Thin-Layer Chromatography (TLC) Uses: To separate the components of a mixture To determine the purity of a compound To see if two compounds are identical To monitor the progress of a reaction A separation/purification technique. Chromatography

Thin-Layer Chromatography TLC Bottle/Chamber Filter Paper TLC Plate: contains A polar stationary phase (alumina or silica gel) & a very small amount of your sample Mobile Phase: organic solvent(s) of varying polarity

Chromatography Basics How it works: Your sample is loaded onto the polar stationary phase Polar compounds will adsorb onto the stationary phase to a greater extent than non-polar compounds The mobile phase (eluting phase) helps “push” or elute the compounds either down a column (for CC) or up a plate (for TLC) The main concept to consider in chromatography is polarity.

Polarity & Intermolecular Attractive Forces More polar compounds will be more attracted to silica gel than non-polar compounds due to intermolecular attractive forces - a dipole-dipole interaction. The more non-polar compounds will travel more easily and more quickly through the stationary phase. The mobile phase helps carry the compounds through the stationary phase. Separation of compounds in a mixture is possible because compounds have different polarities. Silica gel, [SiO 2 ] n

Polarity & Intermolecular Attractive Forces Example: Separate a mixture of butyl amine and cyclohexane using TLC Things to consider: 1. Polarity of each compound in the mixture Butyl amine is polar; cyclohexane is non-polar 2. Polarity of stationary phase Silica gel (or alumina) is polar - predict that butyl amine will interact with it more strongly 3. Polarity of the mobile phase - the solvent: you determine what solvent to use Prediction: Cyclohexane will elute first/faster through the stationary phase. Butyl amine will elute last/slower.

TLC Separation Example: Separate a mixture of butyl amine and cyclohexane using TLC Mobile Phase: Typically use a mixed solvent system. If the mobile phase is non-polar, cyclohexane will travel along with it, but butyl amine will not as readily. If the mobile phase is polar, both cyclohexane and butyl amine will travel with it, but butyl amine will be slower because it’ll be interacting with silica gel as it’s traveling. Note the separation of spots

Chapter 13: TLC Experiment/Separation of Chlorophyll The Experimental Steps 1. Load sample onto stationary phase/TLC plate (labeled) (a) Dissolve sample in a small amount of organic solvent (b) Use capillary tubes to load on sample

TLC plate (labeled) with samples loaded

2. Insert TLC plate into TLC chamber (filled with a layer of mobile phase & allow mobile phase to “run up” the TLC plate. Take out when the solvent reaches 1 cm from top of plate (solvent front). Mark the solvent front line with a pencil.

R f = distance spot traveled from origin line/distance of solvent front