Preparative TLC plates have adsorbent layers thicker than the 250 microns. Thus, preparative plates can be used for separation of larger quantities of materials.
The loading capacity for a given degree of sample component resolution increases roughly as the square root of the adsorbent layer thickness. In preparative TLC, materials to be separated are often applied as long streaks rather than spots. After development, specific compounds may be recovered by scraping the adsorbent layers from the plate in the region of interest and eluting the separated material from the adsorbent using a strong solvent.
Soft-layer Silica plates are the kind of most widely used when recovery of the separated compounds is desirable. No organic substances have been added to these products. They are compatible with all organic solvents except solvent containing greather than 20% water.
Binder Free Silica plates contain neither inorganic nor organic binders. They are best for inorganic TLC. Activates plates at 110oC for 30min before use. A few eluents will cause the adsorbent to separate slightly from the plate in the submerged part of the layer.
Reversed phase plates are C18 bonded-silca. They are used to separated both polar and non-polar compounds by adjusting the solvent system.
Silica impregnated with 10% Silver Nitrate plates permitincreased discrimination of certain compounds, particularly those containing carbon-carbon double bonds. More double or triple bonds (unsaturation) give lower Rf values. The product is light sensitive and should be stored in the dark. Activated plates at 110?C for 60min before use for improved separations.
Silica modified with 7.5% Magnesium Acetate plates decrease the acidity of the layer and allows increased discrimination of phospholipids.
Alumina TLC plates are aluminium oxide containing calcium sulfate hemihydrate as a binder. These TLC plates are recommended for terpenes, alkaloids, steroids, aliphatic and aromatic compounds. Activated plates at 120?C for 10min before use for improved separations.
Microcrystalline Cellulose TLC plates are coated with microcrystalline cellulose (Avicel®). The adsorbent consists of regenerated alpha cellulose particles of nearly spherical shape and 50µm particle size. Layer are binder free and abrasion resistant. Compounds separated on this cellulose tend to form more compact spots than on fibrous cellulose layers. Recommended for carboxilic acids, lower alcohols, urea and purine derivatives.
