I have heard people commenting on usage of silica gel for desalting or flash columns in size exclusion chromatography for biomolecules. Can anyone explain on what could be the chromatographic requirements satisfied by silica gel pertaining to biomolecule separation. i have acquired basic knowledge on FPLC and its types with columns
Hi there,
Silica gel is used for molecule partitioning between the silica based matrix which is polar (silanol function ) and the mobile phase which has to be less polar than the matrix. So basically the separation process is based on the polarity of the molecules: hydrophobic ones will be eluted first and the most polar ones last.
In addition to the partition chromatography described by Dominique Liger there are modified silica gels available for RPC, IEC, HIC, affinity chromatography etc. Compared to crosslinked agarose, silica has the advantage of higher pressure resistance (HPLC vs FPLC), and the disadvantage of lower resistance against alkaline buffers. Merck is an important supplier.
Desalting is commonly done with reverse phase with flash columns. Although not specifically addressing biomolecules, here is an example:
https://www.teledyneisco.com/en-us/liquidChromatography/Chromatography%20Documents/Application%20Notes/Desalting%20Samples%20with%20RediSep%20Rf%20Gold%20C18Aq%20Columns%20App%20Note.pdf
With respect to size exclusion, packings such as sephadex may be used:
https://www.teledyneisco.com/en-us/liquidChromatography/Chromatography%20Documents/Application%20Notes/Self-Pack%20Column%20Options%20for%20the%20CombiFlash%20Rf%20System%20App%20Note.pdf
Thanks Dominique Liger , Engelbert Buxbaum and Jack Silver your answers added value. still im not convinced on the point of why silica columns can not be used with buffers with pH exchange for gradient elution of biomolecules rather than desalting
Silica (SiO2) is an acid anhydride. It will slowly dissolve under neutral and alkaline conditions, forming silicate (X2SIO4, where X denotes a cation. The sodium salt is known as "water glass"). Under acidic conditions silica is stable. Thus, (modified) silica columns can be used for all chromatographic methods, as long as the pH is
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