TABLE OF CONTENTS The basic TLC procedure has largely remained unchanged over the last fifty years. It involves the use of a thin, even sorbent layer, usually about 0.10 to 0.25 mm thick, applied to a firm backing of glass, aluminium or plastic sheet to act as a support. Of the three, glass has always proved the most popular, although aluminium and plastic offer the advantage that they are flexible and can more easily be cut to any size with minimal disruption to the sorbent layer. Numerous sorbents have been used, some more successfully than others, including silica gel, cellulose, aluminium oxide, polyamide and chemically bonded silica gels. The sample is dissolved in an appropriate solvent and applied as spots or bands along one side of the sorbent layer approximately 1 cm from the edge. An eluent (single solvent or solvent mixture) is allowed to flow by capillary action through the sorbent starting at a point just below the applied samples. Most commonly this is achieved by using a glass rectangular tank in which the eluent is poured to give a depth of about 5 mm. The plate is placed in the tank or chromatography chamber and the whole covered with a lid. As the eluent front migrates through the sorbent, the components of the sample also migrate, but at different rates, resulting in separation. When the solvent front has reached a point near the top of the sorbent layer, the plate or sheet is removed and dried.
