Lab 1: Column Chormatography And TLC Flashcards
TLC
Used to monitor progress of reactions and determine optimal combos of solvent and adsorbent for separations
Limit of TLC
Cannot be used on volatile compounds having boiling points below 150 degrees Celsius
Acidic or basic character of solid adsorbent
If substances analyzed contain FG that are sensitive to acids and bases. The adsorbent may function as a catalyst to destroy the functionality by chemical reaction.
Selection of a good Eluant
- must readily dissolve the solute but not compete with it for binding sites on phase
- solvent should not be too polar because may bind strongly to adsorbent and force solvent to remain in the mobile phase
- solvent must significantly less polar than the various components of the mixture to obtain and effective seperation.
Increasing eluding power with polar stationary phases
Water Methanol Ethanol 1-propanol Acetone Ethyl acetate Diethyl ether Chloroform Dicholormehthane Toluene Hexane Petroleum ether
Column chromatography
A more weakly adsorbed compound is eluted faster from the column than is a more strongly adsorbed compound
Normal-phase chromatography
Polar stationary phase in combo with organic solvents as mobile phase.
Reverse-phase chromatography
Stationary phase is glass beads coated with non-polar hydrocarbon film.
Mixture of water and organic solvents are used as elutant.
Air bubbles in column
Liquid level in the column should never be allowed to fall below the top of the adsorbent. If this occurs. Air bubbles form and allow channeling. Which results in poor separation because the components are eluted as ragged rather than sharp bands.
Layer of sand
It allows the sample to flow evenly onto the surface of the adsorbent. And it prevents disruption of the packing material as eluding solvent is added.
