[Chung Yen]

Hi, currently i am having problem with isolating a trans olefin from a mixture of both conformational isomer. The TLC shows that the spots contribute by the 2 isomers are very close. I tried column and I do isolate the trans isomer from only the 1st or 2nd testtubes while the rest are still mixture. How can i go about separating it? Thanks for reading.

[sjb]

What sort of quantity are we talking? Have you tried silver nitrate impregnated silica / alumina? Different solvents?

[Chung Yen]

I have up to around one gram worth of mixture. I tried using 1:10 EA:Hexane isocratic elution but the separation still poor. Can you enlighten me further with the silver nitrate additives? Currently I only have silica gel as my stationary phase.

[sjb]

See, for instance, http://dx.doi.org/10.1016/S0040-4020(00)00927-3 . A colleague of mine was in a similar situation a while back

[Chung Yen]

Ok thanks a lot for the sharing. I read through the paper and it describe that the separation can be achieve by GC with silver nitrate. However currently i can only rely on silica gel. I wonder will the addition of silver nitrate help in doing this job?.

[bolo]

Very efficient is the use of a centrifugal chromatography instead of standard column.

[OC pro]

Try to run the column with a gradient starting from pure hexane going to 50:1, 20:1 and then 10:1. This will help. And you can also use a longer / wider column.
Another option is aluminum oxide as stationary phase. We had quite good results with Alox. There are also TLC plates impregnated with Alox so you can test if the spots separate better.