Morphology and separation efficiency of a new generation of analytical silica monoliths

• Published in: Journal of Chromatography A Vol. 1222; pp. 46 - 58
• Main Authors: Hormann, Kristof, Müllner, Tibor, Bruns, Stefan, Höltzel, Alexandra, Tallarek, Ulrich
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 27.01.2012
• Subjects: Analytical silica monoliths; Chord length distribution; Chromatography; Chromatography, Liquid - instrumentation; Eddy dispersion; Homogeneity; Mathematical analysis; Microscopy, Confocal; Microscopy, Electron, Scanning; Morphological analysis; Morphology; Physical reconstruction; Planetary probes; Porosity; Radial heterogeneity; Reduction; Separation; Silicon dioxide; Silicon Dioxide - chemistry; Radial heterogeneity; Chord length distribution; Eddy dispersion; Analytical silica monoliths; Physical reconstruction; Morphological analysis
• ISSN: 0021-9673; 1873-3778
• DOI: 10.1016/j.chroma.2011.12.008

► A new generation of analytical silica monoliths is presented. ► Macromorphology is reconstructed using confocal laser scanning microscopy. ► Smaller macropore size, thinner skeleton, more homogeneous macropore space. ► 66.5% reduction of minimum plate height compared to previous monolith generation. ► Elimination of radial heterogeneity is key to improved separation efficiency. The heterogeneous morphology of current silica monoliths hinders this column type to reach its envisioned performance goals. We present a new generation of analytical silica monoliths that deliver a substantially improved separation efficiency achieved through several advances in monolith morphology. Analytical silica monoliths from the 1st and 2nd Chromolith generation are characterized and compared by chromatographic methods, mercury intrusion porosimetry, scanning electron microscopy, and confocal laser scanning microscopy. The latter method is instrumental to quantify morphological differences between the monolith generations and to probe the radial variation of morphological properties. Compared with the 1st generation, the new monoliths possess not only smaller macropores, a more homogeneous macropore space, and a thinner silica skeleton, but also radial homogeneity of these structural parameters as well as of the local external or macroporosity. The 66.5% reduction in minimum plate height observed between silica monoliths of the 1st and 2nd Chromolith generation can thus be attributed to two key improvements: a smaller domain size at simultaneously increased macropore homogeneity and the absence of radial morphology gradients, which are behind the considerable peak asymmetry of the 1st generation.