TLC stains

[Horza2002]

Its easy to forget the humble TLC when faced with todays analytical equipment (LC-MS, GC-MS, etc). To this end, I though it would be useful for people to have access to the range of stains that you can use on TLC to reveal a whole range of functional groups. Even now, doing a PhD in a department with plenty of analytical machines, TLC is still usually my first port of call when analysing a reaction mixture.

 

http://pcwww.liv.ac.uk/~jxiao/TLC%20Stain.pdf

[mississippichem]

Its easy to forget the humble TLC when faced with todays analytical equipment (LC-MS, GC-MS, etc). To this end, I though it would be useful for people to have access to the range of stains that you can use on TLC to reveal a whole range of functional groups. Even now, doing a PhD in a department with plenty of analytical machines, TLC is still usually my first port of call when analysing a reaction mixture.

 

http://pcwww.liv.ac.uk/~jxiao/TLC%20Stain.pdf

 

Nice link Horza. Thanks for that. I've often used the hand held UV-light technique as many of my compounds are colorless but fluoresce strongly in the near-UV. It's easy to forget the "old school" techniques in these days; many of which are still very valid and useful.

 

There is also something rewarding about analyzing product mixtures without the aid of an automated Fourier Transform!

[Horza2002]

Yer, I often use the handheld UV light (my compounds containg a pyrrole that shines quiet nicely). And the old school technqiues are sooo cheap as well! In out lab, a 200ml permanganate stain last 4 of us about 2months using it everyday! I have often found using a variety of the stains is amazing for analysising the reactions. Especially amide coupling reactions...get a general permanganate stain to show all the spots, then ninhydrin to see if your starting amines presnent, then Bromocresol green to see if you acids still there.

 

One of the best stains I've found is the DNP one...the plate is stained yellow while aldehydes and ketones change colour...but go a different colour depending on their identity...aldehydes and unconjugated ketones are orange, conjugated ketones are dark orange/red, benzylic ketones are red/pink....

 

I should also note that there are hundreds of other stains that can be used that selectively show a specific group (I've used one that only stains primary alcohols over secondary ones) but the link is to the commonly used ones

Edited February 16, 2011 by Horza2002

[hypervalent_iodine]

I spent ALL DAY doing TLC's today. Stupid phase transfer catalyst wouldn't get out of my compound so my column didn't quite work as I would have liked it to. I generally use a combination of UV and Goofy dip - works fine for most of what I do.

 

Also, the iodine stains are really good for sugars.

[Horza2002]

Another piece of adivce for using TLC; wear gloves. I managed to get a lovely permanganate stain on my thumb print on my TLC plate today from where I'd accidently touched the plate. And of course, the thumb print covered where I wanted to look....

[hypervalent_iodine]

Tisk tisk. Whatever would occupational health and safety say of that!?

[Horza2002]

Propably no much...they don't think we should wear gloves all the time.

[John Cuthber]

Tisk tisk. Whatever would occupational health and safety say of that!?

They would probably ask to see the risk assessment for the process.

[mississippichem]

I think if OSHA (the US's occupational health and safety administration) had their way chemistry would cease to exist as a science.

 

Speaking of OSHA, I found an open can of [ce] CaH_{2} [/ce] just sitting on the bench yesterday. Tisk, Tisk, why do they let first-year undergrads work in labs?

 

[Power trip on]

 

I found the little bugger and forced him to explain to me why caution must be used when working with group I and II hydrides.

 

[/Power-trip off]

[Horza2002]

I think there thinking here is that if you wear gloves all the time, you get complacent and think the gloves will protect you whatever you do.

 

Lol did you make him wash the calcium hydride up in the sink as punishment? At least it wasn't sodium hydride, you could have had some more serious issues with that. Thats actually lucky really, out of the most common hydrides, caclium is the least reactive...not to say its harmless though.

[hypervalent_iodine]

We have to wear gloves all of the time when handling chemicals here. Most people I've encountered aren't complacent enough to suppose that gloves are a be all and end all in terms of protection - with the exception of first years perhaps.

 

Also, they let first years in chemistry labs there? My goodness. That's unheard of here! I had so much trouble finding a spot in a lab for the summer following my first year that I ended up in a biology lab doing PCR for weeks on end.

[mississippichem]

Also, they let first years in chemistry labs there? My goodness. That's unheard of here! I had so much trouble finding a spot in a lab for the summer following my first year that I ended up in a biology lab doing PCR for weeks on end.

 

The get to work but don't get to do anything cool. They mostly mix stock solutions, clean glassware and NMR tubes, and occasionally come along with grad students and upper level undergrads to watch us run spectroscopy or reactions. Their workload is for the most part menial tasks that I don't want to deal with The good workers get trained on various spectrometers toward the end of their first year if they've shown merit thus far.