Rapid analysis of starch, amylose and amylopectin by high-performance size-exclusion chromatography

Starch components, amylose and amylopectin, were analyzed by high-performance size-exclusion chromatography. These two-components were separated using a two-column system (E-Linear and E-1000) and dimethyl sulphoxide as the mobile phase. The void volume (V0 = 2.22 ml) was measured using tobacco mosaic virus. Column calibration was accomplished with dextrans of known average molecular weight (Mw range = 10,100-2,000,000). The elution volume of amylopectin (Ve = 2.5 ml) indicated that this starch component was fractionated on the column system despite its very large molecular size. Standard curves were prepared from various mixtures of purified corn and wheat amylose and amylopectin. From the linear relationships obtained, the percentages of both components in corn and wheat starches were determined. The method developed proved useful to monitor the purity of amylose and amylopectin preparations, and to estimate rapidly the amylose:amylopectin ratio of starch samples.     

Peculiarities of polyacrylamide analysis by aqueous GPC

Various commercially available stationary phases of gel permeation chromatography (GPC) were tested to determine their effectiveness in aqueous exclusion chromatography. It was found that controlled pore glass (GPG) is the most suitable material for the separation of polyacrylamides and poly(acry1amide-co-sodium acrylate), dextrans, and poly(sodium styrene–sulfonates) in 0.1M aqueous Na₂S0₄ solutions of ionic strength 0.3. A calibration curve was established by using broad molecular weight distribution polyacrylamide standards in a trial and error procedure. To avoid artificial oscillations on the evaluated distribution curves a cubic B-spline representation of the calibration curve was used instead of the conventional polynomials. By applying this system the solution instability of polyacrylamides was observed by GPC and is discussed because of its general importance to the applicability of indirect molecular weight determination methods for polyacrylamides. The effectiveness of aqueous GPC was demonstrated in an evaluation of thermal degradation measurements of polyacrylamides. Finally, the feasibility of universal calibration of aqueous GPC by means of poly(sodium styrene–sulfonates) was investigated. It is apparent that in spite of some problems concerning adsorption of the polymer universal calibration is a successful tool for calibrating aqueous GPC.     

以六氟异丙醇为溶剂的聚甲醛凝胶渗透色谱研究

研究了均聚和共聚甲醛在六氟异内醇中的凝胶渗透色谱（ＧＰＣ）。对共聚甲醛出现的缔合现象从主链结构作了解释，并找到了避免缔合的方法；对共聚甲醛ＧＰＣ淋洗曲线上的异常小峰从聚合机理角度进行了探讨，推测得到小峰所对应的物质。确定了以六氟异丙醇为溶剂的聚甲醛的凝胶色谱表征方法，并探索采用凝胶色谱－粘度计联用法得到分子量和分子量分布结果。     

Study of the ceric ion behavior on the initiation of butyl acrylate polymerization onto amylose

A study of the Ce(IV) ion consumption during graft polymerization of butyl acrylate with amylose was carried out. The Ce(IV) consumed was ca. 80% and the ratio of Ce(IV) to anhydroglucose units was 1/15. Poly(butyl acrylate) (PBA) chains were isolated from the grafted copolymer by the perchloric acid hydrolysis method. The molecular distribution was obtained by gel permeation chromatography (GPC). The number-average molecular weight (M_n) of the grafted chains was 276,000 and the weight-average molecular weight (M_w) was 1,320,000. The total number of grafted chains (mmol) ranged from 0.4410^?3 to 8.710^?3 (amylose from 0.08 g to 1.23 g). Frequency of grafting ranged from 1042 to 704.     

A study of aqueous solutions of dextrans by gel permeation chromatography using a multiple detection system

We studied the elution of dextrans in gel permeation chromatography (GPC) using a low-angle laser light-scattering (LALLS) system to monitor the molecular weight and the standard refractive index (RI) detector to measure the concentration. In pure water the dextrans show bimodal chromatograms of the RI response as well as of the LALLS response. The first eluted peak reflects the macroion exclusion due to the repulsion between negatively charged macromolecules and equally charged gel. In spite of the resulting distortion of the chromatograms, correct values of the weight-average molecular weights (M?_w) are obtained from them. If instead of pure water a salt solution (0.1 M KNO₃) is used as eluant, the charge effect is completely suppressed and single-peak chromatograms are found. Again correct values of M?_w are obtained, but number-average molecular weights turn out to be too large owing to axial column dispersion in the coupling arrangement. By introducing a spreading factor, values of M?_n could be corrected. Investigations of the charge effect were also carried out by monitoring the electric conductivity of the eluted dextran zone. In this way, the phenomenon of ion inclusion, evidently provoked by charged dextran molecules, was observed.     

On the number-average molecular weight of poly(1,4-trans isoprene) determined by conventional GPC

We became aware, in the course of our on-going research, that the number-average molecular weight of poly(1,4-trans isoprene) determined by conventional gel permeation chromatography (GPC) in tetrahydrofuran (THF) using polystyrene standards differs from its true value by a factor 2. As far as we know, the Mark-Houwink coefficients of this polymer in a widespread GPC eluent such as THF have never been determined. We provide in this contribution a simple relationship between the number-average molecular weight of poly(1,4-trans isoprene) determined by GPC in THF using polystyrene standards and its true value.     

Gel permeation chromatography with interference refractometry for the rapid assay of polydisperse dextrans in biological fluids

A semi-automatic system incorporating an ultra-sensitive interference refractometer coupled to a dual-column gel permeation apparatus has been devised for measurement of the molecular size distribution of dextrans in small samples of serum and urine. The system was calibrated with seventeen defined dextran fractions with a range of 1200-250,000 weight average molecular weight (Mw). Urine samples were prepared for analysis by passage through small ion-exchange columns; serum was pretreated by precipitation with trichloroacetic acid and centrifuged before the ion-exchange treatment. Internal standard (dextran, 2 X 10(6) Mw) was added to each sample before pretreatment. Data were obtained in a form suitable for computerised analysis.     

Crystallinity and the effect of ionizing radiation in polyethylene. IV. Effect of segregation of low molecular weight chains on determination of main-chain scission in linear polyethylene

Different single crystal preparations of polyethylene with (unfractionated) and without (partially fractionated) low molecular weight chains were irradiated at room temperature. G(crosslink) was determined from the gel point. It is shown that in addition to the molecular weight and molecular weight distribution of polymers, G(crosslink) is determined by three more parameters: thickness of crystalline core, amount of amorphous surface layer, and degree of interlamellar contact. Unlike unfractionated polyethylene, partially fractionated polyethylene showed almost 100% gel at about 250 Mrad. To obtain the same amount of gel, unfractionated polyethylene required a much higher dose than that required by partially fractionated polyethylene. Molecular weight distribution of sol fractions of unfractionated and partially fractionated polyethylene was studied by gel permeation chromatography (GPC) and the solubility data analyzed by Charlesby–Pinner plots. It has been shown that the unattainability of 100% gel from unfractionated polyethylene is due to segregation of low molecular weight chains during crystallization which need very high doses for complete gelation.     

Synthesis of Surface-Functionalized Poly(styrene-co-butadiene) Nanoparticles via Controlled/Living Radical Mini-emulsion Copolymerization Stabilized by Ammonolyzed Poly(styrene-alt-maleic anhydride) (SMA) RAFT Agent

A process for reversible addition-fragmentation chain transfer (RAFT) radical polymerization in a mini-emulsion system stabilized by ammnolyzed poly(styrene-alt- maleic anhydride) copolymer (SMA) as an amphiphilic macro RAFT agent has been applied to the copolymerization of styrene and butadiene to prepare nanoparticles. First, for the RAFT polymerization of styrene, the results of molecular weights (Mns) and polydispersity index (PDIs) determined by GPC showed that the RAFT mini-emulsion polymerization of styrene exhibited good controlled/living nature with a lower degree of aminolysis (～30%). Second, for the copolymerization of styrene and butadiene, before the gel point the molecular weight growth was followed during the polymerization by GPC and the results revealed that the GPC curve moves to the higher molecular weight indicating the formation of the copolymer. At low conversion, molecular weights (Mns) are in good agreement with theoretical prediction. The microphase separation of the copolymer nanoparticles was confirmed by transmission electron microscopy (TEM).     

陶瓷先驱体——含钛聚碳硅烷凝胶渗透色谱校准方程研究

采用以气相渗透法测定了数均分子量的宽分布含钛聚碳硅烷作标样,通过计算机辅助建立了具有较低分子量和较高支化度的陶瓷先驱体聚合物——含钛聚碳硅烷的凝胶渗透色谱校准方程ｌｎＭ＝２０．９－０．８４３Ｔ。将这一方程应用于实际样品分析时,测定的数均分子量值与气相渗透法测定结果基本一致,偏差绝对值小于８．０％。钛的引入使其与聚碳硅烷本体的校准方程相差很大。     

液体色谱,凝胶色谱分析低聚芳砜及其双烯大分子单体

本文用液相色谱和凝胶色谱对双酚A、双酚S型低聚芳砜及α,ω-双甲基丙烯酸聚芳砜酯大分子单体进行了组分分析,通过改合成条件、测定数均分子量等辅助手段确定液相色谱各峰的归属,计算其分子量及分子量分布指数,并对两种方法测定的结果进行了比较。用液相色谱观察低聚体每个组分的含量及其反应过程中的消长情况比凝胶色谱清晰。     

Preparation and Separation of C60 Photopolymers for the Physical Chemistry Instructional Laboratory

We report the development of a new physical chemistry laboratory exercise that uses gel permeation chromatography (GPC) to study pristine and photopolymerized C₆₀ materials. GPC is a well-known method for probing molecular weight distributions because of its ability to separate macromolecules based upon size. In this experiment students are interested in the changing molecular weight distribution with irradiation. Students inject both pristine and photoirradiated C₆₀ into the system and analyze the retention time data with a differential UV detector set at 300 nm. The observation of higher molecular weight oligomers upon irradiation is consistent with intermolecular bond formation by the proposed [2 + 2] cycloaddition pathway. The implementation of this laboratory in the classroom has been very successful, generating consistently positive feedback from the students.     

Low-density polyethylene: Variation of branching frequency with molecular weight and its influence on molecular weight as determined by gel-permeation chromatography

A method for determining long-chain branching frequency and molecular weight averages for unfractionated low-density polyethylene (LDPE) by the combined use of gel-permeation chromatography (GPC) and intrinsic viscosity data has been reported (GPC–IV method). The method assumes that the number of long branches λ per unit molecular weight is a constant independent of molecular weight. Recent data reported on λ as a function of molecular weight M in commercial LDPE indicate that this assumption is not generally valid, and concern has been expressed as to the size of the errors in molecular weights calculated using this assumption. The errors associated with assuming that λ is constant were evaluated in this study by first determining the way in which λ varies with M for two typical commerical LDPE resins by fractionation and application of the GPC–IV method to representative fractions. The experimentally determined relations between λ and M were then employed in the calculation of molecular weight and molecular size averages from GPC–IV data on the original unfractonated samples. Although it was found that λ increases with molecular weight for both samples, the results indicate that the error involved in assuming that λ is a constant is no greater than the precision with which molecular weight averages can be evaluated by GPC.     

凝胶渗透色谱在高聚物分子量测定中的应用

本文综述了近年来凝胶渗透色谱在油溶性和水溶性高聚物分子量测定中的应用,着重分析测试条件对水溶性样品分子量的影响并归纳了解决的办法。同时,介绍了配备紫外可见和示差折光检测器、示差和光散射检测器后凝胶色谱的应用。此外,还概述了几种常见高聚物分子量的标定和校准方法,以便多种方法相互验证,得到较准确的分子量值。     

Laser light scattering as GPC detector

The use of low angle laser light scattering (LALLS) as a detector in gel permeation chromatography (GPC) is discussed. The advantage of this technique is primarily based on the ability of LALLS to continously measure the absolute molecular weight and also to detect minute concentrations of high molecular weight species such as microgel. The weakness of the system is in the low sensitivity for low molecular weight material. In this paper, our experience of the KMX-6 from Chromatix illustrates the possibilities for the characterization of polymers by the combination of LALLS and GPC. The applications discussed are mainly from our work with polyethylene and poly(vinyl chloride). Special emphasis is given to the determination of long chain branching and microgel.     

Molecular Weight Characterization and Structural Properties of Controlled Molecular Weight Dextrans Synthesized by Acceptor Reaction using Highly Purified Dextransucrase

ABSTRACT

Controlled molecular weight dextrans were synthesized using a highly purified dextransucrase from Leuconostoc mesenteroides NRRL B-512F in a multi-step process. Maltose was used as acceptor for the first reaction step. The purified product obtained at a given reaction step was used as acceptor for the next reaction step. Dextrans of molecular weights ranging from 1,000 to 100,000 were thus obtained with a good yield (80 %). After purification, the molecular weight distribution of the products was characterized using size exclusion chromatography coupled with low angle laser light scattering (LALLS). Polydispersity of the products was shown to be similar to that of commerical dextrans.

¹³C NMR spectra and enzymatic hydrolysis data are consistent with the fact that the enzymatically synthesized dextrans are essentially composed of α(1->6) linkages. It was observed that controlled molecular weight dextrans were less branched than commercial products obtained by acidic hydrolysis of high molecular weight dextrans.     

Application of preparative gel-permeation chromatography to studies of low molecular weight carboxy-polybutadienes

Low molecular weight carboxy-polybutadiene liquid polymers are used as the binderfuel fraction in solid composite propellants. Analytical GPC determinations of low molecular weight materials (100 through 500 molecular weight range) were previously found to correlate significantly with final propellant properties. These low molecular weight materials are being characterized, and studies of their role in determining propellant physical properties are being conducted. Sufficient quantities of material in the 100–500 molecular weight range have been isolated by using preparative scale GPC to establish the chemical nature of these materials. Infrared and chemical analysis of fractions collected by using preparative GPC also has permitted the construction of functional group distribution profiles. In addition, narrow fractions isolated over the molecular weight range of the whole polymer were analyzed for average molecular weight by vapor pressure osmometry and have been used as calibration standards for analytical GPC.     

Gel permeation chromatography followed by pyrolysis-gas chromatography-mass spectrometry via a solvent-evaporative interface

The measurement of chemical composition as a function of molecular weight has always been a challenge for analytical chemists. In this paper, we present a unique way to combine gel permeation chromatography (GPC) with pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) for this purpose. A commercially available solvent-evaporative interface, originally designed for GPC-IR measurements, was used to deposit the eluent of GPC onto aluminum foil. Small strips of aluminum foil were cut and subjected to Py-GC-MS analysis. Compared with the GPC-IR measurements, the proposed technique offers the advantage of being able to distinguish between structurally similar monomers in a complex copolymer. As an example, a copolymer composed of four monomers was analyzed. The results clearly demonstrate that this technique can be applied to complex polymeric systems to yield information regarding chemical heterogeneity versus molecular weight.     

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。     

Study on the determination of the molecular weight of polyethylene with ultrahigh temperature GPC

Ultrahigh or high molecular weights of polyethylenes (PE) and their distributions are for the first time determined at 160° or 170°C by gel permeation chromatography (GPC). The thermostability of PE at high temperatures is discussed. In order to calculate the real molecular weight of PE, a new calibration curve is established. For PE with high molecular weight more reliable and accurate results can be obtained by GPC measurements at these temperatures. The application of ultrahigh temperature GPC for polymer characterization is demonstrated in this paper.