Mass spectrometer Ions with same mass/charge ratio but different charges [closed]








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The mass spectrometer identifies ions based on mass/charge ratio. What happens when two ions have the same mass/charge ratio but different charges or masses?




This situation is not uncommon. A mass spectrometer has no way of knowing the absolute mass or absolute charge of ions. Suppose compound A has a peak that appears at $m/z$. You suggest another compound B, which has $2m/2z$ or $nm/nz$. This is the only condition where you will see a peak overlap in MS. Note, $m$, is the nominal mass. Exact masses, measurable by ultrahigh-resolution mass spectrometers, will not masses of two compounds match precisely. Only enantiomers and structural isomers will have identical exact and nominal masses.


However, there are tricks to discern doubly charged ions. For example, you can look at the isotopic patterns. In order to avoid the problems, mass spectrometers are coupled with a chromatography system. With that, such conditions rarely arise.


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