Brain&Force
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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?
At the end of the day, simulating atoms doesn't beat working with the real things...
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blogfast25
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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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DJF90
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This may be helpful/interesting
http://www.compoundchem.com/2015/01/22/highlighters/
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j_sum1
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Nice link.
This might be the beginning of a new project.
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Mailinmypocket
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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!
Note to self: Tare the damned flask.
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Loptr
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Quote: Originally posted by Mailinmypocket  |
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
Hazard to Lanthanides
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| 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.
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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.
At the end of the day, simulating atoms doesn't beat working with the real things...
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Brain&Force
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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.
At the end of the day, simulating atoms doesn't beat working with the real things...
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j_sum1
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Nice work B&F.
Do keep us posted.
I sense a student project coming on...
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Brain&Force
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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.
At the end of the day, simulating atoms doesn't beat working with the real things...
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j_sum1
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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.
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Brain&Force
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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.
At the end of the day, simulating atoms doesn't beat working with the real things...
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j_sum1
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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.
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