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Author: Subject: Detecting Unknown Substances
Ego_and_his_own
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thumbup.gif posted on 27-9-2012 at 19:13
Detecting Unknown Substances


I tried to research how would I be able to determine unknown substances that I might find.

Its tough to find information on this topic. So I guessed that there is two possibilities:

1. We dont know yet how to do that easily.
2. Or I dont know enough to find information on it in satisfactory way to my curiosity.
(In lack of 100% proof for first, I settled with obvious evidence for second)

So i found out that there are several devices that can help in that process, one that seems most promising is mass spectrometry. But even that prices when down a lot (i think i saw some for 40$k) it still is far away from being general commodity.

I have a question about mass spectrometry. Is this method 100% able to detect unknown substance atomic/molecular structure?

Second method what i have found is photo spectrometry, and I found that I can get UV/Visible range for 1.5k with computer interface.
This is something that i could "work for" if it would enable me to get some advantage in detecting unknown substances. But on youtube and information that i have found online its really vague to me to what degree this can be used in that application.
It seems that it always involve comparation with known substances.
I would really appreciate any input on this devices and how/if they can be used in determination of unknown substances.

The rest what i have found is that for most of techniques that are used in general chemistry involves various tests that are performed over unknown sample.
This test involve huge range of substances and apparatus and conditions (high pressure, low pressure, high temperature low temperature, reaction vessels etc) that creates really heavy burden on my curiosity and reality.

Any input and ideas that you have to share I would appreciate.

Thank You

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Ego_and_his_own
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[*] posted on 27-9-2012 at 19:20


I guess my question beyond this is: How you would approach to this problem?

lets say you go somewhere on mountain find some hole in ground, pick some "rocks" that intrigue you and you want to know whats in it?

Replace mountain for desert, jungle, ocean, anything.

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violet sin
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[*] posted on 27-9-2012 at 20:42


I have only used a few machines in a lab, we did IR spectroscopy, refractive index and something else, (was 10yrs ago hard to remember) but most of the tests for our final were hands on with chemicals. what you use to determine stuff is really dependent on what type of material you are trying to figure out. we were determining liquids in a vial. we got 2 samples and had to figure it out by end of the semester
obvious facts, like smell, color etc. then we did tests to determine density, boiling point etc. then we did flame tests, IR absorbtion, refractive index, what ever we could with the sample we were given. and we had to read the NMR chart. mine was a bromine substituted short chain secondary alcohol if I remember correctly.

so start with a log entry. amount to use in tests. etc, then after you have done all you can by observation you will need to start doing things that may "use up" your sample. so gotta be smart unless there is a lot more to be had. you maybe have something you hope this thing to be correct? if so start reading on what the markers are for what you want it to be, against what it is. wishful thinking will get you no where so don't bend the truth to make it seem what it is not. but just keep doing like that and you will have a decent idea what it is.

its all about the journey, so have some fun and get in there n read and look and think. keep a log, and try to be as structured as you can. scientific method in action, go go go. I did this a month ago with rocks from my local creek, turns out I had chromite ore wash down from the mountains :) read about the mines that were in use up there till early 60's
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biggrin.gif posted on 27-9-2012 at 20:49


I would use qualitative analysis,that is what was used before all the expensive equipment they have today. I have a book called (qualitative analysis and the properties of ions in aqueous solution.) I got mine from amozon used for $4.95+shipping. It explaines how to chemically analyze anything from unknown solution to alloys to solid samples.
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Ego_and_his_own
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[*] posted on 27-9-2012 at 20:50


For sure its for journey :)

Thank you very much for sharing your experience.
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Ego_and_his_own
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[*] posted on 27-9-2012 at 20:53


Thank you for pointing me on the book, I will look for it.
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[*] posted on 28-9-2012 at 04:07


First determine organic or inorganic (try burn it), color, smeel, boiling point, melting point, if its inorganic you can done element qualitative analiyssis, after that quantitative (titrating). If it s pure substance youcan determine molmass by ebuloscopy or cryoscopy, it all depends from your aparatus acess, there of coarse is chromatography, NMR, IR.. There is also electrochemical determination methods.
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[*] posted on 28-9-2012 at 06:07


You sound like your on the way with the good advice you've gotten. That book, Quantitative Analysis intrigues me. But thaose methods often will take a BIG chunk of time and experience. Which is the only way to really learn something, anyway. GC\quadrupole, or that $5 Nicollet. Wonder if it needs salt windows. If you KNOW or SUSPECT the possible nature of the compound(s) in question, there are all sorts of simple adjunct tests you could use, which will give you a Yes or a No answer. There are many things you could do. Go to an auction for a scientific company, or look on Ebay for an old HP. It's really just one big long fractionating column with a sort of night vision goggles at the end (if you will excuse the anal ogy). There are specialty places ravers send their whatever for a yes no answer. Sounds simultaneously serious and silly to me. Perhaps for a reasonable amount, someone in China cold identify it for you for $199
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Ego_and_his_own
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[*] posted on 28-9-2012 at 06:50


I would like to hear for sure more opinions and approaches. As this is essentially question of all questions. I mean its one thing to reproduce others experiments and findings and another to be able to start from unknown stuff and come to findings on your own.

If anyone has experience and his example how he did/would approach to this please share.

I am also curious about using spectrometer. Anyone has deeper experience into this?

I found this OS project that looks like step in right direction in making determination of unknown substances much more accessible to people.

http://www.stumbleupon.com/su/2GeSfn/www.kickstarter.com/pro...
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[*] posted on 28-9-2012 at 11:14


Quote: Originally posted by Fennel Ass Ih Tone  
You sound like your on the way with the good advice you've gotten. That book, Quantitative Analysis intrigues me. But thaose methods often will take a BIG chunk of time and experience. Which is the only way to really learn something, anyway. GC\quadrupole, or that $5 Nicollet. Wonder if it needs salt windows. If you KNOW or SUSPECT the possible nature of the compound(s) in question, there are all sorts of simple adjunct tests you could use, which will give you a Yes or a No answer. There are many things you could do. Go to an auction for a scientific company, or look on Ebay for an old HP. It's really just one big long fractionating column with a sort of night vision goggles at the end (if you will excuse the anal ogy). There are specialty places ravers send their whatever for a yes no answer. Sounds simultaneously serious and silly to me. Perhaps for a reasonable amount, someone in China cold identify it for you for $199


Not so big time in university at first analitycal chemistry courses, we done lot of qualitative inorganic analysis. Old HP chromatograph, i need it :D, but its pain in ass to service chromatographs.
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[*] posted on 28-9-2012 at 11:25


It has been a long time since I have done one, but as I recall, melting point depression can be a useful method for determining an organic unknown's molecular weight.

Doesn't require much equipment, and the equipment is very inexpensive.

It won't tell you what your unknown actually is, but it can give you a ballpark estimate of what its molecular weight is.

[Edited on 28-9-2012 by zed]
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[*] posted on 28-9-2012 at 11:42


ebuloscopy and cryoscopy
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[*] posted on 28-9-2012 at 14:07


inorganic substance:
flame color test
borax bead test
solubility tests

If it is a really complex inorgance salt it is going to be nearly impossible to identify it exactly. Consider chiral complex salts for instance.

Organic substances are going to be far more difficult to identify easily, especially if you do not have any clue regarding their nature up front.
The most informative techniques would be IR-spectroscopy, NMR and mass spectrometry, but none of these is really cheap. IR spectroscopy would be the cheapest of the three. UV spectra can also be useful, but to a lesser extent. NMR and multidimensional MS are very powerful.




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