How many times can I reuse my flash chromatography column?

Flash chromatography – a purification tool for both organic chemists and natural product researchers.  This tool is essential when you need to remove impurities from your targeted product, or products, in order to get them pure.  To reduce the costs associated with flash chromatography, some chemists try reusing the same column over and over, not always with success.

A question I am frequently asked is “how many times can I reuse my flash column?” Although I have previously addressed this topic, I feel it is worth another look. In this post, I will attempt to address this question by providing a bit more science behind the cartridge reuse question.

Column reuse is an issue of both economics and chemistry. With reversed-phase chromatography, column reuse is a given.  Why, because the hydrophobic stationary phase is washable with organic solvents to remove highly retained contaminants and the columns can be stored in acetonitrile or methanol for long time periods. Though reversed-phase columns cost more than silica columns, their reusability soon pays for the cost difference.

But, what about reusing normal-phase flash columns? Well, normal-phase flash chromatography does pose some reuse challenges. Unlike reversed-phase columns, which come to you “deactivated”, normal-phase columns packed with dry silica are “active”.

So, what does active mean?  Well, as you know, silica is a drying agent as well as a chromatography sorbent. Its active nature allows it to adsorb water, among other solvents.

Have you ever noticed how warm a new, dry silica column gets when solvent is introduced?  This phenomena is the heat of adsorption and as more solvent is pumped through the column the heat dissipates as the silica becomes “deactivated”.

However, solvent chemistry plays a role with the amount of deactivation taking place.  Hydrocarbons such as hexane or heptane are very non-polar a do not generate nearly as much heat or deactivation as, say, ethyl acetate or an alcohol.  Much of this stationary phase wetting exotherm has to do with solvent polarity, as you can imagine – and that is where the problems regarding reuse start.

The more polar the organic solvent, the more deactivated the silica becomes and the less likely it is to provide the same quality separation as previously achieved.  As an example, I used two different brands of silica columns three consecutive times running a hexane-ethyl acetate gradient with a 5-component sample, Figure 1. The results show decreasing compound retention of the three most polar compounds along with decreased separation with each consecutive run with both brands. Brand R actually degraded enough by the third run that the third and fourth peaks co-elute!

Figure 1. When polar solvents are used in gradients with silica columns the silica becomes deactivated. Even with flushing with a weaker solvent silica activity cannot be restored resulting in continually decreased compound retention and separation.

Once silica deactivates, it is virtually impossible to reactivate it. No amount of washing with hexane or other solvent will remove the adsorbed polar solvent, regardless of its concentration.

Are there exceptions? Of course, including running isocratic methods and using solvents with low polarity, such as dichloromethane. Under these conditions it may be possible to re-use your silica column.

So, the answer to the original question – how many times can I reuse my flash column depends on the type of stationary phase and the solvents used.  For practical purposes, to avoid potentially adding contaminants to subsequent normal-phase purifications, use the silica column only once – its just good science.

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Published by

Bob Bickler

Technical Specialist, Biotage

4 thoughts on “How many times can I reuse my flash chromatography column?”

  1. Hello Bob
    I only use normal phase columns once then throw them away. However there was a time when I had 4.25Kg of crude intermediate to purify and the largest available column was 1.5Kg. I did it batch wise, liquid load then CH2Cl2/EtOAc gradient. After each gradient I washed the column with 2CV of 50:50 CH2Cl2:MeOH then 2CV of 100% EtOAc then back to 100% CH2Cl2 and equilibrated for 3CV. This was for convenience rather than saving money, the solvents used for washing and re-equilibrating cost more than the column!
    We are always looking for ways to save money and the budget for flash columns is a highly visible target. In reality these columns have saved us a fortune compared to the old days of isocratic manual flash chromatography. With dry loading I would guess that I can get about 4x as much material on a column than with the old liquid load manual ones and that means I use 1/4 of the solvent and it’s the solvent that costs the money. Of course the cost of solvent is trivial compared to the cost of time. As a bench chemist I make compound which are sent for testing and perhaps automated flash has doubled my rate of production. I suspect the cost of each compound is enormous if I take into account the cash value of the site where I work and there has to be a return on that cash. The cost of building the facilities, fitting out the labs, NMR machines, Mass Spec, heating, electricity, maintenance. Of course I do get paid and starting materials to make a compound can be pricey. I’d love to see the figures for the total cost of making a molecule and I suspect that the cost of the flash column would be a tiny part.

    1. Hi Derek,

      Valuable input, Derek. Solvent and labor costs are indeed high versus the price of a prepacked cartridge in an industrial setting. It is primarily academia when there is a desire to reuse cartridges as there is little consumables budget, typically for flash cartridges. Labor is “free” and often the school will pick up solvent costs, perhaps burdening the professor with a portion of the cost in an operations budget.

      But as I have mentioned, there is no guarantee you can clean and restore the silica to its original activity and therefore, there is a contamination risk for subsequent purifications using the same silica.

      Bob

  2. I am curious to see what happens if I put used cartridge in the vacuum chamber with heating about 70C. When I need some more performance from my ordinary silica gel, I take the empty cartridge and pack it manually, after that placing it in the vacuum with heat. This procedure improves the efficiency of the column dramatically.

    In theory all the solvents will evaporate, thus reactivating the silica?

    1. Hi Vladislav,

      Heating wet silica at high temperatures will indeed reactivate the silica (including water removal). However, the amount of activation is still something which should be controlled. Most flash chromatography silica is hydrated to ~5% with water for consistency.

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