[bec_freakyfishy]

I need to calculate the minimum resolution of a mass spectrometer that is required to separate the ions of certain compounds eg. Ethyl Toluene (C₉H₁₂)
I know i need to calculate the mass first, but have no idea how to go about the rest of the question?

[sjb]

I need to calculate the minimum resolution of a mass spectrometer that is required to separate the ions of certain compounds eg. Ethyl Toluene (C₉H₁₂)
I know i need to calculate the mass first, but have no idea how to go about the rest of the question?

I suppose you need to calculate the molecular weight of this, then look for other formulae that also have this mass (but including other elements, like nitrogen, oxygen, halogens etc). Then calculate the isotopic mass for your formulae (so exact figures like 12.000 for ¹²C, 1.0079 for ¹H) and see what sort of resolution you need.

So for instance, you can separate CO and N₂, despite them both having a molecular weight of 28. Does this tie up with anything you have been doing?

S

[bec_freakyfishy]

No :/ I have no idea how you calculate resolution at all. We have just been given that question but i can't find information on how to do it anyway! After calculating the mass I don't know how it relates to the resolution

[sjb]

OK, if I am right, ethylbenzene has a molecular weight of 106, (for C₈H₁₀, not C₉H₁₂ - did you mean propylbenzene or something?)

Other formulae with a basic molecular mass of 106 include things like C₇H₆O (benzaldehyde), C₆H₆N₂ (e.g. vinylpyrimidines), C₅H₁₁Cl (for the ³⁵Cl isotopomer). The monoisotopic mass of these are 106.078247, 106.04199, 106.053101 and 106.054932 g mol^-1 respectively, . You can see that they weigh slightly different, and perhaps this is the resolution you need to find, seeing how you can differentiate a reading of 106.053101 and 106.054932...

Not really sure this is what you're after though - can you talk to others on your course or something?