Structural Properties of Monolithic Silica Columns

FIGURE 7.3 Scanning electron micrographs of monolithic silica prepared from sol-gel methods, (a) monolithic silica prepared from TMOS in a test tube, and monolithic silica columns prepared from a mixture of TMOS and MTMS, (b) in a 50-pm fused silica capillary, (c) in a lOO-pm fused silica capillary, and (d) in a 200-pm fused silica capillary tube (reproduced from the reference, Motokawa et al. (2002), with permission from Elsevier). [Pg.155]

External porosity is above 60% for conventional size columns prepared in a test tube (Al-Bokari et al., 2002), and above 80% for those prepared in a capillary. [Pg.155]

Disadvantages of monolithic silica columns include the labor-intensive preparation of individual columns with possible reproducibility problems, limited availability, and relatively short retention caused by the smaller amount of silica existing in a column [Pg.155]

FIGURE 7.4 (a) Plots of column back pressure against linear velocity of mobile phase (29, [Pg.156]

In a sense each monolithic column is unique, or produced as a product of a separate batch, because the columns are prepared one by one by a process including monolith formation, column fabrication, and chemical modification. Reproducibility of Chro-molith columns has been examined, and found to be similar to particle-packed-silica-based columns of different batches (Kele and Guiochon, 2002). Surface coverage of a Chromolith reversed-phase (RP) column appears to be nearly maximum, but greater silanol effects were found for basic compounds and ionized amines in buffered and nonbuffered mobile phases than advanced particle-packed columns prepared from high purity silica (McCalley, 2002). Small differences were observed between monolithic silica columns derived from TMOS and those from silane mixtures for planarity in solute structure as well as polar interactions (Kobayashi et al., 2004). [Pg.157]

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