A Comparison of Silica C and Silica Gel in HILIC Mode: The Effect of Stationary Phase Surface Area

In order to assess the effect of silica gel structure on retention in hydrophilic interaction chromatography, a test system was developed which used quaternary ammonium ions as probes with tetramethylammonium acetate (TMAA) as the counter-ion competing against the interaction of the test probes with ionised silanols in the stationary phase. Four silica gel columns and a silica hydride column were examined. Retention times were obtained for the test probes at 20, 40, 60, 80 and 90 % acetonitrile (ACN) with all the mobile phase mixtures containing 10-mM TMAA buffer at pH 6.0. All phases gave “U”-shaped plots for log k against percentage of ACN with the steepest rise in retention occurring between 80 and 90 % ACN. Benzyltrimethylammonium, the smallest quaternary ammonium ion, was the most strongly retained probe at 90 % ACN and was most retained on a high surface area 60 Å Kromasil column and least retained on a 300 Å ACE silica gel column. The ionic strength of the mobile phase was varied at 80 and 90 % ACN and plots of log k against the inverse of buffer strength followed by fitting of second-order polynomial curves allowed an assessment of the contribution from HILIC to the mixed HILIC/ion-exchange retention mechanism. Toluene and pentylbenzene were used to assess the decrease in accessible pore volume due to water absorption in HILIC mode.     

Influence of Carbon Black and Silica Filler on the Rheological and Mechanical Properties of Natural Rubber Compound

Rubber compounds are reinforced with fillers such as carbon black and silica. In general, filled rubber compounds shows smooth rheological behavior and mechanical properties. Variation in rheological behavior and mechanical properties was studied in terms of the filler composition using natural rubber compounds filled with both carbon black and silica CB/Si = 0/60, 20/40, 30/30, 40/20 and 60/0 phr (parts per hundred rubber is parts of any non-rubbery material per hundred parts of raw gum elastomer (rubbery material)). The rheological behaviour can be showed in measurement of Mooney viscosity and cure time. The Mooney viscosity of rubber compounds increase with the increasing the carbon black in the compounds. The compound filled with CB/Si of 30/30 and 60/0 showed abnormal rheological behaviour in which the cure time decreased suddenly and the increased at certain ratio during the measurement. The mechanical properties such as hardness, abrasion resistance and tensile stress at 300% elongation were studied. In the hardness and abrasion resistance measurement, the higher ratio CB/Si decrease contribution of silica, which resulting smaller of hardness value. Ratio CB/Si 40/20 gives an optimum filler blended. It is also clearly understood that higher abrasion resistance mainly due to the lower hardness value under the same condition. The tensile stress at 300% elongation of rubber compound increased with the increasing carbon black filler.     

One‐pot synthesis of a new high vinyl content hybrid silica monolith dedicated to nanoliquid chromatography

A new vinyltrimethoxysilane‐based hybrid silica monolith was developed and used as a reversed‐phase capillary column. The synthesis of this rich vinyl hybrid macroporous monolith, by cocondensation of vinyltrimethoxysilane with tetramethoxysilane, was investigated using an unconventional (formamide, nitric acid) porogen/catalyst system. A macroporous hybrid silica monolith with 80% in mass of vinyltrimethoxysilane in the feeding silane solution was obtained and compared to a more conventional low vinyl content hybrid monolith with only of 20% vinyltrimethoxysilane. Monoliths were characterized by scanning electron microscopy, ²⁹Si nuclear magnetic resonance spectroscopy and N₂ adsorption–desorption. About 80% of the vinyl precursor was incorporated in the final materials, leading to 15.9 and 61.5% of Si atoms bonded to vinyl groups for 20% vinyltrimethoxysilane and 80% vinyltrimethoxysilane, respectively. The 80% vinyltrimethoxysilane monolith presents a lower surface area than 20% vinyltrimethoxysilane (159 versus 551 m²/g), which is nevertheless compensated by a higher vinyl surface density. Chromatographic properties were evaluated in reversed‐phase mode. Plots of ln(k) versus percentage of organic modifier were used to assess the reversed‐phase mechanism. Its high content of organic groups leads to high retention properties. Column efficiencies of 170 000 plates/m were measured for this 80% vinyltrimethoxysilane hybrid silica monolith. Long capillary monolithic columns (90 cm) were successfully synthesized (N = 120 000).     

Quantitative separation of biological lipids by successive chromatographic runs on juxtaposed thin layers (author's transl)]

During a study on incorporation of 14C-labeled precursors in biological lipids, we had to elaborate a method of quantitative separation of lipid classes, based upon three successive chromatographic runs on juxtaposed thin layers. The first thin layer, on which the lipid extract is applied, consists of silica gel alkalised by means of sodium hydroxide solution. The second thin layer is constituted only by silica gel G. The three one-dimensional migrations are respectively carried out in the following solvent systems: diethyl ether-hexane-benzene (55:30:15), hexane-benzene (80:20) and diethyl ether-benzene-acetic acid (62:20:18). The lipid fractions are scraped out and counted by liquid scintillation. The reproducibility of the whole operation is discussed.     

高分子覆盖型硅胶填料的制备与色谱保留行为

 采用甲基丙烯酸甲酯 (MMA)或MMA 亚乙基二甲基丙烯酸酯 (EDMA)在硅胶表面聚合的方法 ,制备生成了新型高分子覆盖型硅胶填料C或D。借助红外光谱、元素分析、尺寸排阻色谱和反相液相色谱分析对反应过程、覆盖程度、交联剂的影响和填料的色谱保留行为进行了评价和讨论。结果显示 ,在合成时可以通过控制聚合单体的量控制生成高分子层的厚度 ,而合成中加入交联剂可以改变填料表面的微孔构造。通过考察这种色谱填料的疏水性和对芳香族化合物的分离性能 ,认为其柱效和分离效果接近C18填料的性能。     

含吡咯烷酮基的衣康酸酯类聚合物不同酯基对其若干性质的影响

含吡咯烷酮基的衣康酸酯类聚合物不同酯基对其若干性质的影响潘怀忠阎雁唐莉吴志强李福绵（北京大学化学学院北京１００８７１）关键词含吡咯烷酮基的衣康酸酯，折光指数，热性质，平衡吸水率吡咯烷酮基具有良好的亲水保湿性和生物相容性，将其引入聚合物具有其实际应用...     

Development of an O-ring from NR/EPDM filled silica/CB hybrid filler for use in a solid oxide fuel cell testing system

This research presents the effects of oxygen pressure and ambient temperatures on the crack behavior of O-rings from a semi-EV of NR/EPDM rubber with silica/CB filler, exposed to the inlet flow and outflow oxygen pressure in a Solid Oxide Fuel Cell (SOFC) environment. Blends of NR/EPDM were prepared with various ratios of silica/CB filler at 00/60, 10/50, 20/40, 30/30, 40/20, 50/10, and 60/00 phr. The fabricated O-ring complied with the standard for O-rings (TIS 2728-2559), with a minimum hardness of 65–75 Shore A, minimum tensile strength of 9 MPa, minimum elongation at break of 200%, and a minimum 100% modulus of 2.7 MPa. The mechanical properties of the compounds were tested, and the appropriate compound was chosen to make the O-rings to test in SOFC. The crack morphology of the fabricated O-rings was investigated and compared with a commercial O-ring after testing in the SOFC. As a result, the compound with silica/CB of 40:20 ratio provided the optimum mechanical properties, and passed the criteria standard of TIS 2728-2559. The mechanical properties of the prepared and commercial O-rings were similar (P-value of commercial with 60/00 = 0.273, 50/10 = 0.273, 40/20 = 0.144, 30/30 = 0.465, 20/40 = 0.465, 10/50 = 1.000 and 00/60 = 0.273; all > 0.05) and and both could still be continued to be used in SOFC despite some inner cracks after 24 h. The price of the prepared O-ring is cheaper than the commercial O-rings due to the low price of NR used in its formulation. Therefore, a prepared O-ring can be used in a SOFC, or other applications due to their mechanical properties and their reasonable price.     

Influence of the pressure on the properties of chromatographic columns .III. retention volume of thiourea, hold-up volume, and compressibility of the C18-bonded layer

The influence of the average column pressure (ACP) on the elution volume of thiourea was measured on two RPLC columns, packed with Resolve-C18 (surface coverage 2.45 micromol/m2) and Symmetry-C18 (surface coverage 3.18 micromol/m2), and it was compared to that measured under the same conditions on an underivatized silica (Resolve). Five different methanol-water mixtures (20, 40, 60, 80 and 100% methanol, v/v) were used. Once corrected for the compressibility of the mobile phase, the data show that the elution volume of thiourea increases between 3 and 7% on the C18-bonded columns when the ACP increases from 50 to 350 bar, depending on the methanol content of the eluent. No such increase is observed on the underivatized Resolve silica column. This increase is too large to be ascribed to the compressibility of the stationary phase (silica + C18 bonded chains) which accounts for less than 5% of the variation of the retention factor. It is shown that the reason for this effect is of thermodynamic origin, the difference between the partial molar volume of the solute in the stationary and the mobile phase, Delta V, controlling the retention volume of thiourea. While Delta V is nearly constant for all mobile phase compositions on Resolve silica (with Delta V approximately equal to -4 mL/mol), on RPLC phases, it significantly increases with increasing methanol content, particularly above 60% methanol. It varies between -5 mL/mol and -17 mL/mol on Resolve-C18 and between -9 mL/mol and -25 mL/mol on Symmetry-C18. The difference in surface coverage between these two RP-HPLC stationary phases increases the values of Delta V by about 5 mL/mol.     

Chain‐transfer reaction in the radical polymerization of di‐n‐butyl itaconate at high temperatures

Radical polymerizations of di‐n‐butyl itaconate were investigated. Unexpected resonances (C resonances) were observed in ¹³C NMR spectra of C?O of poly(di‐n‐butyl itaconate)s [poly(DBI)s] obtained at temperatures higher than 60 °C, although two kinds of carbonyl groups showed splittings due to triad tacticities in the spectra of polymers obtained at lower temperatures. The poly(DBI)s formed by the different kinds of initiators or formed in the presence of chain‐transfer agents showed hardly any changes in the intensities of the C resonances; this indicated that the C resonances were not due to the structures formed through initiating and terminating reactions. The poly(DBI)s obtained at different yields showed only a slight increase in the intensities of the C resonances with the yield, which suggested that the C resonances were not attributable to the intermolecular chain‐transfer reaction to the monomer and/or polymer. However, the intensities of the C resonances significantly increased with a decreasing feed monomer concentration; this suggested that intramolecular chain‐transfer reactions took place at high temperatures. Furthermore, a Cu complex‐catalyzed atom transfer radical polymerization mechanism was revealed to be effective for suppressing the intramolecular chain‐transfer reaction at 60 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2415–2426, 2002     

Conjugate reduction of α,β-unsaturated esters and amides with tributyltin hydride in the presence of magnesium bromide diethyl etherate

We report herein that the conjugate reduction of α,β-unsaturated esters and amides, such as aryl acrylates, pantolactone esters of acrylic acids, diethyl itaconate and N-crotonylcamphorsultam, with tributyltin hydride proceeded in moderate to high yields in the presence of magnesium bromide diethyl etherate. The effect of metal halide enhancing the yields is also described.     

The thermal degradation of poly(diethyl fumarate)

The kinetics and mechanism of the thermal degradation of poly(diethyl fumarate) (PDEF) were studied by thermogravimetry, as well as by analysis of the thermolysis volatiles and polymer residue. The characteristic mass loss temperatures were determined, as were the overall thermal degradation activation energies of three PDEF samples of varying molar mass. Ethylene and ethanol were present in the thermolysis volatiles at degradation temperatures below 300 °C, while diethyl fumarate was also evidenced at higher degradation temperatures. The amount of monomer increased with increasing degradation temperature. The dependence of the molar mass of the residual polymer on the degradation time and temperature was established and the number of main-chain scissions per monomer unit, s/P₀, calculated. A thermal degradation mechanism including de-esterification and random main-chain scission is proposed. The thermal degradation of PDEF was compared to the thermolysis of poly(ethyl methacrylate) (PEMA), poly(diethyl itaconate) (PDEI) and poly(ethyl acrylate) (PEA).     

Thermoinactivation mechanism of glucose isomerase

In this article, the mechanisms of thermoinactivation of glucose isomerase (GI) from Streptomyces rubiginosus (in soluble and immobilized forms) were investigated, particularly the contributions of thiol oxidation of the enzyme's cysteine residue and a "Maillard-like" reaction between the enzyme and sugars in high fructose corn syrup (HFCS). Soluble GI (SGI) was successfully immobilized on silica gel (13.5 microm particle size), with an activity yield between 20 and 40%. The immobilized GI (IGI) has high enzyme retention on the support during the glucose isomerization process. In batch reactors, SGI (half-life =145 h) was more stable than IGI (half-life =27 h) at 60 degrees C in HFCS, whereas at 80 degrees C, IGI (half-life =12 h) was more stable than SGI (half-life =5.2 h). IGI was subject to thiol oxidation at 60 degrees C, which contributed to the enzyme's deactivation. IGI was subject to thiol oxidation at 80 degrees C, but this did not contribute to the deactivation of the enzyme. SGI did not undergo thiol oxidation at 60 degrees C, but at 80 degrees C SGI underwent severe precipitation and thiol oxidation, which caused the enzyme to deactivate. Experimental results show that immobilization suppresses the destabilizing effect of thiol oxidation on GI. A "Maillard-like" reaction between SGI and the sugars also caused SGI thermoinactivation at 60, 70, and 80 degrees C, but had minimal effect on IGI. At 60 and 80 degrees C, IGI had higher thermostability in continuous reactors than in batch reactors, possibly because of reduced contact with deleterious compounds in HFCS.     

Liquid Chromatography-Electrospray Quadrupole Linear Ion Trap Mass Spectrometric Method for Quantitation of Domperidone in Chinese Healthy Volunteers

A rapid,sensitive,and accurate method based on LC/MS/MS was developed and validated for the determination of domperidone in human plasma.Domperidone and internal standard,tramadol,were extracted from plasma with diethyl ether-dichloromethane(60∶40,volume ratio)and separated by reversed-phase HPLC with methanol-water-ammonia solution(80∶20∶0.2,volume ratio)as the mobile phase.Detection was carried out via multiple-reaction monitoring(MRM)on a Q-trapTM LC/MS/MS system(Q-trapTM).The assay result was linear over a concentration range of 0.1-30 ng/mL with a limit of quantitation(LOQ)of 0.1 ng/mL.The inter-and intra-day precision levels were within 7.52% and 12.9%,respectively,whereas the accuracy was within a range of 87.3%-114%.This method has been successfully applied to evaluate the pharmacokinetics of domperidone in Chinese healthy volunteers given an oral dose of 10 mg.     

固相萃取-高效液相色谱法同时测定苹果中残留的克菌丹和灭菌丹

采用硅镁吸附剂和硅胶作吸附剂,建立了固相萃取-高效液相色谱法同时测定苹果中残留的克菌丹和灭菌丹的分析方法。研究了甲醇-乙腈-水(含0.1 mmol/L乙酸-乙酸钠缓冲溶液（pH 3.80）)三元体系下克菌丹和灭菌丹的最佳分离条件,在波长210 nm下检测,克菌丹和灭菌丹的线性范围为0.40～8.00 mg/kg,线性相关系数均大于0.9999;最低检出限克菌丹为0.27 mg/kg、灭菌丹为0.20 mg/kg;保留时间的相对标准偏差（RSD）≤0.60%。苹果样品中3个添加水平的平均加标回收率为克菌丹69.3%～106%,RSD为3.7%～4.7%;灭菌丹101%～108%,RSD为1.3%～5.4%。     

Thin-layer chromatography of chlorinated anisoles and veratroles

Summary The thin-layer chromatography of chlorinated anisoles (methoxybenzenes) and veratroles (1,2-dimethoxybenzenes) has been examined on silica gel G60 and RP-18 thin-layer plates. More than fifty solvent systems were screened and some of them recommended for particular separations. Acetone was shown to be suitable for group separation of both chlorinated anisoles and veratroles on a silica gel G60 stationary phase having a very narrow range of R_F values. On the other hand, benzene, dichloromethane and the various mixtures of light petroleum (b.p. 40–60°C) and a more polar eluent (such as diethyl ether, acetone or ethyl acetate) were recommended for separation of certain individual isomers. The best separation of chloroanisoles was achieved using RP-18 plates and methanol-water (9010) as the solvent system.     

Effect of nanosilica on thermal oxidative degradation of SBR

The effect of silica content on thermal oxidative stability of styrene–butadiene rubber (SBR)/silica composites has been studied. Morphologies of silica in SBR with different contents are investigated by scanning electron microscopy, which indicates that silica can well disperse in SBR matrix below the content of 40 %, otherwise aggregates or agglomerates will generate. Composites with around 40 % silica content show excellent mechanical properties and retention ratios after aging at 85 °C for 6 days. The values of activation energy (E _a) of pure SBR and its composites are calculated by Kissinger and Flynn–Wall–Ozawa methods based on thermogravimetric (TG) results, which suggests that composite with about 20 % silica has minimum E _a, and composite with 30–40 % silica has maximum E _a. According to TG curves, it is found that silica can suppress the formation of char leading to decline in stability to some extent. On the other side, silica also has positive effect on improving thermal stability of the matrix as filler. Thus, the SBR/silica composites with silica content of 30–40 % can possess both excellent resistance to thermal oxidative degradation and superior mechanical properties.     

Liquid chromatographic separation and thermodynamic investigation of stereoisomers of darunavir on Chiralpak AD‐Hcolumn

Liquid chromatographic separation of stereoisomers of darunavir on Chiralpak AD‐H, a column containing the stationary phase coated with amylose tris(3,5‐dimethylphenylcarbamate) as a chiral selector, was studied under normal‐phase conditions at different temperatures between 20 and 50°C. The effect of quality and quantity of different polar organic modifiers viz: methanol, ethanol, 1‐propanol, and 2‐propanol in the mobile phase as well as column temperature on retention, separation, and resolution was investigated and optimized. The optimum separation was accomplished using a mobile phase composed of n‐hexane/ethanol/diethyl amine (80:20:0.1 v/v/v) at 40°C. Apparent thermodynamic parameters ΔH⁰ and ΔS* were derived from the Van't Hoff plots (lnk′ versus 1/T) and used to explain the strength of interactions between the stereoisomers and amylose tris(3,5‐dimethylphenylcarbamate) coated chiral stationary phase.     

A simple TLC and HPTLC method for separation of selected steroid drugs

Chromatographic properties of five steroid drugs: cortisone, hydrocortisone, methylprednisolone, prednisolone and norgestrel have been studied by normal-, reversed-phase and hydrophilic neutral cyano-bonded silica stationary phase with five binary mobile phases (acetonitrile-water, acetonitrile-DMSO, acetonitrile-methanol, acetone-petroleum ether, acetone-water) in which the concentration of organic modifier was varied from 0 to 100% (v/v). This study reports the optimization of steroid hormones separation. Chromatographic retention data and possible retention mechanisms are discussed. Separation abilities of mobile and stationary phases were studied using the principal component analysis method. The best separation of methylprednisolone and prednisolone is with a chromatographic system included silica gel as stationary phase and mixture of acetonitrile and DMSO (10:90 v/v). These two anti-inflammatory drugs can be fast separated from norgestrel when CN is used as stationary phase and acetone and water (40:60 v/v) as mobile phase. The highest values of the parameter Δ(ΔG°) and alfa for cortisone and hydrocortisone was observed in case of using CN as stationary phase and water-acetonitryle (40:60 v/v) as mobile phase.      

Encapsulation of Satureja montana essential oil in β-cyclodextrin

Inclusion complexes between the Satureja montana essential oil and β-cyclodextrin were prepared by co-precipitation method with the four oil to β-cyclodextrin ratios of 5:95, 10:90, 15:85 and 20:80 (w/w) in order to determine the effect of the ratio on the inclusion efficiency of β-cyclodextrin for encapsulating oil volatiles. The characterization of the complex involved the analysis of the initial essential oil, the surface and the total extracted oils. The retention of essential oil volatiles reached a maximum of 93.15 % at the oil to β-cyclodextrin ratio of 15:85. Though, the maximum inclusion efficiency of β-cyclodextrin was achieved at the ratio of 20:80. The qualitative and quantitative composition of the volatiles in the total oil extracts was similar to the starting oil which is confirmed the high inhibition zone as antifungal and high antioxidant properties after encapsulation to β-cyclodextrin. This justifies the use of β-cyclodextrin as complexion agent for S. montana essential oil in the food and pharmaceutical industries.