Melamine Concentration Research Articles

A study on milk adulteration of Savar Upazila in Bangladesh

Background: Milk adulteration has become a serious concern. Some of the adulterants in milk have serious adverse health effects. This study was designed to assess consumer awareness about milk and determine formalin and melamine in milk.Methods: The study involved a laboratory-based investigation and a survey was conducted to assess consumer awareness about milk adulteration from January 2018 to June 2018. Total 10 samples were collected from local market purposively. 2 adulteration tests were conducted to detect formalin and melamine in samples. 10 brands of milk from 8 companies were collected from different markets of Savar and tested at BCSIR as per Bangladesh Standards. On the other hand; a survey was conducted to assess consumer awareness about milk adulteration. A pre tested semi structured questionnaire, was used to collect the information. Statistical analysis was done by using Excel.Results: We found the concentration of formaldehyde and melamine in all 10 analyzed products below the level of detection. The majority (55.9%) of the respondents knew that there is a law in the country that deals with milk adulteration; among them 41.7% thought that the reduced mobile court activity is reason for unchanged milk adulteration situation and insufficient penalty is also a major factor (45%). Only (55.9%) respondents consider water is main milk adulterant and 31.8% know about Chemicals. The majority of the respondents 87.8% strongly agreed that milk adulteration has harmful effects on health.Conclusions: These findings may be helpful for the concerned government regulatory bodies to monitor the quality of the commercial milk in the market.

Continuing Occurrence of Melamine and Its Derivatives in Infant Formula and Dairy Products from the United States: Implications for Environmental Sources

A total of 52 infant formulas and 42 dairy products, including milk, yogurt, cheese, and butter, as well as bread purchased from Albany, New York, were analyzed for melamine and its derivatives (cyanuric acid, ammeline, and ammelide). ∑Melamine (sum of melamine and its three derivatives) was found in infant formula, milk, yogurt, cheese, butter, and bread at median concentrations of 4.8, 7.9, 5.1, 17, 4.2, and 7.5 ng/g, respectively. Median ∑Melamine concentrations in infant formula collected in 2008 (9.4 ng/g) were significantly higher than those collected in 2018 (2.7 ng/g). Similarly, there were significant differences in ∑Melamine concentrations between powdered (median of 2.3 ng/g) and liquid forms (9.0 ng/g) of infant formula. However, no significant differences in ∑Melamine concentrations were found between milk-based (5.0 ng/g) and soy-based (2.3 ng/g) or between organic (4.4 ng/g) and nonorganic (4.8 ng/g) forms of infant formula. Cyanuric acid was the major derivative found in all products analy...

Distribution Profiles of Melamine and Its Derivatives in Indoor Dust from 12 Countries and the Implications for Human Exposure.

Melamine and its derivatives (i.e., ammeline, ammelide, and cyanuric acid) are extensively used in household products, such as furniture, dinnerware, and food utensils. Nevertheless, limited information is available on human exposures, other than dietary sources, to melamine and its derivatives. In this study, the occurrence of melamine and its derivatives was determined, for the first time, in 341 samples of indoor dust, collected from 12 countries. All of the dust samples contained target analytes, with global median concentrations of 1800, 1100, 48, and 45 ng/g for melamine, cyanuric acid, ammelide, and ammeline, respectively. The total concentrations of melamine and its derivatives varied among countries in the following decreasing order: United States (median: 17 000 ng/g) > Japan (8400) > China (8000) > South Korea (7300) > Saudi Arabia (4400) > Romania (4300) > Greece (3400) > Kuwait (2400) > Vietnam (2300) > Colombia (1300) > Pakistan (820) > India (430). Correlation analysis indicated the existence of multiple and varied sources for melamine and cyanuric acid. Estimated daily intakes of melamine via indoor dust ingestion were at least 2 orders of magnitude below the current tolerable daily intake.

A high‐performance multifunctional substrate of ultrathin‐layer chromatography (UTLC) and surface‐enhanced Raman scattering (SERS) for rapid biochemical mixture screening

AbstractWe present a multifunctional substrate of ultrathin‐layer chromatography (UTLC) and surface‐enhanced Raman scattering (SERS), which enables analytes separation and label‐free detection simultaneously. This integrated substrate is composed of silicon nanowires array (SiNWA), decorated with silver nano‐dendrites (AgNDs). This SiNWA is fabricated by a facile and low‐cost metal‐assisted chemical etching process, and the AgNDs are then decorated onto SiNWA by chemical reduction process. These AgNDs provide abundant hot spots by inducing strong localized electric field, which is confirmed by finite‐difference time‐domain simulation calculations. With the optimized multifunctional substrate, the screening of melamine is successfully validated. The high linear dependence of signal intensity and melamine concentrations from 15 to 1,500 ppm with small deviation was carried out by our developed UTLC–SERS substrate, providing a great potential for quantitative detection. Besides, the SERS signals further show a low relative standard deviation of 8.7%, benefited from the calibration by a peak located at 520 cm−1 of silicon. In short, such a low‐cost, high‐stable multifunctional substrate of UTLC and SERS can be readily employed for practical applications of rapid biochemical mixture screening.

Preparation and characterization of molecularly imprinted solid-phase extraction column coupled with high-performance liquid chromatography for selective determination of melamine.

We synthesized a selective molecularly imprinted solid-phase extraction (MIP-SPE) column and established an extraction and enrichment method using this MIP-SPE column. By coupling with HPLC, we developed a new method to detect trace amounts of melamine in eggs. The MIP-SPE column was synthesized by in situ thermal-initiated polymerization using melamine as the template, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker and azodiisobutyronitrile as the initiator. HPLC was used to evaluate the identification and enrichment capability of the MIP-SPE column and for the measurement of melamine in the sample. The melamine concentration exhibited an excellent linear relationship in the range of 0.1–25.0 µg ml−1 (r = 0.9983). The identification capability of the MIP-SPE column was apparently superior to that of the non-imprinted polymer solid-phase extraction column; an average enrichment factor of 46.8-fold (RSD = 3.5%) was obtained for 0.4 µg ml−1 melamine by the MIP-SPE column. When the MIP-SPE HPLC method was applied to the detection of melamine in eggs, an average recovery rate of 93.5–102.0% (RSD = 3.6–4.9%) and a limit of detection of 0.05 µg kg−1 were obtained. This method is simple, fast and cost-effective; thus, it can greatly simplify the pre-treatment of complex samples and can be used in the detection of residual melamine in eggs and other products.

Bio-polyphenols promoted green synthesis of silver nanoparticles for facile and ultra-sensitive colorimetric detection of melamine in milk

Green, simple and quick melamine sensing assays for highly efficient detection of melamine down to nM level have been reported. Biopolyphenols (rutin & curcumin) were used as reducing and stabilizing agents for the synthesis of silver nanoparticles (AgNPs). The synthesis of AgNPs was confirmed by FTIR, UV–Visible, XRD and HRTEM-EDS analysis. The biopolyphenols reduced AgNPs were well dispersed and spherical in shape. However, the presence of melamine in the reaction medium disrupted their synthesis. This may be attributed to interaction of melamine with Ag+ ions and biopolyphenols. At low concentration of melamine, pale red colored solution was obtained owing to formation of aggregated mass of AgNPs, whereas, at high concentration of melamine, colorless solution was obtained indicating disruption in synthesis of AgNPs. The presented protocol was proposed in light of optical responses, UV–Visible plots and HRTEM-EDS analysis. Using the sensor assays, good limit of detection, 0.01 ppm (79 nM) and 0.24 ppm (1900 nM) by Ag-Rutin and Ag-Curcumin respectively, were obtained. The detection limits offered by both sensing assays were quite lower than safety level recommended by regulatory bodies (20 μM in the USA and EU, 8 μM for infant formula in China). The sensing assays displayed good selectivity as well as sensitivity. The proposed sensor was successfully deployed for detection of melamine in raw milk samples.

Use of a smartphone for visual detection of melamine in milk based on Au@Carbon quantum dots nanocomposites

Gold nanoparticles@Carbon quantum dots nanocomposites (Au@CQDs) were designed for analyzing melamine in milk visually. Fluorescent emission of Au@CQDs enhanced with the increase of melamine concentration. A calibration curve (R2 = 0.9856) and fluorescence standard array were established for detection of melamine in the range of 1 μM–10 μM. Limit of quantification and limit of detection were 12 nM and 3.6 nM, respectively. The approximate concentration of melamine adulterated in milk samples were detected visually by the fluorescence standard array and smartphone. The accurate concentration was obtained by the calibration curve and portable fluorescence spectrometer with recoveries of 105.64%–102.75% and less than 2% of coefficient of variation (CV) (n = 18). This performance was consistent with that of the high-performance liquid chromatography (HPLC) method (recoveries of 105.56%–107.95% with 2.24%–3.56% of CVs). The Au@CQDs-based fluorescent method for visual and accurate detection of melamine in milk was presented and showed strong application potential.

Aptamer-functionalized AuNPs for the high-sensitivity colorimetric detection of melamine in milk samples

Although aptamer-functionalized AuNPs technology exhibits great potential in analytical and biological chemistry, direct analysis of molecules at a low concentration using colorimetric assay remains challenging. The development of intuitive methods has attracted interest for promising detection of melamine in milk samples due to a demand for stable and understandable process. In this study, we propose a rapid and facile colorimetric measurement method of melamine combined aptamer-functionalized AuNPs in contaminated milk samples. To realize the high stability and the lower limit of detection, the aptamer-functionalized surface of AuNPs via a coordinated bond was used in combination with ultra-sonication. The kinetics of this colorimetric assay based on aptamer-functionalized AuNPs was analyzed to illustrate that the higher the concentration of melamine, the faster the aggregation of AuNPs induced. The sensitivity, selectivity, limit of detection and recovery rate were sufficiently validated to understand the measurement principle of melamine using aptamer-functionalized AuNPs. The calibration curve established by the absorption peak ratio (A640 /A520) was linear in the concentration range of 0~1μM of melamine in aqueous solutions with the correlation coefficient (R2) of 0.986 and the limit of detection (LOD) of 22 nM, whereas, the correlation coefficient (R2) of 0.998 and the LOD of 14.9 nM were achieved at the concentration of melamine below 0.5 μM in milk samples. The optimized performance of this colorimetric assay of melamine using aptamer-functionalized AuNPs in milk samples was obtained with 100 μL of 13 nm AuNPs solution, 40 μL of 1 μM (100 dilutions) aptamers and the pre-reaction time of 30 min. This simple colorimetric measurement of melamine using aptamer-functionalized AuNPs provides a promising target for various applications of the sample source with complex sample matrices.

Melamine causes testicular toxicity by destroying blood-testis barrier in piglets

Melamine (MA) exposure causes male reproductive toxicity, however, the mechanism remains unclear. In this study, we investigated the roles of the blood-testis barrier (BTB) in MA-induced reproductive toxicity in piglets. Male weaned piglets were exposed to MA concentrations of 0, 100, 300, and 1000 mg/kg in the diet for 10 weeks. They were euthanized on days 1, 7 and 14 after the final exposure. Body and organ weights, serum biochemistry and testosterone, gross and histopathological changes, and BTB ultrastructure and integrity were assessed. BTB junction protein expression levels and protein levels of the mitogen-activated protein kinase (MAPK) pathway in testes were measured. We found that MA dose-dependently decreased serum testosterone levels and caused gross and histopathological lesions in the testis and epididymis. Marked BTB damage was evidenced by abnormal changes in BTB ultrastructure and increased BTB permeability. Furthermore, MA decreased the protein levels of ZO-1, occludin, N-cadherin, and connexin-43, paralleled by increased the protein levels of p-Erk, p-JNK and p-p38 in testes, suggesting that MA disrupted BTB by downregulating the expressions of BTB junction proteins, with possible involvement of the MAPK signaling pathway. In conclusion, MA exposure gives rise to testicular toxicity in male piglets through destroying BTB integrity.

Understanding of Structure and Thermodynamics of Melamine Association in Aqueous Solution from a Unified Theoretical and Experimental Approach.

The aggregation propensity of melamine molecules in aqueous solutions in a range of melamine concentrations is investigated by means of a combination of theoretical and experimental approaches. It is observed that the hydrogen bonding interactions of sp3 nitrogen atoms of one melamine with sp2 nitrogen atoms of another melamine play a major role in the melamine association. This finding is complemented by the observed favorable electrostatic energies between melamine molecules. The estimation of the orientational probability of melamine aromatic ring rules out any role of π-π interaction in melamine association. Further, the quantum chemical calculations suggest that a melamine molecule prefers to bind with another like molecule with a dihedral angle ranging from 36° to 46°. We have also determined the dimer existence autocorrelation functions to investigate the melamine-dimer stability with time in aqueous solution. Our results are well validated by the experimental findings (Chapman, R. P.; Averell, P. R.; Harris, R. R. Solubility of Melamine in Water. Ind. Eng. Chem. 1943, 35, 137-138. Ahromi, A. J.; Moosheimer, U. Oxygen Barrier Coatings Based on Supramolecular Assembly of Melamine. Macromolecules 2000, 33, 7582-7587. Yang, C.; Liu. Y. Studying on the Steady-State and Time-Resolved Fluorescence Characteristics of Melamine. Spectrochim. Acta A 2010, 75, 1329-1332. Mircescu, N. E.; Oltean, M.; Chis, V.; Leopold, N. FTIR, FT-Raman, SERS and DFT study on Melamine. Vib. Spectrosc. 2012, 62, 165-171. Makowski. S. J.; Lacher. M.; Schnick. W. Supramolecular Hydrogenbonded Structures between Melamine and N-Heterocycles. J. Mol. Struct. 2012, 1013, 19-25. Li, Z.; Chen, G.; Xu, Y.; Wang, X.; Wang, Z. Study of the Structural and Spectral Characteristics of C3N3(NH2)3(n = 1-4) Clusters. J. Phys. Chem. A 2013, 117, 12511-12518. Li, P.; Arman, D. H.; Wang, H.; Weng, L.; Alfooty, K.; Angawi, R. F.; Chen. B. Solvent Dependent Structures of Melamine: Porous or Non-porous. Cryst. Growth Des. 2015, 15, 1871-1875. Chen, J.; Lei, X.; Peng, B. Study on the Fluorescence Spectra of Melamine in Pure Milk. J. Opt. 2017, 46, 183-186.). Moreover, the thermodynamics of melamine association reveals that the association process is essentially driven by enthalpy, and this enthalpy-driven phenomenon is also confirmed by the experimental isothermal titration calorimetry measurements.

Detection of melamine in milk powder using MCT-based short-wave infrared hyperspectral imaging system

ABSTRACTExtensive research has been conducted on non-destructive and rapid detection of melamine in powdered foods in the last decade. While Raman and near-infrared hyperspectral imaging techniques have been successful in terms of non-destructive and rapid measurement, they have limitations with respect to measurement time and detection capability, respectively. Therefore, the objective of this study was to develop a mercury cadmium telluride (MCT)-based short-wave infrared (SWIR) hyperspectral imaging system and algorithm to detect melamine quantitatively in milk powder. The SWIR hyperspectral imaging system consisted of a custom-designed illumination system, a SWIR hyperspectral camera, a data acquisition module and a sample transfer table. SWIR hyperspectral images were obtained for melamine-milk samples with different melamine concentrations, pure melamine and pure milk powder. Analysis of variance and the partial least squares regression method over the 1000–2500 nm wavelength region were used to develop an optimal model for detection. The results showed that a melamine concentration as low as 50 ppm in melamine-milk powder samples could be detected. Thus, the MCT-based SWIR hyperspectral imaging system has the potential for quantitative and qualitative detection of adulterants in powder samples.

Preparation of Gap-Controlled Monodispersed Ag Nanoparticles by Amino Groups Grafted on Silica Microspheres as a SERS Substrate for the Detection of Low Concentrations of Organic Compounds

The synthesis of new surface-enhanced Raman scattering (SERS) substrates for the detection of trace poisonous organic pollutants is important for environmental monitoring. Herein, we designed and prepared monodispersed and uniform Ag NPs anchored on silica microspheres (Ag@ASMs) by the orientation of grafted amino groups and applied it as a SERS substrate for the detection of ultralow concentrations of poisonous organic pollutants (Rhodamine 6G (R6G), crystal violet (CV), and melamine) with high sensitivity and reproducibility in aqueous solution. A ratio of 2:1 Ag@ASMs exhibited optimum SERS performance, allowing the detection of 10–12 M of R6G with an enhancement factor of 6.36 × 107 (collect the normal Raman signal based on 10–4 M R6G) as well as 10–8 M of CV and melamine. The density functional theory calculation also provided evidence that modified 3-triethoxysilylpropylamine molecules are interspaced, and the optimum Ag dosage further tuned the gap between Ag NPs as well as the size of Ag NPs. This ...

Triplex DNA formation-mediated strand displacement reaction for highly sensitive fluorescent detection of melamine

Since melamine is a strong hazard to human health, the development of new methods for highly sensitive detection of melamine is highly desirable. Herein, a novel fluorescent biosensing strategy was designed for sensitive and selective melamine assay based on the recognition ability of abasic (AP) site in triplex towards melamine and signal amplification by Mg2+-dependent DNAzyme. In this strategy, the melamine-induced formation of triplex DNA was employed to trigger the strand displacement reaction (SDR). The SDR process converted the specific target recognition into the release and activation of Mg2+-dependent DNAzyme, which could catalyze the cleavage of fluorophore/quencher labeled DNA substrate (FQ), resulting in a significantly increased fluorescent signal. Under the optimal conditions, the fluorescent signal has a linear relationship with the logarithm of the melamine concentration in a wide range of 0.005–50 μM. The detection limit was estimated to be 0.9 nM (0.1ppb), which is sufficiently sensitive for practical application. Furthermore, this strategy exhibits high selectivity against other potential interfering substances, and the practical application of this strategy for milk samples reveals that the proposed strategy works well for melamine assay in real samples. Therefore, this strategy presents a new method for the sensitive melamine assay and holds great promise for sensing applications in the environment and the food safety field.

Melamine and its derivatives in dog and cat urine: An exposure assessment study

Melamine is a nitrogen-containing organic compound that is used in a wide range of products, including paints, plastics, and paper, as a flame retardant. A few studies have reported the occurrence of melamine and its derivatives in pet food, following a number of deaths of cats and dogs from kidney failure in 2007, which was attributed to melamine contamination in ingredients used in pet food. Nevertheless, studies that report the occurrence of melamine and its derivatives in pet urine are scarce. In this study, we measured melamine and its derivatives (i.e., ammeline, ammelide, and cyanuric acid) in dog (n = 30) and cat (n = 30) urine collected from Albany, New York, USA, during March through July 2017. The mean (±SD) concentrations of melamine, ammeline, ammelide, and cyanuric acid in dog urine were 21.1 ± 51.2, 2.3 ± 3.8, 9.9 ± 1 0.4, and 79.0 ± 105 ng/mL, respectively; the corresponding concentrations in cats were 21.4 ± 26.1, 1.2 ± 2.5, 6.1 ± 3.9, and 105 ± 94.6 ng/mL, respectively. No significant difference was observed in urinary concentrations of melamine derivatives between cats and dogs. Age and gender were important determinants of the concentrations of the target chemicals in cats and dogs. Cumulative daily intake of melamine and its derivatives was calculated on the basis of urinary concentrations and was found to be 10–500-fold below the tolerable daily intake.

Mechanochemical synthesis of melamine doped TiO2 nanoparticles for dye sensitized solar cells application

In a quest for developing new material with performance of dye sensitized solar cells (DSSC) a non-metallic doping i.e., of nitrogen was carried out to commercial TiO2 nanoparticle using simple, facile and sustainable mechanochemistry method. Melamine was used as source of nitrogen and different weight percentages (10, 30, 50, 70 and 90%), mixed with TiO2 mechanically in a ball mill for 12 h at an speed of 500 rotations per minute followed by annealing at 550 °C for 2 h under constant N2 flow. The post nitrogen doping structural analysis indicated anatase phase of TiO2.The morphological observations by transmission electron microscopy did not show change due to melamine and particle size remains less than 30 nm. N-doping resulted in an increased wavelength of peak absorption from 334 nm to about 350 nm and shifting of absorption edge from UV (~ 400 nm) to visible region (~ 500 nm) resulting in the reduction of the band gap from 3.14 to 2.43 eV which is supported by XPS and Tauc plot analysis. The functional analysis reveals amide bond at higher melamine concentration. The DSSC characteristics were measured with source-meter coupled with simulated light source which shows a significant increase of cell efficiency from 26 with 10% of melamine to that of 86 with 90% melamine. The increase in efficiency was linear with increasing nitrogen doping concentration. The study suggested that melamine can be used as a suitable N-dopant source for improved photoconversion properties that can help engineer to develop a device with enhanced performance.

Sensitive detection of melamine by an electrochemiluminescence sensor based on tris(bipyridine)ruthenium(II)-functionalized metal-organic frameworks

Metal-organic frameworks (MOFs) are microporous materials that consist of metal ions or clusters and organic ligands. Their luminescence activities can be improved by functionalization, and the present work describes the synthesis of a luminescence-functionalized MOF in which tris(2,2′-bipyridyl) dichlororuthenium(II) hexahydrate (Ru(bpy)32+) was introduced into the MOF. The synthesized RuMOF was then fabricated as an ECL sensor that can be used for the rapid and sensitive detection of melamine in dairy products. The optimum detection conditions were established by single-factor analysis and surface response multivariate optimization. Under optimum conditions, the ECL intensity was proportional to log(melamine) concentration in the range 10−10–10−4 M with a detection limit of about 3.8 × 10−11 M (signal/noise = 3). In an application to the detection of melamine in milk and infant formula powder, recoveries in the range 98–104% and 95–103%, respectively were obtained from spiked samples. Thus this novel ECL sensor represents a potentially valuable product for the analysis of melamine food samples.

Synthesis of Cr2O3/C3N4 composite for enhancement of visible light photocatalysis and anaerobic digestion of wastewater sludge

Visible light photocatalysts of Cr2O3/C3N4 composites (with different melamine concentrations) were prepared by high temperature calcination method. The composites samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy SEM, energy-dispersive X-ray spectroscopy (EDX), UV–visible spectroscopy and particle size analysis, which clearly indicated the coexistence of both Cr2O3 and C3N4 in the composites. The Cr2O3/C3N4 catalysts were tested for photocatalytic degradation of 2-chlorophenol in wastewater and solubilization of sludge in anaerobic digestion process to enhance biomethane production. The co-catalytic performance of Cr2O3, with 6% of melamine (precursor of C3N4), improved the photocatalytic degradation of 2-chlorophenol (k = 0.0156 min−1) under visible light, where up to 94% removal was achieved at optimum pH 5.0, pollutant concentration of 60 mg/L, and time duration of 180 min. On another hand, application of Cr2O3/C3N4 for photocatalytic pretreatment of sludge released the soluble substances in solution in which sCOD was increased from 431 mg/L to 3666 mg/L after 6 h and VS content decrease by only 9.1%, which indicated that the short time pretreatment could avoid the further mineralization of organic to complete degradation. Thereafter, anaerobic digestion of solubilized sludge was achieved after 30 days with production of 634 ml kg−1VS of methane and 46% of organic matter removal efficiency (OMRE), compared with 472 ml kg−1VS and 402 ml kg−1VS of methane, 35 and 31% of OMRE respectively in photolytic and raw sludge (control) reactors. These results can provide a useful base and reference for the multi applications of visible light Cr2O3/C3N4 photocatalyst in enhancement of degradation of toxic pollutant in wastewater and sludge stabilization with bioenergy production in practice.

Visual detection of melamine by using a ratiometric fluorescent probe consisting of a red emitting CdTe core and a green emitting CdTe shell coated with a molecularly imprinted polymer.

A composite ratiometric fluorescent probe is described for visual detection of melamine (MEL) in milk samples. It is based on the use of red emitting and green emitting CdTe quantum dots, and a mesoporous molecularly imprinted polymer. The red emitting QDs are embedded in the silica microsphere to serve as a core, and the green emitting QDs are coated on the surface of the silica microsphere as a shell. A molecularly imprinted polymer (MIP) with specific recognition sites for MEL was placed on the shell. If MEL is bound by the MIP, the green fluorescence is quenched due to hydrogen bond interaction. The red emission, in contrast, remains unchanged. Quenching leads to a change in the color of fluorescence from red-green to purely red. This effect allows for visual and instrumental detection of MEL. The mesoporous structure of the MIP reduces the mass transfer resistance and enhances the accessibility of sites for MEL. Response is linear in the 50-1000ng mL-1 MEL concentration range, and the limit of detection is 13ng mL-1. The fluorescent probe was successfully applied to the analysis of MEL-spiked milk samples and gave recoveries between 94.1 and 98.7%, with 3.6-5.1% relative standard deviations. Graphical abstract Schematic of the preparation and detection of the composite probe. The probe was applied for the selective recognition and visual detection of melamine (MEL).

Porous carbon nitrification process optimization for enhanced benzene adsorption

ABSTRACTBenzene is one of the aromatic hydrocarbons co-absorbed with acid gases during amine scrubbing that contribute to deactivation of catalyst in the Claus process. The present work attempts to modify the porous carbon surface through nitrogen group functionalization utilizing melamine as the nitrogen source, adopting Design of Experiments (DOE) with concentration of melamine, duration of impregnation and temperature of impregnation being the process variables, while BET surface area was the response variable. The surface modified samples were subjected to benzene adsorption. The optimal nitrogen content that had minimal pore damage was found to be less than 4.3%, with concentration of melamine being the most significant variable. Surface nitrogen functionalization reduced the surface area whereas the benzene adsorption capacity increased. Benzene adsorption capacity as high as 14.72 mmol/g was recorded at 45°C at a pressure of 235 mbar. Such high adsorption capacities have not been reported in open literature and the nitrogen functionalization augmented the adsorption to the tune of 20 to 30% at a pressure of 100 mbar, and only up to 10 to 15% at higher pressures. The adsorption isotherms as well as the kinetics of adsorption were modelled using the well-known popular models. Further, successful regeneration of the surface modified adsorbents were ensured through adsorption/desorption cycle experiments.

Detection of Cyanuric Acid and Melamine in Infant Formula Powders by Mid-FTIR Spectroscopy and Multivariate Analysis

Chemometric methods using mid-FTIR spectroscopy were developed in order to reduce the time of study of melamine and cyanuric acid in infant formulas. Chemometric models were constructed using the algorithms Partial Least Squares (PLS1, PLS2) and Principal Component Regression (PCR) in order to correlate the IR signal with the levels of melamine or cyanuric acid in the infant formula samples. Results showed that the best correlations were obtained using PLS1 (R2: 0.9998, SEC: 0.0793, and SEP: 0.5545 for melamine and R2: 0.9997, SEC: 0.1074, and SEP: 0.5021 for cyanuric acid). Also, the SIMCA model was studied to distinguish between adulterated formulas and nonadulterated samples, giving optimum discrimination and good interclass distances between samples. Results showed that chemometric models demonstrated a good predictive ability of melamine and cyanuric acid concentrations in infant formulas, showing that this is a rapid and accurate technique to be used in the identification and quantification of these adulterants in infant formulas.