The concept of separation media based on monolithic materials can be traced back to the early 1950s, when Nobel-Prize laureates Martin and Synge discussed the benefits of this type of materials for different applications in chromatography. This type of stationary phase is composed of a single monolithic unit with interconnected microglobules and macropores (flow-through pores), and is typically bonded to the column wall via a covalent bonding to enhance the robustness. The separation performance strongly depends on the porous structure of the monolithic material. The morphology and surface chemistry of the nanomaterials will be tailored towards the requirements of tomorrow’s separation techniques: ultra-high-pressure LC, high-temperature LC, and two-dimensional chromatography.
The porous-layer open-tubular (PLOT) columns represent a subgroup of capillary columns in which the wall is coated with a porous material. They were first used in GC. Their current commercial availability makes them a vital alternative to liquid-coated columns for separations in the GC mode. The high permeability make this column format also attractive to achieve high-efficiency separations in LC. Different approaches to create porous coatings are being investigated.
Chip-based columns are developed for one-dimensional LC and multi-dimensional (spatial) LC separations. The chips are constructed in PMMA and COC polymer substrates using a micromilling robot. The chips feature on-chip injection, and open or structured microchannels. In addition, Monolithic stationary phases can be created in-situ in the confines of the separation channel using a UV-initiated free-radical polymerization reaction.
Selected reading
S. Eeltink, S. Dolman, F. Detobel, R. Swart, M. Ursem, P.J. Schoenmakers; High-efficiency LC-MS/MS separations with 50 mm, 250 mm, and 1 m long polymer-based monolithic capillary columns for the characterization of complex proteolytic digests (J. Chromatogr. A. 2010, 1217, 6610-6615).
B. Wouters, A. Vaast, A. Treumann, M. Ursem, Jenny Ho, M. Hornshaw, Marc Raes, Herman Terryn, S. Eeltink; The potential of polymer monolithic capillary columns for the LC-MS analysis of intact proteins (LC-GC Europe, 2012, 25, 10-17).
T.J. Causon, R.A. Shellie, E.F. Hilder, G. Desmet, S. Eeltink; Kinetic optimisation of open-tubular liquid-chromatography capillaries coated with thick porous layers for increased loadability (J. Chromatogr. A 2011, 1218, 8388-8393).