The determination of the molecular weight distribution of amylose by gel permeation chromatography

The universal calibration for gel permeation chromatography (GPC) has been applied to amylose and dextrans. The molecular weight distribution of amylose has been measured starting from known data on dextrans. The agreement found between the molecular weight averages resulting from GPC and those obtained by other methods justifies the procedure followed. The GPC measurements were performed with dimethylsulfoxide as the elution solvent and deactivated silica gel (Porasil) as the column-filling material.     

气相色谱和气相色谱-质谱法测定食品中乙草胺残留

建立了气相色谱和气相色谱-质谱法检测10种植物源性和动物源性食品中乙草胺残留量检测方法.粮谷类和动物源性样品采用乙腈提取,GPC结合硅胶固相萃取柱净化;蔬菜类样品采用乙酸乙酯提取、硅胶固相萃取柱净化;元葱等样品先进行微波消解,然后采用乙酸乙酯提取,硅胶固相萃取柱净化.气相色谱和气相色谱-质谱联用法检测.两种方法检出限均为0.004 mg/kg; 在0.01～0.16 mg/L范围内均呈良好的线性关系,相关系数为0.9998和0.9997;在0.01、0.02和0.05 mg/kg的添加水平下,添加回收率在70%～102%之间;相对标准偏差(RSD)均小于10%.     

Reactions of polystyryl anions with carbon dioxide and oxygen. Analysis of products by silica gel chromatography

Polystyryllithium was prepared by anionic polymerization. This “living polymer” and the polystyrylmagnesium bromide derived from it were treated with carbon dioxide (solid or gas). The highest yields of carboxylic acid were obtained when solid carbon dioxide was used with polystyryllithium or by treatment of polystyrylmagnesium bromide with gaseous carbon dioxide. The products from the reaction of polystyryllithium with oxygen were polymeric ketone X, the alcohols IXa and IXb, and coupling products (e. g., XI). The various functionalized and unfunctionalized polystyrene products were isolated by chromatography on silica gel and were characterized by gel permeation chromatography (GPC), thin layer chromatography (TLC), and high-performance liquid chromatography (HPLC) in combination with chemical transformations.     

Determination of spinosad in vegetables and fruits by high-performance liquid chromatography with UV and mass spectrometric detection after gel permeation chromatography and solid-phase extraction cleanup on a 2-layered column

A simple and reliable method was developed for the determination of spinosyns A and D, the active ingredients of spinosad, in vegetables and fruits, by high-performance liquid chromatography with UV detection (HPLC-UV) and confirmation by mass spectrometry (MS); the method uses selected gel permeation chromatography (GPC) and a 2-layered column for solid-phase extraction system. An aliquot of the crude sample extract obtained by acetonitrile extraction is loaded into the GPC system. The fraction containing spinosyns A and D is selectively collected and loaded directly onto a 2-layered column consisting of graphitized carbon (upper layer) and cyclohexyl-bonded silica gel (lower layer). After the column is washed with the GPC mobile phase acetone-cyclohexane (3 + 7), the column is eluted with acetonitrile containing 2% triethylamine. The eluate is used for HPLC-UV/MS analysis. Average recoveries from fortified cabbage, green perilla, fig, and strawberry at analyte concentrations of 0.05 and 0.25 microg/g were >85%, and the relative standard deviations were <9%. The detection limits for spinosyns A and D in green perilla were 0.005 microg/g by UV detection and 0.001 microg/g by MS detection.     

Analytical multimethod for the determination of low volatile organic pollutants in sediments and sewage sludges

By means of selected target compounds with different physical and chemical properties an analytical method has been developed for the analysis of a wide variety of low volatile xenobiotics in sediments and sewage sludges. After an exhaustive extraction at different pH values first high molecular matrix compounds have been separated by GPC. Fractionation of the samples into five separate groups of substances has been performed by successive column chromatography using deactivated alumina and silica gel. For the determination of phenols a derivatization step with pentafluorobenzolychloride has been incorporated into the sample preparation. Removal of sulphur and aliphatic hydrocarbons has been accomplished by an additional clean up with TBA-sulfite reagent and silica gel. Recoveries of the most target compounds exceeded 80%.     

Radiation effect on polystyrene deposited and grafted on silica gel

The effect of radiation on polystyrene was studied in the presence and absence of silica gel by molecular weight measurement with GPC. Polystyrene crosslinked under vacuum in the absence of silica gel, but it either crosslinked or degraded by radiation, depending on the molecular weight of the polymer in the presence of silica gel. Part of the deposited polymer bonded to silica gel by radiation; the G value for graft-chain formation is in the range of 0.01–0.1. Irradiation of polystyrene grafted on silica gel resulted in degradation of the graft chain because of the transfer of energy from silica gel. The G value for main chain scission was about 2 when graft polymer was irradiated in the absence of homopolymer. The degradation of graft polymer was suppressed when the polymer was irradiated in the presence of homopolymer, and the amount of unextractable polymer from silica gel increased with increasing irradiation. This adds evidence to the estimation that an increase in grafting percent coupled with a slight decrease in molecular weight at a later stage of radiation-induced polymerization of styrene adsorbed on silica gel is due to a secondary effect of radiation on the polymer.     

Application of gel permeation chromatography to polyelectrolytes: Salt rejection mechanism and molecular-weight distribution

Gel permeation chromatography (GPC) of polyelectrolytes in dimethylformamide (DMF) is studied. Three methods of monitoring elution (conductimetry, viscosimetry, refractometry) are used to investigate the molecular-weight distribution and, independently, the chemical composition expressed in terms of the ionic charge density as a function of the chain length in two copolymers of acrylonitrile and sodium methallylsulfonate. The distribution on the gel of the neutral salt NaNO₃ added to the DMF and used for elution is discussed in terms of Donnan exclusion; in addition, it is concluded that to obtain the correct molecular-weight distribution, GPC measurements must be performed with an eluent containing a neutral salt at a concentration at least 5 × 10^?2M to prevent electrostatic exclusion. The main difficulty in reaching rigorous conclusions comes from the dependence of the calibration curve on the salt composition of the eluent owing to interactions—dependent on the quality of the solvent—between the polystyrenes used as standards and the porous silica gel. Nevertheless, this perturbation is small and the agreement between the average molecular weights obtained by GPC and by direct determination is good and indicates that the universal calibration proposed for neutral polymers is also valid for polyelectrolytes.     

Clean-up of plasma extracts by gel permeation chromatography during analysis of isosorbide nitrates by capillary gas chromatography.

This work describes how gel permeation chromatography (GPC) can be used for sample clean-up to reduce the fouling of the column in an automated on-column injector. The analytes were isolated from plasma together with the internal standard (isomannide dinitrate) by liquid-liquid extraction on Extrelut silica columns. The extracts were evaporated and reconstituted in tetrahydrofuran for separation of the analytes from non-volatile plasma components by GPC on a styrene-divinylbenzene column with 100 A pore size. A programmable autosampler with an additional three-way valve was used for injection and fraction collection. The molecular weight fraction between 100 and 700 a.m.u. was collected and transferred to the on-column autosampler for capillary gas chromatography on a 30-m column butt-connected to a 0.2-m pre-column. The pre-column was replaced after 50 sample injections. When the GPC purification was excluded from the work-up procedure a deposit of non-volatile components was formed at the injection zone of the pre-column which resulted in excessive peak-tailing after only five or six injections of plasma extract. The limit of determination was 0.2 ng/ml plasma for isosorbide dinitrate and 0.4 ng/ml for the mononitrates.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. VII. Effect of pretreatment temperature of silica gel on styrene–silica gel system

To investigate the reaction mechanism of radiation-induced polymerization of styrene adsorbed on silica gel, the effect of pretreatment temperature of silica gel was studied. Preheating of silica gel was carried out at 200, 500, and 800°C. The number of silanol groups of silica gel surface decreased as preheating temperature increased. The rate of polymerization on the silica gel preheated at 500°C was faster than that at 200°C, but the polymerization rate on the silica gel preheated at 800°C was the lowest. These results suggest that rate of polymerization on the silica gel is affected by the conditions of silica gel surface such as the number of silanol groups and the pore size. At the same monomer conversion, percent grafting decreased as preheating temperature of silica gel increased. The GPC spectra of both graft polymers and homopolymers have two peaks at all preheating temperatures. The monomer conversion of low molecular weight peaks of graft polymers decreased as preheating temperature of silica gel increased. This result suggests that there is a probability that the grafting sites of low molecular weight peaks of graft polymers somehow interact with silanol groups.     

小分子大豆多肽的分离检测研究

最近的研究表明,多肽特别是二肽和三肽更易被人体吸收,此外小分子大豆肽还具有很好溶解性、稳定性、低粘度和许多生理活性,如降血压,降胆固醇,抗疲劳等,因此大豆肽广泛应用在食品、化妆品、药品等领域 [1,2].     

可保眼滴眼凝胶和素高捷疗眼膏中小分子肽类的对比分析

通过采用先进的凝胶渗透色谱(GPC)和凝胶过滤色谱(GFC)方法,分析了素高捷疗眼膏和可保眼滴眼凝胶中小分子肽的相对分子质量和紫外吸收特征,证明两者确实含有一种相对分子质量约为1 900的小分子肽类生长因子,并且相对分子质量相同。     

Synthesis of siloxane stationary phases for capillary gas chromatography and supercritical fluid chromatography

A comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, ¹H NMR, ²⁹Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free-radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV-1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography.     

Application of thin layer and high performance liquid chromatography to the separation and determination of cephalexin in cephradine,in bulk powder and in pharmaceuticals

Summary A thin-layer chromatographic procedure for the quantitative determination of cephalexin in cephradine formulations is described. The thin-layer chromatography is carried out on a silica gel layer and the quantitation is by UV scanning of the chromatogram. The procedure was transferred to high-performance liquid chromatography on a microparticulate silica gel column with a similar eluent system. The cephalexin content of a few commercial cephradine samples is determined by using these techniques. The results of these procedures are compared to those obtained with high-performance liquid chromatography on a C 18 reverse phase column.     

Improvements of a combined size exclusion chromatography and solid phase extraction approach for the clean-up of marine sediment samples for trace analysis of pesticides

 Two methods based on gel permeation chromatography (GPC) [size exclusion chromatography] for the analysis of traces (ng/kg) of nitrogen and phosphorus containing pesticides (like triazines or phosphothionates) from marine sediment samples are compared: A macro GPC with Biobeads SX-3 and a chromatography on a high-performance (HP-GPC) column with UV-detection. Results for eight triazine herbicides, two triazine metabolites, the phenylurea derivative linuron, two acetanilides and two organophosphorus compounds are given. Concentrations obtained with the HP-GPC are compared with those obtained with a macro GPC approach in an earlier study. Received: 4 October 1996/Revised: 20 December 1996/Accepted: 24 December 1996     

Arginine as an effective additive in gel permeation chromatography

A major problem in gel permeation chromatography (GPC) or size exclusion chromatography is non-specific binding of applied proteins to the column matrix (stationary phase). We have tested an aqueous arginine solution as the GPC mobile phase on silica-based and polymer-based columns, using mouse monoclonal antibody and recombinant human activin, interleukin-6, basic fibroblast growth factor, and interferon-gamma as model proteins. We observed that addition of arginine to the mobile phase improves separation of the proteins and their soluble aggregates from the GPC columns, which suggests that arginine is an effective additive for the GPC mobile phase.     

Study of silica gel and copper silicate gel solubilities in high performance liquid chromatography

Summary After summarizing published results on silica gel and alkyl-bonded silica gel solubilities, the experimental solubility of unmodified silica and copper silicate gel (used in ligand exchange chromatography) in watermethanol-ammonia and water-acetonitrile-ammonia mixtures are given. These results demonstrate that silica gel solubility, measured by a static method, varies greatly with the water volume fraction of a ternary mixture. Curiously, no influence from the organic nature of the solvent was demonstrated. This observation is inconsistent with the fact that the copper silicate gel used in ligand-exchange chromatography with water-methanol-ammonia as mobile phase is attacked more rapidly than with water-acetonitrile-ammonia.An explanation based upon the variations of acid-base properties of silicic acid versus mobile phase dielectric constant values in conjunction with the methanol protophilic properties is proposed. Finally, it is shown that chromatographic columns filled with copper silicate gel have lifetimes of several months, if they are used with a procolumn (of copper silicate gel) and with acetonitrile as organic solvent with a volume fraction greater than 0.5 in the mobile phase.     

Radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. VI. Temperature dependence and effects of additives on methyl methacrylate–silica gel system

To elucidate the reaction mechanism of radiation-induced polymerization of methyl methacrylate adsorbed on silica gel, the temperature dependence and effects of acetone and pyridine were investigated. It was found that even at ?78°C the polymerization rate was quite fast. The amounts of high molecular weight GPC peaks of both graft polymers and homopolymers increased with increasing irradiation temperature. The activation energy of the adsorbed state polymerization was low compared with that of bulk polymerization. The low molecular weight peaks of homopolymers decreased with acetone addition but were almost unaffected by pyridine. The low molecular weight peaks of homopolymers were thus polymerized by an anionic mechanism. In the methyl methacrylate–silica gel system both radical and anionic polymerization take place at the same time in formation of graft polymers and homopolymers. A reaction mechanism for the methyl methacrylate–silica gel system was proposed based on the results obtained to date.     

A Gas Chromatographic Analysis of Light Hydrocarbons on a Column Packed with Modified Silica Gel

IntroductionAnalysis of light hydrocarbons achieved by gas-solid chromatography is important in petrochemical industry, environmental protection and some other areas. A variety of columns have been used, including conventional packed column1, Al2O3 and graphitized carbon black PLOT column2, 3 and silica gel SCOT column4. Al2O3 PLOT column is excellent for the analysis of light hydrocarbons. Conventional packed column also has its own advantages, such as easy column preparation, resistanc…     

HPSEC of Cationic Polymers on a Polyamine Support

Abstract

High performance steric exclusion chromatography of polyvinyl-pyridines (PVP) on silica particles coated with polymerized amine (SynChropak CATSEC) is described. PVP standards were analyzed first on a conventional neutral support (SynChropak GPC), and the results were compared with the amine coated silica. Conditions for analysis were then examined for optimization. Linear recovery was observed for a PVP standard of M.W. 3,000.     

聚甲氧基硅氧烷及其功能化产物研究Ⅱ.分子结构表征

通过正硅酸甲酯(TMOS)的水解缩合反应制备了聚甲氧基硅氧烷(PMOS)，其分子式可表示为：[SiOa(OH)b(OCH3)c]n。用丙烯酸-2-羟乙酯(HEA)进行酯交换后，制的功能化产物聚丙烯酰氧基甲基硅氧：烷(PAMOS)，其分子式可表示为：[SiOd(OH)c(OCH3)f(OCH2CH2OCOCH=CH2)g]k。通过二氧化硅分析、红外光谱(FTIR)、凝胶渗透色谱(GPC)等方法确定了分子式中a、b、c、n及d、e、f、g、k的值，是一种比较方便、快捷且准确的方法。