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Author: Subject: Pyranine, fluorescein, fluorescent pH indicators, and highlighters
Brain&Force
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cool.gif posted on 9-2-2015 at 13:59
Pyranine, fluorescein, fluorescent pH indicators, and highlighters


Pinkhippo11 and I were talking in the Skype chat about fluorescent highlighters.

First of all, we're not sure exactly what is in these highlighters. I think it's pyranine, as it fluoresces blue in acidic solution and turns clear. Pinkhippo11 attempted the extraction and got a red salt characteristic of fluorescein, which he thinks it is. We're both using Sharpie highlighters, and have attempted to look up the composition, with no success.

Second, I've attempted a reaction of the water-solvated material with potassium permanganate, acidified with citric acid, and an interesting thing happens: the fluorescence disappears, then returns slowly. If enough citric acid is added the permanganate turns brown, then clear, and the solution does not fluoresce.

Can anyone shed some light on this?




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blogfast25
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[*] posted on 9-2-2015 at 18:08


Treating these delicate flowers to a chemical bulldozer like KMnO4 is a bit like throwing a stick of dynamite at a house of cards.

I'd suggest a mildly more subtle approach to your investigations. ;)




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[*] posted on 10-2-2015 at 00:03


This may be helpful/interesting

http://www.compoundchem.com/2015/01/22/highlighters/
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[*] posted on 10-2-2015 at 03:03


Nice link.
This might be the beginning of a new project.
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[*] posted on 10-2-2015 at 03:53


Quote: Originally posted by DJF90  
This may be helpful/interesting

http://www.compoundchem.com/2015/01/22/highlighters/


If you follow compoundchem on tumblr they have weekly, sometimes more frequent, posters about all sorts of things... Poisons, medicines, hormones, food additives etc. all really nicely made!




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[*] posted on 10-2-2015 at 12:48


Quote: Originally posted by Mailinmypocket  
Quote: Originally posted by DJF90  
This may be helpful/interesting

http://www.compoundchem.com/2015/01/22/highlighters/


If you follow compoundchem on tumblr they have weekly, sometimes more frequent, posters about all sorts of things... Poisons, medicines, hormones, food additives etc. all really nicely made!


Very nice! I have been working on a set of binders covering Inorganic and Organic chemistry from resources I have found on the web, and several of these infographics have just been included. :)
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Brain&Force
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[*] posted on 10-2-2015 at 13:27


Quote: Originally posted by blogfast25  
Treating these delicate flowers to a chemical bulldozer like KMnO4 is a bit like throwing a stick of dynamite at a house of cards.

I'd suggest a mildly more subtle approach to your investigations. ;)


Hey, it's the only oxidizer I have, other than store-bought H2O2...:(

I was trying to come up with interesting demo ideas for SPARK.

Thanks for the link DJF90, I have a whole bunch of highlighters I want to have fun with.




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Brain&Force
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[*] posted on 14-2-2016 at 15:55


Ok, I've found a reliable method for determining the difference between pyranine and fluorescein - pyranine is very solvatochromic! I extracted some into methanol and was surprised to find an eerie blue solution rather than a bright yellow-green one. Turns out pyranine changes from yellow to clear in less polar solvents - and its fluorescence changes from yellow-green to blue. The solution is actually clear in methanol - it's just that it fluoresces very strongly in sunlight.

<blockquote class="imgur-embed-pub" lang="en" data-id="a/Rkq7y"><a href="//imgur.com/a/Rkq7y">One of these dyes is not like the others.</a></blockquote><script async src="//s.imgur.com/min/embed.js" charset="utf-8"></script>

I made an imgur gallery comparing pyranine (middle and right) with a mix of 5- and 6-carboxyfluorescein. I'm also going to try other highlighters - the pink ones contain rhodamine B, and the blue ones erioglaucine (acid blue 9, D&CM blue 4). Orange ones contain a mix of basonyl red 485 and basic yellow 40. Ideally I'll be able to recover all of these.




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[*] posted on 14-2-2016 at 16:14


Nice work B&F.
Do keep us posted.
I sense a student project coming on...




If you are interested, take a look at the latest offering from sum_lab:
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[*] posted on 14-2-2016 at 21:34


I'm in college and I don't think I'll be able to do a student project on this, but I do have one fun idea. There are plenty of different rhodamines and I don't think rhodamine B is used in highlighter fluid. Reason: Proposition 65 warnings (the ones that say "known to the state of California to cause cancer) would require rhodamine B to be listed on the ingredients. I'm in California and I don't see this on any of my highlighters. It's also sensitive to oxidizers like chlorinated tap water which would be a serious issue for highlighters The other common dye rhodamine 6G might be the more likely constitutent.



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[*] posted on 14-2-2016 at 21:42


I was thinking of my students. Basically an extraction followed by some tests to determine what the compounds are.
Alternatively, comparison of a few different extraction procedures.
Or, even better, based on your discovery, an investigation on the fluorescent properties in solvents of different polarities.
Even just using water and adding NaCl should provide something interesting.

I see possibilities. Thanks for the idea.




If you are interested, take a look at the latest offering from sum_lab:
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[*] posted on 14-2-2016 at 21:48


Don't forget that they're also great indicators and can be affected significantly by solution pH as well. Pyranine fluorescence turns more blue in acidic solution and more green in basic solution. It might also be fun to do liquid-liquid extractions with these dyes.



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[*] posted on 14-2-2016 at 21:53


Loads of possibilities. We can find a visible light absorption spectrum. I am not sure how well we can handle UV with the equipment we have but surely we can come up with some measure of fluorescence.
Between solvent choice, highlighter brand and colour, concentration, pH and a few different ways we could analyse the solutions, I think there are a number of variables to control and a number that could be varied. And some cool chemical theory to back up the observations. That's all that is required for an investigation at this level.




If you are interested, take a look at the latest offering from sum_lab:
A primer on metals and non-metals with at least one novel experiment.
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