Analytical-Chemistry Group, Faculty of Science, van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
J Chromatogr A. 2011 Sep 28;1218(39):6930-42. doi: 10.1016/j.chroma.2011.08.014. Epub 2011 Aug 16.
Ultra-high-pressure liquid chromatography (UHPLC) using columns packed with sub-2 μm particles has great potential for separations of many types of complex samples, including polymers. However, the application of UHPLC for the analysis of polymers meets some fundamental obstacles. Small particles and narrow bore tubing in combination with high pressures generate significant shear and extensional forces in UHPLC systems, which may affect polymer chains. At high stress conditions flexible macromolecules may become extended and eventually the chemical bonds in the molecules can break. Deformation and degradation of macromolecules will affect the peak retention and the peak shape in the chromatogram, which may cause errors in the obtained results (e.g. the calculated molecular-weight distributions). In the present work we explored the limitations of UHPLC for the analysis of polymers. Degradation and deformation of macromolecules were studied by collecting and re-injecting polymer peaks and by off-line two-dimensional liquid chromatography. Polystyrene standards with molecular weight of 4 MDa and larger were found to degrade at UHPLC conditions. However, for most polymers degradation could be avoided by using low linear velocities. No degradation of 3-MDa PS (and smaller) was observed at linear velocities up to 7 mm/s. The column frits were implicated as the main sources of polymer degradation. The extent of degradation was found to depend on the type of the column and on the column history. At high flow rates degradation was observed without a column being installed. We demonstrated that polymer deformation preceded degradation. Stretched polymers eluted from the column in slalom chromatography mode (elution order opposite to that in SEC or HDC). Under certain conditions we observed co-elution of large and small PS molecules though a convolution of slalom chromatography and hydrodynamic chromatography.
超高效液相色谱（UHPLC）使用亚 2μm 颗粒填充的色谱柱，在分离多种类型的复杂样品方面具有很大的潜力，包括聚合物。然而，UHPLC 在聚合物分析中的应用存在一些基本障碍。小颗粒和小口径管与高压相结合，在 UHPLC 系统中会产生显著的剪切和拉伸力，这可能会影响聚合物链。在高应力条件下，柔性大分子可能会伸展，最终分子中的化学键可能会断裂。大分子的变形和降解会影响色谱图中的峰保留和峰形，这可能会导致获得的结果出现误差（例如计算的分子量分布）。在本工作中，我们探讨了 UHPLC 分析聚合物的局限性。通过收集和重新注入聚合物峰以及离线二维液相色谱研究了大分子的降解和变形。发现分子量为 4 MDa 及以上的聚苯乙烯标准品在 UHPLC 条件下会降解。然而，通过使用低线性流速可以避免大多数聚合物的降解。在高达 7mm/s 的线性流速下，未观察到 3-MDa PS（及更小）的降解。柱 frit 被认为是聚合物降解的主要来源。降解的程度取决于柱的类型和柱的历史。在高流速下，即使没有安装柱子也会观察到降解。我们证明聚合物的变形先于降解。拉伸聚合物以蛇形色谱模式洗脱（洗脱顺序与 SEC 或 HDC 相反）。在某些条件下，尽管存在蛇形色谱和流体动力学色谱的卷积，我们还是观察到了大分子量和小分子量 PS 分子的共洗脱。
