Puy G, Roux R, Demesmay C, Rocca J-L, Iapichella J, Galarneau A, Brunel D
Laboratoire des Sciences Analytiques, UMR 5180, Université Claude Bernard Lyon 1, Bâtiment CPE, 43 Boulevard du 11 Novembre, 69622 Villeurbanne Cedex, France.
J Chromatogr A. 2007 Aug 10;1160(1-2):150-9. doi: 10.1016/j.chroma.2007.05.019. Epub 2007 May 10.
In the last decade, silica monolithic capillaries have focused more and more attention on miniaturized separation techniques like capillary electrochromatography (CEC), nano-liquid chromatography (nano-LC) and chip electrochromatography owing to their unique chromatographic properties and their simplified preparation compared with packed columns. They are synthesized according to a sol-gel multi-step process that includes, after a gelation step at 40 degrees C leading to the formation of the macropores network and the silica skeleton, a post-gelation step (hydrothermal treatment at 120 degrees C in basic medium) that allows to tailor the mesopores and finally a calcination or a washing step to remove remaining polymers. In order to reduce the synthesis time, the number of synthesis steps and above all the temperature synthesis, to adapt the synthesis of such silica monoliths in polymeric microsystem devices, we extensively studied the influence of the hydrothermal treatment and its duration on textural (pore size distribution) and chromatographic properties (retention, efficiency) of in situ-synthesized capillary monoliths in nano-LC and CEC. This study was performed on pure silica and octyl chains grafted silica monoliths. Untreated monoliths show small pores (<6 nm), whereas hydrothermally treated monoliths exhibit medium and large mesopores (8-17 nm). It was demonstrated that the hydrothermal treatment at 120 degrees C was not necessary for pure silica monolithic capillaries dedicated to normal phase liquid chromatography or hydrophilic interaction liquid chromatography (HILIC) and electrochromatography: the suppression of the hydrothermal treatment did not impair efficiencies in CEC and in nano-LC but contributed to increase in retention factors. Minimal plate heights of ca. 5 microm in CEC and 6 microm in nano-LC were obtained with or without hydrothermal treatment with bare silica. In the same way, the hydrothermal treatment was not necessary for grafted silica monoliths only dedicated to CEC. However, the results clearly indicate that the hydrothermal treatment becomes essential before grafting in order to preserve the efficiency of the monolithic silica capillaries dedicated to nano-LC: in this particular case, the suppression of the hydrothermal treatment leads approximately to a loss of a factor two in efficiency.
在过去十年中，硅胶整体柱因其独特的色谱性能以及与填充柱相比简化的制备过程，在诸如毛细管电色谱（CEC）、纳升液相色谱（nano-LC）和芯片电色谱等微型分离技术中受到越来越多的关注。它们是根据溶胶-凝胶多步工艺合成的，该工艺包括在40℃进行凝胶化步骤以形成大孔网络和硅胶骨架后，进行一个后凝胶化步骤（在碱性介质中于120℃进行水热处理），以调整介孔，最后进行煅烧或洗涤步骤以去除残留的聚合物。为了减少合成时间、合成步骤数量，尤其是合成温度，以便使这种硅胶整体柱的合成适用于聚合物微系统装置，我们广泛研究了水热处理及其持续时间对原位合成的毛细管整体柱在nano-LC和CEC中的结构（孔径分布）和色谱性能（保留、效率）的影响。这项研究是在纯硅胶和接枝了辛基链的硅胶整体柱上进行的。未经处理的整体柱显示出小孔径（<6 nm），而经过水热处理的整体柱呈现出中等和大的介孔（8 - 17 nm）。结果表明，对于用于正相液相色谱或亲水作用液相色谱（HILIC）以及电色谱的纯硅胶整体柱，120℃的水热处理并非必要：取消水热处理不会损害CEC和nano-LC中的效率，但有助于增加保留因子。使用裸硅胶进行水热处理与否，在CEC中获得的最小板高约为5μm，在nano-LC中约为6μm。同样，对于仅用于CEC的接枝硅胶整体柱，水热处理也不是必需的。然而，结果清楚地表明，为了保持用于nano-LC的整体硅胶毛细管的效率，在接枝之前水热处理变得至关重要：在这种特殊情况下，取消水热处理会导致效率大约损失一半。
