Applied Biosystems Data Explorer 4 Series, User Manual

Page: 344 / 447

Chapter 8 Viewing Voyager PSD Data
8-6 Applied Biosystems
8
How the
composite
spectrum is
generated
The software does the following to generate a composite
spectrum:
• Evaluates all segments in the .DAT file to determine if
there are multiple segments acquired using the same
PSD Mirror Ratio.
• If there are duplicates, selects the most recently acquired
segment to include in the composite spectrum.
• Using the precursor ion mass and calibration constants
from the PSD calibration in the .DAT file (see “PSD
calibration equation” below), determines the region of
each segment to include in the composite spectrum as
illustrated in Figure 8-3 on page 8-7.
• Applies baseline correction and two-standard-deviation
noise removal to the composite region of each segment.
• “Stitches” the composite regions together and displays
the composite spectrum.
PSD calibration
equation
The equation that the Voyager software uses to calculate the
mass for fragment ions is:
where:
t
p
m
p
α
,
β, γ
Precursor ion flight time (at R
i
= 1) calculated
t
f
Fragment ion flight time
m
f
Fragment ion mass
Calibration constants =
=
=
=
R
i
= Mirror Ratio
Precursor ion mass entered in PSD Acquisition settings =
m
f =
(
α
R
i
+
β
)
[(
t
f
– t
p
) +
γ (
t
f
– t
p
)
2
] +
α
R
i
+
β
α
+
β
m
p
before acquisition, or changed in PSD Processing
during acquisition