How to test for a purity of a chemical compound

[brajesh]

TL;DR Summary

How to test for a purity of a chemical compound

If you had this chemical compound, for example, how could you test if its pure?
$$C_{15}H_{11}I_4NO_4$$

 

[mjc123]

That is not a compound, it is a formula. There are numerous possible compounds with the same formula.
There is no "test for purity". It depends what possible impurities you are interested in, and at what level.

 

[DaveE]

In my case, I'd take a whole bunch of chemistry classes. Then I'd understand what to do and what not to do; I'd understand the complexity of the problem. I wouldn't just jump into it looking for a simple solution to implement that someone else understands. I'd also have to have a chemistry lab to work in. Things you might need, like spectrometers and reagents, are expensive. But then, IDK, I'm definitely not a chemist.

 

[DaveE]

https://www.thermofisher.com/elisa/...dWkZzHZ4M0PThJF8IRhjg1kDU7do2FehoCnpUQAvD_BwE

 

[Borek]

If you have a sample of something you can always try find a solvent that dissolves it (might need some trial and error) and run relatively easy and cheap TLC (thin layer chromatography) to see if it splits - that will at least suggest whether you deal with a single compound, or a mixture. One can argue that mixture is never "pure" while single compound is.

But as others already wrote testing for purity is in general quite a complicated task, requiring plenty of knowledge and often quite an expensive hardware.

 

[brajesh]

If you have a sample of something you can always try find a solvent that dissolves it (might need some trial and error) and run relatively easy and cheap TLC (thin layer chromatography) to see if it splits - that will at least suggest whether you deal with a single compound, or a mixture. One can argue that mixture is never "pure" while single compound is.

But as others already wrote testing for purity is in general quite a complicated task, requiring plenty of knowledge and often quite an expensive hardware.

Hey that's an interesting idea.

If I have a real sample, and a "test" sample, then I wonder if I do a TLC, the chromatograms should be identical? Could that work?

 

[berkeman]

Summary:: How to test for a purity of a chemical compound

If you had this chemical compound, for example, how could you test if its pure?
$$C_{15}H_{11}I_4NO_4$$

Why did you ask specifically about that drug?

 

[TeethWhitener]

Closely related compounds (like, for example, two thyroid hormones) can have similar chromatographic retention times. If they separate into multiple peaks, then you definitely have a mixture, but if they give one peak, then all you can say is that either it’s pure or the chromatography technique doesn’t have enough resolution (theoretical plates) to separate the mixture.

 

[brajesh]

Why did you ask specifically about that drug?

For a friend, because of the impacts of the war, the drug is in short supply and she wants to source via alternative sources she but can't be sure of the quality.

 

[DrJohn]

The only reliable source of a drug is from a pharmacy or medical suppliers who service pharmacies.
AND
Normally no medical drug is supplied pure. If it is a tablet there will be the solid materials that form the tablet, a coating to colour the tablet for recognition purposes (but there are more features than just its colour to help its recognition, such as a particular shape and standard marks or groves on it). Sometimes a sweetener is added to mask unpleasant tastes.

If it is supplied in liquid form for ingestion or injection, the vast bulk of the sample will be the carrier liquid, there might be a preservative present, it might not be a particularly soluble substance so it could have other things present to help it dissolve in the carrier liquid. Something to prevent it irritating the veins if it is injected or sweeteners if it is taken orally.

Often the active ingredient is present in very small amounts in the medicine you use, less than 5% is not unusual.

So you will almost never come across a pure drug being used or sold. So just forget buying a drug from some source that is willing to sell directly to a random person, and your efforts to test it for "purity" are doomed to failure. Only ever get something for medical use from a recognised medical supplier or pharmacy. And even a medical supplier is risky, as they might be selling the drug as a pure or nearly pure sample, ready to be manufactured into tablets or a usable liquid form. IE it could be 10s or 100s of times stronger than in normal tablet or liquid form. And you could even end up with the wrong isomer of the drug!

I strongly suggest that you forget this approach. Or someone might end up dead.

PS the chances of you finding a reliable "alternative" source of C₁₅H₁₁I₄NO₄ look somewhat unlikely to me. I can't see why some companies would make a thyroid treatment for any other purpose, and it is patented so it is likely only some places make it.
And I find the idea of searching for an "alternative source" of a drug somewhat worrying.

 

[berkeman]

And with that excellent post by @DrJohn this thread is now closed.