Introducing the MSQ
The Source–An Introduction to API Techniques ________________________________________________
Cone Voltage Ramping
Source voltage ramping can be used in Full Scan operation (see page 1-32)
in electrospray when the compound of interest forms multiply charged ions.
A spectrum similar to that in Figure 1-15 will be produced, showing the
multiply charged envelope.
700
800
900
1000
1100
1200
1300
m/z
0
100
%
848
808
771
738
707
694
893
942
998
944
1060
999
1131
1212
1305
Figure 1-15. Electrospray spectrum of horse heart myoglobin
This envelope is represented in diagrammatic form in Figure 1-16. The first
diagram shows the envelope at a source voltage of 30 V. Next, the envelope
is shown at 60 V. There is no ramping applied here. The envelope has the
same shape but has moved to a higher m/z value. This is due to the charge
stripping that occurs at high source voltages, which lowers the charge state
and produces an apparent higher mass distribution. If the source voltage is
ramped between 30 and 60 V, the charge distribution envelope is extended
and it resembles the lower diagram.
1-18
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