TLC...no not tender loving care I'm afraid :P

Hey all!
I'm currently typing up my chemistry coursework on aspirin for thin layer chromatography (TLC). I did TLC on salicylic acid, the aspirin I synthesised and commercial aspirin.

The results (retention factors) I got from the TLC plates weren't totally great. I only got one blob from each sample instead of several blobs; I thought TLC could separate all the different components of the aspirin samples.
For my synthesised aspirin, I expected there to be a blob corresponding to aspirin and a separate blob corresponding to salicylic acid as I know that this is a major impurity.

So I thought...ok..my results are rubbish but FANTASTIC I can ramble on loads in the evaluation and explain why this has happened.

BUT...

I can't find any retention factors on the internet for the impurities or aspirin. And most importantly, I can't find why I've only just got one blob instead of several for each sample.

I really want to get this finished by this wednesday 12th. Help Me PLEASE!!!

Thanks :smile:

,

oinkoink :confused:

Reply 1

cobra

14

You won't find tlc data on the net which you can use as it's specific to each time you do it thats why you do them all on the same slide. Also TLC never works, I say this from 2 terms of organic synthesis labs where about 1 in 100 peoples worked

Reply 2

CJ Makani

TLCs should work!! I have just used them extensively during my third year project.

Oinkoink you said you used 'blobs' were the 'blobs' you used large? TLC works best when you have small concentrated spots not blobs.

Reply 3

oinkoink

OP

when i was talking about blobs I meant the spot that had risen up on the plate. i found this website talking about the polarity of the solvent and how it affects the separation of the different compounds. Apparently, if the solvent is too polar for the sample then the compounds don't separate and end up as one blob instead of spread out.

Reply 4

CJ Makani

Yeah, the solvent polarity can make a difference, a very polar solvent might move all the compunds in the spot and not show any separation.

Two solvent systems are usually good for controlling how polar the solvent is, for instance, if one uses a solvent like ethanol, and the spots don't separate then you can decrease the polarity by adding something less polar (though it has to be able to mix with the ethanol!).

Sometimes it take a while before the you find the right solvent system.

Reply 5

oinkoink

OP

Yeah, the solvent polarity can make a difference, a very polar solvent might move all the compunds in the spot and not show any separation.

Two solvent systems are usually good for controlling how polar the solvent is, for instance, if one uses a solvent like ethanol, and the spots don't separate then you can decrease the polarity by adding something less polar (though it has to be able to mix with the ethanol!).

Sometimes it take a while before the you find the right solvent system.

I'm glad the thing about the solvent being too polar is a "real" theory to why the spots haven't spread out. I'm always worried that the stuff I find on the Internet is sometimes wrong.

Thanks for your help!

oinkoink

Reply 6

cobra

14

CJ Makani

TLCs should work!! I have just used them extensively during my third year project.

Oinkoink you said you used 'blobs' were the 'blobs' you used large? TLC works best when you have small concentrated spots not blobs.

I think you sum it up well when you say should work they do work if you do them properly and don't have to develop them in some crap iodine tank which has been around for weeks

Reply 7

oinkoink

OP

think you sum it up well when you say should work they do work if you do them properly and don't have to develop them in some crap iodine tank which has been around for weeks

will do