I've done work with "non-aqueous reverse phase". Solvents are methanol with dichloromethane, ethyl acetate, or acetone, for example. This works with carotenoids.
I was searching for that term, 'non-aqueous reverse phase chromatography'. Thank you very much for the help! Best regards!
@Jack Silver- Do you think that it is appropriate to use this therm when n-hexane-ethyl acetate mixture is present as mobile phase on RP 18 HPTLC plates?
@Katerina- I think it is appropriate. I'm assuming that hexane is the "strong" solvent that causes the compound to elute up the plate faster, and ethyl acetate takes the place of water compared to a regular C18 plate solvent system.
Just out of curiousity, if you are able to share the information, what sort of compounds use such a non-polar system? I've purified carotenes with this method using methanol/dichloromethane and I thought those were rather non-polar. If you can't share information, I understand!
Link to my purification (commercial warning: I work for Teledyne Isco):
http://www.isco.com/WebProductFiles/Applications/101/Poster_and_Paper_Reprints/Facile_Isolation_of_Carotenoid_Antioxidants.pdf
@Jack Silver -I'm working with triterpenoids. And thak you very much again!
@Katerina- sorry for the late reply. Those ought to be similar polarity to carotenoids, maybe slightly more polar depending on any functional groups.
Chromatogrpahy is always a competence be the mobile and stationary phase for the analyte (and viceversa???). Mobile phase solvent compositions can be changed to suit the needs of the separation. You can even use mobile phases with a good % of MeOH in noemal phase in order to elute a highly polar analyte (although you would prefer to do this unuder RP conditions).
Since both the phases are non polar possibility is that it may harm the stationary phase derivatised with non polar chain like C18/C8 and the required retention will not be possible in this case.It is very well known fact that like dissolves like.
@Sanjay: If the C8 or C18 is bonded to silica, there will be no harm done to the packing because the C18 is chemically bonded, and the non polar solvents will not attack that bond or interact chemically with the silica.
If we are talking about polymeric packings, all bets are off because the solvents may cause the packing to swell, which causes high back-pressure.
Some silica based chiral packings are solvent sensitive because the chiral modifier is coated on the silica, not chemically bonded. Since there is no chemical bond to hold the modifier in place, some solvents can dissolve it and the column will be damaged.
It seems from the current discussions,non aqueous mobile phase is the real requirement for separation as posted by Katerina. If you want to choose Hexane:Ethyl Acetate , the role of Hexane is like a diluter,it decreases the polarity of the other solvent since Hexane does not have any polarity.Better try this combination considering like dissolves like parameter.
Generally for good separation polarities both stationary & mobile phases should be opposite enabling to separate polar & nonpolar compounds. However Petroleum ether ( hexane) in combination with ethyl acetate so far is one of the best system suited for natural products. The ratio is first determined by trial n error running TLCs of crude plant extract.
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