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Mass Spectrometry

Discussion in 'DAT Discussions' started by skyisblue, Apr 30, 2007.

  1. skyisblue

    skyisblue 2+ Year Member

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    Dec 25, 2006
    In Mass Spectrometry we can determine the molecular weight, which we can use to narrow the choices of molecular formula. A computer can generate a list of of choices. This is what I don't understand:"There are always a number of molecular formulas possible for all but the lowest molecular weights"

    Does that mean that when the compound is small, then there aren't that many choices of molecular formulas??

    I think I'm just tired.
     
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  3. Lonely Sol

    Lonely Sol cowgoesmoo fan! 10+ Year Member

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    Dec 13, 2005
    Atlanta, GA
    I am not sure what you are trying to ask, but as far as Mass spec goes.
    It is basically use to figure out the MW weight of the compound by looking at peaks.

    *I am sorry if this is not enough help!
     
  4. poc91nc

    poc91nc Banned Banned 7+ Year Member

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    Nov 5, 2006
    If you can differentiate between the base peak and molecular ion, know what fragments will not be displayed, a few general cleavage patterns, you should be good to go.
     
  5. DDSABeach

    DDSABeach Got a Dream Go Get it! 2+ Year Member

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    Nov 30, 2006
    Memphis, TN
    A low-resolution mass spectrometer. such spectrometers give the nominal molecular mass of a fragment the mass to the nearest whole number. High-resolution mass spectrometers can determine the exact molecular mass of a fragment to a prescision of 0.0001 amu. If we know the exact molecular mass of the molecular ion, we can determine the compound's molecular formula. Some computer programs can determine the molecular formula of a compound from the compound's exact molecular mass.

    Example: many compounds have a nominal molecular mass of 122 amu, but each of them has a different exact molecular mass. Some compounds with a nominal molecular mass of 122 amu and their exact molecular mass.

    Molecular formula C9H14, C7H10N2, C8H10O, C7H6O2, C4H10O4, C4H10S2
    Exact molecular mass (amu) 122.1096,122.0845, 122.0732, 122.0368,122.0579





    Not sure if this helps.... I am taking my test to day on this section Organic II.
     
  6. skyisblue

    skyisblue 2+ Year Member

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    Dec 25, 2006
    Hi DDS, can you reword this part: "Example: many compounds have a nominal molecular mass of 122 amu, but each of them has a different exact molecular mass. Some compounds with a nominal molecular mass of 122 amu and their exact molecular mass."
     

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