Gritti Fabrice, Guiochon Georges
Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA.
J Chromatogr A. 2006 Sep 22;1128(1-2):45-60. doi: 10.1016/j.chroma.2006.06.038. Epub 2006 Jul 18.
The influence of the degree of coverage of a silica surface with bonded C18 alkyl chains on the mass transfer mechanism in RPLC was investigated. Five packing materials were used, prepared with the same batch of silica particles (5 microm diameter, 90 A average pore size): one column was packed with the silica derivatized by trimethylchlorosilane (TMS) (C1, 3.92 micromol/m2), and the other four with the silica first derivatized with octadecyl-dimethyl-chlorosilane (C18, 0.42, 1.01, 2.03, and 3.15 micromol/m2), and then endcapped with TMS. A solution of methanol and water (25/75, v/v) was used as the mobile phase. The experimental HETP curves were acquired for each column by measuring the first moment and the second central moment of phenol and correcting them for the influence of the temperature increase due to the heat generated by the friction of the stream against the bed. The different kinetic parameters of the mass transfer in these packed chromatographic columns were identified (longitudinal diffusion, eddy diffusion, film mass transfer, and transparticle mass transfer) and quantified by fitting the experimental data to a new general HETP equation recently derived [F. Gritti, G. Guiochon, Anal. Chem., in press (AC-060203R).]. The agreement was excellent and allowed the comparison of the kinetic parameters among the six columns used. The highest column efficiency measured at conventional or fast flow rates (>0.5 ml/min) is obtained for the most retentive column, which has a surface coverage of 2.03 micromol/m2. The smallest HETP measured is as low as 10 microm, only twice the average particle diameter dp, due to the large contribution of surface diffusion (90%) to the particle effective diffusivity. However, no significant difference was observed between the efficiencies of the columns packed with C1 and C18 derivatized silica.
研究了硅胶表面键合C18烷基链的覆盖程度对反相液相色谱（RPLC）传质机理的影响。使用了五种填充材料，它们由同一批硅胶颗粒（直径5微米，平均孔径90埃）制备而成：一根色谱柱填充用三甲基氯硅烷（TMS）衍生化的硅胶（C1，3.92微摩尔/平方米），另外四根填充先用十八烷基二甲基氯硅烷（C18，0.42、1.01、2.03和3.15微摩尔/平方米）衍生化，然后用TMS进行封端的硅胶。以甲醇和水的溶液（25/75，v/v）作为流动相。通过测量苯酚的一阶矩和二阶中心矩，并校正由于流体与固定相床层摩擦产生的热量导致的温度升高的影响，获得了每根色谱柱的实验理论塔板高度（HETP）曲线。通过将实验数据拟合到最近推导的一个新的通用HETP方程[F. Gritti, G. Guiochon, Anal. Chem., in press (AC-060203R).]，确定了这些填充色谱柱中传质的不同动力学参数（纵向扩散、涡流扩散、液膜传质和粒内传质）并进行了量化。拟合结果非常理想，从而可以比较所使用的六根色谱柱之间的动力学参数。在常规或快速流速（>0.5毫升/分钟）下测得的最高柱效是对于保留能力最强的色谱柱，其表面覆盖率为2.03微摩尔/平方米。测得的最小HETP低至10微米，仅为平均粒径dp的两倍，这是由于表面扩散对颗粒有效扩散系数的贡献很大（90%）。然而，填充C1衍生化硅胶和C18衍生化硅胶的色谱柱的柱效之间未观察到显著差异。
