Gritti Fabrice, Guiochon Georges
Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA.
J Chromatogr A. 2004 Feb 27;1028(1):121-37. doi: 10.1016/j.chroma.2003.11.088.
A new two-component competitive adsorption model was derived to account for the competitive adsorption data of mixtures of ethylbenzoate and 4-tert-butylphenol, on a C18-Kromasil column under RPLC conditions (mobile phase, methanol/water, 62/38, v/v). The derivation is based on kinetic arguments and is an extension to multicomponent systems of the single-component BET isotherm. The model assumes that the molecules of the first compound (A) can adsorb on layers made of molecules of either A or B, while molecules of B can only adsorb on layers made of molecules of A. This makes the competitive isotherm consistent with the single-component isotherms of ethylbenzoate and 4-tert-butylphenol, the multilayer BET and the monolayer Langmuir isotherm models, respectively. The competitive adsorption data were acquired by frontal analysis (FA) with equimolar mixtures of eight different concentrations. For the seven lowest concentrations, these data were derived from the retention times of the shocks of the two compounds and the concentration of the intermediate plateau of the less retained compound. At the highest concentration (25 g/l), the individual band profiles were measured by collecting and analyzing twenty fractions. The low concentration data (C < or = 10 g/l) are well accounted for by the two competitive isotherm models derived previously but these models fail to describe the experimental data of 4-tert-butylphenol at high concentrations. By contrast, the new model predicts very well the experimental adsorption data for mixtures of ethylbenzoate and 4-tert-butylphenol in the whole range of concentration studied. Our results suggest that the adsorption constant of 4-tert-butylphenol onto layers made of ethylbenzoate (b(B,A) = 0.0120 l/g) is intermediate between those of ethylbenzoate on layers made of 4-tert-butylphenol (b(A,B) = 0.0105 l/g) and of ethylbenzoate on itself (b(A,A) = 0.0145 l/g). This new model should give an improved description of the band splitting observed for 4-tert-butylphenol in the presence of ethylbenzoate.
推导了一种新的双组分竞争吸附模型，以解释在反相液相色谱（RPLC）条件下（流动相为甲醇/水，体积比62/38），苯甲酸乙酯和4-叔丁基苯酚混合物在C18-Kromasil柱上的竞争吸附数据。该推导基于动力学原理，是单组分BET等温线对多组分系统的扩展。该模型假设第一种化合物（A）的分子可以吸附在由A或B分子构成的层上，而B分子只能吸附在由A分子构成的层上。这使得竞争等温线分别与苯甲酸乙酯和4-叔丁基苯酚的单组分等温线、多层BET等温线和单层朗缪尔等温线模型一致。通过对八种不同浓度的等摩尔混合物进行前沿分析（FA）获取竞争吸附数据。对于七个最低浓度，这些数据来自两种化合物峰的保留时间以及保留较少化合物中间平台的浓度。在最高浓度（25 g/l）下，通过收集和分析二十个馏分来测量各个谱带轮廓。低浓度数据（C≤10 g/l）可以很好地由先前推导的两种竞争等温线模型解释，但这些模型无法描述高浓度下4-叔丁基苯酚的实验数据。相比之下，新模型在整个研究浓度范围内都能很好地预测苯甲酸乙酯和4-叔丁基苯酚混合物的实验吸附数据。我们的结果表明，4-叔丁基苯酚在由苯甲酸乙酯构成的层上的吸附常数（b(B,A)=0.0120 l/g）介于苯甲酸乙酯在由4-叔丁基苯酚构成的层上的吸附常数（b(A,B)=0.0105 l/g）和苯甲酸乙酯在自身层上的吸附常数（b(A,A)=0.0145 l/g）之间。这个新模型应该能更好地描述在苯甲酸乙酯存在下4-叔丁基苯酚观察到的谱带分裂现象。
