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Introducing the Finnigan AQA
The Source – an Introduction to API Techniques ______________________________________
+
322 [M+H]
100
%
[M+Na]+
344 363
241
100
80 99
103
244
181
141 145
261
187
279
282
0
60
80
100
120
140
160
180
200
220
240
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340
360
m/z
Figure 1-11. Electrospray spectrum showing a sodium adduct
The singly charged ions arising from samples of relatively low molecular
masses can be interpreted directly as they represent the protonated or
deprotonated molecule. Electrospray however, can produce multiply
charged ions for analytes that contain multiple basic or acidic sites, for
example, proteins and peptides. As an MS detector measures mass-to-charge
ratio (m/z), these ions appear at a m/z value given by the mass of their
protonated molecule divided by the number of charges:
é M + nH ù
êë n úû
n+
=m z
Where, M = actual mass, n = number of charges and H = mass of a proton.
Electrospray allows molecules with molecular weights greater than the mass
range of the MS detector to be analyzed. This is a unique feature of
electrospray.
Flow Rate
The electrospray source can be used with flow rates from 2.0 µL/min to
2.0 mL/min.
1-14
______________________ Finnigan AQA Hardware Manual ______________________