[peptideismylife]

Hey,

after a reaction and after a columcromatography which is the best method to purify a sample?

What about the lyophilizer? or is just to remove water from powder sample?

[Sepelio]

Well usually after you have the columned fraction you want your product will be pretty pure (ignoring solvent/residual water).

If you want to remove water/solvent just stick it on the buchi at low pressure for a few hours at ~60 degrees or something.

[Honclbrif]

The column chromatography was to purify your product. If you got poor separation there are several ways to go:

Do your compounds separate well by TLC, but poorly by column? You may have overloaded the column and need either a larger column, or to run it in batches. Alternatively, if you have a small enough sample, prep TLC may be an option, but these days prep HPLC is usually a better way to go.

Do they separate poorly by TLC? Try different solvent(s), or try reverse phase instead of normal phase.

There's also the simple things like solvent extraction, recrystallization, distillation...

[veyron103]

Do your compounds separate well by TLC, but poorly by column?

Hi,
sorry bit of a newbie here. I thought TLC separation was based on polarity while column was based on size. So does the TLC separation have to be same as that of column?

[Honclbrif]

So long as the plate and the column share the same chromatographic media, the principle of separation should be the same. In the case of small molecules, you would have to have some pretty darn small pores for size to be a real issue (think molecular sieves). For systems such as silica gel or reverse phase, polarity plays more of a role and you can roughly translate TLC results to column results. I know that when I do a reaction, polarity has a greater affect on Rf than size on both columns and plates.

Size exclusion mainly comes into play when considering macromolecules.