Kaczmarski Krzysztof, Kostka Joanna, Zapała Wojciech, Guiochon Georges
Department of Chemical and Process Engineering, Rzeszów University of Technology, 35-959 Rzeszów, Poland.
J Chromatogr A. 2009 Sep 18;1216(38):6560-74. doi: 10.1016/j.chroma.2009.07.020. Epub 2009 Jul 17.
Heat due to viscous friction is generated in chromatographic columns. When these columns are operated at high flow rates, under a high inlet pressure, this heat causes the formation of significant axial and radial temperature gradients. Consequently, these columns become heterogeneous and several physico-chemical parameters, including the retention factors and the parameters of the mass transfer kinetics of analytes are no longer constant along and across the columns. A robust modeling of the distributions of the physico-chemical parameters allows the analysis of the impact of the heat generated on column performance. We developed a new model of the coupled heat and mass transfers in chromatographic columns, calculated the axial and radial temperature distributions in a column, and derived the distributions of the viscosity and the density of the mobile phase, hence of the axial and radial mobile phase velocities. The coupling of the mass and the heat balances in chromatographic columns was used to model the migration of a compound band under linear conditions. This process yielded the elution band profiles of analytes, hence the column efficiency under two different sets of experimental conditions: (1) the column is operated under natural convection conditions; (2) the column is dipped in a stream of thermostated fluid. The calculated results show that the column efficiency is remarkably lower in the second than in the first case. The inconvenience of maintaining constant the temperature of the column wall (case 2) is that retention factors and mobile phase velocities vary much more significantly across the column than if the column is kept under natural convection conditions (case 1).
色谱柱中会因粘性摩擦产生热量。当这些色谱柱在高流速、高入口压力下运行时，这种热量会导致显著的轴向和径向温度梯度的形成。因此，这些色谱柱变得不均匀，包括保留因子和分析物传质动力学参数在内的几个物理化学参数在色谱柱的轴向和径向上不再保持恒定。对物理化学参数分布进行稳健建模有助于分析所产生的热量对色谱柱性能的影响。我们开发了一种新的色谱柱内热质耦合传递模型，计算了色谱柱内的轴向和径向温度分布，并推导了流动相的粘度和密度分布，进而得出轴向和径向流动相速度分布。利用色谱柱中质量平衡和热量平衡的耦合来模拟线性条件下化合物谱带的迁移。这个过程得出了分析物的洗脱谱带轮廓，从而得出了在两组不同实验条件下的色谱柱效率：（1）色谱柱在自然对流条件下运行；（2）色谱柱浸入恒温流体流中。计算结果表明，第二种情况下的色谱柱效率明显低于第一种情况。保持柱壁温度恒定（情况2）的不便之处在于，与色谱柱在自然对流条件下（情况1）相比，保留因子和流动相速度在色谱柱径向上的变化要大得多。
