TLC (Thin Layer Chromatography)

TLC is based on the separation of constituents (drugs) by the elution of solvents on a thin layer of absorbent material coated on a glass plate. The drugs of interest are first extracted from urine samples with appropriate solvents and reduced to a concentrated state by evaporating the extraction solvent. The concentrated residue is applied to a "spot" at the low end of a TLC plate. The plate is placed on end in a shallow layer of developing solvent mixture in a closed chamber. The solvent is allowed to rise on the plate to a predetermined distance at which point the plates are removed from the chamber and dried. By spraying the plate with various chemical solutions that react with the drugs of interest, they can be visualized. The distance that the drug migrates ("Rf ratio") and the characteristic appearance of the drug/chemical complex allow for the identification of the presence of drug.