Methanol Acid Research Articles

Extraction, purification, and quantification of hesperidin from the immature Citrus grandis/maxima fruit Nepal cultivar

Abstract. Manikyam HK, Tripathi P, Patil SB, Lamichhane J, Chaitanya MVNL, Patil AR. 2022. Extraction, purification, and quantification of hesperidin from the immature Citrus grandis/maxima fruit Nepal cultivar. Asian J Nat Prod Biochem 20: 21-26. Hesperidin, a flavanone group of flavonoids and a 7-O-rutinoside of hesperitin is abundantly present in citrus fruits. Pomelo or Citrus grandis (L.) Osbeck/ C. maxima (Burm.) Merr. is grown and cultivated in Nepal as seasonal edible fruit. Pomelo has flavanone and other chemical constituents. Flavanones like naringin, hesperidin, neohesperidin, and naringenin are present in the fruits of C. grandis. Many extraction techniques have been reported in the extraction and purification of hesperidin citrus fruits like sweet lemons, grapefruits, mandarins, etc. However, little information has been provided on hesperidin content in Pomelo fruits. In order to estimate the quantity of hesperidin in the Pomelo fruits of Nepal, we have first time made study. The immature Pomelo fruits of size 2-7 cm were collected from the cultivation field and dried completely. The pulverized fruit powder with moisture content less than 15% was subjected to 5% methanolic acetic extraction and Dimethylformamide (DMF) solvent extraction in Soxhlet apparatus by refluxing at 90°C in 1:15 ration in three subsequent extractions of each 1 hour. The concentrates were crystalized at freezing temperatures in methanol and further purified by repeating the crystallization process. The white amorphous powder was subjected to RP-HPLC analysis method, chromatographic conditions 285 nm wavelength, C18 column 4.6 mm x 15 cm x 5 µm, flow rate 1.2 mL/minute with injection volume 10 µL run time of 30 minutes, column temperature 40°C. Hesperidin yields were 0.12 g/100 g with acetic acid methanol with a purity of 87% and 0.17 g/100 g in DMF extraction with a purity of 90% with recoveries of 87% in acetic acid methanol extraction and 90% in DMF extraction when compared with standard 93%. Further extraction does not yield any hesperidin content indicating a total of 0.15-0.17 g/100 g of hesperidin content in the whole immature fruit of C. grandis/maxima. Thus we found DMF and 5% methanolic acetic solvents as preferable solvents to extract hesperidin.

Hydrogen evolution and CO2-reduction on a non-supported polypyrrole electrode

Conducting polymers are deposited mostly on a supporting metal of the Pt group and can be used as electrocatalysts. In the present work, a non-supported (bulk) polypyrrole (PPy) is prepared to eliminate any effect of the supporting metal on the desired reactions and is used for the hydrogen evolution reaction (HER) as well as for CO2 reduction in protic methanol for the first time. The physical, chemical, and electrochemical properties of the synthesized materials are studied in the first step. Scanning electron microscope images reveal that PPy particle size had a change in the range of 30–90 nm (conductivity: 6.2 ×10−2 ± 0.004 S/cm; four-probe). Tafel slope (82 mV/dec) and activation energy (41.67 kJ/mol) are calculated for HER using cyclic voltammograms. In the second step, the synthesized materials are used for the hydrogenation of CO2 in acidic methanol. The novel material reduces CO2 specifically to formic acid at −0.55 V with a maximum Faradaic efficiency of 92 %.

Variations in Fatty Acids Affected Their Derivative Volatiles during Tieguanyin Tea Processing.

Fatty acids (FAs) are important precursors of oolong tea volatile substances, and their famous derivatives have been shown to be the key aroma components. However, the relationship between fatty acids and their derivatives during oolong tea production remains unclear. In this study, fresh Tieguanyin leaves were manufactured into oolong tea and green tea (control), and fatty acids and fatty acid-derived volatiles (FADV) were extracted from processed samples by the sulfuric acid–methanol method and solvent-assisted flavor evaporation (SAFE), respectively. The results showed that unsaturated fatty acids were more abundant than saturated fatty acids in fresh leaves and decreased significantly during tea making. Relative to that in green tea, fatty acids showed larger variations in oolong tea, especially at the green-making stage. Unlike fatty acids, the FADV content first increased and then decreased. During oolong tea manufacture, FADV contents were significantly and negatively correlated with total fatty acids; during the green-making stage, methyl jasmonate (MeJA) content was significantly and negatively correlated with abundant fatty acids except steric acid. Our data suggest that the aroma quality of oolong tea can be improved by manipulating fatty acid transformation.

Manipulation of fatty acid profile and nutritional quality of Chlorella vulgaris by supplementing with citrus peel fatty acid

Microalgae could be an excellent resource of functional and essential fatty acids. To achieve viable microalgal biomass production, mass cultivation of microalgae is required; however, the high cost of nutrients is the obstacle. An inexpensive and nutritious material is required to feed Chlorella vulgaris in the pharmaceutical and food sectors. Citrus peel waste with a valuable nutritional quality could be one of the promising and inexpensive candidates. In this study, the fatty acid extract from different citrus peels was used as the organic nutrient source for the cultivation of Chlorella. The proximate composition of bitter orange, sweet orange, grapefruit, and mandarin peels were determined, and their nutritional quality was evaluated. Total fatty acids from the citrus peel were prepared by acidic methanol hydrolysis and hexane extraction. Fourier transforms infrared (FT-IR) and gas chromatography–mass spectrometry (GC–MS) was used to analyze the fatty acid composition and nutrient composition. Fatty acids from the citrus peels were added to the Chlorella culture medium to study their influences on biomass, lipid production, fatty acid profile, and nutritional quality of Chlorella. The most predominant citrus peel fatty acids were linoleic, palmitic, oleic, linolenic, and stearic acids. The citrus peels contain polyunsaturated, saturated, and monounsaturated fatty acids. The most unsaturated fatty acids were omega-6, omega-3, omega-9, and omega-7. The citrus peel had acceptable atherogenicity, thrombogenicity, omega-6/omega-3, peroxidizability, hypocholesterolemic, and nutritive value indices. The major fatty acids of Chlorella were palmitic, linoleic, oleic, alpha-linolenic, gamma-linolenic, 4,7,10,13-hexadecatetraenoic, palmitoleic, 7,10-hexadecadienoic, 7,10,13-hexadecatrienoic, lauric and 5,8,11,14,17-eicosapentaenoic acids. Chlorella contains polyunsaturated, saturated, and monounsaturated fatty acids. The most unsaturated fatty acids contain omega-6, omega-3, omega-9, and omega-7. Chlorella had acceptable atherogenicity, thrombogenicity, omega-6/omega-3, hypocholesterolemic, peroxidizability, and nutritive value indices. Supplementation of Chlorella with citrus peels fatty acid increases total biomass, lipid content, and nutritional quality of Chlorella. The present research shows that citrus peels have good nutritional quality and could be used for the inexpensive cultivation of Chlorella biomass with potential utility for food application.

Antioxidant activity and glycemic index of resistant starch from black glutinous rice

Type 2 diabetes mellitus ((T2DM) is a global public health manifested by hyperglycemia due to insulin resistance. Rice is the main staple food for the world's population but has a high glycemia index (GI) value. Therefore, this research was aimed to produce resistance starch (RS) from black glutinous rice with different methods – autoclave and annealing, freeze-thawing, and acid methanol methods. The RS content, total phenolic compound content, antioxidant activity, and estimated GI (pGI) were investigated. Results showed that the autoclave and annealing method yielded highest RS content of 27.33±8.56%, followed by freeze-thawing, 15-day acid methanol, and 30-min acid methanol methods. The RS from the autoclave and annealing method also had highest total phenolic content (61.55±1.19 mg gallic acid/g sample) and antioxidant activity by 2,2-Diphenyil-picrylhydrazyl (DPPH, IC50 of 7.40±0.24 mg/ml) and ferric reducing antioxidant power (FRAP, 75.47±0.51 mg tocopherol equivalent/g extract). Moreover, The RS from the autoclave and annealing method also had the lowest pGI (57.32±0.74). In conclusion, the autoclave and annealing process gave the highest yield of RS with the highest total phenolic content and antioxidant activity; and with the lowest GI compared to the freeze-thawing and acid methanol methods.

Fast screening and confirmation of 73 common prohibited compounds in cosmetics by ultra performance liquid chromatography-quadrupole-time-of-flight high resolution mass spectrometry

建立了超高效液相色谱-四极杆-飞行时间高分辨质谱(UPLC-Q-TOF HRMS)同时快速筛查确证化妆品中73种常见禁用物质的方法。样品经饱和氯化钠溶液分散均匀后,采用含0.2%甲酸的乙腈溶液超声提取,50 mg PSA净化,以8000 r/min高速冷冻离心除脂,采用Waters Acquity HSS T3色谱柱(100 mm×2.1 mm, 1.8 μm)分离。采用多反应监测高分辨扫描模式(MRM HR),以保留时间、一级母离子精确质量数、同位素丰度比和二级子离子精确质量数实现化妆品中73种禁用物质的快速筛查和确证,基质匹配外标法定量。实验比较了不同提取溶剂、净化吸附剂、色谱条件和质谱扫描模式对73种禁用物质测定的影响,并考察了膏霜剂和水剂的基质效应。结果表明,73种禁用物质线性关系良好,相关系数(R2)>0.99;检出限为5~150 μg/kg;定量限为15~450 μg/kg;膏霜剂及水剂两种基质在3个加标水平下的回收率为60.3%~130.3%,日内、日间RSD分别为0.8%~10.0%(n=6)和1.1%~15.0%(n=3)。日常风险监测中检出磺胺甲基异噁唑、甲基泼尼松、林可霉素、对乙酰氨基酚、甲氧苄啶、阿法骨化醇、倍他米松戊酸酯、溴莫尼定、氯霉素、氯苯那敏、氯倍他索丙酸酯、克罗米通、益康唑、酮康唑、泼尼松醋酸酯和泼尼松,检出含量范围为0.5~1136.1 mg/kg。该方法准确、快速、简便,可用于化妆品中73种常见禁用物质的检测。

Single-crystal-to-single-crystal phase transition of 18β-glycyrrhetinic acid isopropyl ester.

Due to the destruction of the integrity of the parent crystal, single-crystal-to-single-crystal phase transition in organic compounds is still a relatively rare phenomenon. The phase transition in glycyrrhetinic acid isopropyl ester is triggered by temperature change. The increasing volume of the isopropyl substituent as a result of increasing temperature forces a remodelling of the structural motifs. These changes cause a single-crystal-to-single-crystal phase transition. The low-temperature form is isostructural with glycyrrhetinic acid methanol solvate, while the high-temperature phase is isostructural with the ethyl ester of this acid.

Influence of Chlorine Oxyacid on the Electrooxidation of Methanol in Strong Acid

An electrochemical oxidation of methanol in a strong acid solution was investigated at a polycrystalline platinum electrode in the presence of different concentrations of hypochlorite. The addition of a slight amount of hypochlorite brought about drastic increase in the oxidation current of methanol, because the presence of hypochlorite inhibited the formation of a platinum oxide film on platinum electrodes. However, the oxidation current of methanol decreased with increasing the concentration of coexisting hypochlorite. The result may be due to i) the enhancement of the methanol adsorption to the surface of platinum electrodes by the inhibition of the formation of oxide film, and ii) the inhibition of methanol adsorption on platinum electrodes by higher concentration of NaClO and chemical compounds generated by the chemical reaction between methanol and increased hypochlorite.

Developing the liquid chromatography-mass spectrometry method for simultaneously quantifying five components in rat serums after oral administration of hawthorn aqueous extracts and its application to a pharmacokinetic study.

Hawthorn, one of the widely-used traditional Chinese medicines, has been used to treat dyspepsia, hyperlipidemia, and cardiovascular disease in the clinic. Our previous study revealed that gallic acid, neochlorogenic acid, cryptochlorogenic acid, vitexin, and quercetin were active components of hawthorn. In this study, a simple, precise, and reliable liquid chromatography-mass spectrometry method was developed for the simultaneous quantification of five components in rat serums. The separation was achieved on the Hypersil GOLD C18 column, and the mobile phases consisted of 0.1% acetic acid water and methanol at a flow rate of 0.3mL/min. The mass spectrometry data acquisition was performed on Q-Extractive-Orbitrap mass spectrometry with an electrospray ionization source in negative ion mode. The proposed liquid chromatography-mass spectrometry method was validated in terms of linearity, intra- and inter-precision, accuracy, recoveries, matrix effects, and stability. Then this newly proposed liquid chromatography-mass spectrometry method was successfully applied to a pharmacokinetic study on rats after oral administration of hawthorn aqueous extracts. This study provided relevant information on the pharmacokinetics of active components of hawthorn and explained the underlying mechanism of their bioactivity.

Determination of five nonsteroidal anti-inflammatory drugs in water by dispersive solid phase extraction-ultra performance liquid chromatography-tandem mass spectrometry based on metal-organic framework composite aerogel

非甾体类抗炎药(NSAIDs)能在环境水体中长期稳定存在,不仅对生物有慢性毒性还能增加病原体的耐药性,开发可靠的测定水样中痕量非甾体抗炎药的分析方法至关重要。该文制备新型金属有机骨架/壳聚糖复合气凝胶材料Co-UiO-67(bpy)/CS分散固相萃取吸附剂,将其用于环境水体中酮洛芬、萘普生、氟比洛芬、双氯芬酸、布洛芬5种非甾体类抗炎药的富集,结合超高效液相色谱-串联质谱法(UPLC-MS/MS),建立了基于金属有机骨架材料(MOFs)复合气凝胶环境水体中药物残留检测的新方法。为获得最佳的萃取效率,对影响萃取效果的主要因素(材料类型、MOFs用量、萃取时间、水样pH值、离子强度、甲酸体积分数、洗脱时间、洗脱剂体积)进行条件考察及优化。优化结果显示,吸附剂5 min内就可实现目标化合物的完全吸附,用总体积为5 mL的1%甲酸甲醇溶液洗脱6 min,目标化合物就能充分解吸。在最优的固相萃取条件下建立分析方法,结果表明,5种非甾体类抗炎药在各自范围内线性关系良好,线性相关系数均大于0.9937,方法的检出限(LOD)和定量限(LOQ)分别为0.32~2.06 ng/L和1.05~6.78 ng/L。在40、250和1500 ng/L 3个加标水平下进行加标回收试验,5种待测物的平均回收率为74.5%~114.1%。日内、日间相对标准偏差分别为1.3%~12.3%和1.3%~11.5%。将该方法用于实际水样的检测,市政污水检测出微量的酮洛芬和氟比洛芬,含量分别为14.52 ng/L和10.05 ng/L。该方法具有良好的灵敏度、准确度和精密度,操作简便,耗时短,为环境水体中痕量非甾体抗炎药富集检测提供了新方法。

Simultaneous Determination of Fifteen Polyphenols in Fruit Juice Using Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry Combining Dispersive Liquid-Liquid Microextraction.

Polyphenols are secondary metabolites of plants and used as effective antioxidants in dietary supplements, whose main sources are fruits, vegetables, and grains. To clarify the content and distribution of polyphenols in different fruit species samples accurately, a rapid and sensitive ultrahigh-pressure liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) method combining dispersive liquid-liquid microextraction (DLLME) was developed for quantitative determination of fifteen polyphenol compounds in fruit juice. In this method, the targets were first extracted from 1 g of fruit juice sample using 10 mL of 80% ethanol solution by ultrasonic-assisted extraction (UAE). Then, 1.0 mL of UAE extracted solution, 60 μL of n-octanol and 2.0 mL of H2O were performed in the following DLLME procedure. A C18 reversed-phase column, ZORBAX SB (100 × 4.6 mm, 3.5 μm), was proposed under gradient elution with 0.1% formic acid aqueous solution and methanol mobile phases for the determination of 15 polyphenols, allowing us to obtain polyphenolic profiles in less than 23.0 min. Under the optimum conditions, the enrichment factors ranged from 162 to 194. The results showed that the 15 polyphenols had linear correlation coefficients (R2) more than 0.99. The limits of detection (LODs) were between 18.3 and 103.5 ng/g, and the average recoveries were between 96.9 and 116.3% with interday relative standard deviations (RSDs) ranging from 4.4 to 8.2% in all cases. The method was successfully applied to the analysis of real fruit juice samples and presented itself as a simple, rapid, practical, and environment-friendly technique.

Innovative Microstructural Transformation upon CO2 Supercritical Conditions on Metal-Nucleobase Aerogel and Its Use as Effective Filler for HPLC Biomolecules Separation.

This work contributes to enlightening the opportunities of the anisotropic scheme of non-covalent interactions present in supramolecular materials. It provides a top-down approach based on their selective disruption that herein has been employed to process a conventional microcrystalline material to a nanofibrillar porous material. The developed bulk microcrystalline material contains uracil-1-propionic acid (UPrOH) nucleobase as a molecular recognition capable building block. Its crystal structure consists of discrete [Cu(UPrO)2 (4,4′-bipy)2 (H2 O)] (4,4′-bipy=4,4′-bipyridine) entities held together through a highly anisotropic scheme of non-covalent interactions in which strong hydrogen bonds involving coordinated water molecules provide 1D supramolecular chains interacting between them by weaker interactions. The sonication of this microcrystalline material and heating at 45 °C in acetic acid–methanol allows partial reversible solubilization/recrystallization processes that promote the cross-linking of particles into an interlocked platelet-like micro-particles metal–organic gel, but during CO2 supercritical drying, the microcrystalline particles undergo a complete morphological change towards highly anisotropic nanofibers. This unprecedented top-down microstructural conversion provides a nanofibrillar material bearing the same crystal structure but with a highly increased surface area. Its usefulness has been tested for HPLC separation purposes observing the expected nucleobase complementarity-based separation.

LC-MS/MS Analysis of Fumonisin B1, B2, B3, and Their Hydrolyzed Metabolites in Broiler Chicken Feed and Excreta.

An accurate, reliable, and specific method was developed for the quantitative determination of fumonisins B1, B2, B3, and their hydrolyzed metabolites, HFB1, HFB2, and HFB3, in broiler chicken feed and excreta using ultra-performance liquid chromatography combined with tandem mass spectrometry (UPLC-MS/MS). The samples were extracted and diluted for the determination of parent fumonisins. Another portion of the extracted samples was alkaline-hydrolyzed and cleaned using a strong anionic exchange adsorbent (MAX) for the determination of hydrolyzed fumonisins. Chromatographic separation was performed on a CORTECS C18 column (2.1 mm × 100 mm, 1.6 μm) using 0.2% formic acid aqueous solution and methanol with 0.2% formic acid as the mobile phase under gradient elution. The six fumonisins, FB1, FB2, FB3, HFB1, HFB2, and HFB3, were analyzed by tandem mass spectrometry using multiple-reaction monitoring (MRM) mode. The six fumonisins showed good linearity, with relative coefficients of r > 0.99. The limits of quantitation (LOQs) were 160 μg/kg. At the low, medium, and high spiked levels, the recovery of fumonisins in chicken feed and excreta ranged from 82.6 to 115.8%, with a precision (RSD) of 3.9–18.9%. This method was successfully applied to investigate the migration and transformation of fumonisins in broiler chickens.

3D Self-Supported Binary PtCu Aerogel Boosted Methanol Oxidation

Precious metal aerogel has a broad application prospect in the field of fuel cell electrocatalysis because of its unique structure characteristics. In this work, Three-dimensional (3D) self-supporting porous PtCu aerogels have been successfully synthesized via a gelation strategy based on excess NaBH4. The mass activity of optimized PtCu aerogel in acid methanol solution is 6.56 times higher than that of JM-Pt/C. In addition, the optimized PtCu aerogel showed better stability than JM Pt/C. For the methanol oxidation reaction, the optimized PtCu aerogel still maintains the current density of 930 mA mg−1 Pt after 3600 s Chronoamperometric (CA) test. By X-ray photoelectron spectroscopy (XPS), we demonstrate the electron transfer between Cu and Pt. This would arouse the change of electronic state and atomic spacing on the surface of Pt and endow the PtCu aerogel with both prominent activity and excellent stability due to lattice stress and electron effect. This work provides a strategy for reasonable design high performance fuel cell electrocatalysts.

The pH and Potential Dependence of Pb-Catalyzed Electrochemical CO2 Reduction to Methyl Formate in a Dual Methanol/Water Electrolyte.

The conversion of waste CO2 to value-added chemicals through electrochemical reduction is a promising technology for mitigating climate change while simultaneously providing economic opportunities. The use of non-aqueous solvents like methanol allows for higher CO2 availability and novel products. In this work, the electrochemistry of CO2 reduction in acidic methanol catholyte at a Pb working electrode was investigated while using a separate aqueous anolyte to promote a sustainable water oxidation half-reaction. The selectivity among methyl formate (a product unique to reduction of CO2 in methanol), formic acid, and formate was critically dependent on the catholyte pH, with higher pH conditions leading to formate and low pH favoring methyl formate. The potential dependence of the product distribution in acidic catholyte was also investigated, with a faradaic efficiency for methyl formate as high as 75 % measured at -2.0 V vs. Ag/AgCl.

Non-Aqueous Liquid Phase Synthesis of Acetic Acid via Ionic Liquid Promoted Homogeneous Carbonylation of Methanol over Ir(III) Catalysts

Abstract Carbonylation of methanol to acetic acid is an aqueous homogeneous catalytic process widely used in industry. In the existing methanol carbonylation industry, a large amount of water (14–15 wt.%) is required in the Monsanto process to inhibit catalyst deactivation, which also consumes a lot of energy to separate the water from the acetic acid product. Here, non-aqueous liquid phase synthesis of acetic acid was carried out by ionic liquid promoted homogeneous carbonylation of methanol over Ir(III) catalysts. It was found that 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim]Tf2N) and N-butyl pyridinium bis(trifluoromethanesulfonyl)imide ([BPy]Tf2N) could promote the acetic acid selectivity (>98%) and methanol conversion (>99%) under a relatively mild reaction condition of 160 °C and 3.0 MPa. In the reaction, Tf2N− formed an Ir*[Tf2N] complex with Ir to promote the stability of Ir and enhance the activation of CO. From DFT calculation results, the CO insertion was a rate controlling step on the Ir-base catalyst in the reaction cycle, determining the conversion and selectivity of the reaction. The oxygen and nitrogen groups from Tf2N− interacted with Ir to form an Ir*[Tf2N] complex, which could effectively reduce the energy barrier of the CO insertion step, enhancing the selectivity of HAc. Moreover, the catalyst system could be easily recycled and reused with the methanol conversion of 89.66% after five cycles. The methanol carbonylation based on the ionic liquid promoted catalyst is a promising non-aqueous liquid-phase sustainable process.

Optimised biodiesel production from waste vegetable cooking oil catalysed by green synthesised calcium oxide nanoparticles

The current study proposes a simple, cost-effective and environmentally friendly technique for producing biodiesel via transesterification of waste vegetable cooking oil using green synthesised CaO nanoparticles, as a catalyst. The produced CaO nanoparticles were structurally and morphologically analysed using several characterisation techniques. The qualitative analysis of produced biodiesel was carried out by using different analytical techniques recommended by the American Society for Testing Materials, such as the acid number test, methanol test, and copper strip corrosion test, and FTIR spectroscopy. The optimised parameters for maximum biodiesel yield (96%) were determined to be a 1% catalyst loading, 1:8 oil to ethanol ratio, a temperature of 50°C, and reaction duration of 90 minutes. The prepared CaO nanocatalyst has a high surface area to volume ratio, small average size of 32.4 nm and high crystalline structure which gave rise to their potent catalytic properties.

Electrochemical behavior of Ni–Cu foams fabricated by dynamic hydrogen bubble template electrodeposition used for energy applications

This work focuses on studying the effect of bath chemical composition, applied current and deposition time on the morphology, composition and corrosion characterization of the deposited Ni–Cu nano metallic foams (NMFs) using Dynamic Hydrogen Bubble Template (DHBT) technique. The Ni content of the deposited layer was ranged from 50 to 57% and the copper content ranged from 8 to 21%. The corrosion characterization of these NMFs was evaluated in 1 M acidic methanol solution by potentiodynamic polarization tests, cyclic voltammetry, and EIS. At high current density, typical dendritic morphology was developed. From the potentiodynamic test, the lowest corrosion rate was 0.089 mpy for layer deposited at 0.6 A/cm 2 for 30 sec. Increasing both the applied current density and the time of deposition lead to increasing of the forward peak intensity and total charge measured by cyclic voltammetry showing a remarkable effect on the electrochemical activity of the films. From the EIS test, it was observed that the polarization resistance (R po ) decreased as well as the applied electrodeposition time increased. The highest polarization resistance was 272 O at 0.6 A/cm 2 for 30 sec, reflecting the highest corrosion resistance.

Determination of four melamine and its derivatives in urine by ultra-performance liquid chromatography-tandem mass spectrometry

To establish a method for simultaneous detection of melamine(MEL), ammeline(AMN), ammelide(AMD) and cyanuric acid(CYA) in urine by ultra-performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS). After the urine sample was added to the internal standard, they were mixed by acetonitrile, ultrasonic extraction and centrifugation, enriched by MCX or MAX solid phase extraction column, eluted with 5% ammoniated methanol or 2% formic acid methanol, dried under nitrogen at 40 ℃, separated by Amide chromatography column(2.1 mm×100 mm, 1.7 μm), qualitatively and quantitatively analyzed by mass spectrometer in the simultaneous scanning mode of positive and negative ions. Melamine and its derivatives were completely separated with great chromatography peak. The limit of detection(LOD) for melamine, ammeline, ammelide and cyanuric acid were 0.03, 0.04, 0.04 and 0.05 ng/mL, and the limit of quantification(LOQ) were 0.11, 0.12, 0.14 and 0.15 ng/mL, respectively. The recovery rate of standard addition samples of 0.2, 5, 50 and 200 ng/mL ranged from 94.6% to 106.5%, the intra-day precision was between 0.73% and 8.34%, and the inter-day precision was less than 6.80%(n=6). At low concentrations, AMD and CYA mainly showed matrix enhancing effect, while AMN showed matrix inhibitory effect with increasing concentration. The overall detection rate of melamine and its derivatives was 75.0% in 60 parcels of random urine. The average concentration of urinary melamine and its derivatives were higher in men. UPLC-MS/MS can simultaneously determine four melamine and its derivatives in urine. The LOD and LOQ of the current method were low with great accuracy and precision.

Production of renewable aromatics and olefins by catalytic co-cracking of fatty acid methyl esters and methanol

Catalytic cracking of triglycerides and their derivatives (e.g., fatty acid methyl esters, FAMEs) by HZSM-5 zeolite offers a promising route to produce renewable aromatics and olefins, but it is primarily hindered by the rapid catalyst deactivation caused by coke. In this work, the co-cracking of FAMEs and methanol over HZSM-5/Al2O3 composites was developed to regulate the product distribution and slower the catalyst deactivation. Co-feeding methanol with FAMEs enhanced the olefin selectivity at the expense of aromatics, and the total selectivities of aromatics and olefins added up to 70.9% with an optimized methanol content of 60%. The co-feeding of methanol not only promoted the olefin yield but also retarded the consecutive H-elimination of aromatics to polycyclic aromatics, thus reducing the coke formation and prolonging the catalyst lifespan. Under the conditions of 450°C, 0.16 MPa and a space velocity of FAMEs at 4 h−1, increasing the methanol blending ratio in FAMEs from zero to 50% reduced coke from 17.8% to 10.1% after reaction for 12 h. Besides, the spent catalyst for the co-cracking reaction could be easily regenerated by coke combustion, yielding similar structure, acidity and activity to those of the fresh one.