Technical Description: System
Cracking Patterns
Thermo Fisher Scientific
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
B-19
The following definitions are commonly used when defining
cracking patterns for a gas species.
Base or parent peak:
The ion that exhibits the most intense peak
in the mass spectrum for that gas species.
Cracking fragment:
The cracking fragment is given by:
%
100
component
gas
for the
peak
base
the
of
Intensity
m/e
required
the
of
ions
for
peak
the
of
Intensity
C
These are normally expressed in percentages, though some
references normalize to 1000. Although this is the most common
definition used, the intensities are normalized to the molecular ion
rather than to the base peak in some text books and library reference
sources.
On dual detector systems it is possible that different cracking
patterns are observed on the two detectors (and consequently two
different cracking patterns stored in the software gas database).
These different patterns result from the mass and energy-selective
characteristics of the secondary electron multiplier, i.e. the detector
has a different gain for ions of different masses and charges.
In cases where more than one ion peak is required to identify a
component in a mixture with others that have overlapping peaks in
their spectra, there is no real alternative to measuring the individual
cracking patterns.
If a single peak can be used to uniquely identify a species in a
mixture then there is little point in measuring a cracking pattern.
The system configuration can be set to measure the cracking pattern
for a gas species in a given calibration gas bottle by ticking the
Fragmentation box for that gas in that bottle (see the Calibration
Parameters menu in the software). The cracking pattern for a gas
should only be measured in a calibration mixture for which the
required ion peaks are unique for the gas species of interest. This is
known as a non-overlapping mixture.
Definitions
