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Author: Subject: tlc problem
soma
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[*] posted on 27-4-2018 at 03:09
tlc problem


I'm having a tlc problem. I'm using a ipa:hexane:NH4OH 4:1:1 eluant. The 1st run gave 2 spots - 1 at 0 and the other at 1. There were streaks. on both spots. The next day, using the same tlc type plate, the same analyte, and the same eluant - I got 1 spot at rf 1. I kept the eluant solution tightly capped but now I'm wondering if there was maybe a reaction between the solvents that caused the difference.

Any ideas?

Thanks.
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User13579
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[*] posted on 27-4-2018 at 03:45


I've noticed in the past that sometimes (it's compound-specific, of course, mine was a ketone that was presumably reacting with the alcohol on silica) when using alcohols I would sometimes get two spots from a single pure compound. I confirmed this with 2D TLC. One of the spots split into two on developing with the same eluent a second time. Whether or not this is relevant to your case I can't say, it would depend upon the nature of any interactions of your compounds with the eluent, or the plate itself. You'll have to give a lot more details if you're genuinely looking to resolve the problem, such as the type of plate, functional groups in your compounds (or preferably the structure of the compound itself) and details such as that. Maybe the temperature of the eluent was different -- that can affect the Rf values considerably. I don't understand how you can have a streak on a spot with Rf 0. By definition it is at the origin, no?

[Edited on 27-4-2018 by User13579]

[Edited on 27-4-2018 by User13579]

[Edited on 27-4-2018 by User13579]
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brubei
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[*] posted on 27-4-2018 at 16:07


how did you dry your plate before the second run ?
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soma
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[*] posted on 23-5-2018 at 03:32


Quote: Originally posted by User13579  
I've noticed in the past that sometimes (it's compound-specific, of course, mine was a ketone that was presumably reacting with the alcohol on silica) when using alcohols I would sometimes get two spots from a single pure compound. I confirmed this with 2D TLC. One of the spots split into two on developing with the same eluent a second time. Whether or not this is relevant to your case I can't say, it would depend upon the nature of any interactions of your compounds with the eluent, or the plate itself. You'll have to give a lot more details if you're genuinely looking to resolve the problem, such as the type of plate, functional groups in your compounds (or preferably the structure of the compound itself) and details such as that. Maybe the temperature of the eluent was different -- that can affect the Rf values considerably. I don't understand how you can have a streak on a spot with Rf 0. By definition it is at the origin, no?

The compound was an aromatic secondary amine.

The 0 Rf spot was like a triangle with the base at 0
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