I've heard of people running columns with some acetic acid in, but never TFA. I think we used to have a mix called CMAW in my old lab that was chloroform/MeOH/AcOH/water. I don't remember the proportions but I think it was something like 80/15/3/2.Discoderlimide
You can get away with quite a lot in terms of polarity and silica. In many cases I think the dissolving silica issue is over exaggerated (though it will happen, especially if you're using a lot of MeOH).
A polar eluent I use occasionally is 45:5:1 EtOAc/IPA/water. This doesn't dissolve silica, so maybe spiking it with AcOH or TFA will work for you. Mix the IPA/water first, then add EtOAc otherwise you can have miscibility issues.
All this said, I think when you're considering putting water down a silica column then reverse phase is worth a look into.
: Which lipids did you purify and under what conditions? My guy has a 1,2-di-stearoyl-glycerol moiety (and 4 glutamic acid groups) attached and seems to stick pretty solidly to non-polar stationary phases. I know of certain columns that have both polar and nonpolar character (such as diol columns) that are suitable for this kind of things, but sadly I currently don't have access to those.Dan
: I've used CMAW in different ratios a great deal and it has been marvelous for most of my componds. But for this one, the AcOH simply doesn't cut it for dissolution - I can get great Rf's but as it wont dissolve the sample in a reasonable concentration it is quite useless. So my idea is to substitute the AcOH for TFA and mix it with the old friends CHCL3, MeOH and water.
I haven't been playing to much with isopropanol in this case, but it might be a nice idea. I know that it is quite used with amphiphilic compounds.
I am not looking for an especially polar eluant. Something like CHCL3:MeOH:TFA:water - (75:20:3:2). The water is needed in order to get well-defined spots.
The problem with reverse phase (and normal phase) is that this compound is quite the amphiphile and therefore nothing is really optimal.