Why does my silica flash chromatography column get hot?

Silica is the most commonly used sorbent for flash column chromatography. When solvent is pumped through a column packed with dry silica you may notice it gets warm and sometimes down right hot!

In this post I will attempt to explain why this phenomena occurs.

Flash chromatography is a widely utilized purification methodology. Typically used with non-polar and moderately polar solvents and columns packed with silica, this technique has the ability to separate compounds with different polarities and functional groups.

With bulk silica, as well as pre-packed flash cartridges, the media is “active”, meaning it is dry. Because silica is also an adsorbent media as solvent passes through it several things happen…

  • The solvent displaces the air in the silica’s pores
  • The solvent adsorbs to the silica surface and generates heat
  • Friction builds

It is the adsorption process that generates the initial “heat band” and the more polar the solvent, the greater the heat generated. This phenomena is known as the heat of adsorption.

Since silica has a polar surface it preferentially adsorbs polar solvents. The solvent’s polarity and heat capacity influence the amount of heat generated during the initial solvent-sorbent interaction. This is the main reason silica flash cartridges are equilibrated prior to sample injection as the generated heat will negatively influence mass-transfer kinetics and compound retention/separation.

Once fully equilibrated just the act of pumping solvent through the packed column generates friction, and therefore heat.  The amount of heat generated is dependent upon media particle size, flow rate, and solvent viscosity but is typically very low in flash chromatography.

Is this a concern in your daily flash chromatography?  Only if you do not equilibrate your flash cartridge/column prior to loading your sample, Figure 1.  It is not a concern with reversed-phase or other bonded silicas as these media are bonded and therefore, deactivated.

Figure 1. Impact of heat on chromatographic performance. Top –  flash chromatography using a hexane/ethyl acetate gradient without equilibration generates enough heat to disrupt the adsorption/desorption kinetics which reduces performance compared to an equilibrated cartridge (bottom) where the heat has been removed.

Have you experienced this heating phenomena?  If so, how has it impacted your purification?

Published by

Bob Bickler

Technical Specialist, Biotage

6 thoughts on “Why does my silica flash chromatography column get hot?”

  1. I have used silica gel column and I also noticed that by passing methanol through the column the temperature raised from 25 to around 35 C. By continue passing more methanol the temperature slowly returned to room temperature.

    1. Yes, that is the typical phenomena. Rapid heating followed by gradual cooling. Four variables are in play with heat generation 1. solvent polarity, 2. polar solvent heat capacity, 3. polar solvent concentration, and 4. mobile phase flow rate (friction source).

  2. Hey Bob,

    Very nice article, good to see you are still writing the Flash Blog. On rare occasions I have found that running samples on a dry cartridge can give better separations, but have found that is usually when the compounds are slightly more polar and higher polarity solvent mixtures are being used. As with all purification’s it is all about the optimization! Cheers my friend

    1. Hi Jeff,

      Great to hear from you. Yes, the heat factor becomes less important with better-retained compounds which sometimes need a bit more surface activity from silica to separate well. But as you point out, nothing beats an optimized method for purifying crude mixtures.

      Bob

  3. Hi Bob,
    Never thought about it but makes sense. Excellent tip. Love the way chemistry works. Hope all is well. All’s well here. Cheers!
    Kind regards,
    Gabe

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