The purpose of this experiment was to determine the presence of the analgesic compounds acetaminophen, aspirin, caffeine, and salicylamide in the over-the-counter medications Anacin, Bufferin, Excedrin, and Tylenol. Thin-layer chromatography (TLC) was used to analyze solutions of the medications; the TLC plates were visualized using ultraviolet light and iodine staining.The ten micropipets used to spot the TLC plates were made from glass capillary tubes by heating the middle of each tube in a Bunsen burner flame, pulling the ends of the tube away from each other so that the middle was stretched into a thinner tube, and breaking the cooled capillary in the middle to form two micropipets. Two silica-gel TLC plates were spotted with solutions
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Rf values were calculated for the spots using Equation 1. (The distance traveled by each spot was measured as the distance between the starting point of the spot and its center of concentration in its final position; the distance traveled by the solvent was measured from the starting line of the spots to the final position of the solvent front.) Separation of compounds by TLC, such as that observed in this experiment, occurs because the compounds are partitioned between the stationary phase (the adsorbent—silica in this case) and the mobile phase (the development solvent). Stronger intermolecular forces between more-polar compounds and the polar adsorbent cause these compounds to move up the plate more slowly than less-polar compounds, whose weaker forces of attraction to the adsorbent are responsible for their tendency to stay in the relatively nonpolar solvent moving up the plate.5 Thus, compounds are separated according to their differing behavior in the adsorbent-solvent system, with their final heights on the plate and Rf values determined, in general, by their relative degrees of polarity. For best results, acetic acid was a necessary component of the development solvent in this experiment because it was a source of protons, which prevented the
Rf values were calculated for the spots using Equation 1. (The distance traveled by each spot was measured as the distance between the starting point of the spot and its center of concentration in its final position; the distance traveled by the solvent was measured from the starting line of the spots to the final position of the solvent front.) Separation of compounds by TLC, such as that observed in this experiment, occurs because the compounds are partitioned between the stationary phase (the adsorbent—silica in this case) and the mobile phase (the development solvent). Stronger intermolecular forces between more-polar compounds and the polar adsorbent cause these compounds to move up the plate more slowly than less-polar compounds, whose weaker forces of attraction to the adsorbent are responsible for their tendency to stay in the relatively nonpolar solvent moving up the plate.5 Thus, compounds are separated according to their differing behavior in the adsorbent-solvent system, with their final heights on the plate and Rf values determined, in general, by their relative degrees of polarity. For best results, acetic acid was a necessary component of the development solvent in this experiment because it was a source of protons, which prevented the