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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: swissroll on September 19, 2021, 09:10:02 PM

Title: TLC Question
Post by: swissroll on September 19, 2021, 09:10:02 PM

Question is written below. I am confused because the eluan is not dissolved in a solvent so the question does not make sense to me.

When spotting compounds on a TLC plate, do the compounds have to be dissolved in the same solvent as the eluant? Why or why not?

Am I overthinking it?

Title: Re: TLC Question
Post by: wildfyr on September 19, 2021, 09:28:45 PM

For spotting, you just need to transport it on there and make a nice small concentrated spot. So whatever solvent will work is what you use. Usually its something like ethyl acetate or acetone. Typically the spotting solvent then evaporates off before you actually run the TLC

Title: Re: TLC Question
Post by: swissroll on September 19, 2021, 09:41:21 PM

Thank you.

Title: Re: TLC Question
Post by: rolnor on September 20, 2021, 01:37:15 AM

High boiling, polar solvents like DMF or DMSO needs to be evaporated before running the plate, this can be done with a heating-gun or hair-dryer.

Title: Re: TLC Question
Post by: Babcock_Hall on September 20, 2021, 08:34:36 AM

@OP,

What are two properties of acetone that make it useful in TLC spotting.  What other solvents have one of these two properties?

Title: Re: TLC Question
Post by: Meter on September 20, 2021, 09:17:29 AM

You want a volatile solvent where even trace amounts won't interact significantly with the eluent. This can be achieved by either drying your spots with a heating gun or even better, rotavapping your sample and redissolving it in an appropirate solvent. I had trouble with trace THF interacting with my eluent in TLC, so that's where I'm drawing my experience from.