Experiment 5: Column
Chromatography
Separation of Ferrocene & Acetylferrocene
by Column Chromatography
Reading: Mohrig, Hammond & Schatz
Ch. 18 pgs 235-253
watch the technique video on the course website!
Types of Chromatography
1. Thin Layer Chromatography (TLC)
• stationary phase: spread over glass or plastic sheet
• mobile phase: liquid; drawn up plate by capillary action
 2. Column Chromatography
• stationary phase: contained in a column
• mobile phase: liquid; passes through column
(gravity or pressure)
3. Gas Chromatography (GC)
• stationary phase: contained in a column
• mobile phase: gas; passes through column
(pressure)
Column Chromatography
• One of the most important methods for purification of organic compounds
• Based on same principles that govern TLC, except now stationary
phase packed into a glass column rather than spread over a thin
plate.
- separation based on the distribution of individual components
of the mixture between stationary and mobile phases
- effectively establish an equilibrium for each component
• Differences in equilibrium allow separation
• Recall: components adsorbed on the stationary phase do not move
components dissolved in the mobile phase move with the flow
Column Chromatography
Like with TLC:
• the more strongly a compound adsorbs to stationary phase, the slower it
will travel
- adsorption is based on interactions of functional groups in the
molecule with the stationary phase (silica or alumina)
hydrogen bonding
electrostatic interactions
coordination
Van der Waals interactions
• Also true: the more polar the stationary phase, the faster a compound
will travel
- any compound will spend more time in the mobile phase when
the solvent used is more polar
these two principles are NOT mutually exclusive
(be sure you understand why)
TLC vs. Column Chromatography
Two compounds: A ( ) & B ( )
 TLC:
 Column Chromatography:
develop
before
after
mobile phase moves
up the plate
mobile phase moves
down the column
A is the less polar compound
A moves furthest up the plate
(Rf A > Rf B)
A moves fastest down the column
(first compound to come off)
Column Chromatography
• Sample is loaded carefully to the
top of the column
add
• Column is run (eluted) by adding
solvent carefully to the top
• Eluent is collected in fractions at
the bottom
• Fractions are analyzed by TLC
• Pure compounds are isolated
collect
1
2
3
4
5
6
TLC of column chromatography fractions
Chromatography Column
Next Week
(October 10 - October 14)
Experiment 6: Column Chromatography
A. Chromatography of a Mixture of Ferrocene & Acetylferrocene
separate two compounds by column chromatography
DUE:
Extraction Lab Report (exp 4)
Lab Reports are due at the beginning of your regular lab session
Experimental Details
• Column Assembly
- plug tip with cotton
don't go overboard, solvent must flow through
- clamp column securely
column should be vertical
- add a layer of sand
forms a level bed for the silica
- add dry silica gel
use the small funnel in your micro kit
tap column carefully with pencil as you pour to
remove air bubbles
- solvate silica, by carefully pushing ~10mL hexanes
through the column
do not disturb the sand (use a pipet to add solvent)
apply air pressure  Not too much!
do not let the column run dry
Experimental Details
• Prepare & Load Sample
- weigh out ferrocene:acetylferrocene mix (get an exact mass)
- mix sample with dry silica & add resulting powder to top of column.
mix well; don't forget to use the funnel
- top sample with a small layer of sand
helps protect sample as you add solvent
- add enough hexanes to just wet the added silica
use a pipet; do not disturb the surface of the silica
works best to run the solvent down the side of the column
Experimental Details
• Elute the Column
- first with hexanes, then with an ether/hexane mix
- fit thermometer adapter to top of column to help control air flow
forms a nice seal, but still easy to adjust if pressure gets too high
- apply air pressure
rate of elution should be rapid, but should still see individual drops
do not let the column run dry!
- collect two individual fractions (one yellow, one orange)
tip of the column should sit just below rim of the collection beaker
avoid spatter (messy, lowers recovery)
rinse tip of column fequently with additional solvent
Experimental Details
• Isolate fractions
- concentrate using the rotary evaporator
don't forget to weigh (tare) the flask first
- alternatively, blow a gentle stream of air over the sample (not ideal)
Sample cools as solvent evaporated, concentrates water from air
if you choose this method, do it in the hood!
• Analyze fractions
- TLC, melting point, and IR
TLC most easily done before you concentrate your fractions
IRs will be distributed
- analysis can be done in any order  spread out!
Some Pointers:
• Minimize air bubbles when packing column
air pockets cause channelling - can ruin separation
• Do not disturb top layer of sand when adding solvent
may cause dilution of sample
separation will be less efficient
• Do not let the column run dry
stationary phase may crack; air channels may ruin separation
• Be sure to label your fractions!
Writing the Lab Report: Exp #4 Extraction
 Purpose
- technique experiment: what will you learn?
- what conclusions will you reach?
- a general discussion of theory/expected results is not a purpose!
 Results & Discussion
- Identify contents of flasks #1, #2, and #3
clearly explain how your data supports your identification
mp: compare to known values
TLC: what should the relative Rf values be?
consider the functional groups that are present
IR:
what absorbances should you see in each case?
tabulate IR data (one table for each compound)
include position (cm-1), vibration, & functional group
example shown in "Interpretation of Experimental Data"
Writing the Lab Report: Exp # 4 Extraction
O
 Results & Discussion
- IR example: ethyl levinulate
O
O
2950 cm-1
1740 cm-1
1720 cm-1
position (cm-1)
vibration
functional group
1720 cm-1
C=O
ketone
1740 cm-1
C=O
ester
2950 cm-1
C-H
alkane
Writing the Lab Report: Exp #4 Extraction
 Results & Discussion
- Discuss the success of your separation
basically: how well did the compounds separate?
in other words, how pure are they?
1. show & discuss reactions that allowed separation of compounds
be sure the equations are balanced
don't discuss the procedure in gory detail!
2. discuss the purity of your compounds
consider both TLC and mp data (be specific! )
what should you see if each compound is pure?
if each is impure?
how does your data compare?
3. Was the separation successful or not?
Writing the Lab Report: Exp #4 Extraction
 Results & Discussion
- Discuss the efficiency of the extraction process
how much of each compound did you get back (%recovery)
how much should you get back (max)?
Remember! You started with a 1:1:1 mixture by weight
account for any discrepancies in your % recoveries
did recover too much of a given component?
too little?
explain why!
- As always:
do not include a drawing of your TLC plate, measurements or
calculations in this section!
Writing the Lab Report: Exp # 4 Extraction
 Conclusion
- a brief recap of your findings
- make a general statement about extraction (what did you learn?)
- should be brief (2-3 sentences)
 Appendix A: Calculations
- Percent Recovery
started with a 1:1:1 mixture
each compound comprizes 1/3 of this mixture
% recovery =
amount of compound recovered (g)
1/3 original material (g)
- Rf value
 Appendix B: Spectra
- Page of IR spectra (provided)
x 100