Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: PhosMAN30 on April 24, 2008, 01:06:07 PM
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One of the best tips for loading columns w/ sample came from Dylan S. at Stanford. Many compounds are soluble in toluene and it makes an awesome load solvent most of the time. The only times when it does not work well is when the molecule is really non-polar and the conditions for elution are of low polarity ie. 95:5 Hex: EtOAc and/or the compound is simply not soluble in toluene. What's great is when it works you can clearly see the band of toluene fly off the column in the initial flush and in case you're blind you can smell it. **As with any load solvent you should use a minimal amt. when loading.
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I've never heard of doing this. What is the benefit to using a load solvent over just using solvent that you are running the column with?
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Minimizes diffusion into the eluent is the obvious one. The next one is a determination of a more meaningful relative retention time
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That makes sense.. Ill have to give this a try next time I run a column.
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Just curious- why wouldn't the compound fly down the column with the toluene band?
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I've never heard of doing this. What is the benefit to using a load solvent over just using solvent that you are running the column with?
Load solvents help get maximum solubility in minimal solvent (avoiding band broadening for starters). DCM (the minimum quantity to get a pipette-able solution) almost always works out here imho, except for very non-polar compounds. In that case I usually load the compound adsorbed onto a little silica. But I'll give toluene a go next time.
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I usually use DCM as well. However, I always get nervous using it that it'll wisk my compounds away with it, and I'll get no separation. I'm a fan of adsorbing compounds onto silica and loading that way. Pretty easy, and never seem to have any problems with it either. But I may have to give the toluene a shot as well...
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I worked for some time with sugars and also became a big fan of silica adsorption. In my opinion, it's just one of the best methods of sample loading.