[goldy]

Hello,
I am a student of natural product chemistry.
I want to isolate and purify compounds but the compounds are non polar and have the Rf difference of less than 0.1.
Please suggest me the right solvent system (I have tried Hexane:EtOAC, Hexane:Acetone, Hexane:Chloroform and many more,but I could not seperate them.)

[hobobot]

what compounds are they?

[Dan]

We normally use cyclohexane/EtOAc here, but I quite often find toluene/acetone gives better separation, especially if the compounds have aromatic rings. I've had several cases where components that co-spot in hex/EtOAc are separable in toluene/acetone. 9:1 toluene/acetone is roughly equivalent to 2:1 (cyclo)hexane/EtOAc in terms of R_F. I avoid columning in toluene unless absolutely necessary as the vapours are a bit nasty and it's a bit of a pain to vac off. Worth a shot though.

If you can see two spots by TLC then you should at least be able to get partial separation by running a long column starting at very low polarity, increasing with a shallow gradient. Dry-loading on Celite or silica also gives you narrower bands than wet-loading, which can make all the difference in a tough separation of compounds with very low polarity.

[democanarchis]

Long wide column, wider than you'd normally use and dryload to get the narrowest band possible as said. Have had separations like that myself where i just ran it in neat heptane or the like. Takes a while, but did the job.

[goldy]

what compounds are they?

These are hexane extract and looks like oil.

[goldy]

We normally use cyclohexane/EtOAc here, but I quite often find toluene/acetone gives better separation, especially if the compounds have aromatic rings. I've had several cases where components that co-spot in hex/EtOAc are separable in toluene/acetone. 9:1 toluene/acetone is roughly equivalent to 2:1 (cyclo)hexane/EtOAc in terms of R_F. I avoid columning in toluene unless absolutely necessary as the vapours are a bit nasty and it's a bit of a pain to vac off. Worth a shot though.

If you can see two spots by TLC then you should at least be able to get partial separation by running a long column starting at very low polarity, increasing with a shallow gradient. Dry-loading on Celite or silica also gives you narrower bands than wet-loading, which can make all the difference in a tough separation of compounds with very low polarity.

Thank you the reply. I will try your suggestions.

[AC Prabakar]

I just want to add some points!
In such a cases we have used EtOAc with petroleum ether and chloroform/dichloromethane.In many of the cases we separated non polar spots which were differed Rf values by 0.1.
But sufficient care should be taken while handling DCM/Chloroform.

[goldy]

I just want to add some points!
In such a cases we have used EtOAc with petroleum ether and chloroform/dichloromethane.In many of the cases we separated non polar spots which were differed Rf values by 0.1.
But sufficient care should be taken while handling DCM/Chloroform.

Thank you for the reply. Please suggesr me the best ratio of these solvent in wgich I can get the best seperation. Thank you very much.

[democanarchis]

I just want to add some points!
In such a cases we have used EtOAc with petroleum ether and chloroform/dichloromethane.In many of the cases we separated non polar spots which were differed Rf values by 0.1.
But sufficient care should be taken while handling DCM/Chloroform.

Thank you for the reply. Please suggesr me the best ratio of these solvent in wgich I can get the best seperation. Thank you very much.

Only way to know is to run some TLC yourself.

[goldy]

what compounds are they?

These are probably essential oils. They are non polar having weak or no UV absorbance. please suggest me some ways to seperate them. More than 3 compounds co-spot together which make the isolation process more complex.
Thank you for your help.