Gritti Fabrice, Guiochon Georges
Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA.
J Chromatogr A. 2003 Dec 22;1021(1-2):25-53. doi: 10.1016/j.chroma.2003.09.002.
Single-component adsorption isotherm data were acquired by frontal analysis (FA) for six low molecular weight compounds (phenol, aniline, caffeine, o-toluidine, p-toluidine and propylbenzoate) on one Chromolith-C18 column (#30, Merck, Darmstadt, Germany), using different methanol:water solutions (composition between 60/40 and 15/85 v/v, depending on the solute) as the mobile phase. These data were modeled for best agreement between the experimental data points and the adsorption isotherm model. The adsorption-energy distributions were also derived and used for the selection of the best isotherm model. Widely different models were obtained for these six compounds, four being convex upward (i.e., Langmuirian) and two having at least one inflection point. Overloaded band profiles corresponding to two different sample sizes (a low and a high loading factor) were recorded on six monolithic columns (#30-35) belonging to the same manufactured lot. These experimental band profiles were compared to the profiles calculated from the isotherm measured by FA on the first column, using the equilibrium-dispersive (ED) model of chromatography. For four of the six columns (#30, #32, #33, and #35), the reproducibility was better than 5 and 2.5% for the low and the high concentration profiles, respectively. On the other two columns (#31 and #34), the bands showed significant and systematic retention time shifts for all six compounds (with nearly identical band shapes), the relative adsorption being between 6 and 15% stronger on column #31 or between 2 and 7% lower on column #34. These differences seem to be correlated with the differences in the total porosities of these columns, which differ by 3% from columns #31 to #34, the higher porosity column giving the stronger adsorption.
采用迎头分析（FA）法，在一根默克公司（德国达姆施塔特）生产的Chromolith-C18柱（#30）上，以不同比例的甲醇/水溶液（根据溶质不同，体积比在60/40至15/85之间）为流动相，获取了六种低分子量化合物（苯酚、苯胺、咖啡因、邻甲苯胺、对甲苯胺和苯甲酸丙酯）的单组分吸附等温线数据。对这些数据进行建模，以使实验数据点与吸附等温线模型达到最佳拟合。还推导了吸附能分布，并用于选择最佳等温线模型。这六种化合物得到了差异很大的模型，其中四种呈向上凸（即符合朗缪尔模型），两种至少有一个拐点。在同一生产批次的六根整体柱（#30 - 35）上记录了对应两种不同进样量（低和高负载因子）的过载峰形。使用色谱的平衡扩散（ED）模型，将这些实验峰形与通过对第一根柱子进行迎头分析测得的等温线计算得到的峰形进行比较。对于六根柱子中的四根（#30、#32、#33和#35），低浓度和高浓度峰形的重现性分别优于5%和2.5%。在另外两根柱子（#31和#34）上，所有六种化合物的峰均显示出显著且有规律的保留时间偏移（峰形几乎相同），#31柱上的相对吸附比其他柱子强6%至15%，#34柱上则比其他柱子低2%至7%。这些差异似乎与这些柱子的总孔隙率差异有关，从#31柱到#34柱，总孔隙率相差3%，孔隙率较高的柱子吸附更强。
