My Question :

Dear DCHAS group,

I was wondering if anyone had an idea or can direct me to literature on “Flash chromatography” whereby air is directed the solvent column to speed up its elution of the compound wanted. One of our researchers had gotten a cut from the glass column breaking and cutting him on the arm.

Again, when asked, he said: everybody uses this technique! Being an old analytical chemist, I did not remember this method. However, an organic professor had informed me that this method is also called “Flash chromatography” and recommended the air pressure to be no more than 20PSIG and to wrap the column in plastic tapes to protect from breakage! . The lab in question use air spigots on lab benches which runs more than 20PSI if fully opened.

Any thoughts or comments you all have are welcome. Thank you in advance and enjoy your summer

 I asked the safety coordinator for our largest Chem research group, & his answer is:

Flash chromatography is best done in a fume hood because of potential exposure to solvent vapors if done outside of a fume hood.  We do use "house air" but the spigot is not opened all the way.  Just enough to get the air flowing to the column. Flash chromatography column should be wrapped with tape just in case of breakage due to stress on glass or air pressure.  To control the air flow, we use a flow control adapter for chromatography that is available from chemglass (Catalog # is CG-1195) which enable the control of air flow and thus prevents column breakage due to excess air pressure.  If the control valve is use properly, column breakage is rare. The columns should be inspected before each use and columns that show any signs of stress on the glass should not be used.  Since, column breakage during use is always a possibility, gloves, safety glasses or goggles and a lab coat should always be worn when doing flash chromatography.

Kim Auletta
Lab Safety Specialist

Hi Yung,

I remember this being called LPLC (Low Pressure Liquid Chromatography) when I did my under grad research about 8-9 years a go in organic research.  

I used a glass column that looked like the one in Figure 5 that in the Flash Chromatography PDF and also packed it slightly differently.  Our column was about 3ft tall, a 10 gram column.   The top was tapered to a smaller opening to fit a rubber stopper with a center hole., here we connected our compressed air tubing from a cylinder.  The stopper was held in place with 2 rubber bands (one pass each, crisscrossed), which gave enough flexibility for the stopper to blow out if too much pressure built up in the column.  At the air cylinders, we set the regulator to 18 psi to control the pressure being delivered to the column.  To add additional solvent/mobile phase, their pressure was shut off and the stopper was removed from the top and with a funnel, the mobile phase was slowly added.  

I do remember the columns, even though a thicker glass, were extremely fragile and expensive.  They will break very easily, with the slightest bump, over-tightening of the clamps, or too much pressure pumped in (though it should be step with a way to relieve or avoid this). For some protection, I have seen sleeves, plastic/poly- type material that slides over the outside glassware to prevent flying glassware if it shatters or explodes.

Chris Suznovich

I'm an old chemist and used to do tons of "flash chromatography". I don't ever remember reading about it, just learned it from my lab mates in school but continued to use it in industry in the late 80s. We used N2, not air. No regulator, just whatever came out of the hood N2 tap. You could make it faster or slower by changing the pressure. I never had one break but the rapid movement of solvent through a glass column can build up quite a static charge - enough to stand the hair on your arms on end and cause your solvent stream coming out the bottom to veer towards your hand if you put it near by. Scary when running ether columns. I always did mine in the hood but many people did them on the bench top. (I know, I'm really old.) I would wrap copper wire around my column and attach it to the plumbing to help but since it was insulated by the glass, it was of limited value.

Now, as a safety person, I would recommend plastic netting on the column and reservoir to contain breakage, a regulator on the gas to control pressure and some method to ground the whole thing. And, of course, doing it in a hood.

Eventually, we moved away from flash and began to use the automated fraction collector chromatography systems like the Foxy sold by Isco (they may have been sold again and sell under a different name). It is easier since you didn't have to stand there and keep changing the collection flask and refill the reservoir. Tell your guy to go buy one. I'm sure he can find used ones if he doesn't want to buy new.

Hi Yung,

I believe that your researchers are referring to the standard “flash chromatography” used in organic synthesis labs.

See the following link for a copy of the technique as originally described by Clark Still of Columbia University (Still, W.C., Kahn, M., Mitra, A., J. Org. Chem, Vol. 43, No. 14, 1978, p. 2923).

http://siggy.chem.ucla.edu/voh/136/Flash_Chromatography.pdf

Many labs have begun using automated medium pressure flash systems and pre-packed silica gel columns in plastic cartridges (see Teledyne ISCO, Biotage, and Interchim as example manufacturers of these systems), but the flash column as originally described in 1978 still has significant utility today.

In my experience, 10 psi is about the practical limit for this technique, above which you may be putting significant strain on the glass columns.  Sometimes researchers are tempted to put more pressure on the glass to elute the material faster, or if plugs occur in the column.  I would definitely recommend pressure regulators be installed in the air lines.

Steve

This is a very common technique and most investigators that I know use compressed nitrogen tanks with regulators that easily regulate the pressure down to a usable level and you don’t have to worry about contamination from house air lines, i.e. water, dust, etc.  Further, the compressed nitrogen line is usually run through a oil bubbler  as a further verification of low pressure.  I have also seen some researchers cut a small slit in the tygon tubing to prevent the pressure from getting too high.

 < /o:p>

Hope this is helpful,

 < /o:p>

Adam O. Barden

Washington State University

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Disclaimer/whatever: my company is a Chemglass (now Chemglass Life Sciences) distributor.

There are older chromatography columns out there made out of standard wall tubing.  Flash chromatography first came into vogue the late 1970's, so it's possible you may have some thinner wall ones circulating at your organization.  A true flash chromatography column should be constructed out of medium wall tubing to provide an extra margin of safety.   Chemglass not only makes theirs out of medium wall tubing, they are also available from the factory with a clear plastic coating by special order (if anyone wants quotes on these, contact me off list).

Many columns use a fritted glass disc at the bottom.  The maximum differential pressure rating on those is 15 psi.  So 15 or 20 psi should be established as the safe working limit, yes.

Relatively safe pressure control on columns can be achieved by making sure that the gas flow control adapter at the top is not secured **too** tightly.  A Keck clip or such is more than enough to secure the adapter, but can still provide some pressure relief.    It is, of course, more reliable and desirable to provide a pressure gauge and/or some sort of relief system teed into the gas supply line so that researchers know exactly how much pressure they are achieving.   The best solution would be a regulator can be used on the gas/air supply line.

Your written SOP for chromatography should include a discussion of the pressurization hazards, "safe" pressure ranges, and how to mitigate the risks.   The SOP should also explain that proper PPE (lab coats with sleeves, goggles) and engineering controls (fume hood sashes, blast shields etc.) can also go a long way in minimizing any injury should an accident occur.

Rob Toreki