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Author Topic: I don't understand why toluene is the best eluent in this TLC  (Read 11010 times)

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Tootella

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i'm doing thin layer chromotography lab.

we had to make developing chambers with hexane, toluene, and ethyl acetate.

toluene was the best eluent.

but when i read about eluents, it said that the more polar eluents have better eluting power. i think ethyl acetate is more polar than toluene, so I don't understand why toluene was the better eluent in my experiment (and in everyone else's)

I don't know if this is enough information. Does anyone know what I'm talking about? I'm trying to do my write up, and I don't really understand a lot of the theory behind the labs.

is there a reason why toluene is the best eluent for separating benzophenone, biphenyl, and benzhydrol?
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DrCMS

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Re: I don't understand why toluene is the best eluent in this TLC
« Reply #1 on: June 10, 2008, 10:32:17 PM »

toluene was the best eluent.
and
but when i read about eluents, it said that the more polar eluents have better eluting power.

Is "eluting power" and "best solvent for a given separation" the same thing?
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agrobert

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Re: I don't understand why toluene is the best eluent in this TLC
« Reply #2 on: June 12, 2008, 06:35:04 AM »

Part of elution and separation abilities has to do with solubility.  All of these compounds are very similar and are symmetric with two phenyl rings each.  How do the structures of ethyl acetate and toluene compare.  Perhaps ethyl acetate is too polar to achieve good separation of this mixture.  Rationalize your thoughts based on separation.  Do you know which spots are which? 
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In the realm of scientific observation, luck is only granted to those who are prepared. -Louis Pasteur

polychmist

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Re: I don't understand why toluene is the best eluent in this TLC
« Reply #3 on: July 10, 2008, 05:14:16 AM »

Aromatic effect. I believe that because toluene has the benzene ring which is similar with your comounds. So it can disolve your compound better!
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phil81

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Re: I don't understand why toluene is the best eluent in this TLC
« Reply #4 on: July 10, 2008, 05:41:39 AM »

TLC solvent effects are sometimes hard to rationalize. In most cases, hexane/ethyl acetate mixtures work best for me. Even a few per cent of a different solvent can change the outcome tremendously!

In your case, try to sort the solvents according to their polarity. Then think about in which polarity range your compounds fall.
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polyrene

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Re: I don't understand why toluene is the best eluent in this TLC
« Reply #5 on: July 10, 2008, 07:56:35 AM »

Actually ethyl acetate in this case is the most polar solvent, as sometimes called "strongest". If you use only this solvent, your spots will go together with front eluent line. If you use only hexane your spots will be left on the base line. It is the most unpolar solvent, "weak" one. Various mixtures of these solvents will do the trick and you will see all spots separated.

Actually, toluene is not very good solvent for TLC's: it leaves traces on your plate (its aromatic compound you know  ;) ), you have to heat your TLC quite a bit to evaporate it before examination, it is more toxic than EtAc or Hex, it STINKS more. Try to avoid it. Try to use acetone and hexane mixtures.
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adam

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Re: I don't understand why toluene is the best eluent in this TLC
« Reply #6 on: July 11, 2008, 04:40:50 AM »

Polyrene you are right...but are you sure that toluene is more toxic than hexane...???
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