De novo Sequencing of Proteins With Mass Spectrometry
A
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y7
y9
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10
200
400
600
800
1000
1200
mh.amu
B
D
y3
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60
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C
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73
Fig. 5.3. Fragment spectrum of the peptide ILTFDQLALESPK labelled to 50 % with 18 0 and investigated with the differential scanning technique on a quadrupole-time of flight machine. The panels
show the corresponding parts of the fragment spectrum as in figure 5.2 for data acquired with a
quadrupole time of flight machine. The high resolution of the original data allows to generate a nearly
noise free y ions only spectrum (panel C). The comparison of the original data (panel D and E) shows
clearly that only for y ions the ratio of the isotopes change between the two spectra