Given samples of acetylsalicylic acid, acetaminophen, caffeine, and ibuprofen, calculate the Rf values and melting temperatures. Identify solvent system that produces good separation. Identify an unknown analgesic using Thin-Layer Chromatography (TLC).

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Objectives
• Given samples of acetylsalicylic acid, acetaminophen, caffeine, and ibuprofen, calculate the Rf values and melting temperatures.
• Identify solvent system that produces good separation.
• Identify an unknown analgesic using Thin-Layer Chromatography (TLC).

Principle
“Thin-layer chromatography is a method of separation, or identification of a mixture of components by using finely divided adsorbent solid/ liquid over a glass plate, and liquid as a mobile phase. The distinction depends on the relative affinity between the stationary and mobile phases of the compounds.”1
TLC can be used to identify the number of components within a solute mixture. It can be used to compare the retention factor of an unknown against that of a known solute/solvent combination.
TLC has two phases: a mobile phase (solvent) driven by capillary action, and a stationary phase (glass plate coated with silica gel).
The method is simple. You place a small amount of your solute mixture near the bottom of a plate. The plate is placed in a development chamber (a beaker with a small amount of solvent at the bottom, and a watch glass top). The solute mixture is allowed to travel up the plate along with the solvent. The solute mixture may or may not travel upward, depending on the solvent selected. The objective is for the components within your solute mixture to travel at different rates, allowing you to better identify a characteristic. The rate of travel is dependent on the solvent used.