[TSALEX]

Hey guys,

So my problem is that silica gel is coming out of the bottom of my column.  Apparently, I did not pack the bottom of the column tightly enough with steel wool.  I thought I had cause when I set up the column and got the column (with sand on top) completely wet with hexanes, none of the silica gel came out.  I filled 20 tubes of eluent, then stopped for the night cause it was late.  came back about 24 hours later and started trying to fill vile number 21 and the silica gel began coming out.  Is there anyway to recover the product that is coming out with this gel? Or is the product entirely lost now? My first thought was, that I would drain it all into a beaker, then reset the column, but the sand is still on the top.  any ideas?

-Thanks

[discodermolide]

Empty the column and stir the silica with a polar solvent to recover your compound(s). Evaporate the solvent and re-column the residue.
Have you not got a column with a frit at the bottom? I would not use steel wool, that's iron and silica is acidic, with some compounds it may well react, better to use cotton wool.

[TSALEX]

Empty the column and stir the silica with a polar solvent to recover your compound(s). Evaporate the solvent and re-column the residue.
Have you not got a column with a frit at the bottom? I would not use steel wool, that's iron and silica is acidic, with some compounds it may well react, better to use cotton wool.

No, I do not have one with a frit.  So I was going to try using acetone to recover my compound.  Will the silica gel dissolve with acetone then come off in the rotavap with the solvent leaving only my residue? or will the silica gel remain as a slush at the bottom with my compound in solution with the solvent above?(in which case i can just filter the liquid above the silica slush, then rotavap, then re-column with a cotton this time.  Sorry if these questions seem obvious.  I am some what new at this. 

-Thanks

[discodermolide]

All you do is stir the silica-gel with a suitable solvent. Filter it off, remove the solvent and re-chromatograph the residue. If small amounts of silica come through it does not matter, they will be removed on the next column.
Check the solid  by re-suspending in the solvent and them run a TLC, just to make sure you recovered everyting.

[TSALEX]

All you do is stir the silica-gel with a suitable solvent. Filter it off, remove the solvent and re-chromatograph the residue. If small amounts of silica come through it does not matter, they will be removed on the next column.
Check the solid  by re-suspending in the solvent and them run a TLC, just to make sure you recovered everyting.

awesome, thanks a lot!

[salteen]

I filled 20 tubes of eluent, then stopped for the night cause it was late.

Just FYI, I've been advised against leaving columns overnight and then restarting the next morning.  The silica is acidic and sometimes your product will be decomposed by the time you get back the next day.  I also find from personal experience that the "packing" of the silica on the column becomes loose after leaving it for an hour or so, which then can result in separation issues.

[TheUnassuming]

Its less an issue of loss of packing when you abandon a column and more the fractions/compounds spreading out on the column.  As time goes on the fractions/compounds migrate to points of lower concentration, to the eventual point of homogeneity.  Its like those water/soil models you use to demonstrate how water contamination in one place will leech out and contaminate the water in another place.