See the Waters and Agilent's SPE application book.  In general the packing material is the same as in an analytical column.

Hi Valeria,

If you are trying to purify peptides, you can use C18 and it will be efficient in removing Urea in your digest.

Here is a link to a very useful site from Cornell University:

Good luck!

Hediye

http://www.biotech.cornell.edu/sites/default/files/uploads/Documents/Proteomics_protocols/Protocol%2009_SPE%20cartridge%20desalting.pdf

Hediye,

TFA has become fairly standard in reversed-phase systems for peptides, but it isn't ideal. Fluorinated acids often make useful ion pairs with basic analytes. However, these strong acids can also degrade the packing and your analytes; leached C8/C18 material can dominate NMR spectra.

If you have used denaturing concentrations of urea, degradation products like biuret and ammonium ion could cause trouble. You definitely need to be careful with acidic conditions. Size exclusion would seem to be a good option, at least as a preliminary step (the proteins emerge from the column first).

A much older but smelly system that avoids pH extremes (specially during evaporation), and may help deactivate the stationary phase, is pyridine acetate or formate. If you distil these components, you get very clean extracts.

By the way, concentrated formic acid is reactive and likely to contain degradion products. For that reason it used to be sold as the 76% azetrope with water. The commercial product is easily purified by distilling as the azeotrope.

Hi all, thanks for your suggestions. I am trying to purify proteins and not peptides. For this reason, I need a reverse phase column which is less retentive compared to the C18, and I am using the C8. Anyway, I did not find any protocol on the SPE book. I performed the elution with 100% ACN at 0,1% FA (as a friend suggested) and it worked, but after evaporation, the proteins aggregated and could not be reconstituted in water to be injected in the LC system...any suggestions?

Instead of evaporating try freeze drying.  Be sure all required coenzymes and cofactors are present.

Vydac (they specialize in proteins) also has an SPE Application book.