Gin and Tonic
Published on 16/03/2007
Movies, from ChemicalForums Blog, wrote, a few days ago, a brilliant article about quinine. In that post, he mentions that quinine is present in the tonic water we all use for preparing refreshing Gin & Tonics.
Apparently, he took inspiration from my recent post about LSD: he might have liked that little bit of history lesson I put right in the end of the article (as he says in his comment) or the link between drug and everyday life.
By the way, before writing on his blog, he told me I should have posted something dealing with quinine on mine (and in that occasion he mentioned tonic water as well).
As it turned out, he couldn't resist. Fortunately, however, since I'd have never been able to write such a masterpiece of organic chemistry, about cinchona alkaloids.
When I pointed this out he kindly suggested I could "complete" his synphony describing these drugs from a pharmacological point of view.
This will be done in future, but, today, I'm not going to talk about it.
Today, I'm going to do it: I'm going to check how much quinine is actually present is a normal can of tonic water!
To complete my task, I have to use fluorescence: the molecule needs no derivatization, as you can see from its structure, as it's already eligible this technique.
The assay is pretty quick, indeed.
Before we can determine the concentration of drug, we need to prepare a calibration curve: this means we need a standard solution of quinine that will be diluted to yield at least four different points.
To get a stock solution, 14.8 mg of quinine sulphate (MIND THE DIFFERENT MW!) standard are dissolved in a 50 mL volumetric flask with ethanol.
Then 1 mL of the solution is put in a 25 mL volumetric flask, plus 250 μL of acetic acid and water.
To find out the excitation wavelength (346 nm), I start with a UV spectrum.
Four dilutions are therefore prepared: 1:10, 1:20, 1:40 and 1:60. The second is immediately used to detect, at 346 nm, the wavelength at which the highest intensity of emission is observed: 456 nm.
Finally, we mesure the fluorescence emission intensities of the four solutions at 456 nm.
Time to open our can of tonic water: 100 μL are diluted 1:100 with water (not gin, how sad...). So, you just register the spectrum and derive the concentration of quinine.
Our magic number is 55.77 μg/mL.
Time for a massive ingestion of gin&tonics, now! Seeya!
in case someone wants to read about quinine from a structural chemist's point of few, here you go: http://chemical-quantum-images.blogspot.com/2006/12/glowing-gin-tonic.html
Thanks for this post. How far off is the concentration in tonic water from the amount you need to suppress malaria?
Approximately four times less than the therapeutic dose.
so four cans of tonic water supresses Malaria? How many before you approach an O.D.?
Actually, four LITERS of tonic water are equal to a SINGLE dose of quinine, for treating malaria.
That's more than 8 cans. What about belching? ;)