Poe Donald P, Helmueller Shawn, Kobany Stephanie, Feldhacker Hannah, Kaczmarski Krzysztof
Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, 55812, USA.
Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, 55812, USA.
J Chromatogr A. 2017 Jan 27;1482:76-96. doi: 10.1016/j.chroma.2016.12.057. Epub 2016 Dec 23.
When an SFC column is operated in a traditional oven with forced air at low pressures near the critical temperature, severe efficiency losses can occur. The mobile phase cools as it expands along the column, forming axial and radial temperature gradients. In this study we present a simple model based on a virtual fluid to predict the conditions which lead to the onset of efficiency loss. The model shows that the Joule-Thomson coefficient is an important factor leading to efficiency loss in packed columns under forced air conditions. The model was tested experimentally for elution of n-alkylbenzenes on 250×4.6-mm ID columns packed with 5-μm Luna-C18 (fully porous) and Kinetex-C18 (superficially porous) particles at optimum flow rates in a forced air oven at 20-80°C and outlet pressures from 90 to 250bar, with CO mobile phase containing 5, 10 and 20% methanol (v/v). For simplicity, we used a formal J-T coefficient corresponding to the inlet temperature and the outlet pressure to characterize the chromatographic conditions. For 5% methanol, there was no significant loss of efficiency for elution of n-octadecylbenzene as long as the formal J-T coefficient was less than 0.11K/bar for Luna or 0.15K/bar for Kinetex, with minimum reduced plate heights equal to 1.82 and 1.55, respectively, at an average apparent retention factor of approximately 4.0 for both columns. The Kinetex column provided superior efficiency in general, and at 10-20bar lower outlet pressures relative to the Luna column due to the higher thermal conductivity of the packing. Results for 10 and 20% methanol showed similar trends but were less predictable.
当超临界流体色谱（SFC）柱在传统烘箱中，于接近临界温度的低压下通以强制空气运行时，可能会出现严重的柱效损失。流动相沿色谱柱膨胀时会冷却，从而形成轴向和径向温度梯度。在本研究中，我们提出了一个基于虚拟流体的简单模型，以预测导致柱效损失开始的条件。该模型表明，焦耳 - 汤姆逊系数是在强制空气条件下填充柱中导致柱效损失的一个重要因素。该模型通过实验测试了在20 - 80°C的强制空气烘箱中，以最佳流速、90至250 bar的出口压力，使用含5%、10%和20%甲醇（v/v）的CO流动相，在填充有5 - μm Luna - C18（全多孔）和Kinetex - C18（表面多孔）颗粒的250×4.6 - mm内径色谱柱上洗脱正烷基苯的情况。为简单起见，我们使用对应于入口温度和出口压力的形式化焦耳 - 汤姆逊系数来表征色谱条件。对于5%甲醇，只要形式化焦耳 - 汤姆逊系数对于Luna柱小于0.11 K/bar，对于Kinetex柱小于0.15 K/bar，正十八烷基苯洗脱时就不会有显著的柱效损失，两根柱在平均表观保留因子约为4.0时，最小折合板高分别等于1.82和1.55。总体而言，Kinetex柱具有更高的柱效，并且由于填料的热导率较高，相对于Luna柱，其出口压力低10 - 20 bar。10%和20%甲醇的结果显示出类似趋势，但较难预测。
