
Overview of PSD Analysis
Voyager
™
Biospectrometry
™
Workstation User’s Guide 7-5
7
Figure 7-2 Effect of Changing Mirror Ratio
A Mirror Ratio setting of 1.0000 correctly focuses the original
ion. Values of 0.7 and 0.3 correctly focus the lower energy
fragments.
Note that the best focusing conditions occur when the
fragment ion mass is equal to the Mirror Ratio multiplied by the
precursor ion mass.
Immonium ions
Peptide PSD spectra usually include some immonium and
other low mass fragment ions that are useful in determining
peptide composition. For a list of immonium ions for the
20 standard amino acids and for selected modified amino
acids, see Falick, A.M., W.M. Hines, K.F. Medzihradszky, M.A.
Baldwin, and B.W. Gibson, “Low-Mass Ions Produced from
Peptides by High-Energy Collision-Induced Dissociation in
Tandem Mass Spectrometry”,
J. Am. Soc. Mass Spectrom.,
1993,
4
, 882-893.
Reflector
from
ion
Mirror Ratio = 0.7
MH
+
(MW 1,000) not focused
AH
+
(MW 700) correctly focused
BH
+
(MW 300) poorly focused
MH
+
AH
+
BH
+
source
Reflector
from
ion
Mirror Ratio = 0.3
MH
+
(MW 1,000) not focused
AH
+
(MW 700) not focused
BH
+
(MW 300) correctly focused
MH
+
AH
+
BH
+
source
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