Characterization of ethylene oxide–propylene oxide block copolymers by combination of different chromatographic techniques and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy

Block copolymers of ethylene oxide (EO) and propylene oxide (PO) are characterized by combination of two-dimensional chromatography and MALDI-TOF-MS. Liquid chromatography under critical conditions (LCCC) is used as first dimension and fractions are collected, mobile phase evaporated and diluted in the mobile phase used in second dimension (SEC or LAC). This two-dimensional chromatography in combination of MALDI-TOF-MS gives information about purity of reaction products, presence of the byproducts, chemical composition and molar mass distribution of all the products.     

Characterization of poly(ethylene glycol)-b-poly(ε-caprolactone) by liquid chromatography under critical conditions: Influence of catalysts and reaction conditions on product composition

Amphiphilic block copolymers were synthesised by ring opening polymerization of ε-caprolactone with polyethylene glycol monomethyl ether (PEG-MME) using different catalysts (boron trifluoride, sodium hydride, and tin octoate) in a one pot procedure. The products obtained were characterized with respect to their molar mass distribution and content of homopolymers using size exclusion chromatography (SEC), Liquid chromatography under critical conditions (LCCC) and MALDI-TOF-MS. The homopolymers of caprolactone could be separated from the block copolymer by LCCC on a reversed phase column in tetrahydrofurane-water mobile phases with evaporative light scattering detection (ELSD). Residual monomer could be determined under the same conditions using density detection, a separation of the copolymer from residual initiator could be achieved on a normal phase column in acetone-water mobile phases.     

Liquid chromatography at the critical condition: Thermodynamic significance and influence of pore size

Liquid chromatography at the critical condition (LCCC) is a high performance liquid chromatography (HPLC) technique that lies between size exclusion chromatography and adsorption-based interaction chromatography, where the elution of polymers becomes independent of polymer molecular weight. At LCCC, the balance between the entropic exclusion and the enthalpic adsorption interactions between polymers and stationary phases results in the simultaneous HPLC elution of polymers regardless of molecular weight. Using C18-bonded silica chromatographic columns with 5 μm particle size and different average pore size (diameter = 300 Å, 120 Å, 100 Å, and 50 Å), we report (1) the thermodynamic significance of LCCC conditions and (2) the influence of column pore size on the determination of critical conditions for linear polymer chains. Specifically, we used mixtures of monodisperse polystyrene samples ranging in molecular weight from 162 to 371,100 g/mol and controlled the temperature of the HPLC columns at a fixed composition of a mobile phase consisting of 57(v/v)% methylene chloride and 43(v/v)% acetonitrile. It was found that, at the fixed mobile phase composition, the temperature of LCCC (T_LCCC) is higher for C18-bonded chromatographic columns with larger average pore size. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2533–2540, 2009     

Liquid exclusion-adsorption chromatography: a new technique for isocratic separation of non-ionic surfactants. V. Two-dimensional separation of fatty acid polyglycol ethers

Fatty acid polyglycol esters can be fully characterized using two-dimensional liquid chromatography with liquid chromatography under critical conditions (LCCC) as the first and liquid exclusion-adsorption chromatography (LEAC) as the second dimension. LEAC is run under isocratic conditions, which allows the use of the refractive index detector, and thus accurate quantitation. Fractions from LCCC are transferred to LEAC using the full adsorption-desorption technique, by which they are focussed and reconcentrated before injection into the second dimension. This is achieved by increasing the water content of the mobile phase behind the LCCC column. Monoester oligomers of up to 20 oxyethylene units can be resolved to the baseline. Diester oligomers are partially separated in the first dimension (LCCC).     

Characterization of poly(2-oxazoline) homo- and copolymers by liquid chromatography at critical conditions

In this study liquid chromatography at critical conditions for poly(2-ethyl-2-oxazoline)s (PEtOx) has been performed for the first time in order to analyze functional PEtOx homopolymers and block copolymers. Besides the verification of the critical point of adsorption with two series of ester end group functionalized PEtOx homopolymers, to evaluate the effect of both the chain length dependence and the end group polarity, using a cyano column with a solvent combination of 2-propanol and water, also two-dimensional liquid chromatography (2D-LC) has been applied for a poly(2-oxazoline) block copolymer. The combined characterization techniques provided further information about the polymerization procedure with regard to the formation of side-products by separation of the block copolymer from the corresponding homopolymer impurities. In addition, hyphenation of LCCC with MALDI-TOF MS and ESI-Q-TOF tandem mass spectrometry verified the obtained results.     

羟基封端聚丁二烯的临界点色谱定量方法研究

为建立混合物中羟基封端聚丁二烯（HTPB）的临界点色谱定量方法，以C18为固定相，考察了HTPB在四氢呋喃-乙腈和四氢呋喃-水两种流动相体系下的临界点色谱条件。结果表明，四氢呋喃-乙腈体积比为70.7：29.3以及四氢呋喃-水体积比为92：8时，HTPB的保留值与其相对分子质量无关。将该临界点色谱方法用于胶黏剂混合组分中HTPB的测定，结果表明，HTPB在46.7~216.4 mg/L范围内呈良好线性关系，相关系数（r）>0.99，检出限为4.2 mg/L。自配HTPB和矿物油双组分样品的加标回收率为89.2%~101.1%，相对标准偏差小于0.66%（n=6）。应用该方法对市售聚氨酯胶黏剂进行检测，测定结果为HTPB成分占26.6%。该方法快速、准确，能满足聚合物混合产品的生产质量控制和失效分析的要求。     

On-line coupling of liquid chromatography at critical conditions with electrospray ionization tandem mass spectrometry for the characterization of a nitroxide-mediated poly(ethylene oxide)/polystyrene block copolymer

Coupling of liquid chromatography at critical conditions (LCCC) with on-line mass spectrometry (MS) detection was implemented via an electrospray ionization (ESI) interface, using a mobile phase containing the cationizing agent. Critical conditions established for poly(ethylene oxide) were used to characterize a poly(ethylene oxide)/polystyrene block copolymer (PEO-b-PS) in both MS and MS/MS modes. As co-oligomer molecules were successfully separated according to the PS block size, structural information could be reached from simplified MS spectra. The microstructure of this copolymer, synthesized by nitroxide-mediated polymerization, could further be unambiguously characterized in LCCC/ESI-MS/MS experiments since the PS block size could be reached by both the co-oligomer chromatographic behavior and its MS/MS pattern.     

Characterization of complex copolymers by two-dimensional Liquid Chromatography

Complex polymers were characterized by combinations of different chromatographic separation mechanisms: liquid adsorption chromatography (LAC), liquid chromatography under critical conditions (LCCC), and liquid exclusion-adsorption chromatography (LEAC). These techniques were combined off-line and on-line in two-dimensional separations. Fatty acid ethoxylates, fatty esters of polyethylene glycol (PEG) and polysorbates were analyzed by two-dimensional liquid chromatography with normal phase LAC as the first and liquid chromatography at critical conditions (LCCC) or liquid exclusion adsorption chromatography (LEAC) as the second dimension. A full separation of all oligomers to the baseline could be achieved in both dimensions. In two-dimensional separations, the offline approach is compared to comprehensive chromatography, and the scope and limitations of both techniques are discussed.     

色谱分析中离子液体的应用及其测定

离子液体作为一种优良的溶剂越来越受到人们的关注。由于离子液体特殊的物理化学性质使其在色谱分析中也得到了较广泛的应用。本文综述了离子液体在气相色谱、高效液相色谱和毛细管电泳中的应用,其中包括离子液体作为气相色谱的固定相、高效液相色谱的固定相及流动相添加剂和毛细管电泳的电解质添加剂等,并对离子液体的色谱分离检测作了详细介绍。     

采用不同疏水相互作用色谱柱从包涵体中快速制备重组人干细胞因子

为了提高重组人干细胞因子(rhSCF)的复性效率,改进了高效疏水相互作用色谱(HPHIC)纯化和复性rhSCF的方法。首先将目标蛋白溶解于8.0 mol/L脲中,然后将rhSCF包涵体的提取液直接进样到不同规格的HPHIC柱进行纯化和复性。优化了固定相配基结构和流动相组成等实验条件,结果表明,本方法可以快速地获得高质量回收率和高生物活性的rhSCF,rhSCF在40 min内即可完成复性与纯化,目标蛋白的纯度在95.5%以上,质量回收率高于49.6%。通过体积排阻色谱和基质辅助激光解吸离子化飞行时间质谱(MALDI-TOF-MS)的分析,确认rhSCF以单体存在。结果进一步证明HPHIC法是同时复性和纯化重组蛋白的有效工具。     

模拟移动床色谱分离二十碳五烯酸乙酯和二十二碳六烯酸乙酯

二十碳五烯酸和二十二碳六烯酸是两种非常重要的ω-3多不饱和脂肪酸,广泛用于膳食补充剂和药品,同时它们的生理作用并不完全相同,因此分离制备它们的高纯度单体十分必要。首先以聚苯乙烯/二乙烯基苯（PS/DVB）聚合物为固定相,在液相色谱上分离二十碳五烯酸乙酯（EPA-EE）和二十二碳六烯酸乙酯（DHA-EE）,考察了流动相、填料粒径、温度对分离的影响。然后采用粒径20 μ m、孔径10 nm的PS/DVB填料装填了8根150 mm×10 mm的半制备色谱柱,测定了半制备柱装填的均一性。最后尝试在模拟移动床（SMB）色谱上分离EPA-EE和DHA-EE的混合物,探究了Ⅱ区和Ⅲ区的流量、进料流量、进料浓度对分离的影响,结果表明SMB制备的EPA-EE和DHA-EE的相对纯度分别为91.6%和93.6%,回收率分别为97.0%和91.6%,固定相生产率为5.97 g/（L\5h）,溶剂消耗为1.52 L/g。SMB制备EPA-EE和DHA-EE具有较大的应用潜力。     

Preparation of tea glycoprotein and its application as a calibration standard for the quantification and molecular weight determination of tea glycoprotein in different tea samples by high-performance gel-permeation chromatography

Tea glycoprotein (TGC) was purified by Sephadex G-100 gel filtration, and its purity and molecular weight (MW) were determined by high performance gel permeation chromatography. The gel permeation chromatography (GPC) elution behavior of TGC on an Ultrahydrogel 500 (7.8×300 mm) column was studied using a mobile phase with various concentrations of NaCl. A dextran T system was found to be unsuitable as MW calibration standards in GPC because the MW of TGC was changed with the change of ionic concentration in the mobile phase. Thus, the purified TGC obtained in this study was standardized and used instead as the calibration standards for the determination and comparison of TGCs in tea samples collected from different geographic locations and species varieties. The GPC was run at 35°C on an Ultrahydrogel 500 column (7.8×300 mm) with a refractive index detector. Distilled water was used as the mobile phase at a flow rate of 0.6 ml·min⁻¹. The calibration curve was linear over the TGC concentration range of 0.604–6.04 mg·ml⁻¹, with a correlation coefficient of r=0.9997. The TGC mass recovery ranged from 80.4 to 93.2%, with a relative standard deviation of 5.42%. The assay method developed in this paper was found to be simple, reproducible, and reliable and, thus, ideally suitable for the quality control of TGC-derived products and raw materials.     

Pressurized planar electrochromatography

Theoretical backgrounds, development, examples of separations, constructional details and principle of action of devices of pressurized planar electrochromatography (PPEC) are presented. Development of the mode is described in respect of operating variables (composition of the mobile phase, pressure exerted on adsorbent layer, mobile phase flow velocity, temperature of separating system, etc.) influencing separation efficiency (kinetic performance, repeatability, separation time). Advantages of PPEC such as high kinetic performance, short separation time and different separation selectivities, especially relative to conventional thin-layer chromatography, are described. Examples of two-dimensional separations are demonstrated to show high separation potential of the mode when combined with conventional thin-layer chromatography (TLC). The PPEC mode is in infancy stage of development, so its challenges are presented as well.     

Microwave assisted synthesis and characterization of end functionalized poly(propylene oxide) as model compounds

End functionalized poly(propylene oxide)s with n-alkyl endgroups are synthesized by anionic ring opening polymerization of propylene oxide (PO) in bulk employing controlled microwave heating in sealed vessels. Different alcohols ranging from n-butanol to n-octadecanol are used as initiator and 2-10 propylene oxide units are added on average. A continuous decrease of internal pressure during the sealed vessel experiment reflects the consumption of PO monomer and the completion of the reaction is confirmed by a drop of the internal pressure to zero. The products are characterized by size exclusion chromatography (SEC), liquid chromatography at critical conditions (LCCC) and liquid adsorption chromatography (LAC). SEC with coupled density and refractive index (RI) detection provides information on the chemical composition along the molar mass distribution. LCCC allows a separation of the individual polymer homologous series according to their end groups. In LAC, the alkyl terminated chains elute later than the non-functional chains and can be separated to the baseline according to the number of repeat units.     

Analysis of long-chain polyprenols using supercritical fluid chromatography and matrix-assisted laser desorption ionization time-of-flight mass spectrometry

The separation of long-chain polyprenols was successfully achieved using supercritical fluid chromatography (SFC). Each 100-mer greater component was separated using tetrahydrofuran as a mobile phase modifier. The molecular mass distributions derived from SFC analyses agreed with the results of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analyses. The number-average molecular mass calculated by MALDI-TOF-MS data were also in accord with the results of quantitative 1H-NMR analysis of terminal groups. A combination of SFC and MALDI-TOF-MS analyses is a powerful tool for the elucidation of the complicated structures of natural polyprenols.     

Comprehensive two‐dimensional monolithic liquid chromatography of polar compounds

Two‐dimensional liquid chromatography largely increases the number of separated compounds in a single run, theoretically up to the product of the peaks separated in each dimension on the columns with different selectivities. On‐line coupling of a reversed‐phase column with an aqueous normal‐phase (hydrophilic interaction liquid chromatography) column yields orthogonal systems with high peak capacities. Fast on‐line two‐dimensional liquid chromatography needs a capillary or micro‐bore column providing low‐volume effluent fractions transferred to a short efficient second‐dimension column for separation at a high mobile phase flow rate. We prepared polymethacrylate zwitterionic monolithic micro‐columns in fused silica capillaries with structurally different dimethacrylate cross‐linkers. The columns provide dual retention mechanism (hydrophilic interaction and reversed‐phase). Setting the mobile phase composition allows adjusting the separation selectivity for various polar substance classes. Coupling on‐line an organic polymer monolithic capillary column in the first dimension with a short silica‐based monolithic column in the second dimension provides two‐dimensional liquid chromatography systems with high peak capacities. The silica monolithic C₁₈ columns provide higher separation efficiency than the particle‐packed columns at the flow rates as high as 5 mL/min used in the second dimension. Decreasing the diameter of the silica monolithic columns allows using a higher flow rate at the maximum operation pressure and lower fraction volumes transferred from the first, hydrophilic interaction dimension, into the second, reversed‐phase mode, avoiding the mobile phase compatibility issues, improving the resolution, increasing the peak capacity, and the peak production rate.     

高温二维液相色谱系统的构建及其评价

在二维液相色谱中, 第二维的分离速度是制约其发展的重要因素. 升高色谱柱温度可以有效降低流动相粘度, 加快溶质在两相间的传质速率, 有效加快分析速度. 以离子交换色谱法(WAX)为第一维分离模式和反相色谱法(RP)为第二维分离模式, 十通阀和两个捕集柱为接口, 通过将第二维色谱柱温度升高到80 ℃和提高流量到3 mL/min, 构建了高温WAX/RP二维液相色谱系统. 以4种标准蛋白的酶解物为样品评价系统的分离性能, 第一维共有33个馏分被捕集并导入到第二维分析, 高温二维液相色谱系统识别出187个色谱峰.     

Amphiphilic polymers based on higher alkylene oxides: Synthesis and characterization by different chromatographic techniques

Homopolymers and block copolymers of higher epoxides (butene oxide and hexene oxide) are synthesized using 1-alkanols and polyethylene glycol monomethyl ether (PEG-MME) 1100 as initiators by anionic ring opening polymerization in bulk. Most of the samples were synthesized with controlled microwave heating in sealed vessels. Tri- and tetrablock copolymers with different repeat units in the individual blocks are synthesized by living polymerization with addition of the next monomer after complete consumption of the previous one. The products thus obtained are characterized using size exclusion chromatography (SEC), liquid chromatography under critical conditions (LCCC) and liquid adsorption chromatography (LAC).     

纤维堆囊菌发酵液中埃博霉素含量的HPLC法分析

采用反馈神经网络结合遗传算法(BPANN-GA)对高效液相色谱(HPLC)法同时测定纤维堆囊菌(Sorangium cellulosum)代谢物中埃博霉素A(Epo A)和埃博霉素B(Epo B)含量的条件进行优化, 采用均匀设计(U₁₂³)方案对流动相中乙腈的体积分数、色谱柱温度和流动相的pH等3个因素进行实验设计; 以色谱函数(COF)值为优化指标, 运用双层反馈神经网络建立色谱优化函数(COF)值, 考察因素间的预测模型, 采用Levenberg-Marquardt backpropagation算法对所建立的神经网络预测模型进行训练, 以逼近度(D_a)为优化参数, 选择预测模型的最适隐含层节点数. 最优预测模型预测的COF值与实验值之间的相关系数(R)达到0.98165, 采用遗传算法在实验考察范围内进行全局寻优, 得到最优化的HPLC分析条件: 流动相中乙腈体积分数为29.2%, 色谱柱温度为34 ℃, 流动相pH为4.23. 在此最优条件下对纤维堆囊菌代谢产物进行HPLC分析, 结果表明, 该方法对两种埃博霉素色谱峰均具有较好的分离度.     

超高效超临界色谱分析聚合物制品中的7种添加剂

采用超高效超临界色谱(UPSFC)-二极管阵列检测器(PDA)建立了快速分析高分子材料中7种常用聚合物添加剂的方法。在检测波长为220 nm条件下,通过考察样品的稀释溶剂、流动相添加剂、柱温、背压、柱流速对分离的影响,最终确定7种添加剂分离的最优化条件：采用正己烷/异丙醇(1/1,v/v)为稀释溶剂,流动相添加剂为甲醇/乙腈(1/1,v/v),流速2 mL/min,柱温50 ℃,背压12.41~13.79 MPa条件下,7种聚合物添加剂能够在5 min之内达到完全基线分离。利用微波辅助萃取方法对实际样品中的添加剂进行提取,经UPSFC-PDA分析,7种添加剂的回收率为69.9%~118.9%,相对标准偏差(RSD,n=9)低于10%。该方法简便、快速,选择性强,能够准确快速地分析聚合物制品中的添加剂。