Fluorine Peak Height Difference on Mass Spec

[SteveDave89]

I have these three compounds with a Fluorine attached to different carbons. If you look at the chromatograph, two of the Fluorine peaks (the 213) are relatively the same size, however one of the compounds the fluorine does not come off as readily (3-fluoro-AMB). I've been researching on why this is occuring for that compound. Can anyone lead me in the right direction?

[hypervalent_iodine]

Actually, if you look at the ratio relative intensities of the M peak : M-F peak of the 3-fluoro compared to the 4- and 5-fluoro, you'll see it decreases in both cases. It doesn't decrease by as much in the 4-fluoro, but it does drop. Given that, the trend becomes fairly obvious. Fragmentation drops as you get further away from the nitrogen, so one might assume that this is because the fragmentation isn't as favoured (probably due to stability of the fragment ion). 

I am curious as to why you are bothering to research into it though? It seems like quite a minor and tedious detail, though I am of course not familiar with what you are doing. ¹⁹F NMR seems like it would be more informative if the purpose is to distinguish between the three, if you have the facilities to do it.