People oftens only look at the losses, and use very little of the exact information the intensities gives them. There must be some kind of way to evaluate this information against possible ions? Isnt there a handbook or something for this? Or a modeling software of some sort?
Intensities is the second dimension of MS. The third dimension must be the fragmentation mechanisms.
This is my recipe for determining structures from MS:
- Rule out silica-peaks if your column is bleeding
- Look up in a MS-database, if you get a good or only bad hits you should doublecheck anyway
- Find the molecular ion peak (check this against the losses), and determine the number of carbons at that peak (if possible, estimate the number of A+2 elements also)
- Look up in a molecular weight table, and find the possible combination of atoms
- Work out the DBE-value (Double bond equivalents)
- Look at your substrate, use it as an backbone
- Now, draw all possible combinations of your molecular formula and DBE
- Look for low-ion series. A series of 39 and 65 is a strong evidence that 91 is the tropylium ion (and your your substance is aromatic).
- Then look at the nearest ion-peak. Determine the losses, and carboncontent if possible.
- Look for strong odd-ions, determine the losses
- Now evaluate your selection of molecules
At this step, you should isolate the product and do an NMR. If you cant isolate, remove the solvent, and take your crude mixture and do an analysis of that, and your pure substrate.