Recoveries Of Melamine Research Articles

High and stable surface-enhanced Raman spectroscopy activity of h-BN nanosheet/Au1Ag3 nanoalloy hybrid membrane for melamine determination

In this work, a hexagonal boron nitride (h-BN)/AuAg nanoalloy hybrids (NAHs) was synthesized to fabricate h-BN/Au1Ag3 membrane as a solid surface-enhanced Raman spectroscopy (SERS) substrate for sensitive SERS detection of melamine. The AuAg nanoalloys were in situ grown on h-BN by chemical reduction method, and the Au/Ag molar ratio was tuned to achieve optimal SERS performance. After the SERS performance of h-BN/AuAg NAHs with different Au/Ag ratios was analyzed, h-BN/Au1Ag3 NAHs were chosen for SERS analysis. The h-BN/Au1Ag3 membrane can be obtained through simple filtration of h-BN/Au1Ag3 NAHs on chromatographic paper. As expected, the solid SERS substrates of h-BN/Au1Ag3 membrane were uniform and demonstrated good selectivity, repeatability and reproducibility for SERS detection of melamine. The results demonstrate that h-BN/Au1Ag3 membrane exhibited high SERS activity for 4-mercaptobenzoic acid (4-MBA) with limit of detection (LOD) at 1.0 ng L−1, and its analytical enhancement factor (AEF) reached 3.6 × 108. The possible enhancement mechanism, including electromagnetic mechanisms (EM) and chemical mechanisms (CM) were illustrated by finite-difference time-domain (FDTD) and density functional theory (DFT) simulations in detail, respectively. The concentration of melamine in the 0.05–5.0 mg L−1 range showed good linear relationship (R2 = 0.9940) with SERS intensity with LOD of 0.01 mg L−1. Finally, the recoveries of melamine in liquid milk samples are 87.7–105.7% with relative standard deviations (RSDs) in range of 0.6–2.6%, providing precise safety evaluation of melamine in milk samples.

Aptamer/derivatization-based surface-enhanced Raman scattering membrane assembly for selective analysis of melamine and formaldehyde in migration of melamine kitchenware

The analysis of contaminants in migration of food contact material (FCMs) is an urgent demand for food safety. In this study, melamine and formaldehyde in melamine kitchenware were selectively analyzed by surface-enhanced Raman scattering (SERS) via aptamer/derivatization-based membrane assembly. The membrane assembly was designed by simple filtration of Ag nanoparticles-decorated “stellate” silicon dioxide (SiO2/Ag) and composites of reduced graphene oxide and Ag nanoparticles (rGO/Ag) functioned with specific reagents. High selectivity can be realized by melamine aptamer and derivatization reagent of formaldehyde, respectively. The relative standard deviations (RSDs) of melamine and formaldehyde analysis for 11 replicate measurements, 14 consecutive days and 25 batches are less than 6.0 %, which shows excellent repeatability and reproducibility. After the method was validated, the limits of detection (LOD) for melamine and formaldehyde are 0.15 mg/L and 0.21 mg/L, respectively. The developed method was applied to determine the content of melamine and formaldehyde in migration of melamine kitchenware with low relative errors (less than 5.3 %) compared to chromatographic results. The recoveries of melamine and formaldehyde for migrations of melamine kitchenware are 91.2–110.0 % and 94.0–106.0 % with RSDs in range of 1.8–8.3 % and 4.7–9.1 %, respectively. The method proposed a new concept of convenient, portable and reliable strategy for analysis of melamine and formaldehyde in migration from FCMs.

An isotope dilution liquid chromatography-mass spectrometry method for detection of melamine in milk powder

ABSTRACT Adulteration/unintentional contamination of milk with melamine could have negative health and economic implications especially in the developing countries due to insufficient laboratory support and surveillance. This paper presents an Isotope Dilution Liquid Chromatography-Mass Spectrometry (ID LC-MS) method developed for detection of melamine in powdered milk. The rapid sample preparation involved dissolution of 1g of milk powder in 2.5% formic acid, precipitation of protein with acetonitrile, spiking of samples with melamine (triamine-15N3) at 200 µg L–1 and detection of intrinsic 14N-melamine molecular ratio to the spike. The isotope dilution calibration procedure was free from matrix effects, unlike other methods where the detector sensitivity can fluctuate up to several orders of magnitude. Limit of detection of the method was 13 µg kg–1, and the recovery of melamine at 50, 100, and 250 µg kg–1 was 78.7–126.3%. The method was used to determine melamine levels in 22 milk powder products (local and imported) available in Sri Lanka. Melamine was detected in all the samples (range = 0.33–0.96 mg kg–1). Full cream milk powders (both local and imported) contained melamine in the range of 0.39–0.84 mg kg–1, and various health and pregnancy formulas contained <0.5 mg kg–1 of melamine. Two imported infant formula samples contained the highest levels of melamine (0.96 and 0.94 mg kg–1). Although these melamine levels are below the regulatory limit in Sri Lanka (1 mg kg–1), a monitoring programme would ensure consumer safety.

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%.

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%).

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.

Electrochemical Determination of Melamine on Static Mercury Drop Electrode and on Gold Nano Particle Modified Carbon Paste Electrode

An electrochemical method was developed for the determination of melamine (2,4,6 triamino- 1,3,5-triazine) on static mercury drop electrode (SMDE) and on gold nano particle modified carbon paste electrode. Interaction of melamine with Cu2﹢ ion was investigated and the decrease of Cu stripping peak was measured for the determination of melamine using SMDE. Oxidation property of melamine was improved using gold nano particle modified carbon paste electrode. Direct determination of melamine was proposed from the oxidation peak with three sigma detection limit of 0.43 μML﹣1. Recovery in milk powder sample has shown good recovery of melamine using the modified carbon paste electrode.

Simultaneous determination of melamine and cyanuric acid in foodstuffs by solid phase extraction-hydrophilic interaction chromatography-tandem mass spectrometry

A method based on solid phase extraction-liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the simultaneous determination of melamine and cyanuric acid in foodstuffs is presented. The melamine and cyanuric acid residues were extracted by acetonitrile and water, degreased by hexane, and the extract was cleaned-up by a mixed-mode solid phase-extraction column (MCT) of hydrophilic functional silica gel sorbent and cation exchange resin. The LC separation was performed on a hydrophilic interaction chromatograph, the melamine and cyanuric acid were determined by MS/MS in positive-negative switched electrospray ionization mode, multiple reaction monitoring (MRM) mode, and quantified by isotope internal standard method. The melamine and cyanuric acid were linear in the range of 10-2 500 microg/L with the correlation coefficients (r) higher than 0.99, and the limits of quantification were 25 microg/kg and 50 microg/kg, respectively. The recoveries of melamine and cyanuric acid spiked in animal-derived foods, plant-derived foods, milk and milk products were in the range of 70.0%-129.6% and 70.0%-128.6%, respectively, with the relative standard deviations (RSD) of 1.4%-23.3% and 2.8%-18.7%, respectively. The method can meet the requirement for the determination of melamine and cyanuric acid in foodstuffs simultaneously.

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%.

Simultaneous determination of melamine and creatinine in milk and milk products by gas chromatography-mass spectrometry

A method established for determining melamine and creatinine in milk and milk products. The samples were extracted with 1% trichloracetic acid solution. The extract was cleaned-up by using a mixed-mode cation ion exchange SPE column and evaporated to dryness under nitrogen. The residue was derived by bis (trimethylsilyl) trifluoroacetamide-chlorotrimethylsilane (BSTFA-TMCS), then determined by gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode. Melamine and creatinine had good linearity in the range of 0.1 - 50 mg/L with the correlation coefficients higher than 0.99, and the limits of quantification were 0.10 mg/kg and 0.20 mg/kg, respectively. The recoveries of melamine and creatinine were 80.7% - 116.8% and 77.6% - 107.5% with RSD no more than 9.4% and 8.5% in the spiked range of 10 - 100 mg/kg and 0.1 - 5.0 mg/kg, respectively. The method is accurate, sensitive, and suitable for the determination of creatinine in milk and milk products.

Determination of Melamine in Fresh Milk with Hollow Fiber Liquid Phase Microextraction Based on Ion-Pair Mechanism Combined with High Performance Liquid Chromatography

In this work, a novel analytical method based on hollow fiber liquid phase microextraction (HF-LPME) and high performance liquid chromatography (HPLC) was developed for the analysis of melamine in fresh milk. The conditions of the HF-LPME were investigated and optimized. As a result, a supported liquid membrane containing 6-undecanone and di-2-ethylhexyl phosphoric acid (D2EHPA) was selected. The extractions were made from 25 mL aqueous donor phase (prepared from milk) with pH 5.0 to a more acidic acceptor phase (36 µL 1 M HCl) and the mass transfer was driven by the proton gradient between these phases. Other optimum conditions of the HF-LPME were 60 min extraction time at 360 rpm stirring rate and an extraction factor of 21 times (extraction efficiency 3%) was obtained. The C8 column was operated at 1 mL/min at room temperature and the UV detection wavelength was 240 nm for HPLC. The mobile phase was 10 mM sodium n-octanesulfonate (pH 3.0) mixed with acetonitrile (85:15, v/v). The relative recovery of melamine for milk samples spiked with 0.5–25 mg/kg was in the range of 89.1–120.6% with the RSDs (n = 4) of 4.0–8.5%. It was found that the proposed method provided a linear range from 0.1 to 50 mg/kg (r 2 = 0.9993), method detection limit (MDL) of 0.003 mg/kg and method quantification limit (MQL) of 0.01 mg/kg. The obtained results demonstrated that HF-LPME combined with HPLC is a simple and cheap method for the determination of melamine in fresh milk.

Preparation and Evaluation of Melamine Molecularly Imprinted Polymers by Thermal‐ and Photo‐initiation Methods

AbstractMelamine imprinted polymers (MIPs) have been prepared using identical polymer formulation by both thermal‐ and photo‐initiation method, respectively. Physical characterization of the polymers revealed that the different polymerization methods led to the slight differences in both polymer structures and performance by scanning electron microscope (SEM), infrared absorption (IR), and mercury analyzer (MA). Both MIPs were used as selective sorbents for the solid phase extraction (SPE) of melamine in milk powders, followed by the determination coupled to HPLC. The recoveries of melamine in spiked milk powders were obtained in the range of 92.4‐97.7% and 94.6‐99.7%, for both MIPthermal and MIPphoto, respectively.

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.

Determination of Melamine Residue in Liquid Milk by Capillary Electrophoresis with Solid-Phase Extraction

A novel solid-phase extraction-capillary electrophoresis (SPE-CE) method was developed for the determination of melamine residue in liquid milk. The conditions of SPE and CE were investigated and optimized. A 1% trichloroacetic acid plus 2.2% lead acetate solution were used for the extraction of analyte and the removal of protein. A Cleanert PCX SPE cartridges column was used for clean up. The 50 mM sodium dihydrogenphosphate running buffer (pH adjusted to 3.2 with citric acid) was used as a running buffer. The linearity is satisfactory in the range of 0.8-100 μg/mL with a correlation coefficient of 0.9998. Under the optimal conditions, the method limit of detection (LOD) and method limit of quantification were 0.12 mg/kg and 0.37 mg/kg, respectively. The recovery of melamine from different liquid milk samples was in the range of 89.5-98.5% with a relative standard deviation of 1.8-3.5%. The intra- and inter-day assay precision was 2.8% (n = 6) and 4.1% for five days, respectively. The developed method has been applied successfully for the determination of melamine residue in liquid milk samples. The results obtained by the proposed method agree with those obtained by high-performance liquid chromatographic method. The proposed method enables the quantitative determination of melamine residues at levels as low as 0.37 mg/kg in different liquid milk.

Preparation of magnetic strong cation exchange resin for the extraction of melamine from egg samples followed by liquid chromatography–tandem mass spectrometry

In the work, magnetic strong cation exchange (MSCX) resins were prepared using hydrophobic Fe 3O 4 magnetite as the magnetically susceptible component, styrene and divinylbenzene as polymeric matrix components, acetyl sulfonate as the sulfonation agent. The resins were successfully applied to the extraction of melamine (MEL) from egg samples. The extraction procedure was carried out in a single step by blending and stirring the sample, extraction solvent and the magnetic resins. The MEL was extracted from the sample matrix then adsorbed onto the resins directly through ion-exchange interaction. When the extraction was completed, the resins with adsorbed analyte were easily separated from the sample matrix by applying an appropriate magnetic field. Main factors affecting the extraction of MEL such as the amount of MSCX resins, extraction time, washing and eluting conditions were optimized. The MEL eluted from the resins was determined by liquid chromatography–tandem mass spectrometry. The linearity of quantification obtained by analyzing matrix-matched standards is in the range of 10–1000 ng g −1. The limit of detection and quantification obtained are 2.6 and 8.8 ng g −1, respectively. The relative standard deviations of intra- and inter-day ranging from 1.6% to 6.5% and from 2.1% to 7.2% are obtained. The recoveries of MEL are in the range of 77.2–99.3%. The proposed method was successfully applied to determine MEL in eggs obtained from different local markets. MEL was detectable with the contents of 43.5 and 234.1 ng g −1 in two samples.

Determination of melamine in animal feed based on liquid chromatography tandem mass spectrometry analysis and dynamic microwave-assisted extraction coupled on-line with strong cation-exchange resin clean-up

In this work, a new method was developed for the determination of melamine (MEL) in animal feed. The method was based on the on-line coupling of dynamic microwave-assisted extraction (DMAE) to strong cation-exchange (SCX) resin clean-up. The MEL was first extracted by 90% acidified methanol aqueous solution (v/v, pH = 3) under the action of microwave energy, and then the extract was cooled and passed through the SCX resin. Thus, the protonated MEL was retained on the resin through ion exchange interaction and the sample matrixes were washed out. Some obvious benefits were achieved, such as acceleration of analytical process, together with reduction in manual handling, risk of contamination, loss of analyte, and sample consumption. Finally, the analyte was separated by a liquid chromatograph with a SCX analytical column, and then identified and quantitatived by a tandem mass spectrometry with positive ionization mode and multiple-reaction monitoring. The DMAE parameters were optimized by the Box-Behnken design. The linearity of quantification obtained by analyzing matrix-matched standards is in the range of 50-5,000 ng g(-1). The limit of detection and limit of quantification obtained are 12.3 and 41.0 ng g(-1), respectively. The mean intra- and inter-day precisions expressed as relative standard deviations with three fortified levels (50, 250, and 500 ng g(-1)) are 5.1% and 7.3%, respectively, and the recoveries of MEL are in the range of 76.1-93.5%. The proposed method was successfully applied to determine MEL in different animal feeds obtained from the local market. MEL was detectable with the contents of 279, 136, and 742 ng g(-1) in three samples.