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NMR versus GC/MS, HPLC/GC, HCLtitration, meltingpoint test

  1. May 19, 2012 #1
    Is it true that only a NMR test is able to detect the effectiveness, quality, quantity of a product?
    That it is able to detect wrong raw material, over-reaction, or isomers occurring during synthesis?
    But what about the other tests like GC/MS, HPLC/GC, HCLtitration, meltingpoint test. Is one or a combination of these tests not able to do the same as a NMR, tell you the effectiveness, purity, quality of a product? How do these other tests compare
    to NMR?
     
  2. jcsd
  3. May 19, 2012 #2
    if i remember correctly from o-chem class 10 years ago:

    GC can tell you how many components you have and the relative amounts
    MS can tell you the mass of those components and some structure info

    so long as you know what by-products to expect this should/could be enough

    with NMR you can determine the relative amounts of products and byproducts so long as you know what you are looking for and the spectrum isn't too messy. Multidimensional NMR can further clean up a messy spectrum - for example: you can see peaks from one molecule hiding with the peak from another molecule in a 1-D spec

    if you don't know what is in the mixture you'll want all 3 - with this information you could determine the composition of an unknown mixture.
     
  4. May 19, 2012 #3
    NMR is not sensitive. If you need something 99% pure, you won't be able to confirm that with a typical NMR run. Something like LC/MS can be used to determine purity. NMR can also be extremely complicated once your molecules start getting bigger or have all sorts of sterochemistry involved. It is good to always use both.
     
  5. May 20, 2012 #4
    In my experience, a starting material that was involved in manufacturing an analgesic related to ibuprofen, was tested for extreme purity by melting point/freezing point. GC was available, but wasn't sensitive enough and the impurity was not completely resolved using capillary columns. It was an extremely slow analysis with freezing point determined with an extremely accurate thermocouple reading plotted on a chart.

    The story was that the unwanted isomer was responsible for liver damage in early work on the compound.
     
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