[Jon P]

Does anyone have any suggestions for thin layer chromatography solvent systems that could uniquely detect Boc-protected amino acids and a homoanhydride of the Boc-protected amino acid. 

The amino acid is valine.  The closest solvent system I have created was a 3:1 mixture of ethyl acetate and hexane.  I have also tried 1-butanol:acetic acid:H20 at a 4:1:1 volume ratio and a 4:2:2 ratio of the same components. 

Has anyone had any experience with this?

[Arkcon]

This is a pretty common topic, these days:

http://www.chemicalforums.com/index.php?topic=31159.0

http://www.chemicalforums.com/index.php?topic=24439.0

Let's see if someone with specific experience on this subject can pull it all together for us.

[alphahydroxy]

You may find that ninhydrin gives different coloured spots for each compound...

[Jon P]

I will try ninhydrin first thing next week!  Thanks for the suggestion.

[Jon P]

Alpha or anyone who may know, 

Do you have a procedure used when staining a TLC plate with ninhydrin?  e.g. concentration of solution? solvent used? do you apply heat after addition of ninhydrin?

I am using standard silica TLC plates. 

Thanks in advance. 

[sjb]

Here's a set of recipes for stains (google ninhydrin recipe)

http://orgprepdaily.wordpress.com/2006/09/27/tlc-staining-solutions/

As to whether you need to heat, sometimes you do, sometimes you don't - without doing the TLC I don't know which this is.

[Jon P]

Thank you sjb!  That is perfect!

[alphahydroxy]

To be honest, I normally just sling enough ninhydrin in a jar of methanol/ethanol so that it turns a nice yellow colour.

I think the "official" method is to use tert-butanol, but it's not really necessary - while the solution does last longer without evaporating, it also takes longer to evaporate when heating plates, and I've never noticed any actual difference in the end result. If the methanol evaporates you can just addd some more and give it a stir...

As regards heat, sometimes you will need to heat it, sometimes you will see the spots appear straight away. However, even if they do appear immediately, you should still heat the plate, to reveal anything else on it - perhaps something you were not expecting (side products etc.). Heat fairly gently -  if you use methanol you can use a lower heat - because the plates will burn if the temp is too high and you won't be able to see anything except a brown plate! Also, don't be tempted to keep the plates for reference as some people do, just draw them out if you want a record - they WILL rot and just fall apart...

[Jon P]

Also, don't be tempted to keep the plates for reference as some people do, just draw them out if you want a record - they WILL rot and just fall apart...

That saved me another post!  Thanks for all the advice!

[macman104]

Also, don't be tempted to keep the plates for reference as some people do, just draw them out if you want a record - they WILL rot and just fall apart...

That saved me another post!  Thanks for all the advice!

I take pictures of mine !  And I was working on a little UVbox to take pictures under UV light as well.

[Jon P]

Thanks for all the help guys! 

Just for posterity, I used about 1 gm of ninhydrin and 30 mL ethanol plus 30-45 drops of acetic acid. 

It produced beautiful purple/red spots almost immediately!