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Topic: Spectrophotometry and glycine betaine  (Read 3356 times)

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Offline biscuitses

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Spectrophotometry and glycine betaine
« on: April 15, 2018, 06:21:48 PM »
Does anyone know the value of extinction coefficient for glycine betaine in diethil ether solution? I honestly dont know where more to look.

Offline wildfyr

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Re: Spectrophotometry and glycine betaine
« Reply #1 on: April 15, 2018, 10:18:39 PM »
I quick glance says to me that this compound is not going to be at all soluble in ether

https://en.wikipedia.org/wiki/Trimethylglycine

Its a quaternary amine and carboxylic acid.

Its often the case with compounds that it's easier to make stock solutions yourself and use Beers law to determine the extinction coefficient at a given wavelength.

Offline biscuitses

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Re: Spectrophotometry and glycine betaine
« Reply #2 on: April 16, 2018, 05:56:06 AM »
Oh sorry it was late when I was writing this! I meant 1,2-dichloroethane. But its actually dissolving periodide crystals with glybet in it (its part of a glycine betaine estimation protocol).

As for the stock solution, I cant make it since I dont have pure glycine betaine, only samples where I have to determine the concentration. And I cant use unknown concentration to make a curve.

On the other hand without some pure gly bet I also cant make a calibration curve, so Im traying to find out the value of the extinction coefficient.

Offline Arkcon

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Re: Spectrophotometry and glycine betaine
« Reply #3 on: April 16, 2018, 08:14:13 AM »
Hi there, biscuitses:, you've asked a common question, and I'm sorry to say, I don't suspect you're going to be successful in getting the information you want.

There's no grand master resource of extinction coefficients for every obscure chemical.  You might have gotten lucky, one time, with a Google search, for a very commonly used reagent.  But that's doen't make what I said false.

You'll get a different extinction coefficient for various solvents.  Resources that give extinction coefficients pick one or two solvents.  You even switched solvents mid-thread with nothing more than a "Oops."  This is going to go nowhere even faster.

I was going to say you should be following a defined protocol.  But now it seems you're developing a complete assay on your own.  In which case its, as was said, up to you to develop all steps.  But you don't have pure standard?  Thedre's too many layers of uncertainty here.

Oh by the way, what wavelength?  You didn't even mention that.  A compound has no extinction coefficient at wavelengths it doesn't absorb.  Did you pick a good wavelength? How will we know?  How did you decide what wavelength to work at?  What reference did you use for that?

You have to refine your question -- where did you come up with this procedure, how much of a procedure do you have, and why don't you have a more complete procedure.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline wildfyr

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Offline biscuitses

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Re: Spectrophotometry and glycine betaine
« Reply #5 on: April 16, 2018, 04:03:26 PM »

Oh by the way, what wavelength?  You didn't even mention that.  A compound has no extinction coefficient at wavelengths it doesn't absorb.  Did you pick a good wavelength? How will we know?  How did you decide what wavelength to work at?  What reference did you use for that?


290nm is the wavelength. But youre right my question is vague. The protocol Im using is just a slightly altered one as described here:
"A reliable method for spectrophotometric determination of glycine betaine in cell
suspension and other systems" from Ma. Guadalupe Valadez-Bustos et al.

Its a long protocol. Basically glycine betaine makes periodite complex at low temperature in an acidic medium. Those crystals are then dissolved in 1,2-dischloroethane and the apsorbance is read at 290nm. I understand how varied those extinction coefficients are. I asked the question hoping there might be a tiny chance someone might come across and know. Its alright Ill just buy the pure samples and make a calibration curve.

Thank you for your time and help

Offline wildfyr

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Re: Spectrophotometry and glycine betaine
« Reply #6 on: April 16, 2018, 04:29:12 PM »
Just noticing a fine point, from what you said the UV-Vis is of the betaine-periodate complex in acidic solution, not plain betaine in neutral solvent.

That involves several more moving parts. Variation of absorbance with periodate concentration while betaine is held constant? Influence of pH? How constant does the temperature need to be? Lastly, many things absorb at 290nm, are you sure impurities won't interfere?

Science is hard  :-[

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