Extraction Of Melamine Research Articles

Selective extraction of melamine using 11-mercaptoundecanoic acid–capped gold nanoparticles followed by capillary electrophoresis

This study describes the use of 11-mercaptoundecanoic acid–capped gold nanoparticles (MUA–AuNPs) for selective extraction of melamine prior to analysis by capillary electrophoresis with UV detection. The highest degree of melamine-induced aggregation of MUA–AuNPs was found to occur at pH 5.0, indicating that the NP aggregation is mainly because of hydrogen bonding between the carboxylate groups of MUA and the amine groups of melamine. Moreover, the degree of melamine-induced NP aggregation gradually increased when the chain length of the mercaptoalkanoic acid was increased from two to 12 carbon atoms. At pH 5.0, the extraction efficiency of melamine was highly dependent on the concentration of MUA–AuNPs, the concentration of dithiothreitol (DTT), the extraction time between MUA–AuNPs and melamine, and the incubation time between melamine-adsorbed AuNPs and DTT. The separation of the extracted melamine and DTT (releasing agent) was accomplished using a solution of 10 mM phosphate (pH 6.0) containing 1.6% (v/v) poly(diallyldimethylammonium chloride). Under the optimum extraction and separation conditions, the limit of detection at a signal-to-noise ratio of 3 was estimated to be 77 pM for melamine, with linear range of 1–1000 nM. The proposed method was successfully applied to the determination of melamine in tap water and in milk.

Synthesis and application of core‐shell complex‐imprinted polymer for the solid‐phase extraction of melamine from dairy products

A core-shell complex-imprinted polymer (CIP) was synthesized and evaluated for selective extraction of melamine from dairy products. The CIP synthesis based on surface modification of home-made silicon microspheres was conducted via a metal complex as functional monomer, ethylene glycol dimethylacrylate as cross-link and melamine as template. The resulting CIP was characterized by SEM and Fourier transform infrared spectroscopy. When the amount of silica microspheres was 100 mg and the molar ratio of copper(II) methacrylate to EDGMA was 1:10, well-dispersed particles were obtained. The complex-imprinted SPE condition was optimized and the maximum enrichment factor of melamine can be up to 40. The reliability of complex-imprinted SPE for extraction and enrichment of melamine was investigated and proved by using spiked samples including milk and milk powder with the recoveries ranging from 87 to 92%.

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.

Use of Methanol for the Efficient Extraction and Analysis of Melamine and Cyanuric Acid Residues in Dairy Products and Pet Foods

The recent worldwide shortage of acetonitrile has prompted the development of a new method using methanol as an alternative organic solvent in the extraction and liquid chromatographic analysis of melamine and cyanuric acid that may be present as contaminants in dairy products and pet foods. A simple extraction of melamine and cyanuric acid residues in fortified samples was successfully achieved, using a methanol-water mixture and analysis by isotopic dilution high-performance liquid chromatography-triple-quadrupole mass spectrometry (HPLC-MS/MS). A two-step centrifugation procedure was employed to remove matrix components from extracts. The separation of melamine and cyanuric acid was carried out on a Dionex Acclaim Trinity P1 column, with a methanol and ammonium acetate buffer used as the mobile phase. Excellent linearity was achieved for both the melamine and cyanuric acid calibrations. A variety of dairy products and pet foods were fortified with melamine and cyanuric acid at three levels, 1, 2.5, and 10 microg/g, producing recovery yields of 101-119% for melamine and 84-123% for cyanuric acid. The lower limit of quantification (LLOQ) of melamine was 0.03 microg/g for liquid milk and 0.05 microg/g for dry infant milk formula. The quantitative results were comparable with those derived from previous methods that have been proposed by the U.S. Food and Drug Administration for the screening of melamine and its analogues in foods.

Solid‐phase extraction of melamine from aqueous samples using water‐compatible molecularly imprinted polymers

A method for molecularly imprinted SPE of the melamine from environmental water samples was investigated. Cyromazine-imprinted polymers were synthesized in water-methanol systems for the selective extraction of melamine from aqueous samples, followed by HPLC analysis. Molecular recognition properties and binding capability to melamine were evaluated by adsorption test and Scatchard analysis, which showed the dissociation constant (KD) and the maximum binding quantity (Qmax) were 0.032 micromol/L and 4.77 micromol/g for high affinity binding site, and 0.26 micromol/L and 19.10 micromol/g for lower affinity binding site, respectively. Under the optimum extraction protocol, the method can be successfully applied to selectively extract and enrich melamine in environmental water. The linearity was ranged from 0.500 to 100.0 ng/mL (r > 0.999) in tap water, lake water, and seawater analysis. When 50 mL of the water samples loaded, the LODs of the method were ca. 0.1 ng/mL, and the LOQs were ca. 0.5 ng/mL. The mean recoveries of melamine from blank water samples spiked at 0.5, 5.0, and 50 ng/mL were more than 86.3%, with the RSD less than 8.8%.

Molecularly imprinted polymer as SPE sorbent for selective extraction of melamine in dairy products

In this paper, a highly selective sample cleanup procedure combining molecular imprinting and solid-phase extraction (MI-SPE) was developed for the isolation of melamine in dairy products. The molecularly imprinted polymer (MIP) was prepared using melamine as the template molecule, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linking monomer. The melamine imprinted polymer was used as selective sorbent for the solid-phase extraction of melamine from dairy products. An off-line MI-SPE method followed by high-performance liquid chromatography with diode-array detection for the detection of melamine was also established. The mean recoveries of melamine from ultra-heat treatment (UHT) milk and milk powders were 92.9–98.0% and 91.6–102.8%, respectively. Good linearity was obtained from 0.5 μM to 10 μM ( r > 0.999) with a quantitation limit of 0.5 μmol/L (0.06 ppm) which was sufficient to analyse melamine at the maximum level permitted by U.S. Food and Drug Administration (1 ppm) in dairy products. It was demonstrated that the proposed MI-SPE-HPLC method could be applied to direct determination of melamine in dairy products.

Novel cyromazine imprinted polymer applied to the solid-phase extraction of melamine from feed and milk samples

A water compatible molecularly imprinted polymer (MIP) using cyromazine as a mimic template, methacrylic acid as the functional polymer and ethylene glycol dimethacrylate as the cross-linker was synthesized and used to extract melamine from feed and milk samples via a molecularly imprinted solid-phase extraction (MISPE) protocol. Optimum retention of melamine on the MISPE cartridge was achieved using methanol, and the interferences in the samples were effectively washed out. The binding capacity of the polymer toward melamine was found to be about 500 μg of melamine/g of polymer. The recoveries of 2 μg and 20 μg melamine standard spiked into water extract of blank feeds and milk samples were between 83.4% and 103%, with relative standard deviation <5.6%. The cyromazine-MIP demonstrated high cross-reactivity for melamine and low affinity to cyanuric acid. The ionic bond interaction was regarded as the main factors that dominated the retention of the melamine on the MISPE cartridge.