 2 minutes, a much shorter time compared to the ultrasonic bath, which required a total time of 40 min. The repeatability of the method was approximately 3%. The limits of quantification were 0.55 mg kg−1 for MAE and 1.9 mg kg−1 for the ultrasonic bath; the linearity was confirmed up to 10 mg kg−1. In conclusion, the MAE procedure was shown to be an excellent alternative to the official method.

Preparation of magnetic molecularly imprinted polymer for the extraction of melamine from milk followed by liquid chromatography-tandem mass spectrometry

In this work, a simple and selective method was successfully developed for the determination of melamine (MEL) in milk using magnetic molecularly imprinted polymer (MMIP) as sorbent. The MMIP has been prepared by using MEL as template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as crosslinking agent and Fe3O4 magnetite as magnetic component. The extraction procedure was performed in a single step by blending and stirring the MMIPs and the milk sample which was diluted with water. The experimental results showed that the MMIP had high affinity and selectivity toward MEL. When the extraction was completed, the MMIPs absorbed MEL was separated from the sample matrix by an external magnet. The MEL eluted from the MMIPs was analysed by liquid chromatography-tandem mass spectrometry. For achieving optimal preconcentration and reducing non-specific interactions, various parameters affecting the extraction efficiency such as extraction solvent, the amount of MMIPs, extraction time, washing solution and eluting solution were evaluated. Under the optimal conditions, the linearity of quantification obtained by analyzing matrix-matched standards is in the range of 10–1000 ng mL−1. The detection limit of MEL is 2.6 ng mL−1. The relative standard deviations of intra- and inter-day ranging from 4.3% to 7.2% are obtained. The proposed method was successfully applied to determine MEL in five milk samples from different provenances. The recoveries of MEL are in the range of 88.0%–95.8%.

Preparation and application of surface molecularly imprinted silica gel for selective extraction of melamine from milk samples

Highly selective molecularly imprinted layer-coated silica gel (MIP@SiO2) for melamine (MEL) was prepared by the surface molecular imprinting technique on the supporter of silica gel. Non-imprinted polymer layer-coated silica gel (NIP@SiO2) and bulk molecularly imprinted polymer (MIP) were also prepared for comparison. Characterization and performance tests of the obtained products revealed that MIP@SiO2 not only had excellent selectivity to the target molecule MEL compared with NIP@SiO2, but also displayed absorption capacity superior to MIP due to the molecular recognition sites on the surface of silica gel. As the MIP@SiO2 were adopted as the adsorbents of solid-phase extraction for detecting MEL in milk samples, the recoveries of spiked samples ranged from 75.6% to 96.8% with the relative standard deviation of spiked samples less than 10%, which reveals that the MIP@SiO2 were efficient SPE adsorbents for melamine.

Rapid and selective screening of melamine in bovine milk using molecularly imprinted matrix solid-phase dispersion coupled with liquid chromatography-ultraviolet detection

A simple, convenient and high selective molecularly imprinted matrix solid-phase dispersion (MI-MSPD) using water-compatible cyromazine-imprinted polymer as adsorbent was proposed for the rapid screening of melamine from bovine milk coupled with liquid chromatography-ultraviolet detection. The molecularly imprinted polymers (MIPs) synthesized by cyromazine as dummy template and reformative methanol–water system as reaction medium showed higher affinity and selectivity to melamine, and so they were applied as the specific dispersant of MSPD to extraction of melamine and simultaneously eliminate the effect of template leakage on quantitative analysis. Under the optimized conditions, good linearity was obtained in a range of 0.24–60.0μgg−1 with the correlation coefficient of 0.9994. The recoveries of melamine at three spiked levels were ranged from 86.0 to 96.2% with the relative standard deviation (RSD)≤4.0%. This proposed MI-MSPD method combined the advantages of MSPD and MIPs, and could be used as an alternative tool for analyzing the residues of melamine in complex milk samples.

The assessment of melamine and cyanuric acid residues in eggs from laying hens exposed to contaminated feed

The aim of this study was to monitor the carry-over of melamine and its metabolite cyanuric acid from melamine-contaminated feed administered to layers into eggs. Ten experimental Isa Brown layers (36 week of age) were fed melamine-contaminated feed containing 100 mg of melamine per kg of feed. The duration of the experiment was 6 weeks. Eggs were collected during whole experiment. Analysis of eggs was done by a simple extraction of melamine and cyanuric acid residues, using a water-acetonitrile mixture and analysed by gas chromatography - triple quadrupole mass spectrometry. Melamine and cyanuric acid residues were detected in all eggs collected from the experimental layers, immediately after the first administration of melamine-contaminated feed. The mean concentrations of melamine in the egg yolk and egg white recalculated on a dry matter basis were 1.90 mg·kg-1 ± 0.158 and 10.84 mg·kg-1 ± 3.951 (P ≤ 0.01); the cyanuric acid contents were 6.54 mg·kg-1 ± 0.2.466 and 4.07 mg·kg-1 ± 0.909, respectively. Melamine and cyanuric acid were not detected in eggs from control layers. Concentrations of melamine and cyanuric acid in eggs decreased quickly after melamine feeding was stopped. Our results indicate that melamine undergoes biotransformation to cyanuric acid in the layer’s body that also passed into the eggs. The results verified the presence of distribution metabolic pathway of melamine and its easiest transfer into egg yolk. Moreover, the biotransformation of melamine into cyanuric acid in eggs of layers was confirmed.

Preparation and characterization of molecularly imprinted microspheres for selective extraction of trace melamine from milk samples

We describe molecularly imprinted microspheres (MIMs) for the selective extraction of melamine from milk. The MIMs were made from melamine as the template molecule, methacrylic acid as the functional monomer, and ethylene glycol dimethacrylate as the linking agent. The MIMs were synthesized by suspension polymerization and characterized by rebinding experiments. They displayed high adsorption capacity, fast rebinding kinetics, and highly specific rebinding of melamine. The imprinting factor is 4.1. Scatchard analysis revealed a one-type rebinding behavior, the dissociation constant and maximum rebinding capacity being 37.59 g L−1 and 30.85 μmol g−1, respectively. The MIMs exhibited a 25% cross-reactivity towards atrazine, but less than 3.0% towards prometryn, clenbuterol and metronidazole. In addition, a MIM-based solid phase extraction (MISPE) column for melamine was prepared by packing MIMs into a common SPE cartridge. The MISPE extraction gave recoveries of 89.8 to 100.6% of melamine, with relative standard deviations of 5.9 to 7.5%. There was no significant loss of rebinding capacity after more than 60 repeated uses, thus demonstrating the high stability of the MISPE column. The MSPE column also was applied to the extraction of melamine from spiked liquid and powdered milk with satisfying accuracy and precision.