When ethylene-vinyl acetate copolymer, EVA, is heated, a two-stage thermal degradation occurs following its melting. The vinyl
acetate content of the copolymer was determined to be 43.8% by using TA 2950 and TA 2050 thermogravimetric instruments. TG/FTIR
was used to detect the evolved gas. Acetic acid and trans-1-R-4-R'-cyclohexane were the main products evolved from EVA in
the first and second stage, respectively. The apparent activation energies were determined for both stages by differential
Authors:X. Cai, H. Shen, C. Zhang, Y. Wang, and Z. Kong
A simple operation mode to determine the apparent activation energy Ea is introduced. Ea can be determined with a double-curve method by using a constant reaction rate (CRR) approach of Hi-Res TG. The most appropriate
mechanism function f(α) and frequency factor A are determined by a single-curve method when the activation energies provided by the two methods are in good agreement with
each other. The deacetylation of EVA copolymer has been used for illustration. Advantages of the CRR are discussed.
Authors:J. Liu, H. Xu, W. Shen, X. Pan, and Y. Xiang
Mn2O3/-Al2O3 catalysts were prepared by the impregnation method, and the maximum monolayer dispersion capacity or dispersion threshold value of Mn2O3 on the surface of -Al2O3 was determined to be 13.08% from the decomposition mass loss of supported Mn(NO3)2 in the monolayer state. This was compared with the values estimated from a close-packed monolayer model and an interaction model. It was confirmed that the high activities and selectivities of the catalysts for benzoic acid hydrogenation to benzaldehyde are due to the monolayer dispersion of the Mn2O3 on the surface of -Al2O3.
Authors:H. Zhao, S. Bennici, J. Shen, and A. Auroux
The surface acidic properties of sulfated vanadia–titania catalysts prepared by various methods were investigated by adsorption
microcalorimetry, using ammonia as probe molecule. The acidic characteristics of the samples were shown to be strongly affected
by the preparation method, calcination temperature, and sulfur content. The samples prepared by sol–gel and mechanical grinding
exhibited higher acidity than co-precipitated samples. Moreover, increasing the calcination temperature of co-precipitated
samples resulted in a decrease in surface area from 402 to 57 m2 g−1 and sulfur content from around 4 to 0.2 mass%, but up to a certain point generated a stronger acidity. The optimal calcination
temperature appeared to be around 673 K.
Authors:Q. Ren, Y. Hua, H. Shen, L. Zhong, C. Jin, Y. Mi, H. Yao, Y. Xie, S. Wei, and L. Zhou
The uptake of rare earth elements (REE) by Euglena gracilis cells has been investigated in Fudan University. The remarkable ability to transport REEs to these cell’s compartments had
been observed. X-ray absorption fine structure experiments (XAFS) of cerium in Euglena gracilis were performed at Beijing Synchrotron Radiation Facility (BSRF) to directly determine the cerium valence state and coordination
structure in situ. Extended X-ray absorption fine structure (EXAFS) derived calculation showed that cerium was surrounded
by 8 N atoms with bond length of 0.258 nm. Combining with other measurements, it may indicate that most likely REEs are mainly
located in chlorophyll molecules.
Authors:H. Dong, Y. Wang, Y. Ou, J. She, X. Shen, J. Li, C. Zhang, and L. Liu
Molecularly imprinted polymers (MIPs) were synthesized by imprinting a new template—S(-)-1,1′-binaphthalene-2,2′-diamine (S-DABN) and applied as chiral stationary phases for chiral separation of DABN racemates by high-performance liquid chromatography (HPLC). The influence of some key factors on the chiral recognition ability of MIPs, such as the type of functional monomers and porogen and the molar ratio of template to monomer, was systematically investigated. The chromatographic conditions, such as mobile phase composition, sample loading, and flow rate, were also measured. The chiral separation for DABN racemates under the optimum chromatographic conditions by using MIP chiral stationary phase (CSP) of P3, prepared with the S-DABN/MAA ratio = 1/4 and used acetonitrile (2 mL) and chloroform (4 mL) as porogen, showed the highest separation factor (2.14). Frontal analysis was used to evaluate affinity to the target molecule of MIPs. The binding sites (Bt) of MIPs and dissociation constant (Kd) were estimated as 4.56 μmol g−1 and 1.40 mmol L−1, respectively. In comparison with the previous studies, this approach had the advantages, such as the higher separation factor, easy preparation, and cost-effectiveness, it not only has the value for research but also has a potential in industrial application.
Authors:Y. Shen, H. Yang, G. Xia, J. Wang, B. Cai, and X. Jia
Silica-gel column chromatography and preparative reversed-phase high-performance liquid chromatography (RP-HPLC) were sequentially employed for the isolation of two antioxidants including gallic acid and methyl gallate from Folium Toonea Sinensis. An RP-HPLC-UV method was then developed and validated to rapidly determine their content in this herb with ethyl gallate as internal standard. The quantitation was performed on an XBridge Shield RP18 column (150 mm × 4.6 mm, 5 μm) under 40°C. The mobile phase consisting of acetonitrile and 0.1% formic acid aqueous solution was driven at 1.0 mL min−1 under gradient elution, and 270 nm was selected to monitor the separation. To evaluate the fitness for purpose of the method and to investigate the difference in the content of analytes among different samples, the leaves collected from five production sites were analyzed. The newly established method is suitable for routine analysis of gallic acid and methyl gallate in the herb and, hence, can assist in its quality assessment. It was also found that not only the content of two antioxidants but also the ratio varied significantly among different geographical origins. In addition, three samples from Yantai, Zumadian, and Zhenjiang were distinguished as they have a much higher content ratio than the other two.
Authors:Q. Liu, K. Qin, B. Shen, H. Cai, and B. Cai
To evaluate the quality of Fructus Arctii, an accurate and reliable method of high-performance liquid chromatography/diode array detection—electrospray ionization—mass spectrometry (HPLC/DAD—ESI—MS) was developed. Nine compounds, including chlorogenic acid, caffeic acid, trans-p-hydroxycinnamic acid, arctiin, arctignan A, ethyl caffeate, matairesinol, arctigenin, and lappaol B, were determined simultaneously in 19 batches of Fructus Arctii samples collected from different localities. Nineteen common peaks were identified or tentatively assigned by comparing their mass spectrometric data with reference compounds, self-established compound library, and published literatures. Also, the 19 common peaks were selected as characteristic peaks to assess the similarity of chromatographic fingerprinting of these samples. Moreover, hierarchical clustering analysis (HCA) and principal components analysis (PCA) were successfully applied to demonstrate the variability of samples. The results indicated the content of nine compounds that varied greatly among the samples, and 19 samples collected from different localities could be discriminated. Furthermore, chlorogenic acid, arctiin, and arctigenin were found to be chemical markers for evaluating the quality of Fructus Arctii.