SEC-Gradients, an alternative approach to polymer gradient chromatography: 1. Proof of the concept

A new approach to gradient chromatography of polymers is presented, in which the sample is introduced at the end of the gradient and elutes within the elution volume range typical for size exclusion chromatography (SEC). Due to the gradient the samples are retarded and elute nearly independent of molar mass at the adsorption threshold. The concept was proven for a series of narrowly distributed poly(methy methacrylate)s (PMMA) in a chloroform-tetrahydrofuran (THF) SEC-gradient. The application of the SEC-gradient to a blend of PMMA and polystyrene standards of similar molar masses, which could not be separated by SEC due to their similar hydrodynamic sizes, resulted in a clear separation according to chemical composition. Since SEC-gradients allow dissolving the sample in strong eluents, which might result in breakthrough peaks in conventional gradients, the new approach is a valuable alternative to conventional gradient chromatography.     

Characterization of amphiphilic polymers: Independent analysis of blocks in poloxamers by liquid chromatography under critical conditions

Block copolymers of ethylene oxide (EO) and propylene oxide (PO) are characterized by liquid chromatography under critical conditions (LCCC) for EO on a Diol column in acetone water 78:12 (w/w) and for PO on a poly(divinyl benzene) column in acetone water 92:8 (w/w) or on a silica based poly(ethylene glycol) phase in 45:55 (w/w). Under these conditions, the other (non-critical) block elutes in exclusion mode, which allows an independent determination of the molar mass distribution of the individual blocks. These systems allow also the identification of homopolymers. The results thus obtained are compared to those from size exclusion chromatography (SEC) with coupled density and refractive index (RI) detection, which allows the determination of the entire MMD and the chemical composition along the MMD.     

Dependence of critical condition in liquid chromatography on the pore size of column substrates

The dependence of critical condition in liquid chromatography on the pore size of column substrates was investigated by Lattice Monte Carlo simulations. In the current study, the pore was modeled by a square channel and polymer chains were modeled by both the random walk (RW) and the self-avoiding walk (SAW) models. When the polymer chains were modeled by the RW model, the critical conditions in the square channels with different channel widths remained the same as the critical condition on a single surface if the special edge effect was eliminated. For the SAW chain, the shift of critical condition with the square channel width was still observed even when the special edge effect of square channel was eliminated. This confirms the results reported in our earlier study (Macromolecules 2004, 37, 10073-10078) that the critical condition in square channel pore shifts as pore width decreases. Since the square channel pore is a better representation of the actual pore shapes in a liquid chromatography column than the slit pore, the current study confirms that the shift in critical condition with pore size is a true phenomenon. A recent experimental study also confirms the shift (J. Polym. Sci. Polym. Phys. 2009, 47, 2533-2540).     

毛细管胶束电动色谱法快速测定葛根素和大豆甙元

通过优化缓冲溶液pH值和浓度、SDS浓度和 β -CD浓度等条件 ,建立了一种毛细管胶束电动色谱法测定葛根素和大豆甙元的方法。在优化的条件下 ,两种物质在 5min内得到良好分离。葛根素和大豆甙元的峰高和质量浓度分别在 0 . 0 2～ 1. 2 0mg·mL-1和 0 . 0 2～ 1. 0 0mg·mL-1浓度范围内呈良好线性。 2种物质基于迁移时间和峰高的相对标准偏差分别为 0 . 4 3%、0 . 2 2 %和 2 . 0 0 %、1. 39%。检出限分别为0. 0 0 5mg·mL-1和 0 . 0 0 4mg·mL-1。该方法被用于分析葛根和葛根芩连片实际样品 ,得到令人满意的结果。     

Microstructural characterization of aromatic copolyesters made by step reactions,by gradient polymer elution chromatography

The potentials of Gradient Polymer Elution Chromatography (GPEC) in both the Reversed‐Phase (RP) and Normal‐Phase (NP) mode, for the characterization of aromatic copolyesters made by step reactions, according to their chemical microstructure, were studied. Hereto, a number of copolyesters, varying in molar mass and chemical composition (CC) were synthesized, which allowed a systematic study on the effects of those parameters in GPEC. By RP‐GPEC, highly detailed separations were obtained. Information on chemical composition differences could, however, only be obtained for the lower molar masses. From these results, qualitative evidence for differences in the chemical microstructure of two strongly resembling copolyesters was found that could not be obtained by other methods such as SEC and NMR. Nevertheless, it was found difficult to unambiguously assign observed differences in the high molar mass parts of RP‐GPEC chromatograms. Therefore, RP‐GPEC must mainly be considered as a versatile, qualitative fingerprinting tool. In contrast, NP‐GPEC provides more and quantitative information on microstructural differences. By a combination of SEC and NP‐GPEC the Molar‐Mass‐Functionality‐Type‐Distribution (MMFTD) of the (co)polyesters, and the Molar‐Mass‐Chemical‐Composition‐Distribution (MMCCD) of the fraction containing two alcoholic end groups of the copolyesters could be studied. Significant differences between strongly resembling copolyesters were found which, for the MMCCDs, can only be the cause of the relative importance of reaction kinetics in step reaction copolymers. This makes the assumption that a predictable, theoretical statistically determined CCD is formed in all cases, questionable. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 183–201, 1999     

Fast determination of tobramycin by reversed-phase ion-pair high performance liquid chromatography with a refractive index detector

A simple and direct method without a derivation step for routine analysis of tobramycin has been developed. This method used reversed-phase ion-pair high performance liquid chromatography (HPLC) with a refractive index (RI) detector and a C18 column which is stable at pH above 1.00. The presence of 4.50 mg·mL^-1 trifluoroacetic acid (TFA) in the mobile phase improved the protonation of tobramycin and the formation of ion-pairs, and thus reduced its hydrophility. This unique separation–detection combination showed good linearity with correlation coefficients 0.9996 in the concentration range of 0.25–2.50 mg·mL^-1. The quantitation limit and detection limit were determined to be 0.23 mg·mL^-1 and 0.071 mg·mL^-1, respectively. Tobramycin was recovered in 98.00%, 98.84% and 99.64% for tobramycin solutions at concentrations of 2.25 mg·mL^-1, 1.50 mg·mL^-1 and 0.75 mg·mL^-1, respectively. The relative standard deviations for six spiked samples ranged from 0.20% to 2.40%, indicating a good reproducibility of this method.     

气相色谱法测定黄瓜中百菌清含量的不确定度评定

本文介绍了气相色谱法测定黄瓜中百菌清含量的不确定度评定方法,分析了测量过程中不确定度的来源,对该方法所得分析结果的已识别来源的不确定度影响进行评价.黄瓜中百菌清残留的评定结果为(0.0319±0.0016)mg·kg-1;k=2 P=95%.     

凝胶层析法测定蛋白含量的方法

利用蛋白纯化仪建立一种凝胶层析测定蛋白含量的方法,采用HiTrapTMDesalting 5×5 mL色谱柱,流动相为超纯水,以蛋白浓度为横坐标,以蛋白出峰面积为纵坐标,建立标准曲线。与BCA试剂盒法比较,BCA试剂盒法相对误差范围为9.13%～144.00%,此法的相对误差范围为0.78%～44.72%,可见凝胶层析法测定结果准确性高,操作简单,快速,是一种可行的测蛋白含量的方法。     

离子色谱法测定化妆品中的海藻糖

建立了一种高效阴离子交换-脉冲安培检测(HPAE-PAD)测定化妆品中海藻糖的方法。采用不同的样品前处理方法,用METROSEP CARB 1分离柱(150 mm×4.0 mm)进行分离,以200.0 mmol·L-1的NaOH溶液为流动相进行洗脱,7 min内可完成对样品的分析。结果表明,海藻糖的检出限为0.02 mg·L-1,峰面积的相对标准偏差为0.17%,保留时间的相对标准偏差为0.28%;化妆品中常见的甘油和丙二醇不会对其测定产生干扰,平均回收率为95.2%～99.2%。     

Fluorescence technique for the determination of low critical micelle concentrations

A technique for determining low critical micelle concentrations (CMC) by means of a hydrophobic fluorescence probe has been developed. The amount of the fluorescent probe at the CMC is so small that the effect of the probe on micelle formation is negligible. The fluorescence intensity was measured at fixed dye/surfactant ratios, and it decreased with concentration. A quantity proportional to fluorescent quantum yield was calculated and found to be high for concentrations of surfactant above the CMC and almost zero below the CMC, giving a distinct break in the quantum yield vs. the concentration curve.     

离子液体作薄层色谱添加剂对麻黄碱分离的影响

以1-烷基-3-甲基咪唑基四氟硼酸盐类离子液体作为薄层色谱展开剂添加剂,考察了对4种麻黄碱分离的影响。添加离子液体能有效改善麻黄碱的展开效果及分离选择性,而且所有分析物的Rf值随离子液体浓度的增加呈规律性的变化,即先增加后保持不变。咪唑基离子液体能有效抑制硅胶基固定相表面自由硅羟基的有害作用。     

利用裂解气相色谱分析丙烯酸树脂的组成

采用裂解气相色谱仪迅速获得了溶剂型丙烯酸树脂中溶剂和合成树脂的组成。对于溶剂系统,柱箱从45℃开始,保温5 min,以5℃/min的速率升到200℃,保温5 min,裂解温度和裂解时间分别为200℃和10 s;对于固体树脂,柱箱从40℃开始,保温5 min,以7℃/min的速率升到250℃,保温5 min,裂解温度和裂解时间分别为550℃和30 s。对于含量较高的组分,其相对标准偏差<0.5%。树脂组成的分析结果与验证结果符合良好。该方法简便易行,对于丙烯酸树脂及其涂料生产企业开发新产品和了解市场信息,具有重要的参考价值。     

A theory of topological separation of linear and star-shaped polymers by two-dimensional chromatography

Topology influences the size of macromolecules, but polymers are usually distributed with respect to molar mass, which also results in the size distribution within a polymeric sample. Due to this fact size-exclusion chromatography (SEC) is not able to separate even moderately polydisperse polymers by topology; the same is also true for the adsorption chromatography (AC). The full separation by molar mass and topology is not possible by any single mode of chromatography. These problems can be solved by means of two-dimensional chromatography which combines SEC and AC mechanisms. A theory of interactive chromatography of linear and star-shaped ideal-chain polymers is used to analyze two-dimensional chromatographic separation of polydisperse linear and star polymers. Basing on this theory, we simulate 2D-chromatograms for model mixtures of polydisperse linear and star-shaped polymers of equal average molar mass, and demonstrate that 2D-separation of such polymers by topology is possible. A possibility to separate symmetric and very asymmetric stars by 2D-chromatography is predicted. The influence of the molar-mass heterogeneity, pore size and adsorption interaction parameter on the 2D chromatographic pattern is analysed, and the conditions for a good separation of linear and star polymers are formulated. The theoretical results are in a qualitative agreement with the experimental data, which have been reported previously by Gerber and Radke.     

工业中气相色谱法对氧含量的测定

讨论了利用空气作为标准气校准气相色谱的可行性,以及采用氢气作为载气,测出空气及氮中的氩含量。论述了测量氮中舍氧及氢中含氧的方法。     

Characterization of branched polymers by size exclusion chromatography coupled with multiangle light scattering detector. I. Size exclusion chromatography elution behavior of branched polymers

The elution behavior of branched macromolecules during their separation by size exclusion chromatography (SEC) was studied. The elution behavior of branched polymers was investigated using samples of randomly branched polystyrene and star branched poly(benzyl methacrylate) of different levels of branching by means of a SEC chromatograph coupled with a multiangle light scattering detector. Abnormal SEC elution behavior was found to be typical for highly branched polymers. After a normal elution at small elution volumes the molar mass and root mean square radius of the eluting molecules increased with increasing elution volume. Several SEC experiments were carried out to find explanation for this effect and SEC separation was compared with the separation by thermal field flow fractionation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1588–1594, 2001     

Temperature gradient interaction chromatography of low molecular weight polystyrene

Separation of low molecular weight polystyrene (PS) by temperature gradient interaction chromatography (TGIC) is reported. As in the separation of high molecular weight PS, temperature is an efficient variable to control the retention of low molecular weight PS in the reversed phase HPLC separation. However, a right choice of the eluent, typically a marginal solvent for the polymeric solute of interest, is crucial for the temperature to play an effective role in the retention control. For an example, PS oligomers were well separated by TGIC under the isocratic elution condition of C18 bonded silica and methanol as the stationary and the mobile phase, respectively.     

顶空气相色谱法测定乙炔和氯乙烯

阐述了以硅油Ⅲ型与β,β′-氧二丙腈为混合固定液，上试101白色担体为固定相，运用1102G型气相色谱仪的FID检测器，采用顶空气相色谱法测定氯乙烯生产过程产生的盐酸溶液中的乙炔和氯乙烯。     

Liquid chromatography at critical conditions of polyethylene

Olefin copolymers are of increasing scientific interest due to their important application potential. Liquid chromatography can deliver important information, especially on their molecular structure. In particular, liquid chromatography at critical conditions (LCCC) is of interest because, in this chromatographic mode, the elution is molar mass independent for a given repeat unit. LCCC is conducted at conditions where the entropic effect of size exclusion is equal to the enthalpic effect of interaction between the macromolecules and the stationary phase and can be used to separate copolymers as well as some homopolymers containing one single repeat unit but having different end groups. For the first time, critical conditions for linear PE were experimentally identified by using porous graphite (Hypercarb™) as the stationary phase, and either 1-decanol/ortho-dichlorobenzene (ODCB), 1-decanol/1,2,4-trichlorobenzene (TCB), n-decane/ODCB, or n-decane/TCB as the mobile phase at 160 °C. The identified critical conditions for PE using the above approach in the above solvents have been verified to be correct, barring slight deviations, by two different techniques which were previously used to determine critical conditions for polymers soluble at ambient temperature. The critical conditions for polyethylene were applied to separate statistical copolymers of ethylene/1-octene with similar molar mass.     

稀土元素螯合物分离和色谱定性测定

将化学性质近似的稀土元素转化为稳定而定量挥发的螯合物,可用气相色谱把他们良好分离。本文用H(TPM)配位体合成了Sc、Y、Er、Eu和La的螯合物,考察了其气相色谱的分离行为,讨论了该螯合物在气相色谱条件下,保留时间随稀土元素离子半径增大而增长的规律。