[diablo]

Hi,

i have a problem to interpretate this (ESI-MS):

i got a ms-peak at e.g. 556.1 Da (single charged = 1 proton = charged with 1H-atom)

Now the autor wrote:

"If the sample ions had been doubly charged, then the m/z values would only differ by 0.5 Da as z, the number of charges, would then be equal to 2"

(Original source:
http://www.astbury.leeds.ac.uk/facil/MStut/mstutorial.htm)

see 5.3. "Data processing"


That would mean : double charged= 556,05 or 556,15

but if you scroll down, there's a formula :

m/z = (MW + nH)/n ... and if you enter for example n = 2 (charges), you get a total different m/z ... ( much more than 0,5 Da difference...)

Would be very grateful if anyone could explain this to me
( i hope you understand my question^^)

thx,
Diablooo

[AWK]

You are quite right - this should be a printing error
may be 0.5 x (times) M(Da)

[diablo]

thx for your fast answer !

But if i assume that the formula :

m/z = (MW +nH)/n is right , then for MW = 551, n = 2 it would be:

m/z = (551 +2 x 1,008)/2 =276,5

and the other way ( with 0,5) would be:

551 x 0,5 = 275,5 .

whats wrong ?

thx,
Diablooooo

[AWK]

m/z = (551 +2 x 1,008)/2 =276,5

Double charged ions have 2 charges not 2 chrges + 2 hydrogens