Preparative MCC using silica gel

[robin]

Most of the published literature on this topic covers separations on chiral products using CSPs. or binary separations using RPsilicas . I recently had an occasion to use MCC on naked silica -and key to this was the careful control of water adsorbed onto the silica.Generally water tends to deactivate with loss of resolution but I found the opposite for our particulal separation. Has anyone any experience on this.

[Supercritical]

what's MCC?

[robin]

MCC refers to multi-column continuous chromatography. This term is now replacing the possibly more familiar acronym SMB which refers to simulated moving bed chromatography. MCC is rapidly finding application in the large scale chromatographic resolution of enantiomers and a number of drugs are now being manufactured commercially using this technology.

[Kostas Petritis]

Well...

The abbreviation is still shared among:

Mutli Column Chromatography
Multi Capillary Chromatography
Multi column Continuous Chromatography
MicroCrystalline Cellulose

[Supercritical]

Well, I'm not sure if your asking about this in respect to the continous column procedure or not. I have noticed that in preparative normal phase chromatography any water tends to deactivate a bare silica column, causing lower capacity factors. Water can cause a loss in resolution typically with non polar solutes, but I have seen peak sharpening due to water in the mobile phase. Water seems to alter the amount I'm able to load on the column as well. I have used this to my advantage. I have added water to mobile phases using up to 2% as a modifier to sharpen peaks, similar to adding NH4OH or acetic acid. This of course is typically for very polar solutes. When using solvents such as methanol or acetone, % water in the solvent can be critical. Columns that are "deactivated" as such are not used for other samples. Column lifetimes are reduced and the silica seems to become brittle and compressed. You may experience some dissolution of the silica and voids may form. Bottom line is, depending on the sample, water can be useful or harmful to the separtion.

[Black Sunshine]

In prep and process chromatography (using bare silica) I have had good luck by maintaining the water level in my mobile phase. The water does occupy some of the active sites of the bed, therefore decreasing the runtime. This is beneficial if the desired separation/yield is not compromised. It has been a huge time saver.