Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35032 Marburg, Germany.
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599-3290, United States.
J Chromatogr A. 2018 Sep 28;1569:44-52. doi: 10.1016/j.chroma.2018.07.037. Epub 2018 Jul 7.
We study axial heterogeneities in capillary ultrahigh pressure liquid chromatography (UHPLC) columns through kinetic performance and bed morphological analysis. Two columns are used in this work, a 75 μm i.d. × 100 cm column packed with 1.3 μm C18-silica particles and a 75 μm i.d. × 45 cm column packed with 1.9 μm C18-silica particles. The long column is chromatographically characterized and is afterwards sectioned into three segments, each analyzed individually. The column packed with the 1.9 μm particles is subjected to a bed morphological analysis using confocal laser scanning microscopy near the inlet, center, and outlet of the column. Chromatographic and morphological characterizations reveal highest separation efficiency and most homogeneous bed microstructure towards the column outlet. Kinetic performance data for inlet and central packing segments indicate enhanced contributions from wall effects to a transcolumn flow heterogeneity. Bed morphological data reveal systematic changes in geometrical and frictional wall effects along the bed: from inlet to outlet, bed morphologies increasingly reflect packing microstructures associated with concentrated slurries. Variations in separation efficiency and bed morphology can be related to the constant-pressure packing mode; the decrease in packing rate along the bed leaves fewer chances for particle rearrangement and bed consolidation from inlet to outlet. It explains the relatively uniform bed morphology towards the outlet and also the relatively loose wall region near the inlet. Bed microstructural features are discussed in a context of previous observations made in the characterization of capillary UHPLC columns.
我们通过动力学性能和床形态分析研究了毛细管超高压液相色谱（UHPLC）柱中的轴向各向异性。这项工作使用了两根柱子，一根是 75μm 内径×100cm 长的柱子，填充了 1.3μm C18-硅胶颗粒，另一根是 75μm 内径×45cm 长的柱子，填充了 1.9μm C18-硅胶颗粒。我们对长柱进行了色谱特性分析，然后将其分成三段，分别进行单独分析。对填充有 1.9μm 颗粒的柱子进行了床形态分析，使用共聚焦激光扫描显微镜对柱子入口、中心和出口附近进行了分析。色谱和形态特征表明，在柱子出口处的分离效率最高，床微观结构最均匀。入口和中心填充段的动力学性能数据表明，壁效应对跨柱流的非均质性的贡献增强。床形态数据表明，几何和摩擦壁效应沿床层发生系统变化：从入口到出口，床形态越来越多地反映了与浓缩浆料相关的填充微观结构。分离效率和床形态的变化可能与恒压填充模式有关；沿床层的填充速率下降，从入口到出口，颗粒重排和床层固结的机会减少。这解释了出口处相对均匀的床形态，以及入口附近相对疏松的壁区。床微观结构特征在毛细管 UHPLC 柱特性研究中的先前观察结果的背景下进行了讨论。
