Department of Chemical and Process Engineering, Rzeszów University of Technology, 35-959 Rzeszów, Poland.
J Chromatogr A. 2010 Oct 15;1217(42):6578-87. doi: 10.1016/j.chroma.2010.08.035. Epub 2010 Aug 19.
When chromatography is carried out with high-density carbon dioxide as the main component of the mobile phase (a method generally known as "supercritical fluid chromatography" or SFC), the required pressure gradient along the column is moderate. However, this mobile phase is highly compressible and, under certain experimental conditions, its density may decrease significantly along the column. Such an expansion absorbs heat, cooling the column, which absorbs heat from the outside. The resulting heat transfer causes the formation of axial and radial gradients of temperature that may become large under certain conditions. Due to these gradients, the mobile phase velocity and most physico-chemical parameters of the system (viscosity, diffusion coefficients, etc.) are no longer constant throughout the column, resulting in a loss of column efficiency, even at low flow rates. At high flow rates and in serious cases, systematic variations of the retention factors and the separation factors with increasing flow rates and important deformations of the elution profiles of all sample components may occur. The model previously used to account satisfactorily for the effects of the viscous friction heating of the mobile phase in HPLC is adapted here to account for the expansion cooling of the mobile phase in SFC and is applied to the modeling of the elution peak profiles of an unretained compound in SFC. The numerical solution of the combined heat and mass balance equations provides temperature and pressure profiles inside the column, and values of the retention time and efficiency for elution of this unretained compound that are in excellent agreement with independent experimental data.
当以高密度二氧化碳作为流动相的主要成分进行色谱分析（通常称为“超临界流体色谱”或 SFC）时，沿柱所需的压力梯度适中。然而，这种流动相具有很高的可压缩性，在某些实验条件下，其密度沿柱可能会显著降低。这种膨胀会吸收热量，使柱冷却，从而从外部吸收热量。由此产生的热传递导致轴向和径向温度梯度的形成，在某些条件下，这些梯度可能会变得很大。由于这些梯度，流动相速度和系统的大多数物理化学参数（粘度、扩散系数等）在整个柱内不再恒定，导致柱效率降低，即使在低流速下也是如此。在高流速下，在严重的情况下，保留因子和分离因子随流速的增加以及所有样品组分的洗脱曲线的重要变形可能会发生系统变化。这里对以前用于解释 HPLC 中流动相粘性摩擦加热影响的模型进行了调整，以解释 SFC 中流动相的膨胀冷却，并将其应用于 SFC 中未保留化合物洗脱峰曲线的建模。热和质量平衡方程的数值解提供了柱内的温度和压力分布，以及该未保留化合物的保留时间和洗脱效率的值，与独立的实验数据非常吻合。
