Gritti Fabrice, Guiochon Georges
Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA.
J Chromatogr A. 2003 Aug 29;1010(2):153-76. doi: 10.1016/s0021-9673(03)01071-9.
Single component adsorption and desorption isotherms of phenol were measured on a high-efficiency Kromasil-C18 column (N = 15000 theoretical plates) with pure water as the mobile phase. Adsorption isotherm data were acquired by frontal analysis (FA) for seven plateau concentrations distributed over the whole accessible range of phenol concentration in pure water (5, 10, 15, 20, 25, 40, and 60 g/l). Desorption isotherm data were derived from the corresponding rear boundaries, using frontal analysis by characteristic points (FACP). A strong adsorption hysteresis was observed. The adsorption of phenol is apparently modeled by a S-shaped isotherm of the first kind while the desorption isotherm is described by a convex upward isotherm. The adsorption breakthrough curves could not be modeled correctly using the adsorption isotherm because of a strong dependence of the accessible free column volume on the phenol concentration in the mobile phase. It seems that retention in water depends on the extent to which the surface is wetted by the mobile phase, extent which is a function of the phenol concentration, and of the local pressure rate, which varies along the column, and on the initial state of the column. By contrast, the desorption profiles agree well with those calculated with the desorption isotherms using the ideal model, due to the high column efficiency. The isotherm model accounting best for the desorption isotherm data and the desorption profiles is the bi-Langmuir model. Its coefficients were calculated using appropriate weights in the fitting procedure. The evolution of the bi-Langmuir isotherm parameters with the initial equilibrium plateau concentration of phenol is discussed. The FACP results reported here are fully consistent with the adsorption data of phenol previously reported and measured by FA with various aqueous solutions of methanol as the mobile phase. They provide a general, empirical adsorption model of phenol that is valid between 0 and 65% of methanol in water.
以纯水为流动相，在高效Kromasil - C18柱（理论塔板数N = 15000）上测定了苯酚的单组分吸附和解吸等温线。通过前沿分析（FA）获取吸附等温线数据，针对分布在纯水相中苯酚浓度整个可及范围内的七个平台浓度（5、10、15、20、25、40和60 g/l）。解吸等温线数据通过特征点前沿分析（FACP）从相应的后沿边界得出。观察到强烈的吸附滞后现象。苯酚的吸附明显由第一类S形等温线模拟，而解吸等温线由向上凸的等温线描述。由于可及的自由柱体积强烈依赖于流动相中的苯酚浓度，使用吸附等温线无法正确模拟吸附穿透曲线。似乎在水中的保留取决于流动相对表面的润湿程度，该程度是苯酚浓度以及沿柱变化的局部压力速率的函数，还取决于柱的初始状态。相比之下，由于柱效率高，解吸曲线与使用理想模型通过解吸等温线计算得到的曲线吻合良好。最能拟合解吸等温线数据和解吸曲线的等温线模型是双朗缪尔模型。其系数在拟合过程中使用适当的权重进行计算。讨论了双朗缪尔等温线参数随苯酚初始平衡平台浓度的演变。此处报告的FACP结果与先前报道的以及用各种甲醇水溶液作为流动相通过FA测量的苯酚吸附数据完全一致。它们提供了一个通用的苯酚经验吸附模型，该模型在水中甲醇含量为0至65%的范围内有效。
