TABLE OF CONTENTS Planar chromatography includes thin-layer and paper chromatography and electrophoresis. In thin-layer chromatography (TLC), a stationary phase is coated on an inert plate of glass, plastic, or metal. The samples are spotted or placed as streaks on the plate. Development of the chromatogram takes place as the mobile phase percolates through the stationary phase and the spot locations. The sample travels across the plate in the mobile phase, propelled by capillary action. Separation of components occurs through adsorption, partition, exclusion, or ion-exchange processes, or a combination of these. Paper chromatography employs special paper supports, but otherwise resembles TLC. Electrophoresis utilizes the electromigration of ions and molecules in an applied electric field as an auxiliary separation aid. Each charged species moves at a rate that is a function of its charge, size, and shape. In planar chromatography the position of the resultant bands or zones after development is observed or detected by appropriate methods. Because of its convenience and simplicity, sharpness of separations, high sensitivity, speed of separation, and ease of recovery of the sample components, planar chromatography finds many applications.
Resolution of the sample in thin-layer chromatography is accomplished by passage of the mobile solvent mixture through the initial spot and beyond until the solvent front reaches within 2.5 cm of the opposite edge (top of plate in vertical development). Interaction of individual sample components with the stationary phase and the mobile phase, if each is properly selected, will cause the components...
