Water Studies Centre and School of Chemistry, Monash University, Clayton Campus, Melbourne, VIC, 3800, Australia.
Water Studies Centre and School of Chemistry, Monash University, Clayton Campus, Melbourne, VIC, 3800, Australia.
J Chromatogr A. 2018 Feb 23;1538:60-66. doi: 10.1016/j.chroma.2018.01.041.
The commonly used theory to describe the normal Brownian mode of field-flow fractionation (FFF) assumes the particles to be point masses and hence the shape is ignored. Beckett and Giddings extended this theory to include the effect of thin rods and discs being forced very close to the accumulation wall. By including the decrease in the entropy this causes, they derived new expressions for the retention of such nonspherical particles in FFF. The steric-entropic theory predicts that when the sample cloud thickness is less than the major dimension of the rods or discs then particles elute earlier than predicted by the Brownian mode theory. This leads to an underestimation of the buoyant mass and equivalent spherical diameter calculated from FFF data. In this paper we report for the first time experimental data for the retention of thin illite particles in centrifugal FFF that agrees well with these steric-entropic predictions. Not only do the size distributions calculated using the Brownian mode theory shift to lower size when the field is increased but the shift in the retention ratio of the peak maxima of the FFF fractograms could be predicted fairly accurately by the steric-entropic equations.
通常用于描述场流分级（FFF）的正常布朗模式的理论假设粒子为质点，因此忽略了形状。Beckett 和 Giddings 将这一理论扩展到包括非常靠近累积壁的薄棒和圆盘的影响。通过包括由此引起的熵的减少，他们推导出了用于保留 FFF 中非球形颗粒的新表达式。位阻熵理论预测，当样品云厚度小于棒或圆盘的主要尺寸时，颗粒的洗脱时间早于布朗模式理论预测的时间。这导致从 FFF 数据计算的浮力质量和等效球形直径的低估。在本文中，我们首次报告了离心 FFF 中薄伊利石颗粒保留的实验数据，这些数据与这些位阻熵预测非常吻合。不仅使用布朗模式理论计算的尺寸分布在增加场时会向较小的尺寸转移，而且 FFF fractogram 峰最大值的保留比的转移也可以通过位阻熵方程相当准确地预测。
