Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA.
J Chromatogr A. 2011 Nov 11;1218(45):8209-21. doi: 10.1016/j.chroma.2011.09.034. Epub 2011 Sep 28.
The influence of the particle size distribution (PSD) on the band broadening and the efficiency of packed columns is investigated on both theoretical and practical viewpoints. Each of the classical contributions to mass transfer kinetics, those due to longitudinal diffusion, eddy dispersion, and solid-liquid mass transfer resistance are measured and analyzed in terms of their expected and observed intensity as a function of the PSD of mixtures of the commercially available packing materials, 5 and 3 μm Luna-C₁₈ particles (Phenomenex, Torrance, CA, USA). Six 4.6 mm × 150 mm columns were packed with different mixtures of these two materials. The efficiencies of these columns were measured for a non-retained and a retained analytes in a mixture of acetonitrile and water. The longitudinal diffusion coefficient was directly measured by the peak parking method. The solid-liquid mass transfer coefficient was measured from the combination of the peak parking method, the best model of effective diffusion coefficient and the actual PSDs of the different particle mixtures measured by Coulter counter experiments. The eddy diffusion term was measured according to a recently developed protocol, by numerical integration of the peak profiles. Our results clearly show that the PSD has no measurable impact on any of the coefficients of the van Deemter equation. On the contrary and surprisingly, adding a small fraction of large particles to a batch of small particles can improve the quality of the packing of the fine particles. Our results indirectly confirm that the success of sub-3 μm shell particles is due to the roughness of their external surface, which contributes to eliminate most of the nefarious wall effects.
从理论和实践两个角度研究了粒径分布（PSD）对带展宽和填充柱效率的影响。从商业可用填充材料 5 和 3 μm Luna-C₁₈ 颗粒（Phenomenex，Torrance，CA，USA）混合物的 PSD 的预期和观察强度的角度，测量和分析了传质动力学的每个经典贡献，这些贡献归因于纵向扩散、涡流分散和固液传质阻力。用不同比例的这两种材料填充了六个 4.6 mm×150 mm 的柱子。这些柱子的效率用非保留和保留分析物在乙腈和水的混合物中进行测量。通过峰停车法直接测量纵向扩散系数。从峰停车法、有效扩散系数的最佳模型和通过库尔特计数器实验测量的不同颗粒混合物的实际 PSD 的组合，测量了固液传质系数。根据最近开发的协议，通过峰轮廓的数值积分测量涡流扩散项。我们的结果清楚地表明，PSD 对范德默尔方程的任何系数都没有可测量的影响。相反，令人惊讶的是，向一批小颗粒中添加少量大颗粒可以提高小颗粒的填充质量。我们的结果间接证实了亚 3 μm 壳颗粒的成功是由于其外表面的粗糙度，这有助于消除大部分有害的壁效应。
