Need Help on TLC~

[ruffian]

Hi, guys:

I am now working on TLC for separating some fraction which I got from eluent 10% isopropanol with ethyl acetate. I used alot of solvents to try to separate it by TLC like isopropanol/hexane, ethyl acetate/hexane and methanol/ hexane. Moreover I used three mixture solvent. But none of them works very well. What's next solvent should I try? Anybody can help me out from this? Thanks, I appreciate it.

[Alex Buske]

hi ruffian,

There is a paper on TLC optmisation by Sz. Nyiredy et. al Plant medica 1985, p241f. It is in german. the paper is based on Snyders solvent classification.
In short: Solvents are classified by polarity and three further factors. Alkanes (hexane) are just unpolar no further properties. They are used to adjust the polarity of the solvent mixture.
Other solvents are arranged in 8 groups: I: mostly simple ethers, II: alkanoles, III: THF, pyridine, IV: acetic acid , V: methylen chlorid..., VI: ethylacetate, dioxan, acetonitril, VII: some aromatic liquids, VIII: chloroform, nitromethan, water.
Try solvents from other groups. You can even use ternary solvent mixtures.
My favorite mixtures were: Hexan/chloroform (97/3-9/1) and ethylacetate/methanol.

Alex

[ruffian]

Thank u so much. I will try some later.