Tuesday, November 28, 2006

Let's talk about TLCs Part 2 - Hanessian's Stain

Don't you just love that feeling when you are checking your reaction mixture by TLC and no matter which stain you use nothing appears on the plate. If your compound also isn't UV active you've got a real problem. Well the good news is that there is one stain that will do the job for you - Hanessian's Stain! Hanessian's stain is an excellent multi-purpose stain that when used the right way usually gives blue spots (TLC plate A). Since it is a water based stain it requires vigorous heating for development. However, if you overdo it the entire plate goes dark blue (TLC plate B).

Hanessian's Stain Recipe 1
100 ml container
90 ml Water
5 g Ammonium molybdate, (NH4)6Mo7O24-4H20
1 g Cerium sulfate, Ce(SO4)2
10 ml Concentrated sulfuric acid
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Hanessian's Stain Recipe 2
100 ml container
90 ml Water
2.5 g Ammonium molybdate, (NH4)6Mo7O24-4H20
1 g Cerium ammonium sulfate, Ce(NH4)4(SO4)4-2H2O
10 ml Concentrated sulfuric acid
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Dissolve ammonium molybdate and cerium sulfate in water (with heating if required) followed by careful addition of concentrated sulfuric acid. Sometimes an insoluble residue is observed. If that happens remove it by filtration. Cerium sulfate can be replaced with Cerium ammonium sulfate which is significantly cheaper (Recipe 2). Hanessian's stain is used just as previously described for the Vanillin Stain although it requires more vigorous heating. Because rather harsh heating is required this stain may prove inefficient with volatile compounds. Also keep in mind that this a very sensitive stain so even trace impurities can appear as significant spots on your TLC plate. D!

18 comments:

Anonymous said...

yeah, that's my usual stain...stains almost anything, but particularly alcohols and silyl ethers well. then...anisaldehyde and permanganate...

Christian Bech said...

Arrhhhh.... so that is what we have in this jar labelled "cerium". Excellent stain indeed!

Anonymous said...

Is that Hanessian as in Stephen Hanessian at Universite de Montreal? We always call this stuff CAM.

Daniel Sejer said...

Oooops a bit of an inconsistency between formulas and names in the recipe. Should all be OK now. There are numerous variations on this recipe. It doesn't seem to make any difference if you use Cerium Ammonium Nitrate / Sulfate / etc. As far as I know it all works fine so it's basically down to availablility and price. I've corrected the previous recipe and added another version of the stain. I don't know if the stain is named after Steve Hanessian. Maybe we should drop him an email. He might also be able to give us the original recipe. BTW how sweet is it to have a stain names after you? All the other dudes have reactions and reagents named after them but Hanessian is the only person to have named a stain (as far as I know). Oh and yes it is also sometimes called CAM (cerium ammonium molybdate) stain. D!

homer Simpson said...

This is the best general stain there is. I have run into compounds that don't work with phosphomolybdic acid and CAM has always saved my bacon!(mmmm...baaaacon...gggrrrggggg gggrrrrgggg) This is my first choice stain.

Thomas said...

The thing I like about anisaldehyde is that often times analogs in a series will stain with very similar color. In a past project it made quick work of finding my product (stained a characteristic blue color)amongst a myriad of other stuff.

Anonymous said...

thomas...

it certainly is nice when products have a characteristic color on TLC. I make compounds that very commonly turn red after sitting on the TLC plate in air for an hour or so (they have sulfur in them). This has often been more indicative than the crude NMR data.

Organic Chemistry said...

Thanks for the stain recipe...i have heard of it, but never tracked down the recipe. thanks again.

Anonymous said...

Well, another good recipe is the Vanillin-one as it stains almost the same things like CAM and gives different colours as well!

Daniel Sejer said...

I would have to disagree regarding vanilin stains capabilities when compared to Hanessian stain. Vanilin is my preferred stain (see post at Curly Arrow by following the TLC label) because it is easy to handle and it colours different types of compounds differently. However, Hannessian stain is significantly more sensitive. I have had many compounds that didn't show up with vanilin at all but are easily detected with Hanessian stain. D!

morridin said...

Hi,

At our lab we have been using PAM for a few years now, but lately when trying to apply quantitative measuring procedures problems came up; so i ended up here today, thinking about moving to CAM. My question is about the heating - what do you use for heating? what temperature and for how long do you heat it? I would greatly appreciate your help :)

Daniel Sejer said...

Morridin, standard lab heatgun at maximum heating until spots appear on the plate. The stain is water based so it needs a fair bit of heating. D!

morridin said...

Ok, so it probably takes a few minutes only for the spots to appear. I forgot to ask - as was mentioned PMA is quite light-sensitive reagent - is it the same with CAM, or it is more stable? And thanks for the quick answer :)

Daniel Sejer said...

Morridin, spots appear within a minute with a powerful heatgun. Spots do fade realtively fast but different spots fade at different rates. I usually photocopy my plates the same day that I have developed them. D!

morridin said...

Thanks, and what about the light sensitivity and general stability of the CAM reagent? Is it better than PMA?

Daniel Sejer said...

Morridin, I don't know. I've never had any problems with the stability of PMA or CAM. I normally store it in the fridge so it lasts a long, long time. D!

morridin said...

Hmm, we don't store it in the fridge, so that might be it :D.

Vikram said...

Can anybody explain the mechanism involved in this stain?