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Identify unknown compound/element

  1. Feb 17, 2016 #1
    Hello, i have a need to identify unknown substances. Ive been researching spectroscopy and and the various methods. I've read all about the different types and uses and I've settled on a uv/vis spectrophotometer as the instrument. i know its not 100% used for qualitative analysis but its good enough for my needs. my main question is, so i get a spectra output but id like to compare it to known substances to see what i have. I've seen tons of EXPENSIVE software to do this but I'm wondering if there is some open source or simpler way to do this. my budget is VERY limited, around a grand but i wanted to reach out and see what someone who knows more about spectroscopies thoughts are. I'm not a chemist, i have some knowledge but I'm motivated to learn. is this biting off too much or or is there something available that i just don't know about that can assist me in interpreting the data in simple way? thank you!
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  3. Feb 17, 2016 #2


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  4. Feb 18, 2016 #3
    Thank you for the info. i have not researched that particular method. I did some quick digging, it appears it is way out of my price range for equipment, although does seem to be a great fit. I guess thats why i keep coming back to uv/vis spectrophotometer (the price). So circling back, any other ideas or known software packages that aren't terribly expensive? where I'm having the issue is once you get a good output from the spectrophotometer, how can i tell what the substance is made of? after researching quite a bit, most spectrophotometers have software that allows analysis. i just don't know if those exist in open source or inexpensive (grand or so) range. i realize the complexity of what I'm asking, I'm trying to see if this is something that can be made very simple and accurate for say 75% of tests. i know it won't hit all of them. from the options available its either find some software to do what I'm looking for or abandon the whole setup altogether (which is what its sounding like). thank you again!
  5. Feb 18, 2016 #4


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    Identifying compounds by their UV-vis spectra is not a good way of identifying compounds, in general. What sorts of compounds are you trying to identify? In general, mass spectrometry is what I would look to as a first solution.
  6. Feb 18, 2016 #5
    You need to know what kind of compound it may be. UV-VIS only works for a special group of substances, namely molecules that contain electrons that are excited exactly by a photon in the UV-VIS energy range. The same is true for most other analytical methods, though there are universal methods.

    Best way to minimize cost is to pick a method that is exactly suitable to the type of compound and the type of sample.

    Is your sample pure?
    It doesn't help that you don't even tell if it is a gas, a solid or a liquid.
  7. Mar 3, 2016 #6
    What kind of compound are you trying to identify? Mass spec might be good for inorganic molecular complexes, powder x-ray diffraction works extremely well for crystalline solids, NMR and/or IR spectroscopy works well for organics. For $1000 I would not try to buy an instrument, you need to spend well over that for a quality instrument, even for a UV/vis.

    As far as interpretation goes, there are many tables available online that list known absorbances in the UV/visible region, which is how you would need to go about analysis.

    That said, your best bet would be to send you samples off to a lab for analysis considering your budget.
  8. Mar 9, 2016 #7
    Need more info. Are they organic or inorganic. Are they basic or acidic? Have you tested for presence of halogens? Functional group analysis? UV-vis is not a great way to identify unknown compounds. If organic, proton or carbon 13 NMR in conjunction with FTIR and MS will get you close. What about physical data? BP, MP, refractive index, density, etc. these are all things you should know to identify a compound. XRF and AA will help with the inorganics. Hopes this helps.
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