Experiment 2, B: Column Chromatography

procedure 1: column prep

• ensure column is clean and dry before starting

• place a small wad of glass wool at the bottom of the column using a long glass rod

• using a funnel add a small layer of sand so that the bottom of the column will be even

procedure 1: column prep

• add 7g of silica to the column

• mix 0.3 g of silica with 0.2g of the 50/50 mixture of o- and p-nitroaniline and then add to the top of the column

• pour a small layer of sand on top of the column (to prevent the silica column from being disturbed when eluent is added. 

procedure 2: column chromatography

• based on your results from part 1: prepare 20 mL of eluent

• ^ mix together 10 mL of cyclohexane and 10 mL of ethyl acetate (this is the eluent)

• use a pipette to add the eluent to the column (turn the stopcock so mobile phase is slowly descending the column, elution should occur at approx 1 drop/2 seconds

procedure 2: column chromatography

• add eluent as required so there is always mobile phase on top of the column

• when the coloured zones are eluting, collect in approx 2 mL fractions in test tubes

procedure 3: TLC

• test all fractions by TLC and determine which fractions are pure for each of the components of the mixture

• using 50:50 cyclohexane and ethyl acetate as the solvent system

• o-nitro is less polar (farther from baseline)

• p-nitro is more polar (closer to baseline)