column chromatography adsorbent

[SuperOrchestra]

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Just did some practice questions, one was on slica gel and what qualities of the adsorbent. I got it wrong because it says that you want to maximize the surface area of the beads.
Now that makes some sense because you need the solution to interact with the polar phase and what not... except I remember in Organic Lab it stating the opposite, you want to minimize the surface area as to reduce the hold up (amount of unrecovered solution).

What do you guys think?

Should I lose any sleep over this?

 

[Quantum Chem]

I don't know what the question was, but what I remember from my analytical chem class was that smaller sized silica beads give a better separation but takes a longer time. I know that surface area has a purpose as well, something like it causes greater interaction or something, but I can't remember because I never went to lecture and sold my book, so I can't look it up. And I could be wrong about what is said above too.

 

[CdanceNS]

Basically you use silica gel in column chromatography to separate compounds. Silica gel would be chosen as an adsorbent when you are separating a polar, and a less or non-polar compund. The non-polar compound would not be retained and will elute with the non-polar solvent. The polar compound would interact with the silica and elute more slowly. Increasing surface area will increase the interaction with the polar compound allowing better separation of the two compounds. However, this also takes more time to complete the column. It is always a trade off between time and resolution.

 

[StIGMA]

It's simply about obtaining better separation (resolution). More area, such as having a longer column, guarantees greater separation between compounds. Similar to running a longer agarose gel, for instance.

 

[SuperOrchestra]

Yeah, I think I looked too far into the question, if I had just kept the general concept of separation in my head, probably would have come to that conclusion.