[Babcock_Hall]

Dry loading has become our preferred technique for normal phase chromatography.  This week we had a C18-coated silica column to run using methanol/water.  Could this have been dry loaded?  I imagine that the ratio of coated silica to crude product will be higher: I recall a suggestion to have a greater ratio of coated silica to product than would be done in normal phase.

[Guitarmaniac86]

I've dry loaded on RP silica, it can be done.

[rolnor]

I preferre wet-loading, if your sample does not dissolve in the eluent you should change it, for example use toluene instead of hexane. I think generally you get a more narrow band of the sample if you use wet-load and thus better separation. I have never tried dry-loading a RP column.

[kriggy]

Im assuming we are talking about some kind of preparative flash system ?
Is it because of poor solubility of your mixture ? Have you tried loading in DMSO or DMF? I load all my RP purifications in DMSO with the method being isocratic in high aq. for first 3-5 minutes to wash away the DMSO

[Babcock_Hall]

My department is getting a preparative flash system soon; we just packed a column with C18-coated silica beads.  My student may have used more solvent than was needed, but I am not sure.

[rolnor]

Im assuming we are talking about some kind of preparative flash system ?
Is it because of poor solubility of your mixture ? Have you tried loading in DMSO or DMF? I load all my RP purifications in DMSO with the method being isocratic in high aq. for first 3-5 minutes to wash away the DMSO

This method can make everything go with the front, so use as little DMSO or DMF as possible is my tip.

[kriggy]

Yes that is a good point. I never had issues with that but its good idea to dilute in as small volume as possible and then add some water. I think I used 3 ml DMSO for 40 ml/min flow with no issues. On small columns it can be more significant issue. There should be guidlines in the operating manual of the instrument