1. FLASH CHROMATOGRAPHY
 Also called as “medium pressure chromatography”
 “An air pressure driven hybrid of medium and short
column chromatography optimized for rapid separation"
 Popularized by Clark Still of Columbia University
 An alternative to slow and often inefficient gravity-fed
chromatography

2. Introduction..
 Differs from the conventional technique in 2 ways:
 Slightly smaller silica gel particles (250-400 mesh)
are used, and
 Due to restricted flow of solvent caused by the small
gel particles, pressurized gas (10-15 psi) used to
drive the solvent through the column of stationary
phase
The net result is a rapid “over in a flash” and high
resolution chromatography.

3. Column vs Flash Chromatography
Traditional Column Flash chromatography
chromatography
• Pre-packed plastic
• Glass columns with silica cartridges
gel
• Solvent is pumped
• Separation is very slow through the cartridge
(typically many hours)
• Much quicker and more
• End of the run, silica gel reproducible
must be
removed, cleaned, dried • Remaining solvent
and re-packed flushed out of the column
using pressurized gas
• Both time consuming
and hazardous

4. Column chromatography Flash chromatography

7. Modern flash chromatography systems are sold as pre-packed
plastic cartridges, and the solvent is pumped through the
cartridge.
Systems may also be linked with detectors and fraction
collectors providing automation.
The introduction of gradient pumps resulted in quicker
separations and less solvent usage.
Flash chromatography is not expected to provide the resolution
or reproducibility of HPLC; it is a technique that can quickly
improve the purity of samples to an acceptable level.

8. Selection of solvent system
Solvent system
 Compound should have TLC Rf of 0.15 to 0.20 in the solvent
system
 Binary solvent system –
 Polarity can be adjusted
 Rate of elution can be determined
Common solvents used :
dichloromethane/hexane, ether/hexane, hexane/ethyl
acetate, and dichloromethane/methanol
High polarity of solvents increase the rate of elution of all
compounds.

9. Quantity of silica gel required..
 40-63 µm silica gel particles are used
 Amount depends on 2 factors :
– Rf difference of the compounds to be separated
– Amount of sample
 ↑ silica gel -↑ the length of time for chromatography
 For,
– Easier separations, ratios closer to 30 : 1 are effective
– Difficult separations, more silica gel is often required

10. Packing the column
 Glass column / plastic cartridges
 Has either a glass frit or a plug of cotton wool directly above the
stopcock (To prevent the silica gel from escaping from the
column through the stopcock)
 ~1/2 inches layer of clean sand above the plug of glass wool
 Make sure that surface is flat
 Pour in the silica gel using a funnel.(Do this step in hood)

11. Method
• A solvent is chosen which gives good separation and moves the
desired component to Rf = 0.20 on analytical TLC
• A column of the appropriate diameter is selected and filled with 5-6
in. of dry 40-63 µ silica gel
• Column is solvated
– The column is filled with solvent and pressure is used to rapidly
push all the air from the silica gel
• The sample is applied and the column is refilled with solvent and
eluted at a flow rate of 2 in./min
• Top of the column should never run dry

12. Procedure for Microscale Flash Column
Chromatography
 In microscale flash chromatography, the column need neither a
pinchclamp or a stopcock at the bottom of the column to control
the flow, nor does it need air-pressure connections at the top of
the column.
 Instead, the solvent flows very slowly through the column by
gravity until you apply air pressure at the top of the column with
an ordinary Pasteur pipet bulb.

13. (1) Prepare the column.
1. Plug a Pasteur pipet with a small Add dry silica gel adsorbent, 230-400
amount of cotton; use a wood applicator mesh -- usually the jar is labeled "for
stick to tamp it down lightly. flash chromatography." One way to fill
the column is to invert it into the jar of
2. Take care that you do not use either
silica gel and scoop it out . . .
too much cotton or pack it too tightly. You
just need enough to prevent the
adsorbent from leaking out.

14. . . . then tamp it down before scooping Another way to fill the column is to pour the
more out gel into the column using a 10 mL beaker.

15. (2) Pre-elute the column.

16. (3) Load the sample onto the silica gel column
Two different methods are used to load the column: the wet
method and the dry method:
Wet loading method
The sample to be purified (or separated into components) is dissolved in a small amount
of solvent, such as hexanes, acetone, or other solvent. This solution is loaded onto the
column.

17. Dry loading method

18. (4) Elute the column.

19. 5) Elute the column with the second elution solvent.
If separating a mixture of one or more compounds, at this point
change the eluting solvent to a more polar system, Elution would
proceed as in step (4).
(6) Analyze the fractions.
If the fractions are colored, simply combine like-colored
fractions, although TLC before combination is usually advisable.
If the fractions are not colored, they are analyzed by TLC
(usually). Once the composition of each fraction is known, the
fractions containing the desired compound(s) are combined.

20. Advantages
• Large quantities of the sample can be separated (0.5-2g)
• Fast ( 1o to 15 minutes)
• Cost efficient
• Elaborate equipment and the purchase of expensive
equipment is not necessary
• If high resolution is required, flash chromatography is
carried out before HPLC to avoid contamination of the
expensive plates

21. Applications
• Purification of various peptides, antibiotics
• Separation of closely related organic compounds
• Purification of closely related drug intermediates
• High speed fractionation of natural products –
tocopherols, alkaloids, lignans, xanthones, stilbenes, flavonoids
• Drug discovery
• Agrochemistry
• Petrochemistry

22. Conclusion