Permeable Chromatographic Media

Packing materials in bead form can be grouped into four classes: homogeneous cross-linked polysaccharides (e.g. agarose), macroporous polymers based on synthetic polymers (e.g. POROS particles used in perfusive chromatography with large pores of 600-800 nm and diffusive pores of 50-100 nm), tentacular adsorbents allowing faster interaction between proteins to be separated and functional groups and materials based on the concept of 'soft gel in a rigid shell' combining the good capacity of soft gels with the rigidity of composite materials.

Prinzis S, Fraudeau C, Hutchinson G and Paulus M (1997) Gilson Guide to SPE Automation. Villiers-le-Bel, France: Gilson. Stevenson D and Wilson ID (eds) (1994) Sample Preparation for Biomedical and Environmental Analysis. New York: Plenum Press.

In conventional packings, solutes are carried to sites on the particle surface by bulk convective flow of the mobile phase through the column and then diffuse to binding surfaces inside the particle. The intra-particle diffusion process can be quite slow for large molecules (proteins, peptides). In order to maximize capacity and resolution, interaction with as many sites as possible is required; however, this will be more difficult at high flow rates and therefore trade-offs between speed, resolution and capacity are needed. In permeable, flow-through particles used in perfusive chromatography the flow rate can be increased one order of magnitude compared with conventional packings because of the short diffusion path length inside the microspheres.

New materials aim to achieve higher sorption capacity and better sorption kinetics. Some developments consider new geometries: fibres, membranes or discs (cellulose, polymethacrylate) or continuous beds (rods, monoliths). In continuous rods of acrylamide-acrylate polymers, flow pores are of 3-4 |im diameter and in methacrylate-styrene polymers large pores of 0.5-2 |im and even 20 |im are obtained with micro-spheres of less than 0.5 | m. Similar developments on continuous silica rods are taking place. In continuous bed technology, channels are of 3-5 | m with micro-spheres of 0.5-1 | m, whilst in bead form, packings are typically of 3-50 | m with pore size of 0.1 | m. Also superagarose beads of 300-500 |im have been prepared with superpores of 30 | m as well as 3 mm thick membranes. Table 1 reports examples of con-vective chromatographic media.

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Solar Panel Basics

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