What is the difference in Da of ESI analytes with multiple charges?
More realistically if you have a molecule with Br, then the distance between isotopes:


Will be 2 $m/z$ units in case of 1 charge
And 1 $m/z$ units in case of 2 charges


You can use this information to determine if there are molecules ionized twice — their isotopes appear closer than expected. 

Eventually since ESI/APCI adds $\ce{H+}$ for each charge, given original EMW was 100 Da, then:


$m/z$ in case of 1 charge: $(100+1)/1=101$ and $(102+1)/1=103$
$m/z$ in case of 2 charges: $(100+2)/2=51$ and $(102+2)/2=52$


Or in case of negative ionization you'll need to subtract 1 and 2 Da, respectively.